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ArticleSeptember 30, 2024

Intermolecular Hydrogen-Bonded Interactions of Oxalic Acid Conformers with Sulfuric Acid and Ammonia
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Eduardo da Silva Carvalho
Eduardo da Silva Carvalho
Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil
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Angsula Ghosh
Angsula Ghosh
Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil
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https://orcid.org/0000-0002-1798-3643
Puspitapallab Chaudhuri*
Puspitapallab Chaudhuri
Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil
*E-mail: [email protected]
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https://orcid.org/0000-0001-9748-9890

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ACS Omega

Cite this: ACS Omega 2024, 9, 41, 42470–42487

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https://doi.org/10.1021/acsomega.4c06290

Published September 30, 2024

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Abstract

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Oxalic acid is one of the simplest naturally occurring dicarboxylic acids that is abundantly found in the atmosphere, and it has several stable structural conformers. Hydrogen-bonded interactions of oxalic acid with other atmospheric molecules are important, as they might influence the chemical composition of the atmosphere, thereby impacting atmospheric chemistry and environmental processes. In this work, we used density functional calculations with the M06–2X/6-311++G(3df,3pd) model to examine the interaction of five oxalic acid conformers with sulfuric acid and ammonia─two widely recognized atmospheric nucleation precursor molecules─with the aim of observing the hydrogen-bonding characteristics of the conformers individually. An extensive and systematic quantum-chemical calculation has been conducted to analyze the structural, thermodynamical, electrical, and spectroscopic characteristics of several binary and ternary clusters mediated by five oxalic acid conformers. Our analysis of the electronic-binding energies and free energy changes associated with the formation of the clusters at ambient temperature reveals that multiple conformations of oxalic acid have the potential to engage in stable cluster formation in the atmosphere. In fact, the highest energy oxalic acid conformer exhibits the lowest bonding free energy in most cases. According to our calculations, clusters of oxalic acid with sulfuric acid demonstrate greater thermodynamic stability, a higher probability of formation, and more intense light scattering compared to clusters with ammonia. Furthermore, the analysis of successive cluster formation reveals that clusters formed between sulfuric and oxalic acids are more likely to grow spontaneously than those formed between ammonia and oxalic acid.

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Subjects

1. Introduction

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Hydrogen-bonding interactions among organic molecules are of great importance in many different branches of chemical sciences such as biochemistry and molecular biology, medicinal chemistry and drug designing, materials science/polymer chemistry, astrochemistry, atmospheric chemistry, and so on. The nature of the hydrogen bonds (HBs) may directly influence the stability of molecular structures, reactivities, and functions. In living organisms, HBs are fundamental in maintaining the secondary and tertiary structures of biomolecules such as proteins and nucleic acids. Understanding HBs is crucial in materials science for designing and manipulating the properties of polymers, supramolecular assemblies, and other advanced materials. In the atmosphere, organic compounds, such as carboxylic acids, can interact with other molecules via hydrogen bonding to form small stable clusters. These clusters can grow in size and eventually lead to the formation of secondary organic aerosols. Oxalic acid (OA, C₂H₂O₄) is one such molecule of significant atmospheric importance. (1−24) It is the simplest naturally occurring water-soluble dicarboxylic acid (DCA) found in various environmental sources, such as plants, fungi, and some marine organisms. (1,20,25−27) In human body, OA is produced through the metabolism of certain plant-based foods like leafy greens (such as spinach, rhubarb, amaranth), nuts, seeds, tea, sweet potatoes, okra, etc. (28−31) In the atmosphere, it may be formed via oxidation of larger compounds such as isoprene and monoterpenes, volatile organic compounds emitted by transpiration from plant leaves. (32−34) DCAs, in general, are common organics identified both in the urban and rural areas mainly due to the intense agricultural and industrial activities and are an important constituent of the nucleation process due to their low vapor-pressure. (19,21−23,35−42) Moreover, being water-soluble, DCAs may serve as cloud condensation nuclei, becoming relevant in the global climate system. OA is reported to be the most-abundant atmospheric DCA detected in the air as a major constituent of ultrafine and fine aerosol particles. (8,21−23,38,43−45) Notably, the gas-phase concentration of OA is reported to be in the range of 9.3 × 10¹⁰ to 5.4 × 10¹² molecules/cm³, (23,24,45) which is much higher than that of ammonia (AM) and sulfuric acid (SA), as the typical concentrations of SA and AM are in the range of 10⁴–10⁸ molecules/cm³ and 10⁷–10¹¹ molecules/cm³, respectively. (5,16,23,24,46,47) OA and SA are two crucial precursor molecules in atmospheric nucleation, contributing significantly to the formation of secondary aerosols. (48−55) The molecular configuration of OA, with two carboxylic (COOH) groups on either side of a C–C bond, imparts substantial rotational flexibility, leading to the possible existence of several conformers, each with distinct structural arrangements. Over the past few decades, several experimental (56−61) and theoretical (21,60−69) investigations explored the intricate conformational landscape of OA. Theoretical predictions suggest that in the gas phase, OA should have at least five different structural conformations. The three lowest energy conformations predicted by theory have been observed experimentally. (59−61) On the other hand, the presence of two COOH groups enables OA to engage in a greater number of hydrogen bonding interactions, compared to monocarboxylic acids, with two carbonyl (C═O) groups acting as proton acceptors and the OH groups acting as proton donors. Recent theoretical investigations on atmospheric nucleation and new particle formation reveal that OA can generate thermodynamically stable hydrogen-bonded clusters with atmospherically relevant molecules such as SA, water, AM, amines, and methanesulfonic acid. (3−8,12−19,21,23,24) While the contribution of hydrogen-bonded interactions of oxalic acid, particularly considering its lowest energy conformations or a few others, in atmospheric aerosol formation has been widely studied, the hydrogen-bonding characteristics of individual oxalic acid conformers have not yet been fully explored. Quantum chemical calculations on the binary and ternary clusters OA with AM and H₂O, (5,6) hydration of OA dimer, (15) OA-catalyzed hydration reaction of SO₃, (21) and dissociation of oxalic acid in water clusters (67) are the few ones that considered all the five OA conformers. In the present work, we consider the effect of hydrogen-bonded interactions of five stable OA conformers with atmospheric molecules such as SA and AM. A detailed quantum-chemical analysis has been conducted, and relevant structural, thermodynamical, and spectroscopic properties of multiple conformations of various binary and ternary clusters are reported.

2. Computational Methods

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The molecular geometries of OA, SA, and AM and those of the hydrogen-bonded binary and ternary clusters formed with these molecules were fully optimized without any constraint in the gas phase. The hybrid DFT functional M06–2X, which is parametrized to account for dispersion interactions, was used for this purpose with Pople’s split-valence triple-ζ 6–311++G(3df,3pd) basis set, maintaining consistency with our recent work on organic atmospheric molecules. (70,71) This M06–2X/6-311++G(3df,3pd) model is well recommended in the literature for quantum-chemical analysis of hydrogen-bonding interactions among atmospheric molecules. (50,72−75) Five structurally different conformers of OA monomer have been considered whose initial geometries were prepared based on previous works. (21,60−69) The initial structure clusters were then prepared following a multistep approach, considering the fact that all the monomers (OA, SA, and AM) can simultaneously act as proton-acceptor and proton-donor, facilitating the formation of multiple HBs. Moreover, depending on the relative position of the COOH groups on either side of the central C–C bond, different forms of intermolecular arrangement for hydrogen bonding are possible. As the main objective of this work is to observe how different conformations of OA influence its hydrogen-bonding characteristics, we searched for different possible HB patterns for each OA conformation. Initially, several binary or ternary clusters were prepared by strategically placing SA and/or AM around the hydrogen-bonding sites of OA using the GaussView molecular visualization program, (76) and all of them were optimized using the M06–2X/6-31++G(d,p) model. Some of these optimized structures were then selected based on energy and structural distinctness, and further optimized by the larger M06–2X/6-311++G(3df,3pd) model. Finally, a few of the lower energy cluster geometries for each OA monomer were chosen for the final analysis. After each geometry optimization, the vibrational frequencies were obtained at the same level of calculation to ensure that all frequencies are positive and that the optimized geometry is a local minimum on the potential energy hypersurface.

Thus, in this work, we consider each of the five OA conformers individually interacting with AM and SA to form the (OA)(AM) and (OA)(SA) dimers, as well as the (OA)(AM)₂, (OA)(SA)₂ trimers. This results in a total of 10 different dimer compositions and 10 different trimer compositions. Each cluster composition, on the other hand, contains multiple structural conformations with varying electronic energies in most cases, as we discuss in the next section.

The binding electronic energy (ΔE) and the binding Gibbs free energy of formation (ΔG) were calculated for each cluster considering the usual supermolecular approach:

Δ X = X_{cluster} - \sum X_{monomer}

(1)

where X = E (electronic energy of the system) or G (electronic energy with thermal free energy correction). Both E and G are corrected for the zero-point energy (ZPE). As each cluster composition may possess several energetically stable conformers, the effect of multiple conformers on the cluster-binding free energy is calculated as, (50,77,78)

Δ G_{M C} = R T \ln [\sum_{k = 1}^{n} \exp (\frac{- Δ G_{k}}{R T})]

(2)

where R = 8.314J/(mol K) is the universal gas constant and T is the ambient temperature (298.15 K).

When molecules come together to form a cluster or complex, they may undergo changes in their geometries to adapt to a new environment or interactions. The energy required for these structural adjustments is commonly termed the distortion energy or relaxation energy. In mathematical terms, the distortion energy of a molecule engaged in clustering is determined by subtracting the electronic energy of that molecule (monomer i) in its isolated form (E_i) from the energy of the same monomer with its geometry altered and fixed within the cluster (

E_{i}^{N}

). The total distortion energy of the cluster containing N monomers, ΔE_D (tot), is the sum of the individual distortion energies of all monomers within the cluster. Thus,

Δ E_{D} (tot) = \sum_{i = 1}^{N} [E_{i}^{N} - E_{i}]

(3)

In physical terms, ΔE_D, a positive quantity, is a measure of the strain or perturbation introduced into the system due to the molecular clustering process.

Since the probability of a given set of molecules arranging themselves in a particular configuration k with Gibbs free energy change of ΔG_k is proportional to the Boltzmann factor of the cluster formation, exp(−ΔG_k/RT), the relative population fraction, RPF(k) of different conformations in a particular cluster composition were calculated by using the following relation:

R P F (k) = \frac{\exp (- \frac{Δ G_{k}}{R T})}{\sum_{i} \exp (- \frac{Δ G_{k}}{R T})} \times 100 %

(4)

The optical properties, such as the Rayleigh scattering intensities (

R

) and depolarization ratios (σ) for natural light, of the monomers and OA-mediated clusters were obtained, at the same M06–2X/6-311++G(3df,3pd) level, using the following definitions. (79−82)

R = 45 {(\bar{α})}^{2} + 13 {(Δ α)}^{2}, σ = \frac{6 {(Δ α)}^{2}}{45 {(\bar{α})}^{2} + 7 {(Δ α)}^{2}}

(5)

where,

\bar{α}

and Δα are the mean isotropic polarizability and the anisotropy of polarizability of the molecular system,

\bar{α} = \frac{1}{3} (α_{x x} + α_{y y} + α_{z z})

{(Δ α)}^{2} = \frac{1}{2} [{(α_{x x} - α_{y y})}^{2} + {(α_{y y} - α_{z z})}^{2} + {(α_{z z} - α_{x x})}^{2}] + 3 (α_{x y}^{2} + α_{x z}^{2} + α_{y z}^{2})

(6)

All calculations were performed using the Gaussian 16 (83) computational chemistry software package. Preparation of the initial molecular structures and partial analysis of the calculated results were done by the GaussView interface. (76)

3. Results and Discussion

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3.1. Isolated Molecule of Oxalic Acid

The geometries of the five oxalic acid (OA) conformers, optimized by the M06–2X/6-311++G (3df,3pd) model, are illustrated in Figure 1. The structures are arranged in order of increasing relative electronic energy (ΔE_R), with zero-point energy corrections applied, calculated relative to the conformer with the lowest electronic energy. The conformers are named hereafter as cTc, cTt, tTt, tCt, and cCt following the literature. (5,21,59,60,62,66,67) The nomenclature is based on the torsional degrees of freedom of the OA structures. The uppercase letters C and T represent the cis and trans configurations, respectively, of the O═C–C═O dihedral angle corresponding to the internal rotation of the carboxyl COOH groups around the C–C bond. The lower case letters c and t, on the other hand, signify the cis and trans configurations of the two C–C–O–H dihedral angles, representing the rotation of the OH group about the C–O bond in each COOH group.

Figure 1. Structures of the five stable oxalic acid (OA) conformers, optimized using the M06–2X/6-311++G(3df,3pd) model, showing intramolecular hydrogen bonds (dotted lines) along with the relative electronic energy (ΔE_R) and relative Gibbs free energy (ΔG_R), calculated with respect to the lowest energy conformer, cTc.

In the lowest energy conformation of OA (cTc), two carboxyl groups are trans to each other, i.e., φ(0═C–C═0) = 180°, and both OH groups are cis with respect to the C–C bond. As a result, cTc is stabilized by the formation of two intramolecular O–H···O HBs of equal bond length (2.12 Å) and bond angle (115.5°). The second-most stable conformation (cTt) differs from cTc by the internal rotation of one of the two OH groups about the C–O bond, making it trans with respect to the C–C bond. As a result, cTt possesses only one intramolecular HB, which has a bond length of 2.09 Å. The energy difference between cTc and cTt is 2.68 kcal/mol which matches with 2.62 and 2.75 kcal/mol, obtained by higher level energy calculations with MP2/aug-cc-pVDZ and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G(d,p) models, respectively. (5) Other relative energies from MP2 (CCSD) calculation, (5) are ΔE_R(tTt) = 3.89 (4.31) kcal/mol, ΔE_R(tCt) = 4.43 (4.99) kcal/mol and ΔE_R(cCt) = 5.69 (6.02) kcal/mol. As can be observed from Figure 1, these values are also in good agreement with those obtained by the M06-2X calculation. The cTc, cTt, and tTt are the only conformers that have been detected by experiments. (59−61)

The calculated values of the structural parameters like bond lengths and bond angles of the OA conformers agree well with experiments and previous calculations. (62,66) Since, detailed discussions on each of these OA conformer structures are available in several previous works on OA, we provide the structural parameters obtained by our M06–2X/6-311++G(3df,3pd) along with others from the literature in Table S2. Here, we discuss briefly some of the electric and spectroscopic parameters reported in Table 1, which are also important for characterization of the conformers.

Table 1. Calculated Values of Dipole Moment (μ), Mean Dipole Polarizabilty (

), Polarizability Anisotropy (Δα), Rotational Constants (A, B, and C)^a, Degree of Depolarization (σ), and Rayleigh Activity (

) for Natural Light of the Five OA Conformers as Obtained by M06–2X/6-311++G(3df, 3pd) Model

	cTc	cTt	tTt	tCt	cCt
μ (D)	0.00	3.15	0.00	2.98	4.89
α (a.u.)	37.36	37.84	38.13	38.16	37.99
Δα (a.u.)	20.37	19.72	19.53	19.60	19.72
A (GHz)	5.878	6.027	6.149	6.120	6.000
B (GHz)	3.855	3.708	3.611	3.619	3.672
C (GHz)	2.328	2.296	2.275	2.274	2.278
σ (a.u.)	0.044	0.041	0.039	0.039	0.040
(a.u.)	68188.7	67140.3	68103.4	68198.4	69983.7

^{^a}

Experimental values of the rotational constants (GHz): A = 5.951, B = 3.684, C = 2.276. (61).

As can be seen from Table 1, cTc and tTt are the only OA conformers among the five that have zero dipole moment, as a consequence of their structural feature. Both possess C_2h symmetry, with the two COOH groups having a trans configuration with respect to each other. So, the dipole moment vectors corresponding to each group acts in opposite direction nullifying the total dipole of the system. The dipole moment of 3.15D for cTt, calculated by the present M06–2X/6-311++G(3df, 3pd), agrees well with the experimentally measured value of 3.073(6)D (61) and B3LYP/aug-cc-pVDZ calculated value of 3.14D. (5) Apart from cTc and cTt, the highest energy conformer cCt also has one intramolecular HB. Curiously, it has the shortest HB length (2.12 Å) and highest dipole moment (4.89 D) among all the clusters. The same observation was also found in B3LYP/6-311++G(d,p) calculation. (5) Since both the OH groups in the lowest energy cTc conformer are oriented inwardly, it has the lowest molecular volume with an electronic spatial extent (ESE) of 479 au. On the other hand, both the tTt and tCt conformers with their OH groups looking outward in opposite directions have the highest volume with ESE ≈ 491 au. ESE is a measure of the average size of the electron distribution in a molecule. Molecules with a larger ESE have more diffuse electron clouds, which generally leads to greater polarizability, as the extended electron cloud can be more easily distorted by an external field. As a result, tTt and tCt have the highest mean dipole polarizabilities with α = 38.13 au and 38.16 au, respectively, while cTc has the lowest polarizability (α = 37.36 au). However, in general, the difference in polarizability between the conformers is minimum. In case, of degree of depolarization (σ) all the conformers have the same and a very small value with σ ≈ 0.04 au which signifies that the polarization state of the incident light will remain almost unaltered during the scattering process with OA conformers. As far as the elastic light scattering (Rayleigh scattering) is concerned, the scattering intensities also do not vary appreciably from one conformer to another, but the highest energy cCt shows the highest Rayleigh activity, suggesting most effective scattering of incident radiation by this conformer.

A sequential interconversion among the conformations in either decreasing or increasing order of electronic energy (cCt ⇄ tCt ⇄ tTt ⇄ cTt ⇄ cTc) is possible just by rotation of a single dihedral angle in each confirmation. Figure 2 illustrates a schematic representation of the rotational energy barriers for these interconversions, obtained through the constrained optimizations (energy scan) of the molecule, rotating a selected dihedral angle in small increments of 3° and optimizing the molecular geometry while keeping the dihedral angle fixed at the incremented value. For instance, rotating a COOH group about the central C–C bond or the C–C–O–H dihedron allows the transition from the tCt to the tTt conformer. The rotational energy barrier in this case is remarkably low, measuring just 0.86 kcal/mol for tCt → tTt and 1.48 kcal/mol for tTt → tCt, representing the minimum barrier encountered by our calculation at the M06–2X/6-311++G(3df, 3pd) level. The highest energy barriers are observed for the cTc → cTt and cTt → cTc interconversions, with values of 13.98 and 11.07 kcal/mol, respectively. These transitions involve the rotation of a specific O─C–O–H dihedral, transitioning from a trans to cis configuration. The calculated barriers agree well with previous predictions with different models. (62,63) As can be observed in the figure, with the exception of tCt ⇄ tTt, the rotational barriers are significantly high, suggesting that the cCt, cTt, and cTc conformers possess considerable stability under normal conditions.

Figure 2. Schematic diagram of the rotational barriers for the possible interconversions among the OA conformers as obtained by the M06–2X/6-311++G(3df, 3pd) level.

Among the five OA conformers, cTc, tTt, and tCt contain degenerated vibrational stretching modes for the OH group as a consequence of the symmetry of the molecule. In the cTc conformer, the two equivalent OH groups asymmetrically stretch at 3727 cm^–1 with an intensity of 306.6 km/mol, while they symmetrically stretch at 3723 cm^–1 with an almost negligible intensity of 0.012 km/mol. For both tTt and tCt conformers, the vibrational frequencies for these coupled symmetric and asymmetric stretching modes are practically the same, measuring 3832 cm^–1 for tTt and 3821 cm^–1 for tCt. However, the intensity of the asymmetric vibration is significantly higher than the symmetric vibration in both cases. In contrast, for cTt and cCt conformers, the OH groups exhibit independent stretching modes with similar intensities of vibration. The calculated OH stretching frequencies for the cis-CCOH (trans-CCOH) of cTt and cCt are approximately 3773 (3819) cm^–1 and 3824 (3830) cm^–1, respectively. Considering the experimentally observed OH stretching frequencies in the range 3453–3461 cm^–1, we notice that the M06–2X/6-311++G(3df,3pd) level of calculation overestimates the OH stretching frequencies by ca. 7%.

3.2. Clusters of Oxalic Acid and Ammonia, (OA)(AM)_n (n= 1,2)

In this section, we analyze the structural and thermochemical properties of the binary and ternary clusters formed by one molecule of the five conformers of OA (cTc, cTt, tTt, tCt, cCt) with AM. Figure 3 exhibits the optimized geometries of the seven binary (OA)(AM) clusters, with (cTt)(AM) and (cCt)(AM) compositions having two conformations each, while (cTc)(AM), (tTt)(AM), and (tCt)(AM) have a single conformation because of structural symmetry. Figure 4 displays the optimized structures of 10 ternary (OA)(AM)₂ clusters, considered for the present work, with each of the five cluster compositions having two structural conformations. Although more than two conformations were identified for certain (OA)(AM)₂ compositions, we selected the two lowest energy conformations, with distinct structural features, for each ternary composition.

Figure 3. Equilibrium geometries of the stable (OA)(AM) cluster compositions optimized at the M06–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths, obtained using the present model shown in black color, while those from other models─B3LYP/aug-cc-pVDZ (6) and PW91PW91/6-311++G(3df,3pd) (7)─are shown in red and blue, respectively. The numbers in square brackets represent the relative energy differences of the conformations within each cluster composition in kcal/mol.

Figure 4. Equilibrium geometries of the stable (OA)(AM)₂ cluster compositions. optimized at the M06–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths, obtained using the present model shown in black, and those from PW91PW91/6-311++G(3df,3pd) (7) in blue. The numbers in square brackets represent the relative energy differences of the conformations within each cluster composition in kcal/mol.

Some of these hydrogen-bonded structures have been previously studied. Specifically, the binary structures (cTc)(AM), (cTt)(AM)-1, (cTt)(AM)-2, (tTt)(AM), and (cCt)(AM)-1 were investigated using the B3LYP/aug-cc-PVDZ model. (6) Additionally, the binary (cTc)(AM) and ternary (cTc)(AM)₂-1 structures were studied by the PW91PW91/6-311++G(3df,3pd) model. (7) The intermolecular hydrogen bond (HB) distances obtained by these models are shown in the figures alongside those obtained by the present model. As evident, the HB distances calculated by the M06–2X/6-311++G (3df,3pd) model are in excellent agreement with those of the B3LYP/aug-cc-PVD model, while PW91PW91/6-311++G(3df,3pd) predicts shorter HB distances. The HB interactions occur via the −OH and −CO groups of OA where it acts simultaneously as a proton donor and proton-acceptor, respectively. As the figures show, the HB distances in the possible (N)H···O type interactions between OA and AM, with the former being the proton acceptor, are, in general, much larger than the (O)H···N HB distances when OA acts as proton donor. The HB bond angles are also larger in the case of the (O)H···N bonds. Thus, we assume that the formation of (O)H···N HBs between OA conformers and AM molecules with OA being the proton-donor via its O–H moiety and AM being the proton acceptor via the nitrogen atom is responsible for the energetic stability of the (OA)(AM) clusters. We report in Table 2 some structural and spectroscopic parameters required for the characterization of these (O)H···N HBs like the distance between the two electronegative heavy atoms (oxygen and nitrogen) participating in the HB formation (R_O–N), The HB length (R_(O)H···N), HB angle (∠O–H···N), elongation of the O–H bond due to HB formation (ΔR_O–H), O–H stretching frequency in the clusters and its red-shift with respect to the isolated OA molecule. The Cartesian coordinates of all the optimized geometries of (OA)(AM) and (OA)(AM)₂ clusters are given in Table S2a,b, respectively.

Table 2. Relevant HB Parameters of the Binary (OA)(AM) and Ternary (OA)(AM)₂ Clusters Including the HB Distance, O–H Bond Length, Variation of the Bond Length, HB Angle, and O–H Frequencies and the Variation of the O–H Frequencies upon Cluster Formation^a

		R_O–N (Å)	R_(O)H···N (Å)	∠O─H···N (degrees)	ΔR_O–H (Å)	v_O–H (cm^–1)	Δv_O–H (cm^–1)
(OA)(AM)
(cTc)(AM)		2.638	1.619	171.1	0.054	2692	–1035
(cTt)(AM)-1		2.659	1.649	170.7	0.052	2786	–1034
(cTt)(AM)-2		2.685	1.690	167.4	0.040	2974	–799
(tTt)(AM)		2.681	1.682	168.6	0.045	2904	–928
(tCt))(AM)		2.678	1.678	168.2	0.046	2917	–904
(cCt)(AM)-1		2.641	1.632	168.4	0.056	2753	–1071
(cCt)(AM)-2		2.696	1.719	164.1	0.037	3063	–767
(OA)(AM)₂
(cTc)(AM)₂-1		2.678	1.678	168.2	0.042	2894^b	–833
(cTc)(AM)₂-2		2.562	1.503	172.1	0.094	2121	–1607
(cTt)(AM)₂-1	C	2.722	1.740	166.4	0.034	3101	–672
	T	2.692	1.693	170.3	0.041	2977	–843
(cTt)(AM)₂-2		2.596	1.545	177.7	0.084	2287	–1532
(tTt)(AM)₂-1		2.704	1.714	167.5	0.039	2997^c	–835
(tTt)(AM)₂-2		2.623	1.586	178.2	0.071	2495	–1337
(tCt)(AM)₂-1		2.701	1.710	167.3	0.040	2985^d	–836
(tCt)(AM)₂-2		2.622	1.567	178.7	0.072	2478	–1343
(cCt)(AM)₂-1		2.584	1.526	179.8	0.092	2167	–1657
(cCt)(AM)₂-2	C	2.727	1.763	161.8	0.030	3173	–657
	T	2.686	1.690	167.7	0.044	2921	–903

^{^a}

The labels “C” and “T” have been indicated in Figure 4.

^{^b}

Asymmetric stretching mode of the two O–H groups with intensity of 4171 km/mol. The calculated value of the symmetric stretching mode of the same bonds is 2892 cm^–1 with an intensity of just 5.2 km/mol.

^{^c}

Asymmetric stretching mode of the two O–H groups with intensity of 3785 km/mol. The calculated value of the symmetric stretching mode of the same bonds is 3023 cm^–1 with a negligible intensity.

^{^d}

Asymmetric stretching mode of the two O–H groups with intensity of 3831 km/mol. The calculated value of the symmetric stretching mode of the same bonds is 3023 cm^–1 with an intensity of just 6.6 km/mol.

As can be seen, all five conformers of OA form strong O–H···N type HB with an average HB distance (angle) of 1.67 Å (168.4°) in the case of binary clusters and 1.64 Å (171.3°) in the case of ternary clusters. The average red shift of the OA O–H stretching frequency is 934 (1088) cm^–1 in binary (ternary) clusters. Among the two conformations of (cTt)(AM) and also of (cCt)(AM), Conf. (1) with AM interacting with the single COOH moiety of OA shows stronger hydrogen bonding. For ternary clusters involving two AM molecules interacting with OA, we sought configurations that consistently allow interaction with both the OH and CO moieties of OA, originating from either the same or different COOH groups, which yielded two scenarios. The first one involves direct hydrogen bonding between the two AM molecules, while both interact with OA. In the second scenario, each AM molecule interacts separately with OA, remaining spatially distant from each other. Clusters formed under the second scenario exhibit higher energetic stability for all OA conformers, as can be verified from the relative electronic energy difference provided in Figure 4. Furthermore, in the second scenario, the vibrational degeneracy of the OH stretching mode persists as the symmetry of the system is maintained. Thus, in the cTc, tTt, and tCt conformers, the coupled asymmetric and symmetric stretchings of the two equivalent OH groups continue, both experiencing similar red-shifts. However, in the first scenario, where two AM molecules act jointly on one side of OA, the symmetry is altered and the degeneracy is lifted. In this case, only one of the OH groups directly forms HB by donating a proton to the nitrogen of AM, resulting in a substantial red-sift for that specific OH group.

In Table 3, we present the calculated binding electronic energy (ΔE), binding Gibbs free energy (ΔG) at 298.15 K along with the distortion energy (ΔE_D) of the OA monomers and their corresponding binary and ternary clusters with AM. Table 3 additionally reports the population distributions within each cluster compositions, denoted as relative population fraction (RPF), the multiple-conformer cluster binding free energy, ΔG_MC in kcal/mol, for each composition and the equilibrium constants (K_eq) at 298.15 K for each cluster.

Table 3. Calculated Values of Binding Electronic Energies (ΔE), Binding Free Energy (ΔG) Associated with Different (OA)(AM) and (OA)(AM)₂ Clusters at 298.15 K, in kcal/mol, Along with their Relative Population Fraction (RPF), the Multi-Conformation Average Binding Free Energy (ΔG_MC) and the Equilibrium Constants (K_eq) of each Cluster Composition Obtained at M06–2X/6-311++G(3df,3pd) Level

	ΔE_B	E_D(OA)	E_D(tot)	ΔG	RPF	ΔG_MC	K_eq
(OA)(AM)
(cTc)(AM)	–11.89	4.32	4.39	–3.65	100.00	–3.65	4.8 × 10²
(cTt)(AM)-1	–12.76	3.16	3.22	–4.51	99.79	–4.51	2.1 × 10³
(cTt)(AM)-2	–9.73	1.84	1.88	–0.87	0.21	–4.51	2.1 × 10³
(tTt)(AM)	–11.72	1.48	1.53	–3.39	100.00	–3.39	3.1 × 10²
(tCt)(AM)	–11.81	1.50	1.55	–2.71	100.00	–2.71	9.8 × 10¹
(cCt)(AM)-1	–13.57	2.06	2.11	–5.03	99.68	–5.03	4.9 × 10³
(cCt)(AM)-2	–8.90	2.60	2.63	–1.63	0.32	–5.03	4.9 × 10³
(OA)(AM)₂
(cTc)(AM)₂-1	–21.33	5.91	6.05	–5.86	99.92	–5.86	2.0 × 10⁴
(cTc)(AM)₂-2	–18.13	8.00	8.18	–1.66	0.08	–5.86	2.0 × 10⁴
(cTt)(AM)₂-1	–20.26	3.53	3.65	–3.68	89.15	–3.75	5.7 × 10²
(cTt)(AM)₂-2	–19.37	4.65	4.84	–2.43	10.85	–3.75	5.7 × 10²
(tTt)(AM)₂-1	–22.42	2.19	2.31	–5.75	99.92	–5.75	1.7 × 10⁴
(tTt)(AM)₂-2	–18.33	3.59	3.76	–1.52	0.08	–5.75	1.7 × 10⁴
(tCt)(AM)₂-1	–22.70	2.34	2.46	–5.43	99.88	–5.43	9.7 × 10³
(tCt)(AM)₂-2	–18.74	3.56	3.73	–1.44	0.12	–5.43	9.7 × 10³
(cCt)(AM)₂-1	–21.21	5.12	5.20	–4.51	48.04	–4.95	4.3 × 10³
(cCt)(AM)₂-2	–20.83	3.30	3.40	–4.56	51.96	–4.95	4.3 × 10³

The structural data reported in Table 2 and the large negative electronic-binding energies reported in Table 3 demonstrate that all five conformers of OA can form stable hydrogen-bonded molecular clusters with AM under ambient conditions, and if the gas-phase molecular concentrations are sufficient, these clusters may further nucleate and grow in size. Among the binary clusters, the lowest binding energy is obtained for (cCt)(AM)-1 with ΔE_B = −13.57 kcal/mol, followed by (cTt)(AM)-1 with ΔE_B = −12.76 kcal/mol. Both cCt and cTt have the same Cs symmetry, and in both cases, AM interacts with one COOH group where the CO and OH are in cis configuration, Notably, neither cCt nor CTt is the lowest energy conformer of OA. In fact, cCt is the highest energy OA conformer with ΔE_R = 5.78 kcal/mol relative to the most stable cTc conformer. The binary cluster formed by the lowest energy cTc conformer ranks third with ΔE_B = −11.89 kcal/mol, closely followed by (tCt)(AM) and (tTt)(AM) with ΔE_B = −11.81 and −11.79 kcal/mol, respectively.

Concerning the total distortion energy, E_D(T), of the binary clusters, it is found that (cTc)(AM) exhibits the highest value with E_D(T) = 4.39 kcal/mol, which accounts for almost 37% of its binding energy, ΔE_B. In contrast, the most stable (cCt)(AM)-1 binary conformer has E_D(T) = −2.63 kcal/mol, constituting 19% of its ΔE_B. The (tTt)(AM) binary cluster has the lowest distortion energy with E_D(T) = 1.53 kcal/mol, followed very closely by (tCt)(AM) with E_D(T) = 1.55 kcal/mol. In both clusters, E_D(T) corresponds to 13% of ΔE_B. Thus, the distortion energy of (cTc)(AM) is nearly three times that of (tCt)(AM), although their ΔE_B has almost the same magnitude. Furthermore, in all the binary clusters, the distortion energies of the individual OA monomers, E_D(OA) contribute to 95–99% of E_D(T), which implies that the OA monomers undergo the most structural modifications during clustering. So, the lowest energy OA conformer cTc experiences significantly higher structural strain compared to others, as its E_D(T) is substantially higher than all other conformers. OA conformers with trans-COOH interacting with AM, suffer lesser distortion, benefiting from steric advantages over others.

Upon addition of thermal correction to electronic energy, all binary clusters exhibit negative values of binding free energy (ΔG), signifying the spontaneous formation of the cluster at ambient temperature and pressure, if monomer concentrations are sufficient at the specific location. The order of thermodynamic stability aligns with that of ΔE_B, where the (cCt)(AM)-1 conformer exhibits the lowest ΔG value of −5.03 kcal/mol, followed by (cTt)(AM)-1 and (cTc)(AM) with higher values of −4.51 kcal/mol and −3.65 kcal/mol, respectively. The K_eq values were calculated by using the formula: where R = 8.314 J/(mol·K) is the universal gas constant and T = 298.15 K is the ambient temperature. The equilibrium constant of a chemical system is a measure of the proportion of products and reactants present in a given equilibrium state. In atmospheric particle cluster formation, this constant is closely linked to changes in Gibb’s free energy, with smaller free energy changes corresponding to larger equilibrium constants. This suggests that clusters are more likely to form and remain stable in the atmosphere. Hence, a higher equilibrium constant indicates a preference for cluster formation over dissociation.

For (cTc)(AM), (tTt)(AM), and (tCt)(AM), each having one conformation, ΔG_MC = ΔG. On the other hand, (cTt)(AM) and (cCt)(AM) compositions possess two conformations each, but the Gibbs free energy difference between the two conformations exceeds 3 kcal/mol in both cases. As a result, in these two cases, the value of ΔG_MC = ΔG of the more stable conformation This substantial free energy difference significantly influences the RPF of the clusters. The RPF of (cTc)(AM), (tTt)(AM), and (tCt)(AM) is 100% as they have one conformation each. However, in the case of (cTt)(AM) and (cCt)(AM), where the difference between the ΔG values of conformation-1 and conformation-2 exceeds 3 kcal/mol, conformation-1 is the dominant fraction retaining over 99% of the total population. Furthermore, as can be observed from Table 3, the (cCt)(AM) binary cluster has the highest equilibrium constant (K_eq = 4.9 × 10³), followed by (cTt)(AM) with K_eq = 2.1 × 10³, while (tCt)(AM) has the lowest value with K_eq = 9.8 × 10¹ which implies that, under ambient conditions, the population of (cCt)(AM) cluster should be approximately 2.3 times greater than that of (cTt)(AM), and about 100 times greater than that of (tCt)(AM).

In the case of ternary clusters of OA with AM, a total of 10 clusters is considered, with each cluster composition having two conformations. Similar to the previous case, all clusters exhibit large negative values of ΔE_B. However, they have a different profile this time, as the cCt and cTt conformers with Cs symmetry no longer constitute the most stable clusters, in terms of binding energy. Instead, the ternary cluster with the lowest ΔE_B is (tCt)(AM)₂-1 with ΔE_B = –22.70 kcal/mol, closely followed by (tTt)(AM)₂-1 with ΔE_B = −22.42 kcal/mol. In both of these clusters, the two AM monomers interact separately with the COOH moieties of OA, with no direct hydrogen bonding between them. The lower energy conformation, i.e., conformation-1 of the ternary clusters formed by cTc (the lowest energy OA conformer) and cCT (the highest energy OA conformer) have practically the same ΔE_B (around −21 kcal/mol), but the corresponding higher energy conformations, i.e., conformation-2 differ by almost 3 kcal/mol, with (cCt)(AM)₂-2 having the lower ΔE_B.

The total distortion energies, E_D(T), of the two conformations of (cTc)(AM)₂ generally have higher magnitudes compared to others, while the ternary clusters of tTt and tCt, both with C_2v symmetry, exhibit the lowest E_D(T), as can be verified from the table. Similar to the binary clusters, distortion of the OA monomer alone in each ternary cluster contributes to 95–98% of E_D(T). Regarding the Gibb’s free energy variation, all ternary clusters show negative values, with those of cTc, tTt and tCt, in particular, having the ΔG’s closely similar in magnitudes. Specifically, (cTc)(AM)₂-1, (tTt)(AM)₂-1, and (tCt)(AM)₂-1 have ΔG in the range of −5.43 to −5.86 kcal/mol. On the other hand, the higher energy conformations, (cTc)(AM)₂-2, (tTt)(AM)₂-2, and (tCt)(AM)₂-2 exhibit ΔG’s varying between −1.44 and −1.66 kcal/mol. Since the difference of ΔG between conformation-1 and conformation-2 of these cluster compositions exceeds 3 kcal/mol, it strongly impacts the RPF, rendering the population of conformation-2 negligible. However, in the case of (cCt)(AM)₂, where the ΔG values of the two conformations differ only by 0.05 kcal/mol with conformation-2 having the lower value, the RPF reflects a more balanced distribution, with conformation-1 occupying approximately 48% and conformation-2 around 52%. Regarding the equilibrium constants of the ternary clusters, (cTc)(AM)₂ exhibits the highest value (K_eq = 2.0 × 10⁴), closely followed by (tTt)(AM)₂ with K_eq = 1.7 × 10⁴, suggesting that both should have similar relative populations under ambient conditions. Further considering the K_eq values of the other ternary clusters, it is evident that the population of (cTc)(AM)₂ should be nearly double that of (tCt)(AM)₂ and about five times greater than that of (cCt)(AM)₂.

The previous discussion of the binding free energy of the clusters assumed that monomers interact simultaneously to form clusters. However, clusters can also form through successive interactions, where a preformed molecular cluster interacts with another free molecule to create a larger cluster. In our case, a ternary (OA)(AM)₂ cluster may form from the interaction of a binary (OA)(AM) cluster with an AM monomer. Table 4 presents the different possible pathways for forming (OA)(AM)₂ through successive cluster formation, which is relevant to the growth of the cluster size. Successive binding free energies (ΔG_s) are calculated for all five ternary (OA)(AM)₂ clusters, corresponding to the five OA conformers, assuming that any conformation of a ternary cluster composition can be formed from the hydrogen bonded interaction of one AM monomer with any of the corresponding binary composition.

Table 4. Successive Binding Free Energies (ΔG_S) for the Formation of Various (OA)(AM)₂ Ternary Clusters, Derived from the Addition of an AM Monomer to Pre-Existing (OA)(AM) Binary Clusters

Final channel (ternary cluster)	Initial channel (binary cluster + AM)	ΔG_S (kcal/mol)
(cTc)(AM)₂-1	(cTc)(AM) + AM	–2.21
(cTc)(AM)₂-2	(cTc)(AM) + AM	1.99
(cTt)(AM)₂-1	(cTt)(AM)-1 + AM	–2.81
(cTt)(AM)₂-1	(cTt)(AM)-2 + AM	0.83
(cTt)(AM)₂-2	(cTt)(AM)-1 + AM	–1.56
(cTt)(AM)₂-2	(cTt)(AM)-2 + AM	2.08
(tTt)(AM)₂-1	(tTt)(AM) + AM	–2.36
(tTt)(AM)₂-2	(tTt)(AM) + AM	1.87
(tCt)(AM)₂-1	(tCt)(AM) + AM	–2.72
(tCt)(AM)₂-2	(tCt)(AM) + AM	1.27
(cCt)(AM)₂-1	(cCt)(AM)-1 + AM	0.52
(cCt)(AM)₂-1	(cCt)(AM)-2 + AM	–2.88
(cCt)(AM)₂-2	(cCt)(AM)-1 + AM	0.47
(cCt)(AM)₂-2	(cCt)(AM)-2 + AM	–2.93

In the case of simultaneous cluster formation, as shown in Table 3, all ten ternary structures show negative ΔG values, with conformation-1 consistently having a significantly lower ΔG than conformation–-2, except in (cCt)(AM)₂. However, in successive cluster formation, not all binding free energies (ΔG_S) are negative, indicating some selectivity or preference. For binary compositions with a single conformation─(cTc)(AM), (tTt)(AM), and (tCt)(AM)─only for the formation of (cTc)(AM)₂-1, (tTt)(AM)₂-1, and (tCt)(AM)₂-1 shows negative ΔG_S values. These are the ternary conformations with a lower ΔG of simultaneous cluster formation within their respective compositions. On the other hand, for binary compositions with two conformations, only the one with lower ΔG is capable of forming a ternary cluster with negative ΔG_S. For example, theoretically, both (cCt)(AM)₂-1 and (cCt)(AM)₂-2 could be formed from either (cCt)(AM)-1 or (cCt)(AM)-2 via successive cluster formation. However, since ΔG[(cCt)(AM)-2] < ΔG[(cCt)(AM)-1], the thermodynamically favorable cluster formation pathways are (cCt)(AM)-2 + AM → (cCt)(AM)₂-1 with ΔG_s = −2.88 kcal/mol and (cCt)(AM)-2 + AM → (cCt)(AM)₂-2 with ΔG_s = −2.93 kcal/mol. Thus, (cCt)(AM)-2 can spontaneously grow in size through successive cluster formation, while (cCt)(AM)-1 cannot. Similarly, (cTt)(AM)-1 can grow through successive cluster formation due to its lower ΔG value, while (cTt)(AM)-2 cannot.

3.3. Clusters of Oxalic Acid and Sulfuric Acid, (OA)(SA)_n (n = 1,2)

In this section, we analyze the structural and thermochemical properties of the binary and ternary clusters formed by each of the five conformers of OA (cTc, cTt, tTt, tCt, cCt) with SA at ambient condition. The configurational space of the OA–SA system is larger than that of OA–AM and we have larger numbers of cluster conformations for each OA conformation in this case. In order to be concise, we have selected three (five) lowest energy conformations of each binary (ternary) cluster composition in the present work. Figure 5 exhibits the optimized geometries of the 15 binary (OA)(SA) clusters, with each OA conformer having three conformations. Figure 6 displays the optimized structures of 25 ternary (OA)(SA)₂ cluster conformations, with five for each OA conformer. Each row in the figures corresponds to the conformations of a particular composition, labeled according to the respective OA conformer nomenclature. The relative energy differences of the conformations, in kcal/mol, are indicated in square bracket. The intermolecular HBs are indicated by black dashed lines, with respective calculated bond lengths in angstroms. The M06–2X/6-311++G(3df,3pd) optimized structure of (cTc)(SA)-1, which is the global minimum of the (cTc)(SA) conformers has an excellent agreement with binary (OA)(SA) global minimum obtained by PW91PW91/6-311++G(3df,3pd) model. (8)

Figure 5. Equilibrium geometries of stable (OA)(SA) cluster compositions. optimized at the MO6–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths given in angstrom. The numbers in square brackets represent the relative energy differences of the conformations in each cluster composition, in kcal/mol.

Figure 6. Equilibrium geometries of the stable (OA)(SA)₂ cluster compositions. optimized at the MO6–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths given in angstrom. The numbers in square brackets represent the relative energy differences of the conformations in each cluster composition, in kcal/mol.

As can be seen from Figure 5, the HB lengths of the HBs vary between 1.57 and 2.39 Å, with more than 80% of them remaining below 2.00 Å. Unlike the binary (OA)(AM) clusters, the HBs in (OA)(SA) clusters, with OA being the proton donor, are longer than those where OA acts as proton acceptor. Moreover, the differences between the bond lengths of these two types of HBs are also considerably smaller than those in (OA)(AM) systems. For example, in (cTc)(AM), we observe R_O–H···N = 1.62 Å (OA as proton donor) and R_N–H···O = 2. 25 Å (OA as proton acceptor), while in (cTc)(SA), considering its lowest energy conformation, R_O–H···O = 1.75 Å (OA as proton donor) and R_O–H···O = 1.72 Å (OA as proton acceptor), with R denoting the HB length. Similar trends are observed in other clusters as well. The HB bond angles are also similar in the case of the two – H···O HBs in the latter case. Thus, in the case of (OA)(SA) clusters, both OA and SA contribute equivalently acting as simultaneous proton donor and acceptor. The Cartesian coordinates of all the optimized geometries of OA)(SA) and (OA)(SA)₂ clusters are given in Table S3a,b, respectively. In Table S4, we report the relevant structural and spectroscopic parameters for the HBs present in (OA)(SA) binary clusters.

As illustrated in Figure 6, the ternary (OA)(SA)₂ clusters, in general, are stabilized by the formation of three-five intermolecular HBs. Depending on the positions of the two SA molecules around OA, the later may have direct participation in the formation of two to four HBs. The O–H···O HB lengths range between 1.35 and 2.16 Å, with 93% of them remaining below 2.00 Å and almost 70% below 1.80 Å. The average HB angles of the ternary cluster compositions, except (cTc)(SA)₂, are larger than those of corresponding binary clusters. For example, the average HB angle of the binary (tCt)(SA) conformers is 154.8°, while in (tCt)(SA)₂, it is 174.2°. In (cTc)(SA) and (cTc)(SA)₂ the average bond angle remains around 161°. In Table S5, we report the relevant structural and spectroscopic parameters for the HBs present in (OA)(SA)₂ clusters.

The proton-donor O–H groups of both OA and SA suffer a strong red-shift upon cluster formation. If we consider the lowest energy conformation of each binary (OA)(SA) cluster compositions, the average red-shift suffered by OH of OA is 504 cm^–1, with cTc being the only OA conformer having a red-shift below this average. On the other hand, the average red-shift experienced by the OH of SA in these same systems is 712 cm^–1. Thus, although cTc is the lowest energy OA monomer, its binary clusters with SA demonstrate weaker HB strength compared to others, and in all clusters, SA appears as a stronger proton-donor. However, in ternary (OA)(SA)₂ clusters, the average red-shift OH of OA (∼ 630 cm^–1) is almost same as that of OH of SA (∼ 620 cm^–1) showing that OA participates more effectively in HB formation in ternary clusters.

Regarding the energetics, all clusters of OA with SA display large negative ΔE_B values, as can be verified from the data reported in Tables 5 and 6. Among the conformations within each cluster composition, there is considerable variation in ΔE_B. Considering the average binding energy, ⟨ΔE_B⟩ of each cluster composition in Table 5, the binary (OA)(SA) clusters can be arranged in the following order of increasing ⟨ΔE_B⟩: (tTt)(SA) [−13.62] <; (tCt)(SA) [−13.34] <; (cTt)(SA) [−12.94] <; (cCt)(SA) [−11.82] <; (cTc)(SA) [−11.05], where the numbers in the square brackets represent the values of ⟨ΔE_B⟩ in kcal/mol. In case of ternary (OA)(SA)₂ clusters, this order is different, and it is as follows: (cCt)(SA)₂ [−35.51] <; (tCt)(SA)₂ [−33.24] <; (tTt)(SA)₂ [−31.92] <; (cTt)(SA)₂ [−28.74] <; (cTc)(SA)₂ [−27.33] from Table 6. However, when considering the lowest energy conformer of each cluster composition, among the binary clusters, (cCt)(SA)-1 exhibits the least binding energy with ΔE_B = −18.03 kcal/mol, while (cTc)(SA)-1 shows the highest value with ΔE_B = −13.69 kcal/mol. Notably, among the five OA conformers, cTc has the lowest electronic energy, while cCt has the highest. Thus, like the case of (OA)(AM) clusters, the highest energy OA conformer also forms a binary cluster with SA that has the lowest binding energy among all cluster compositions. The binding energy of (cCt)(SA)-1 is closely followed by (tCt)(SA)-1 and (tTt)(SA)-1 with ΔE_B values of −17.61 kcal/mol and −17.28 kcal/mol, respectively. In case of the ternary clusters also, the highest energy OA conformer forms the cluster (cCt)(SA)₂-1, that possesses the least binding energy with ΔE_B = −37.70 kcal/mol.

Table 5. Calculated Values of Binding Electronic Energies (ΔE), Binding Free Energy (ΔG) Associated with Different (OA)(SA) Clusters at 298.15 K, in kcal/mol, Along with their Relative Population Fraction (RPF), the Multi-Conformation Average Binding Free Energy (ΔG_MC) and the Equilibrium Constants (K_eq) of each Cluster Composition Obtained at M06-2X/6-311++G(3df,3pd) Level

	ΔE_B	E_D(OA)	E_D(tot)	ΔG	RPF	ΔG_MC	K_eq
(cTc)(SA)-1	–13.69	1.76	2.70	–3.39	99.10
(cTc)(SA)-2	–11.54	1.09	1.96	–0.58	0.88	–3.39	3.1 × 10²
(cTc)(SA)-3	–7.91	0.34	0.62	1.67	0.02
(cTt)(SA)-1	–16.10	1.39	3.42	–5.30	99.70
(cTt)(SA)-2	–11.50	1.62	2.27	–1.84	0.29	–5.30	7.8 × 10³
(cTt)(SA)-3	–11.21	1.55	3.99	0.24	0.01
(tTt)(SA)-1	–17.28	1.48	3.94	–6.69	99.99
(tTt)(SA)-2	–12.97	0.66	1.61	–1.30	0.01	–6.69	8.1 × 10⁴
(tTt)(SA)-3	–10.61	1.05	1.98	–0.26	0.00
(tCt)(SA)-1	–17.61	1.53	4.13	–6.26	99.99
(tCt)(SA)-2	–12.83	0.49	1.17	–0.41	0.01	–6.26	3.9 × 10⁴
(tCt)(SA)-3	–9.58	0.61	0.95	2.41	0.00
(cCt)(SA)-1	–18.03	1.74	4.40	–7.04	100.00
(cCt)(SA)-2	–9.68	0.35	0.81	0.13	0.00	–7.04	1.5 × 10⁵
(cCt)(SA)-3	–7.76	4.25	5.07	2.95	0.00

Table 6. Calculated Values of Binding Electronic Energies (ΔE), Binding Free Energy (ΔG) Associated with Different (OA)(SA)₂ Clusters at 298.15 K, in kcal/mol, Along with their Relative Population Fraction (RPF), the Multi-Conformation Average Binding Free Energy (ΔG_MC) and the Equilibrium Constants (K_eq) of each Cluster Composition Obtained at M06-2X/6-311++G(3df,3pd) Level

	ΔE_B	E_D(OA)	E_D(T)	ΔG	RPF	ΔG_MC	K_eq
(cTc)(SA)₂-1	–32.84	1.92	12.57	–9.65	96.61
(cTc)(SA)₂-2	–28.32	2.95	5.02	–7.67	3.38
(cTc)(SA)₂-3	–27.62	2.19	7.23	–4.20	0.01	–9.67	1.3 × 10⁷
(cTc)(SA)₂-4	–25.46	2.76	4.79	–2.92	0.00
(cTc)(SA)₂-5	–22.42	2.00	7.45	–0.32	0.00
(cTt)(SA)₂-1	–30.38	1.98	5.12	–7.01	60.15
(cTt)(SA)₂-2	–30.15	1.91	8.58	–6.66	33.10
(cTt)(SA)₂-3	–28.78	1.71	6.41	–5.26	3.15	–7.31	2.3 × 10⁵
(cTt)(SA)₂-4	–29.38	10.39	23.55	–5.28	3.23
(cTt)(SA)₂-5	–25.01	1.64	4.01	–4.00	0.37
(tTt)(SA)₂-1	–34.25	2.96	7.56	–11.82	99.43
(tTt)(SA)₂-2	–32.15	3.28	11.42	–7.70	0.10
(tTt)(SA)₂-3	–31.90	2.17	9.81	–8.56	0.40	–11.83	4.8 × 10⁸
(tTt)(SA)₂-4	–30.68	1.89	5.09	–7.11	0.03
(tTt)(SA)₂-5	–30.63	1.25	10.04	–7.19	0.04
(tCt)(SA)₂-1	–35.76	3.29	13.57	–10.08	6.53
(tCt)(SA)₂-2	–34.71	2.90	7.59	–11.65	92.27
(tCt)(SA)₂-3	–33.36	1.63	17.43	–8.91	0.91	–11.70	3.9 × 10⁸
(tCt)(SA)₂-4	–32.54	2.26	10.05	–8.25	0.30
(tCt)(SA)₂-5	–29.83	1.71	7.28	–5.22	0.00
(cCt)(SA)₂-1	–37.70	4.36	13.19	–13.31	99.41
(cCt)(SA)₂-2	–33.70	1.81	17.50	–10.16	0.49
(cCt)(SA)₂-3	–32.98	2.40	9.77	–9.24	0.10	–13.31	5.9 × 10⁹
(cCt)(SA)₂-4	–29.80	2.92	8.67	–5.83	0.00
(cCt)(SA)₂-5	–28.38	5.78	11.18	–4.57	0.00

Considering the thermal correction to electronic energy, we observe that not all binary cluster conformers show thermodynamic stability at ambient temperature. In the case of the three conformers of (cCt)(SA) composition, for example, only (cCt)(SA)-1 has negative ΔG, and it is also the one with lowest binding free energy among all the binary clusters considered here, with ΔG = −7.04 kcal/mol. Only binary composition whose all conformations show negative ΔG values at room temperature is (tTt)(SA), with (tTt)(SA)-1 having the binding free energy very close to (cCt)(SA)-1 with ΔG = −6.69 kcal/mol. The binary cluster of cTc, the lowest energy OA monomer, with SA shows the highest ΔG value. The ternary clusters of OA with SA, however, show a different nature where all the five conformations of each cluster composition show negative ΔG valuess of varying magnitudes at 298.15K. The lowest energy conformation of each cluster composition has the lowest ΔG of the respective group except (tCt)(SA)₂ where second lowest conformer (tCt)(SA)₂-2 shows lowest value with ΔG = −11.65 kcal/mol, followed by (tCt)(SA)₂-1 with ΔG = −10.08 kcal/mol. Considering the ΔG_MC values, the ternary clusters can be arranged in the order of increasing thermodynamical stability as follows: (cTt)(SA)₂ <; (cTc)(SA)₂ <; (tCt)(SA)₂ <; (tTt)(SA)₂ <; (cCt)(SA)₂. Thus, in both the binary and ternary clusters of OA with SA, cCt, the highest energy OA conformer, forms the most thermodynamically stable interaction with the lowest ΔG values. Overall, the ΔG values of the (OA)(SA)₂ clusters are much lower than those of the binary (OA)(SA) clusters, indicating higher stability for the ternary clusters.

Regarding the relative population fraction (RPF) of the binary (OA)(SA) clusters, a similar trend to that observed in (OA)(AM) clusters is observed, with the lowest energy conformer of each cluster dominating the population with an RPF of nearly 100%. In the case of (OA)(SA) trimers, a similar trend is observed, with the lowest ΔG conformer of each cluster composition having the dominant RPF. This dominance is over 90% in all cases except for (cTt)(SA)₂, where due to the small difference in ΔG values between (cTt)(SA)₂-1 and (cTt)(SA)₂-2, the RPFs of these two conformers are 60.15% and 33.10%, respectively.

Both in the binary and ternary clusters of OA with SA, the conformers cCt, tTt, and tCt of OA form the three most stable clusters, as indicated by their low ΔG values, which correspond to the highest equilibrium constants. Among the binary clusters, (cCt)(SA) shows the highest equilibrium constant (K_eq = 1.5 × 10⁵), followed by (tTt)(SA) and (tCt)(SA) with K_eq values of 8.1 × 10⁴ and 3.9 × 10⁴, respectively. Therefore, under ambient conditions, the (cCt)(SA) population should be nearly double that of (tTt)(SA) and about three times greater than that of (tCt)(SA). For the ternary clusters, [(cCt)(SA)₂ shows the highest equilibrium constant (K_eq = 5.9 × 10⁹) which is 13 and 15 times higher than those (tTt)(AM)₂ and (tCt)(AM)₂, respectively.

Similarly to the (OA)(AM)₂ clusters, an analysis of successive cluster formation was conducted for the (OA)(SA)₂ clusters under the same theoretical assumption that any conformation of a ternary cluster composition can form through the hydrogen-bonded interaction between an SA monomer and any corresponding binary cluster. The calculated values of successive binding free energies (ΔG_S) for all conformations of the five ternary (OA)(SA)₂ cluster compositions, corresponding to the five OA conformers, are presented in Table S5. As seen from the table, unlike the case of (OA)(AM)₂ clusters, the selectivity is much less pronounced in the successive formation of (OA)(SA)₂ clusters, with the majority of successive interactions yielding negative ΔG_S values. This suggests that clusters of SA with any OA conformer can grow in size more readily than the corresponding AM clusters.

3.4. Atmospheric Relevance of the Binding Free Energies

Determining the concentrations of various binary and ternary clusters of OA with AM and SA under realistic atmospheric conditions is of interest, regarding the atmospheric relevance of these systems. These concentrations can serve as potential indicators of their presence in the atmosphere. The equilibrium constants (K_eq) for the formation of these clusters from simultaneous agglomeration of the respective monomers, derived from their standard multiple-component binding free energies (ΔG at 298.15 K and 1 atm) and presented in Tables 3, 5, and 6, can be utilized for this analysis.

As has been discussed previously in the literature, (5−8) K_eq can also be defined for a cluster formation reaction like OA + nX→(OA)(X)_n as

K_{eq} = \frac{[(OA) {(X)}_{n}]}{[OA] {[X]}^{n}}

In the present case, X = AM or SA and n = 1,2. [OA], [X], and [(OA)(X)_n] are the vapor pressures of OA, X, and their cluster (OA)(X)_n, respectively. With this we can determine the percentage population fraction (%PF) of the OA clusters with respect to the OA monomer as,

% P F = \frac{[(OA) {(X)}_{n}]}{[OA]} \times 100 = K_{eq} {[X]}^{n} \times 100

Baesd on the atmospherically relevant gas-phase concentrations of OA, AM, and SA, which are 5.0 × 10¹¹, 2.5 × 10¹⁰, and 5.0 × 10⁷ molecules/cm³, respectively, as reported in the literature, (5−8) we calculate the determine the %PF and the concentration of all the binary and ternary OA-clusters at the standard atmospheric condition of 298.15K and 1 atm, as reported in Table 7.

Table 7. Calculated Values of the Percentage Population Fraction (%PF) and Estimated Concentrations [C], in molecules/cm³, for Different Binary and Ternary (OA)(AM) and (OA)(SA) Cluster Compositions at 298.15K and 1 atm

AM-containing cluster	%PF	[C]	SA-containing cluster	%PF	[C]
(cTc)(AM)	4.77 × 10^–5	2.39 × 10⁵	(cTc)(SA)	6.24 × 10^–8	3.12 × 10²
(cTt)(AM)	2.04 × 10^–4	1.02 × 10⁶	(cTt)(SA)	1.57 × 10^–6	7.87 × 10³
(tTt)(AM)	3.08 × 10^–5	1.54 × 10⁵	(tTt)(SA)	1.65 × 10^–5	8.25 × 10⁴
(tCt)(AM)	9.75 × 10^–6	4.87 × 10⁴	(tCt)(SA)	7.98 × 10^–6	3.99 × 10⁴
(cCt)(AM)	4.92 × 10^–4	2.46 × 10⁶	(cCt)(SA)	2.98 × 10^–5	1.49 × 10⁵
(cTc)(AM)₂	2.00 × 10^–12	9.99 × 10^–3	(cTc)(SA)₂	5.15 × 10^–15	2.58 × 10^–5
(cTt)(AM)₂	5.85 × 10^–14	2.83 × 10^–4	(cTt)(SA)₂	9.55 × 10^–17	4.77 × 10^–7
(tTt)(AM)₂	1.66 × 10^–12	8.30 × 10^–3	(tTt)(SA)₂	1.98 × 10^–13	9.91 × 10^–4
(tCt)(AM)₂	9.66 × 10^–13	4.83 × 10^–3	(tCt)(SA)₂	1.59 × 10^–13	7.96 × 10^–4
(cCt)(AM)₂	4.29 × 10^–13	2.15 × 10^–3	(cCt)(SA)₂	2.42 × 10^–12	1.21 × 10^–2

As can be seen from the table, the binary clusters show atmospherically relevant concentrations, and it varies in the range of 10⁴ – 10⁶ molecules/cm³ for (OA)(AM) and 10² – 10⁵ molecules/cm³ for (OA)(SA) compositions. Thus, some of the binary cluster concentrations are comparable to gas-phase SA concentrations. The estimated concentration of 2.39 × 10⁵ molecules/cm³ for (cTc)(AM) is also comparable with 8.02 × 10⁵ molecules/cm³ obtained for the same system previously by PW91PW91/6-311++G(3df,3pd) level of theory. (7) Calculated concentrations of the ternary clusters are considerably smaller, with the (cCt)(SA)₂ composition showing the maximum value.

Although the binding free energies calculated at standard atmospheric conditions are useful to assess the thermodynamical stability of the molecular clusters from quantum thermochemistry point of view, they may not be sufficient to evaluate their atmospheric relevance as no atmospherically relevant molecules actually have a partial pressure of 1 atm. (84) Correction of ΔG by considering the effect of partial pressure of the reactant species may provide more realistic insight regarding the atmospheric relevance of these interactions which can be accomplished by the following general expression: (84)

Δ G (p_{1}, p_{2} \cdot\cdot\cdot p_{n}) = Δ G_{ref} - k_{B} T (1 - \frac{1}{n}) \sum_{i}^{n} \ln (\frac{p_{i}}{p_{ref}})

Here, n is the number of different monomers in the cluster, and p_i is the partial pressure of monomer i. In the present case, n = 2 as we consider the clusters of OA conformers either with AM or with SA, p_ref = 1 atm and ΔG_ref = ΔG_MC, calculated at standard temperature and pressure and reported in Tables 3, 5, and 6. The above expression then reduces to

Δ G (p_{OA}, p_{X}) = Δ G_{MC (X)} - \frac{1}{2} k_{B} T (\ln \frac{p_{OA}}{p_{ref}} + \ln \frac{p_{X}}{p_{ref}})

Where, X represents AM or SA monomer, p_OA is the partial pressure of OA, and p_X is the partial pressure of either AM or SA. ΔG_MC(X) denotes the ΔG_MC values for clusters containing either AM or SA, depending on whether X corresponds to AM or SA. For the gas-phase concentrations of OA, AM, and SA, mentioned above, the second term of the above equation evaluates to −11.26 and −13.01 kcal/mol, when X is AM and SA, respectively. Thus, for ΔG(p_OA, p_X) to be negative at 298.15K, indicating spontaneous cluster formation under atmospherically relevant conditions, ΔG_MC values of the (OA)(AM)_n and (OA)(SA)_n clusters must be lower than −11.26 and −13.08 kcal/mol, respectively. Thus, from the ΔG_MC values for simultaneous cluster formation reported in Tables 3, 5,and 6, we observe that (cCt)(SA)₂, with ΔG_MC = −13.31 kcal/mol, is the only cluster composition which is thermodynamically stable in realistic atmospheric conditions at 298.15K. This is the same composition that showed highest concentration among the ternary clusters.

3.5. Interaction with Solar Radiation

The molecules present in the atmosphere interact with solar radiation. In fact, the elastic and inelastic scattering of solar radiation by atmospheric particles plays a significant role in understanding various phenomena related to visibility and radiative forces in the atmosphere. Elastic scattering of light, also known as Rayleigh scattering, stands out as the predominant optical phenomenon for small atmospheric molecular clusters, playing a vital role in various atmospheric processes. The intensity of Rayleigh scattering, often termed Rayleigh activity, depends on the dipole polarizability of the molecular system and its anisotropy. Polarizability (α) is a measure of how easily the electron cloud of a molecule can be distorted by an external electric field, that results in the creation of an induced dipole moment in the molecule. Anisotropy of polarizability refers to the directional dependence of the polarizability. Together, these characteristics govern the extent of interaction between incident radiation and the molecules, thereby influencing the scattering intensity. This fundamental interplay sheds light on the intricate dynamics of light-matter interactions within the atmosphere, providing insights into their complex behavior and processes. The formation of hydrogen-bonded molecular clusters can significantly affect the Rayleigh scattering intensity compared to their respective monomers due to variations in polarizability and anisotropy besides different cooperative effects.

In Figure 7, we present the percentage variation of mean dipole polarizability

(\bar{α})

, anisotropy of the polarizability (Δα), Rayleigh Activity (

R

), and degree of depolarization for natural light (σ) in all the clusters, relative to respective OA monomers. The values of these parameters for the monomers are reported in Table 1. Given that the clusters exhibit multiple conformations, we calculated the weighted average of each parameter (x) for each cluster composition by considering the Boltzmann factor of the respective members, exp(-ΔG_k/RT) and using the formula

⟨ x ⟩ = \frac{\sum_{k} x_{k} \exp (- \frac{Δ G_{k}}{R T})}{\sum_{i} \exp (- \frac{Δ G_{i}}{R T})}

where R = 8.314 J/(mol·K) is the universal gas constant, T is the ambient temperature, and ΔG_k is the binding free energy of the kth member of a given cluster composition. These average values were then used to evaluate the percentage variations.

Figure 7. Percentage variation of mean dipole polarizability, anisotropy of the polarizability, Rayleigh activity, and degree of depolarization for natural light in all the clusters, relative to respective OA monomers.

Since polarizability depends on molecular volume, it is expected that polarizability will increase upon cluster formation. This is confirmed by the figure, which shows an almost linear increase in mean polarizability as we progress from OA to (OA)(AM) or (OA)(SA) and then to (OA)(AM)₂ or (OA)(SA)₂ with OA representing any of the five OA monomers. Given that SA has a larger volume than AM, clusters of OA with SA show much higher increase in mean polarizability compared to clusters of AM with OA. For all OA monomers, polarizability increases by nearly 37% when they form binary clusters with AM and by almost 94% when forming binary clusters with SA. Similarly, in ternary clusters, the increase in mean polarizability is almost 75% for interaction with AM and 185% when interacting with SA. Considering the weighted average value of mean polarizability,

⟨ \bar{α} ⟩

, for each cluster composition individually, we find that the values are quite similar for five OA conformers. However, the anisotropy of polarizability does not exhibit the same regular and linear increase pattern as that of polarizability, although it increases upon cluster formation in all cases. Maximum increase of anisotropy, compared to the OA monomer, is observed for (tTt)(SA)₂, followed very closely by (tCt)(SA)₂. Conversely, the binary clusters formed between OA conformers and AM show less variation in Δα, consistently remaining below 50% in all cases. The average degree of depolarization (<σ > ,) decreases in all clusters, except (cTc)(AM)₂, when compared to the respective OA monomers. Among the ternary OA–AM clusters, (cTc)(AM)₂ possesses the highest polarizability with α = 67.24 au as well as the highest anisotropy with Δα = 42.23 au, while the average α and Δα for this ternary group are 66.51 and 31.76 au, respectively. Consequently, the < σ > value of (cTc)(AM)₂ is high compared to others. The increase in the weighted average value of Rayleigh intensity (<

R

>) in the ternary (OA)(SA)₃ clusters with respect to the OA monomer (exceeding 600%) is significantly higher than that of all other clusters. For the (OA)(AM)₂ and (OA)(SA) cluster configurations, the increase of <

R

> ranges from 250% to 350% compared to the respective OA monomers, while in all (OA)(AM) binary clusters, the increase is limited to 100% or less.

We can also analyze the increase in the Rayleigh scattering intensities due to clustering relative to all participating monomers using a supermolecular approach, where the excess Rayleigh intensity (Δ

R

) will be determined by taking the difference in the scattering intensity between the cluster and the sum of the individual molecular intensities. Considering the weighted average value of Rayleigh intensity (<

R

>) of the clusters and the

R

of the corresponding monomers, we again observe an appreciable of Rayleigh intensity increase upon clustering in all cases which is illustrated in Figure 8.

Figure 8. Excess Rayleigh scattering intensity (Δ $R$ ) due to clustering of OA with AM and SA.

In all the binary (OA)(AM) clusters, Δ

R

values remain consistently close to an average of 5.4 × 10⁴ au, indicating that all five OA conformers interacting with an ammonia molecule via hydrogen bonding acquire similar molecular volumes, which leads to comparable polarizability and thus similar Rayleigh activities. A similar trend is observed in the ternary (OA)(AM)₂ clusters, albeit with a higher average Δ

R

of 13.0 × 10⁴ a.u., reflecting that the intermolecular interactions increase consistently across all the compositions of ternary (OA)(AM)₂ clusters. The binary (OA)(SA) clusters also show a consistent increase in Rayleigh activity, with Δ

R

values very similar to those of the (OA)(AM)₂ clusters. In fact, (cTc)(AM)₂ and (cTc)(SA) exhibit identical increases in Rayleigh activity upon cluster formation, with Δ

R

= 14.2 × 10⁴ a.u., suggesting that sulfuric acid interacts more strongly with oxalic acid than ammonia does. Moreover, this value also represents the highest increase in Rayleigh activity within both the (OA)(AM)₂ and (OA)(SA) families. The Δ

R

values of ternary (OA)(SA)₂ clusters are significantly higher than those of all other clusters, with an average value of 37.7 × 10⁴ a.u. Unlike the other cluster families, the Δ

R

values of (OA)(SA)₂ show appreciable composition dependence, with (cCt)(SA)₂ having the lowest Δ

R

(34.8 × 10⁴ a.u.) and (tTt)(SA)₂ cluster the highest (40.5 × 10⁴ a.u.). This large increase in Δ

R

(OA)(SA)₂ compared to (OA)(SA) clusters indicates that the increase of sulfuric acid molecules leads to significantly stronger intermolecular interactions.

On a different perspective, comparison of <

R

> values among the four cluster families─(OA)(AM), (OA)(AM)₂, (OA)(SA), and (OA)(SA)₂─each having five members (compositions corresponding to the five OA conformers), either by composition or size, also reveals appreciable variations, as can be verified from the data reported in Table S6. For example, Considering the increase in cluster size, the average increase in

R

is 97% for (OA)(AM)₂ ternary clusters and 114% for (OA)(SA)₂ ternary clusters compared to their respective binary clusters─(OA)(AM) and (OA)(SA). Among the (OA)(AM) clusters, the highest increase (117%) is observed in (cTc)(AM)₂, while the lowest (50%) occurs in (cCt)(AM)₂. In case of (OA)(SA)₂, all compositions show over 100% increase in

R

values going from binary to ternary cluster, with (tTt)(SA)₂, showing the highest increase (124%) while (cTt)(SA)₂ and (cCt)(SA)₂, showing lowest increase, both with 105%.

When the compositions are compared, clusters of OA with SA consistently show higher Rayleigh intensity than the clusters of OA with AM due to their larger molecular volume. On average, the

R

values in binary (OA)(SA) and ternary (OA)(SA)₂ clusters are higher than their corresponding (OA)(AM) and (OA)(AM)₂ counterparts by 98% and 118%, respectively. However, there is a big difference in the individual behaviors of the members. However, significant variation is observed among the individual members. In the binary clusters, the largest difference is seen between (cTt)(SA) and (cTt)(AM), with the former’s

R

value being 99% higher, while the smallest variation of 96% is found between (cTc)(SA) and (cTc)(AM), indicating a consistent behavior with only a 3% difference between the maximum and minimum increases. On the other hand, for ternary clusters, the largest difference is observed between (cCt)(SA)₂ and (cCt)(AM)₂, with the former having 170% higher

R

value, while the smallest difference, 91%, is observed between (OAA)(SA)₂ and (OAA)(AM)₂. Other ternary clusters in this series─ (cTt)(SA)₂, (tTt)(AM)₂, and (tCt)(AM)₂─show increases of 111%, 110%, and 107%, respectively, with respect to their corresponding (OA)(AM)₂ counterparts. These variations reflect considerable variation in molecular volume among ternary (OA)(SA) clusters

Finally, examining the four cluster families individually, we observe that the OA conformer cTc forms the clusters with the highest Rayleigh activity in all families except for (OA)(SA)₂, It is (tTt)(SA)₂ that has the highest

R

value in the (OA)(SA)₂ family. Within the (OA)(AM) and (OA)(AM)₂ families, the lowest

R

is observed in (cTt)(AM) and (cCt)(AM)₂, respectively, and within the (OA)(SA) and (OA)(SA)₂ families, (cCt)(SA) and (cTt)(SA)₂ exhibit the lowest values. The difference between the highest and lowest

R

values in the (OA)(AM)₂ family is nearly 50%, the most significant variation within any family, followed by the (OA)(SA)₂ family, where the highest Rayleigh intensity is approximately 11% greater than the lowest.

4. Conclusions

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In the present work, an extensive DFT calculation, employing the M06 – 2X/6-311+ +G(3df,3pd) model, was performed on the hydrogen-boned molecular interactions between five stable structural conformers of OA (cTc, cTt, tTt, tCt, and cCt) and two important atmospheric nucleation precursor molecules, SA and AM. Several structural, thermodynamical, electrical, and spectroscopic parameters of the binary and ternary clusters mediated by oxalic acid were analyzed to gain insight into the hydrogen bonding nature of each OA conformer at standard atmospheric conditions. Multiple stable configurations for each kind of cluster composition, obtained by a combination of different quantum-chemical approaches and chemical intuition, were considered for the analysis. All OA conformers form strong hydrogen bonding with AM, showing thermodynamic stability at the ambient temperature, with average red shift of the OA O–H stretching mode of 934 (1088) cm^–1 in binary (ternary) clusters. In ternary OA–AM clusters, the lowest energy OA conformer, cTc, has the lowest binding free energy, followed very closely by other conformers like tTt and tCt. In (OA)(SA) binary clusters, this same conformer exhibits the lowest binding energy. Although some of the binary (OA)(SA) clusters show positive values of binding free energy, ΔG at ambient temperature, the ternary (OA)(SA)₂ clusters, however, show a different nature where all the conformations of each cluster composition show stability with negative ΔG values of varying magnitudes. Considering the effect of different conformations, the ternary OA–SA clusters can be arranged in the order of decreasing multiple-conformation binding free energy, ΔG_MC as follows: (cTt)(SA)₂ >; (cTc)(SA)₂ >; (tCt)(SA)₂ >; (tTt)(SA)₂ >; (cCt)(SA)₂, with the highest energy OA conformer, cCt once again showing lowest free binding energy. Overall, the ΔG values of the (OA)(SA)₂ clusters are much lower than those of the binary (OA)(SA) clusters, indicating higher stability for the ternary clusters. In general, OA–SA clusters have lower ΔG values than the OA-AM clusters according to the present calculations. Comparing the ΔG_S values for successive cluster formation for both (OA)(AM)₂ and (OA)(SA)₂, it is observed that the clusters of SA with OA are more likely to grow spontaneously. Consideration of partial pressures of the monomers in the calculation of binding free energy reveals that the ΔG values of the (OA)(AM)_n and (OA)(SA)_n clusters should be lower than −11.26 and −13.01 kcal/mol, respectively, in order to have a thermodynamical stability in a realistic atmospheric condition at 298.15K. Among all the clusters considered, only (cCt)(SA)₂ satisfies this condition with ΔG = −13.31 kcal/mol. When comparing the Rayleigh activity of the clusters to that of the OA monomer, a notable increase in Rayleigh scattering intensity is observed due to the hydrogen-bonded molecular interactions present in all OA-mediated clusters. Specifically, the Rayleigh activity in the ternary (OA)(SA)₂ clusters shows a variation exceeding 600% with respect to OA, which is the highest and significantly greater than that observed in all other clusters. The determination of excess Rayleigh activity due to clustering, calculated using a supermolecular approach, also shows a significant increase in all cases. Notably, the (OA)(SA)₂ clusters exhibit considerably superior activity compared with other clusters. A less pronounced, but appreciable variation of Rayleigh activities is also observed when comparing the cluster among themselves, considering both size and composition. The average increase in Rayleigh scattering intensities observed going from binary to ternary clusters of OA, either with AM or SA, is close to 100%. Rayleigh intensities in (OA)(SA)₂ clusters exceed those of (OA)(SA)₂ clusters also by 100%, on average. The results obtained provide insights into the behavior of each stable structural conformer of oxalic acid, particularly in terms of their interaction potential with key atmospheric molecules under standard atmospheric conditions. We believe that this information may be relevant in the studies of environmental processes, given that oxalic acid is one of the most abundant naturally occurring dicarboxylic acids in the atmosphere.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c06290.

Containing the optimized bond lengths and bond angles of different oxalic acid conformers; the Cartesian coordinates of the optimized geometries of binary and ternary clusters of OA with AM and SA; relevant structural parameters related to hydrogen bond formation in (OA)(SA) and (OA)(SA)₂ clusters, supported by the ternary cluster images (Figure S1); successive binding free energies (ΔG_S) for the formation of various (OA)(SA)₂ ternary clusters and Boltzman-averaged values of Rayleigh scattering intensities of the OA conformers and their binary and ternatry clusters with AM and SA (PDF)

ao4c06290_si_001.pdf (677.52 kb)

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Author Information

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Corresponding Author
- Puspitapallab Chaudhuri - Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil; https://orcid.org/0000-0001-9748-9890; Email: [email protected]
Authors
- Eduardo da Silva Carvalho - Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil
- Angsula Ghosh - Department of Materials Physics, Federal University of Amazonas, Manaus, AM 69080-900, Brazil; https://orcid.org/0000-0002-1798-3643
Funding
The Article Processing Charge for the publication of this research was funded by the Coordination for the Improvement of Higher Education Personnel - CAPES (ROR identifier: 00x0ma614).
Notes
The authors declare no competing financial interest.

Acknowledgments

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The authors acknowledge financial support from the Brazilian funding agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)─finance code 001, Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

References

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Xu, Wen; Zhang, Renyi
Journal of Physical Chemistry A (2012), 116 (18), 4539-4550CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
Dicarboxylic acids are important products from photooxidn. of volatile org. compds. and are believed to play an important role in the formation and growth of atm. secondary org. aerosols. In this paper, the interaction of five dicarboxylic acids, i.e., oxalic acid (C2H2O4), malonic acid (C3H4O4), maleic acid (C4H4O4), phthalic acid (C8H6O4), and succinic acid (C4H6O4), with sulfuric acid and ammonia has been studied, employing quantum chem. calcns., quantum theory of atoms in mols. (QTAIM), and the natural bond orbital (NBO) anal. methods. Several levels of quantum chem. calcns. are considered, including coupled-cluster theory with single and double excitations with perturbative corrections for the triple excitations (CCSD(T)) and two d. functionals, B3LYP and PW91PW91. The free energies of formation of the heterodimer and heterotrimer clusters suggest that dicarboxylic acids can contribute to the aerosol nucleation process by binding to sulfuric acid and ammonia. In particular, the formation energies and structures of the heterotrimer clusters show that dicarboxylic acids enhance nucleation in two directions, in contrast to monocarboxylic acids.
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Weber, K. H.; Morales, F. J.; Tao, F. Theoretical study on the structure and stabilities of molecular clusters of oxalic acid with water. J. Phys. Chem. A 2012, 116, 11601– 11617, DOI: 10.1021/jp308499f
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Theoretical Study on the Structure and Stabilities of Molecular Clusters of Oxalic Acid with Water
Weber, Kevin H.; Morales, Francisco J.; Tao, Fu-Ming
Journal of Physical Chemistry A (2012), 116 (47), 11601-11617CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
The importance of aerosols to humankind is well-known, playing an integral role in detg. Earth's climate and influencing human health. Despite this fact, much remains unknown about the initial events of nucleation. In this work, the mol. properties of common org. atm. pollutant oxalic acid and its gas phase interactions with water have been thoroughly examd. Local min. single-point energies for the monomer conformations were calcd. at the B3LYP and MP2 level of theory with both 6-311++G(d,p) and aug-cc-pVDZ basis sets and are compared with previous works. Optimized geometries, relative energies, and free energy changes for the stable clusters of oxalic acid conformers with up to six waters were then obtained from B3LYP calcns. with 6-31+G(d) and 6-311++G(d,p) basis sets. Initially, cooperative binding is predicted to be the most important factor in nucleation, but as the clusters grow, dipole cancellations are found to play a pivotal role. The clusters of oxalic acid hydrated purely with water tend to produce extremely stable and neutral core systems. Free energies of formation and atm. implications are discussed.
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Weber, K. H.; Liu, Q.; Tao, F.-M. Theoretical study on stable small clusters of oxalic acid with ammonia and water. J. Phys. Chem. A 2014, 118, 1451– 1468, DOI: 10.1021/jp4128226
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Theoretical Study on Stable Small Clusters of Oxalic Acid with Ammonia and Water
Weber, Kevin H.; Liu, Qian; Tao, Fu-Ming
Journal of Physical Chemistry A (2014), 118 (8), 1451-1468CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
Thermodynamically stable small clusters of oxalic acid (CO2H)2, ammonia (NH3), and water (H2O) are studied through quantum chem. calcns. The (CO2H)2-NH3 core system with up to three waters of hydration was examd. by B3LYP d. functional theory and MP2 MO theory with the aug-cc-pVDZ basis set. The (CO2H)2-NH3 core complexes are obsd. to hydrogen bond strongly and should be found in appreciably significant concns. in the atm. Subsequent hydration of the (CO2H)2-NH3 core, however, is found to be somewhat prohibitive under ambient conditions. Relative populations of the examd. clusters are predicted and the binding patterns detailed. Atm. implications related to new particle formations are discussed.
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Peng, X.-Q.; Liu, Y.-R.; Huang, T.; Jiang, S.; Huang, W. Interaction of gas phase oxalic acid with ammonia and its atmospheric implications. Phys. Chem. Chem. Phys. 2015, 17, 9552– 9563, DOI: 10.1039/C5CP00027K
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Interaction of gas phase oxalic acid with ammonia and its atmospheric implications
Peng, Xiu-Qiu; Liu, Yi-Rong; Huang, Teng; Jiang, Shuai; Huang, Wei
Physical Chemistry Chemical Physics (2015), 17 (14), 9552-9563CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Oxalic acid is believed to play an important role in the formation and growth of atm. org. aerosols. However, as a common org. acid, the understanding of the larger clusters formed by gas phase oxalic acid with multiple ammonia mols. is incomplete. In this work, the structural characteristics and thermodn. of oxalic acid clusters with up to six ammonia mols. have been investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that oxalic acid forms relatively stable clusters with ammonia mols., and that ionization events play a key role. The analyses of the thermodn. and atm. relevance indicate that the heterodimer (H2C2O4)(NH3) shows an obvious relative concn. in the atm., and thus likely participates in new particle formation. However, with increasing no. of ammonia mols., the concn. of clusters decreases gradually. Addnl., clusters of oxalic acid with ammonia mols. are predicted to form favorably in low temp. conditions and show high Rayleigh scattering intensities.
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Miao, S.-K.; Jiang, S.; Chen, J.; Ma, Y.; Zhu, Y.-P.; Wen, Y. Hydration of a sulfuric acid-oxalic acid complex: acid dissociation and its atmospheric implication. RSC Adv. 2015, 5, 48638– 48646, DOI: 10.1039/C5RA06116D
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Hydration of a sulfuric acid-oxalic acid complex: acid dissociation and its atmospheric implication
Miao, Shou-Kui; Jiang, Shuai; Chen, Jiao; Ma, Yan; Zhu, Yu-Peng; Wen, Yang; Zhang, Miao-Miao; Huang, Wei
RSC Advances (2015), 5 (60), 48638-48646CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
Oxalic acid (OA), one of the most common org. acids in the Earth's atm., is expected to enhance the nucleation and growth of nanoparticles contg. sulfuric acid (SA) and water (W); however, the details about the hydration of OA-SA are poorly understood, esp. for the larger clusters with more water mols. We have investigated the structural characteristics and thermodn. of these clusters using d. functional theory at the PW91PW91/6-311++G(3df,3pd) level. The favorable free energies of formation and obvious concns. of the OA-SA-Wn (n = 0-6) clusters at 298.15 K predict that oxalic acid can contribute to the aerosol nucleation process by binding to sulfuric acid and water until n = 6. There is strong temp. dependence for the complexes formation, and the energy order of these complexes is altered from 100 to 400 K, regardless of different cluster sizes or different isomers within the same cluster size. The lower temp. and higher relative humidity promote the formation of hydrates. Addnl., the investigation of acid dissocn. predicts that several acid-dissocd. models could coexist in the atm., specifically when more water mols. are present. Fewer waters may be needed to cause the acid dissocn., as the relative acidity of the cluster increases, which plays a key role in forming relatively stable hydrated clusters of OA-SA. Finally, the Rayleigh scattering properties of OA-SA-Wn (n = 0-6) have been systematically investigated for the first time to further discuss its atm. implication.
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Pavuluri, C. M.; Kawamura, K.; Mihalopoulos, N.; Swaminathan, T. Laboratory photochemical processing of aqueous aerosols: Formation and degradation of dicarboxylic acids, oxocarboxylic acids and α- dicarbonyls. Atmos. Chem. Phys. 2015, 15, 7999– 8012, DOI: 10.5194/acp-15-7999-2015
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Wang, G.; Cheng, C.; Meng, J.; Huang, Y.; Li, J.; Ren, Y. Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface. Atmos. Environ. 2015, 113, 169– 176, DOI: 10.1016/j.atmosenv.2015.05.013
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Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface
Wang, Gehui; Cheng, Chunlei; Meng, Jingjing; Huang, Yao; Li, Jianjun; Ren, Yanqin
Atmospheric Environment (2015), 113 (), 169-176CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
Chem. evolution of East Asian dust during transpacific transport has been given much attention for inorg. species such as sulfate, nitrate and ammonium. However, the role of org. species during the transport has almost entirely been ignored. To understand the formation mechanism of secondary org. aerosols (SOA) on dust surfaces, this study investigated the concns. and compns. of dicarboxylic acids, keto-carboxylic acids, α-dicarbonyls and inorg. ions in size-segregated aerosols (9-stages) collected in Xi'an, central China during the two dust storm episodes in the springs of 2009 and 2011 and compared with those in nondust storm periods. During the events the ambient particulate dicarboxylic acids were 932-2240 ng m-3, which are comparable and even higher than those in nondust periods. Mol. compns. of the above SOA are similar to those in nondust periods with oxalic acid being the leading species. In the presence of the dust storms, all the above mentioned SOA species in Xi'an were predominantly enriched on the coarse particles (>2.1 μm), and oxalic acid well correlated with NO3- (R2 = 0.72, p < 0.001) rather than SO42-. This phenomenon differs greatly from the SOA in any other nondust period that is usually characterized by an enrichment of oxalic acid in fine mode and a strong correlation of oxalic acid with SO42-. We propose a formation pathway to explain these observations, in which nitric acid and/or nitrogen oxides react with dust to produce Ca(NO3)2 and form a liq. phase on the surface of dust aerosols via water vapor-absorption of Ca(NO3)2, followed by a partitioning of the gas-phase water-sol. org. precursors (e.g.,glyoxal and methylglyoxal) into the aq.-phase and a subsequent oxidn. into oxalic acid. To the best of our knowledge, we found for the first time the enrichment of glyoxal and methylglyoxal on dust surface. Our data suggest an important role of nitrate in the heterogeneous formation process of SOA on the surface of dust.
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Kawamura, K.; Bikkina, S. A review of dicarboxylic acids and related compounds in atmospheric424 aerosols: Molecular distributions, sources and transformation. Atmos. Res. 2016, 170, 140– 160, DOI: 10.1016/j.atmosres.2015.11.018
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A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation
Kawamura, Kimitaka; Bikkina, Srinivas
Atmospheric Research (2016), 170 (), 140-160CODEN: ATREEW; ISSN:0169-8095. (Elsevier B.V.)
This review aims to update our understanding on mol. distributions of water-sol. dicarboxylic acids and related compds. in atm. aerosols with a focus on their geog. variability, size distribution, sources and formation pathways. In general, mol. distributions of diacids in aerosols from the continental sites and over the open ocean waters are often characterized by the predominance of oxalic acid (C2) followed by malonic acid (C3) and/or succinic acid (C4), while those sampled over the polar regions often follow the order of C4 ≥ C2 and C3. The most abundant and ubiquitous diacid is oxalic acid, which is principally formed via atm. oxidn. of its higher homologues of long chain diacids and other pollution-derived org. precursors (e.g., olefins and arom. hydrocarbons). However, its occurrence in marine aerosols is mainly due to the transport from continental outflows (e.g., East Asian outflow during winter/spring to the North Pacific) and/or governed by photochem./aq. phase oxidn. of biogenic unsatd. fatty acids (e.g., oleic acid) and isoprene emitted from the productive open ocean waters. The long-range atm. transport of pollutants from mid latitudes to the Arctic in dark winter facilitates to accumulate the reactants prior to their intense photochem. oxidn. during springtime polar sunrise. Furthermore, the relative abundances of C2 in total diacid mass showed similar temporal trends with downward solar irradn. and ambient temps., suggesting the significance of atm. photochem. oxidn. processing. Compd.-specific isotopic analyses of oxalic acid showed the highest δ13C among diacids whereas azelaic acid showed the lowest value, corroborating the significance of atm. aging of oxalic acid. On the other hand, other diacids gave intermediate values between these two diacids, suggesting that aging of oxalic acid is assocd. with 13C enrichment.
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Peng, X.-Q.; Huang, T.; Miao, S.-K.; Chen, J.; Wen, H.; Feng, Y.-J. Hydration of oxalic acid–ammonia complex: atmospheric implication and Rayleigh-scattering properties. RSC Adv. 2016, 6, 46582– 47593, DOI: 10.1039/C6RA03164A
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Zhao, H.; Zhang, Q.; Du, L. Hydrogen bonding in cyclic complexes of carboxylic acid–sulfuric acid and their atmospheric implications. RSC Adv. 2016, 6, 71733– 71743, DOI: 10.1039/C6RA16782A
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Elm, J.; Myllys, N.; Kurtén, T. What is required for highly oxidized molecules to form clusters with sulfuric acid?. J. Phys. Chem. A 2017, 121, 4578– 4587, DOI: 10.1021/acs.jpca.7b03759
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What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?
Elm, Jonas; Myllys, Nanna; Kurten, Theo
Journal of Physical Chemistry A (2017), 121 (23), 4578-4587CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
We have studied the specific requirements of a given neutral org. mol. to act as a stabilizer in sulfuric acid induced new particle formation. Based on an anal. of the reaction Gibbs free energies between simple functional groups and sulfuric acid, carboxylic acid groups are identified to show the strongest hydrogen bonding interaction with sulfuric acid. The free energy assocd. with the hydrogen bonding between sulfuric acid and 14 different carboxylic acids of atm. relevance reveal that the binding strength is very dependent on the ability of sulfuric acid to form an addnl. hydrogen bond via its vacant S-OH group to a γ-carbonyl group in the org. mol. Extending the anal. to monoterpene oxidn. products and further to large dimer esters, we identify the following necessary criteria for a given org. oxidn. product to efficiently stabilize sulfuric acid clustering: (1) weak or no intramol. hydrogen bonds in the isolated monomer; (2) more than two carboxylic acid groups. As a proof of concept we show that these requirements correspond to the docking of a sulfuric acid mol. between two non-interacting carboxylic acid groups in the org. mol. These findings suggests that, for a given org. oxidn. product to participate in the initial steps in new particle formation involving sulfuric acid, very distinct mol. features are required.
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Hu, Y.-C.; Zhang, X.-H.; Li, Q.-S.; Zhang, Y.-H.; Li, Z.-S. Effect of water on the structure and stability of hydrogen-bonded oxalic acid dimer. ChemPhyschem 2017, 18, 3375– 3383, DOI: 10.1002/cphc.201700950
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Effect of Water on the Structure and Stability of Hydrogen-Bonded Oxalic Acid Dimer
Hu, Yuan-Chun; Zhang, Xiu-Hui; Li, Quan-Song; Zhang, Yun-Hong; Li, Ze-Sheng
ChemPhysChem (2017), 18 (23), 3375-3383CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
As the simplest and most abundant dicarboxylic acid in the atm., oxalic acid (OA) not only plays a key role in aerosol nucleation, but also acts as a prototypical compd. for the investigation of intra- and intermol. hydrogen-bonding interactions. A systematic theor. study on the hydrated OA dimers performed by using DFT at the M06-2X/6-311++G(3df, 2p) level is discussed herein. The properties of hydrogen bonds in clusters are inspected through topol. anal. by using atoms in mols. (AIM) theory. The most stable OA dimer involves a cyclic structure with two intermol. hydrogen bonds. Calcns. show that one H2O has a slight effect on the hydrogen bonds, whereas two water mols. weaken and three water mols. break the two intermol. hydrogen bonds between OAs. Furthermore, there are no hydrogen-bond interactions between OAs in almost all stable clusters as the no. of H2O mols. increases to four and five. Addnl., ionization and isomerization of OA through water-assisted proton-transfer phenomena are obsd. in tetra- and pentahydrates. This work provides new insights into the conversion of anhyd. OA into hydrated clusters that are helpful for further understanding the atm. nucleation process and nature of hydrogen bond.
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Xu, J.; Finlayson-Pitts, B. J.; Gerber, R. B. Proton transfer in mixed clusters of methanesulfonic acid, methylamine, and oxalic acid: implications for atmospheric particle formation. J. Phys. Chem. A 2017, 121, 2377– 2385, DOI: 10.1021/acs.jpca.7b01223
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Proton Transfer in Mixed Clusters of Methanesulfonic Acid, Methylamine, and Oxalic Acid: Implications for Atmospheric Particle Formation
Xu, Jing; Finlayson-Pitts, Barbara J.; Gerber, R. Benny
Journal of Physical Chemistry A (2017), 121 (12), 2377-2385CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
Understanding the properties of atm. particles made of several components is a very challenging problem. In this paper, we perform quantum chem. calcns. for small multicomponent clusters of atm. relevance that incorporate methanesulfonic acid (MSA), methylamine (MA), oxalic acid (OxA), and water (H2O). Potential correlations between theor. predictions of proton transfer in the small clusters and findings of recent expts. on formation of particles of detectable sizes (>2 nm) from the same components are studied. It is proposed that proton transfer from the acid to the amine in the 1:1 clusters correlates with expts. on particle formation in systems, such as MSA-MA and MSA-MA-OxA. In the case of OxA + MA, which has been obsd. to give few particles, proton transfer does not occur for the 1:1 cluster but does for the 2:2 cluster. Adding H2O to OxA-MA promotes the occurrence of proton transfer, and corresponding particles are slightly enhanced. The partial charge on the MA component increases by adding OxA or H2O to MSA-MA, which is correlated with enhanced particle formation compared to MSA-MA alone. Ab initio mol. dynamics simulations show that proton transfer at room temp. (T = 298 K) and high temp. (T = 500 K) is little affected compared with the equil. structure (T = 0 K). These results suggest that small cluster calcns. may be useful in predicting the formation of multicomponent particles in the atm.
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Chen, J.; Jiang, S.; Liu, Y.-R.; Huang, T.; Wang, C.-Y.; Miao, S.-K. Interaction of oxalic acid with dimethylamine and its atmospheric implications. RSC Adv. 2017, 7, 6374– 6388, DOI: 10.1039/C6RA27945G
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Interaction of oxalic acid with dimethylamine and its atmospheric implications
Chen, Jiao; Jiang, Shuai; Liu, Yi-Rong; Huang, Teng; Wang, Chun-Yu; Miao, Shou-Kui; Wang, Zhong-Quan; Zhang, Yang; Huang, Wei
RSC Advances (2017), 7 (11), 6374-6388CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
Oxalic acid and dimethylamine are the most common org. acid and base in the atm., and are recognized as significant precursor species in atm. new particle formation. However, the interaction between oxalic acid and dimethylamine in the presence of hydration is not yet understood. In this study, the most stable geometric structures and thermodn. of (C2H2O4)m(CH3NHCH3)(H2O)n (m = 1-2, n = 0-4) clusters are investigated using M06-2X coupled with the 6-311+G(2d,p) basis set. A high level explicitly cor. CCSD(T)-F12/VDZ-F12 method is utilized to benchmark the d. functional theory (DFT) methods. Hydration promotes proton transfer from oxalic acid to dimethylamine for (C2H2O4)(CH3NHCH3)(H2O)n (n = 0-4) clusters, while proton transfer from oxalic acid to dimethylamine occurs without hydration for (C2H2O4)2(CH3NHCH3)(H2O)n (n = 0-4) clusters. With regards to the isomer distribution at the potential energy surface, temp. seems not to be an important parameter, since almost all of the global min. for the investigated size range dominate within the investigated temp. range, except for in the (C2H2O4)m(CH3NHCH3)(H2O)2 clusters. Under atm. conditions, the peak hydration distribution shifts from unhydrated clusters to trihydrates for the (C2H2O4)(CH3NHCH3)(H2O)n (n = 0-4) clusters, while for the (C2H2O4)2(CH3NHCH3)(H2O)n (n = 0-4) clusters, unhydrated clusters clearly dominate the cluster distribution, irresp. of whether the humidity is low or high. Finally, the formation free energies obtained from quantum calcns. are used to calc. the evapn. rates. We find that evapn. of dimethylamine is preferred compared to oxalic acid for the (C2H2O4)(CH3NHCH3)(H2O)n clusters, while the results are reversed for the (C2H2O4)2(CH3NHCH3)(H2O)n clusters.
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Arquero, K. D.; Xu, J.; Gerber, B.; Finlayson-Pitts, B. J. Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study. Phys. Chem. Chem. Phys. 2017, 19, 28286– 28301, DOI: 10.1039/C7CP04468B
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Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study
Arquero, Kristine D.; Xu, Jing; Gerber, R. Benny; Finlayson-Pitts, Barbara J.
Physical Chemistry Chemical Physics (2017), 19 (41), 28286-28301CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Atm. particles affect visibility, health, and climate but the mechanisms of their formation from initial clusters and their growth to detectable particles remain largely unknown. Previous studies showed methanesulfonic acid (MSA) reactions with NH3 and amines form particles, a process enhanced by water. Results of a combined exptl./theor. study of oxalic acid (OxA) effect on particle formation and growth from the MSA reaction with trimethylamine (TMA) in the presence/absence of water are reported. Gas phase reactants were mixed in an aerosol flow reactor at 1 atm pressure and 294° K. Particle no. concns. and size distributions were measured as a function of reaction time from 0.8-12 s. The interaction of OxA with TMA with/without water did not lead to significant particle formation. When OxA was present during the MSA reaction with TMA, there was little change (≤2 times more) in particle no. concn., but particles were larger compared vs. the base case (MSA with TMA alone). However, the presence of water with MSA and TMA overwhelmed the OxA effect so that OxA has no significant impact on particle no. concn. or size. Exptl. results suggested MSA hydrate is important for particle formation and growth in the four component OxA/MSA/TMA/water system. Results were compared to earlier studies of the OxA effect on the MSA/methylamine reaction and interpreted based on theor. calcd. properties of small clusters of the components.
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Hong, Y.; Liu, Y.-R.; Wen, H.; Miao, S.-K.; Huang, T.; Peng, X.-Q. Interaction of oxalic acid with methylamine and its atmospheric implications. RSC Adv. 2018, 8, 7225– 7234, DOI: 10.1039/C7RA13670F
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Interaction of oxalic acid with methylamine and its atmospheric implications
Hong, Yu; Liu, Yi-Rong; Wen, Hui; Miao, Shou-Kui; Huang, Teng; Peng, Xiu-Qiu; Jiang, Shuai; Feng, Ya-Juan; Huang, Wei
RSC Advances (2018), 8 (13), 7225-7234CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
Oxalic acid, which is one of the most common dicarboxylic acids, is expected to be an important component of atm. aerosols. However, the contribution of oxalic acid to the generation of new particles is still poorly understood. In this study, the structural characteristics and thermodn. of (C2H2O4)(CH3NH2)n (n = 1-4) were investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that clusters formed by oxalic acid and methylamine are relatively stable, and the more the atoms participating in the formation of a ring-like structure, the more stable is the cluster. In addn., via the anal. of atm. relevance, it can be revealed that clusters of (C2H2O4)(CH3NH2)n (n = 1-4) have a noteworthy concn. in the atm., which indicates that these clusters could be participating in new particle formation. Moreover, by comparison with (H2C2O4)(NH3)n (n = 1-6) species, it can be seen that oxalic acid is more readily bound to methylamine than to ammonia, which promotes nucleation or new particle formation. Finally, the Rayleigh scattering properties of clusters of (C2H2O4)(CH3NH2)n (n = 1-4) were investigated for the first time to det. their atm. implications.
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Boreddy, S. K. R.; Kawamura, K. Investigation on the hygroscopicity of oxalic acid and atmospherically relevant oxalate salts under sub- and supersaturated conditions. Environ. Sci.: Processes Impacts 2018, 20, 1069– 1080, DOI: 10.1039/C8EM00053K
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Lv, G.; Sun, X.; Zhang, C.; Li, M. Understanding the catalytic role of oxalic acid in SO₃ hydration to form H₂SO₄ in the atmosphere. Atmos. Chem. Phys. 2019, 19, 2833– 2844, DOI: 10.5194/acp-19-2833-2019
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Understanding the catalytic role of oxalic acid in SO3 hydration to form H2SO4 in the atmosphere
Lv, Guochun; Sun, Xiaomin; Zhang, Chenxi; Li, Mei
Atmospheric Chemistry and Physics (2019), 19 (5), 2833-2844CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
The hydration of SO3 plays an important role in atm. sulfuric acid formation. Some atm. species can be involved in and facilitate the reaction. In this work, using quantum chem. calcns., we show that oxalic acid, the most common dicarboxylic acid in the atm., can effectively catalyze the hydration of SO3. The energy barrier of the SO3 hydration reaction catalyzed by oxalic acid (cTt, tTt, tCt and cCt conformers) is a little higher or less than 1 kcal mol-1, which is lower than the energy barrier of 5.17 kcal mol-1 for water-catalyzed SO3 hydration. Compared with the rates of the SO3 hydration reaction catalyzed by oxalic acid and water, it can be found that in the upper troposphere the OA-catalyzed SO3 hydration can play an important role in promoting SO3 hydration. It leads us to conclude that the involvement of oxalic acid in SO3 hydration to form H2SO4 is significant in the atm.
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Deshmukh, D. K.; Kawamura, K.; Gupta, T.; Haque, M. M.; Zhang, Y.-L.; Singh, D. K.; Tsai, Y. I. High Loadings of Water-soluble Oxalic Acid and Related Compounds in PM2.5 Aerosols in Eastern Central India: Influence of Biomass Burning and Photochemical Processing. Aerosol Air Qual. Res. 2019, 19, 2625– 2644, DOI: 10.4209/aaqr.2019.10.0543
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Zhao, Y.; Liu, Y.-R.; Jiang, S.; Huang, T.; Wang, Z.-H.; Xu, C.-X. Volatile organic compounds enhancing sulfuric acid-based ternary homogeneous nucleation: the important role of synergistic effect. Atmos. Environ. 2020, 233, 117609, DOI: 10.1016/j.atmosenv.2020.117609
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Volatile organic compounds enhancing sulfuric acid-based ternary homogeneous nucleation: The important role of synergistic effect
Zhao, Yu; Liu, Yi-Rong; Jiang, Shuai; Huang, Teng; Wang, Zi-Hang; Xu, Cai-Xin; Feng, Ya-Juan; Huang, Wei
Atmospheric Environment (2020), 233 (), 117609CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
New particle formation (NPF) is an important source of atm. aerosols. Sulfuric acid (SA) and water (W) are recognized as essential participating substances in the nucleation of the atm. In addn., as one of the most common org. acids, oxalic acid (OA) can improve NPF when amine such as methylamine (MA) is present. However, exploring the properties of atm. particles made up of different components is challenging and the role of volatile org. compds. in SA-based ternary homogeneous nucleation is still lacking in research. In this work, the structures and energies of (SA)x(OA)y(MA)z(W)m (0 ≤ x, y, z ≤ 3, 0 ≤ m ≤ 1) are investigated. The results indicate that it is accessible for SA to form clusters with OA and MA mols. through hydrogen bonds and proton transfer interactions. The anal. of non-covalent interactions and proton transfer reveals that ternary nucleation systems have stronger hydrogen bonds and more proton transfers than binary systems to stabilize the clusters. In terms of the thermodn. properties, the Gibbs free energies of the clusters will decrease as the addn. of SA, OA or MA mols. indicating that the synergistic effect of these three substances may be of potential in forming the initial cluster and subsequent growth processes. Moreover, the evapn. rates of clusters show that the synergistic effect of ternary clusters leads to a decrease in evapn. rate which may promote atm. nucleation.
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Chen, J. Theoretical analysis of sulfuric acid–dimethylamine–oxalic acid–water clusters and implications for atmospheric cluster formation. RSC Adv. 2022, 12, 22425– 22434, DOI: 10.1039/D2RA03492A
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Palmieri, F.; Estoppey, A.; House, G. L.; Lohberger, A.; Bindschedler, S.; Chain, P. S. G.; Junier, P. Oxalic acid, a molecule at the crossroads of bacterial-fungal interactions. Adv. Appl. Microbiol. 2019, 106, 49– 77, DOI: 10.1016/bs.aambs.2018.10.001
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Oxalic acid, a molecule at the crossroads of bacterial-fungal interactions
Palmieri Fabio; Estoppey Aislinn; Lohberger Andrea; Bindschedler Saskia; House Geoffrey L; Chain Patrick S G; Junier Pilar
Advances in applied microbiology (2019), 106 (), 49-77 ISSN:0065-2164.
Oxalic acid is the most ubiquitous and common low molecular weight organic acid produced by living organisms. Oxalic acid is produced by fungi, bacteria, plants, and animals. The aim of this review is to give an overview of current knowledge about the microbial cycling of oxalic acid through ecosystems. Here we review the production and degradation of oxalic acid, as well as its implications in the metabolism for fungi, bacteria, plants, and animals. Indeed, fungi are well known producers of oxalic acid, while bacteria are considered oxalic acid consumers. However, this framework may need to be modified, because the ability of fungi to degrade oxalic acid and the ability of bacteria to produce it, have been poorly investigated. Finally, we will highlight the role of fungi and bacteria in oxalic acid cycling in soil, plant and animal ecosystems.
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Rudnick, M. B.; van Veen, J. A.; de Boer, W. Oxalic acid: a signal molecule for fungus-feeding bacteria of the genus Collimonas ?. Environ. Microbiol. Rep. 2015, 7 (5), 709– 714, DOI: 10.1111/1758-2229.12290
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Hsieh, L.; Chen, C.; Wan, M.; Tsai, C.; Tsai, Y. Speciation and temporal characterization of dicarboxylic acids in PM2. 5 during a PM episode and a period of non-episodic pollution. Atmos. Environ. 2008, 42, 6836– 6850, DOI: 10.1016/j.atmosenv.2008.05.021
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Radek, M.; Savage, G. P. Oxalates in Some Indian Green Leafy Vegetables. Int. J. Food Sci. Nutr. 2008, 59, 246– 260, DOI: 10.1080/09637480701791176
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Oxalates in some Indian green leafy vegetables
Radek, M.; Savage, G. P.
International Journal of Food Sciences and Nutrition (2008), 59 (3), 246-260CODEN: IJFNEH; ISSN:0963-7486. (Informa Healthcare)
The sol. and total oxalate contents of 11 leafy vegetables grown in India were detd. Spinach, purple and green amaranth and colocasia contained high levels of total oxalates, which ranged from 5,138.0±37.6 mg/100 g dry matter up to 12,576.1±107.9 mg/100 g dry matter. Seven other leafy vegetables (curry, drumstick, shepu, fenugreek, coriander, radish and onion stalks) contained only insol. oxalate, which ranged from 209.0±5.0 mg/100 g dry matter to 2,774.9±18.4 mg/100 g dry matter. In vitro digestion of the samples showed that the gastric available oxalate was 10% lower than the values obtained from acid extn. and that intestinal available oxalate was 20% lower than the values obtained following hot water extn. The percentage calcium bound in the insol. oxalate fraction of the dried leafy vegetables ranged from 3.3% to 86.7% of the total calcium. Addn. of four different sources of calcium (low fat milk, whole milk, calcium carbonate and calcium sulfate) resulted in a range of 32-100% redns. of intestinal available oxalate in the mixt.
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Holmes, R. P.; Kennedy, M. Estimation of the Oxalate Content of Foods and Daily Oxalate Intake. Kidney Int. 2000, 57, 1662– 1667, DOI: 10.1046/j.1523-1755.2000.00010.x
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Estimation of the oxalate content of foods and daily oxalate intake
Holmes, Ross P.; Kennedy, Martha
Kidney International (2000), 57 (4), 1662-1667CODEN: KDYIA5; ISSN:0085-2538. (Blackwell Science, Inc.)
Background. The amt. of oxalate ingested may be an important risk factor in the development of idiopathic calcium oxalate nephrolithiasis. Reliable food tables listing the oxalate content of foods are currently not available. The aim of this research was to develop an accurate and reliable method to measure the food content of oxalate. Methods. Capillary electrophoresis (CE) and ion chromatog. (IC) were compared as direct techniques for the estn. of the oxalate content of foods. Foods were thoroughly homogenized in acid, heat extd., and clarified by centrifugation and filtration before diln. in water for anal. Five individuals consuming self-selected diets maintained food records for three days to det. their mean daily oxalate intakes. Results. Both techniques were capable of adequately measuring the oxalate in foods with a significant oxalate content. With foods of very low oxalate content (<1.8 mg/100 g), IC was more reliable than CE. The mean daily intake of oxalate by the five individuals tested was 152 ± 83 mg, ranging from 44 to 352 mg/day. Conclusions. CE appears to be the method of choice over IC for estg. the oxalate content of foods with a medium (>10 mg/100 g) to high oxalate content due to a faster anal. time and lower running costs, whereas IC may be better suited for the anal. of foods with a low oxalate content. Accurate ests. of the oxalate content of foods should permit the role of dietary oxalate in urinary oxalate excretion and stone formation to be clarified. Other factors, apart from the amt. of oxalate ingested, appear to exert a major influence over the amt. of oxalate excreted in the urine.
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Salgado, N.; Silva, M. A.; Figueira, M. E.; Costa, H. S.; Albuquerque, T. G. Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications. Foods 2023, 12, 3201, DOI: 10.3390/foods12173201
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Siener, R.; Seidler, A.; Hönow, R. Oxalate-rich foods. Food Sci. Technol. 2021, 41, 169– 173, DOI: 10.1590/fst.10620
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Mochizuki, T.; Kawamura, K.; Miyazaki, Y.; Wada, R.; Takahashi, Y.; Saigusa, N.; Tani, A. Secondary formation of oxalic acid and related organic species from biogenic sources in a larch forest at the northern slope of Mt. Fuji. Atmos. Environ. 2017, 166, 255– 262, DOI: 10.1016/j.atmosenv.2017.07.028
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Secondary formation of oxalic acid and related organic species from biogenic sources in a larch forest at the northern slope of Mt. Fuji
Mochizuki, Tomoki; Kawamura, Kimitaka; Miyazaki, Yuzo; Wada, Ryuichi; Takahashi, Yoshiyuki; Saigusa, Nobuko; Tani, Akira
Atmospheric Environment (2017), 166 (), 255-262CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
To better understand the formation of water-sol. org. aerosols in the forest atm., we measured low mol. wt. (LMW) dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, unsatd. fatty acids (UFAs), and water-sol. org. carbon (WSOC) in aerosols from a Larix kaempferi forest located at the northern slope of Mt. Fuji, Japan, in summer 2012. Concns. of dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and WSOC showed maxima in daytime. Relative abundance of oxalic acid in LMW dicarboxylic acids was on av. 52% and its av. concn. was 214 ng m-3. We found that diurnal and temporal variations of oxalic acid are different from those of isoprene and α-pinene, whereas biogenic secondary org. aerosols (BSOAs) derived from isoprene and α-pinene showed similar variations with oxalic acid. The mass concn. ratios of oxalic acid/BSOAs were relatively const., although a large variation in the concns. of toluene that is an anthropogenic volatile org. compd. was obsd. These results suggest that formation of oxalic acid is assocd. with the oxidn. of isoprene and α-pinene with O3 and other oxidants in the forest atm. In addn., concns. of UFAs were obsd., for the first time, to decrease dramatically during daytime in the forest. This study demonstrates that forest ecosystem is an important source of oxalic acid and other dicarboxylic acids in the atm.
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Kawamura, K.; Bikkina, S. A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation. Atmos. Res. 2016, 170, 140– 160, DOI: 10.1016/j.atmosres.2015.11.018
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A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation
Kawamura, Kimitaka; Bikkina, Srinivas
Atmospheric Research (2016), 170 (), 140-160CODEN: ATREEW; ISSN:0169-8095. (Elsevier B.V.)
This review aims to update our understanding on mol. distributions of water-sol. dicarboxylic acids and related compds. in atm. aerosols with a focus on their geog. variability, size distribution, sources and formation pathways. In general, mol. distributions of diacids in aerosols from the continental sites and over the open ocean waters are often characterized by the predominance of oxalic acid (C2) followed by malonic acid (C3) and/or succinic acid (C4), while those sampled over the polar regions often follow the order of C4 ≥ C2 and C3. The most abundant and ubiquitous diacid is oxalic acid, which is principally formed via atm. oxidn. of its higher homologues of long chain diacids and other pollution-derived org. precursors (e.g., olefins and arom. hydrocarbons). However, its occurrence in marine aerosols is mainly due to the transport from continental outflows (e.g., East Asian outflow during winter/spring to the North Pacific) and/or governed by photochem./aq. phase oxidn. of biogenic unsatd. fatty acids (e.g., oleic acid) and isoprene emitted from the productive open ocean waters. The long-range atm. transport of pollutants from mid latitudes to the Arctic in dark winter facilitates to accumulate the reactants prior to their intense photochem. oxidn. during springtime polar sunrise. Furthermore, the relative abundances of C2 in total diacid mass showed similar temporal trends with downward solar irradn. and ambient temps., suggesting the significance of atm. photochem. oxidn. processing. Compd.-specific isotopic analyses of oxalic acid showed the highest δ13C among diacids whereas azelaic acid showed the lowest value, corroborating the significance of atm. aging of oxalic acid. On the other hand, other diacids gave intermediate values between these two diacids, suggesting that aging of oxalic acid is assocd. with 13C enrichment.
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Claeys, M. Formation of secondary organic aerosols through photooxidation of isoprene. Science 2004, 303, 1173– 1176, DOI: 10.1126/science.1092805
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Formation of Secondary Organic Aerosols Through Photooxidation of Isoprene
Claeys, Magda; Graham, Bim; Vas, Gyorgy; Wang, Wu; Vermeylen, Reinhilde; Pashynska, Vlada; Cafmeyer, Jan; Guyon, Pascal; Andreae, Meinrat O.; Artaxo, Paulo; Maenhaut, Willy
Science (Washington, DC, United States) (2004), 303 (5661), 1173-1176CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
Detailed org. anal. of natural aerosols from the Amazonian rain forest showed considerable quantities of previously unobserved polar org. compds. identified as a mixt. of 2 diastereoisomeric 2-methyltetrols: 2-methylthreitol and 2-methylerythritol. These polyols, which have an isoprene skeleton, can be explained by OH--initiated photooxidn. of isoprene. They have low vapor pressure, allowing them to condense onto pre-existing particles. It was estd. that photooxidn. of isoprene results in an annual global prodn. of ∼2 Tg of the polyols, a substantial fraction of the Intergovernmental Panel on Climate Change est. of 8-40 Tg/yr of secondary org. aerosol from biogenic sources.
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Kawamura, K.; Ikushima, K. Seasonal changes in the distribution of dicarboxylic acids in the urban atmosphere. Environ. Sci. Technol. 1993, 27, 2227– 2235, DOI: 10.1021/es00047a033
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Seasonal changes in the distribution of dicarboxylic acids in the urban atmosphere
Kawamura, Kimitaka; Ikushima, Kouichi
Environmental Science and Technology (1993), 27 (10), 2227-35CODEN: ESTHAG; ISSN:0013-936X.
Low-mol.-wt. dicarboxylic acids were studied in urban aerosol samples collected from Tokyo atm. in 1988-1989, by a capillary GC and GC-mass spectrometry method using a di-Bu ester derivatization technique. A homologous series of C2-C10 dicarboxylic acids were detected in the aerosols, including straight-chain satd., unsatd., branched-chain, and hydroxylated species. Mol. distributions of the diacids demonstrated that oxalic (C2) acid was the most abundant throughout the 4 seasons, followed by C3 and C4 diacids; the C2 diacid comprised 37-69% of the total diacid concns. Diacids with higher C nos. were less abundant, although C6 and C9 diacids were relatively abundant. Total concns. of diacids were 90-1370 ng/m3, which corresponded to 0.06-1.1% of the total aerosol mass. Their concns. relative to aerosol mass showed a seasonal trend with a max. in Aug. The C2-C4 diacid C normalized by aerosol total C also showed a strong seasonal change with a max. in the summer and indicated a pos. correlation with oxidant concns. Interestingly, lower diacids showed higher values for correlation coeff. (e.g., r = 0.80 for oxalic acid), suggesting a preferential prodn. of low mol. wt. dicarboxylic acids, esp., C2 diacid. Possible reaction mechanisms are discussed in relation to the preferential accumulation of lower diacids in the atm.
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Prenni, A. J.; DeMott, P. J.; Kreidenweis, S. M.; Sherman, D. E.; Russell, L. M.; Ming, Y. J. Phys. Chem. A 2001, 105, 11240– 11248, DOI: 10.1021/jp012427d
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The effects of low molecular weight dicarboxylic acids on cloud formation
Prenni, Anthony J.; DeMott, Paul J.; Kreidenweis, Sonia M.; Sherman, D. Eli; Russell, Lynn M.; Ming, Yi
Journal of Physical Chemistry A (2001), 105 (50), 11240-11248CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
The ubiquitous presence of org. compds. in tropospheric particles requires that their role in aerosol/cloud interactions be accounted for in climate models. In this paper, we present studies that investigate the hygroscopic behavior of org. compds. and their efficiency as ice nuclei. Specifically, results for sol. and partially sol. dicarboxylic acids that have been obsd. in atm. aerosol are discussed. At room temp., we use a humidified tandem differential mobility analyzer (HTDMA) and a condensation particle counter interfaced with a cloud condensation nuclei counter to characterize the water uptake behavior of these acids. The HTDMA data agree quite well with modeled hygroscopic behavior. However, we find that some of the compds. retain water to very low humidities, never exhibiting efflorescence. The studies are extended to lower temps. using a continuous flow ice thermal diffusion chamber to investigate the role of these species in ice nucleation at cirrus conditions. Results suggest that ice formation occurs via homogeneous nucleation for most of these acids, and that nucleation for these acids is not as efficient as that for sulfate aerosol.
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Makar, P. A. The estimation of organic gas vapour pressure. Atmos. Environ. 2001, 35, 961– 974, DOI: 10.1016/S1352-2310(00)00343-5
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Limbeck, A.; Puxbaum, H.; Otter, L.; Scholes, M. C. Atmos. Environ. 2001, 35, 1853– 1862, DOI: 10.1016/S1352-2310(00)00497-0
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Semivolatile behavior of dicarboxylic acids and other polar organic species at a rural background site (Nylsvley, RSA)
Limbeck, A.; Puxbaum, H.; Otter, L.; Scholes, M. C.
Atmospheric Environment (2001), 35 (10), 1853-1862CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
In this study aerosol samples from the South African savanna were analyzed for their polar org. constituents. Samples were collected with a front/back-up filter tandem system of quartz fiber filters (dual filter strategy). In all samples (n=15) dicarboxylic acids and a variety of phthalates, aldehydes and monocarboxylic acids were obsd. Oxalic acid was the dominating compd. with an av. amt. of 79.2 ng m-3 on the front filter and 11.3 ng m-3 on the back-up filter. The presence of significant concns. of dicarboxylic acids on the back-up filter was rather unexpected. There are two possible sources to explain the presence of individual compds. on the back-up filter - particle penetration through the front filter or adsorption of compd. parts from the gas phase. Interpretation of the data indicates that the dicarboxylic acid concns. on the back-up filters appear to be caused by the adsorption of gaseous org. species. Dicarboxylic acids semivolatile behavior is evident with this results. This conclusion refutes the commonly held view that dicarboxylic acids in the atm. were assocd. with the aerosol phase only. Addnl., it was found that the distribution of dicarboxylic acids between the gas and particle phase in the atm. is not only dependent on their vapor pressures. The actual gas phase concn. appears to be more detd. by the chem. properties of the particles than by pure phys. influences. Surprisingly, malonic acid exhibits an anomaly, as it does not show a semivolatile tendency.
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Cheng, C.; Li, M.; Chan, C. K.; Tong, H.; Chen, C.; Chen, D.; Wu, D.; Li, L.; Wu, C.; Cheng, P. Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implications for the formation mechanism of oxalic acid. Atmos. Chem. Phys. 2017, 17 (15), 9519– 9533, DOI: 10.5194/acp-17-9519-2017
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Mixing state of oxalic acid containing particles in the rural area of pearl river delta, china: implications for the formation mechanism of oxalic acid
Cheng, Chunlei; Li, Mei; Chan, Chak K.; Tong, Haijie; Chen, Changhong; Chen, Duohong; Wu, Dui; Li, Lei; Wu, Cheng; Cheng, Peng; Gao, Wei; Huang, Zhengxu; Li, Xue; Zhang, Zhijuan; Fu, Zhong; Bi, Yanru; Zhou, Zhen
Atmospheric Chemistry and Physics (2017), 17 (15), 9519-9533CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
The formation of oxalic acid and its mixing state in atm. particulate matter (PM) were studied using a single-particle aerosol mass spectrometer (SPAMS) in the summer and winter of 2014 in Heshan, a supersite in the rural area of the Pearl River Delta (PRD) region in China. Oxalic-acid-contg. particles accounted for 2.5 and 2.7 % in total detected ambient particles in summer and winter, resp. Oxalic acid was measured in particles classified as elemental carbon (EC), org. carbon (OC), elemental and org. carbon (ECOC), biomass burning (BB), heavy metal (HM), secondary (Sec), sodium-potassium (NaK), and dust. Oxalic acid was found predominantly mixing with sulfate and nitrate during the whole sampling period, likely due to aq.-phase reactions. In summer, oxalic-acid-contg. particle no. and ozone concn. followed a very similar trend, which may reflect the significant contribution of photochem. reactions to oxalic acid formation. The HM particles were the most abundant oxalic acid particles in summer and the diurnal variations in peak area of iron and oxalic acid show opposite trends, which suggests a possible loss of oxalic acid through the photolysis of iron oxalato-complexes during the strong photochem. activity period. In wintertime, carbonaceous particles contained a substantial amt. of oxalic acid as well as abundant carbon clusters and BB markers. The general existence of nitric acid in oxalic-acid-contg. particles indicates an acidic environment during the formation process of oxalic acid. The peak areas of nitrate, sulfate and oxalic had similar temporal change in the carbonaceous type oxalic acid particles, and the organosulfate-contg. oxalic acid particles correlated well with total oxalic acid particles during the haze episode, which suggests that the formation of oxalic acid is closely assocd. with the oxidn. of org. precursors in the aq. phase.
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Yu, S. Role of organic acids formic, acetic, pyruvic and/ oxalic in the formation of cloud condensation nuclei CCN: A Review. Atmos. Res. 2000, 53, 185– 217, DOI: 10.1016/S0169-8095(00)00037-5
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Role of organic acids (formic, acetic, pyruvic and oxalic) in the formation of cloud condensation nuclei (CCN): a review
Yu, S.
Atmospheric Research (2000), 53 (4), 185-217CODEN: ATREEW; ISSN:0169-8095. (Elsevier Science B.V.)
A review, with many refs., is given. Although it is believed that org. aerosols play a key role in cloud nucleation and make an important contribution to the cloud condensation nuclei (CCN) population, their specific species remain poorly characterized. This paper reviews the current knowledge of org. acids (mainly formic, acetic, pyruvic and oxalic acids). Without specification, org. acids in this paper refer to these four org. acids in the gas and aerosol phases. This paper analyzes the extent to which org. acids act as CCN and compares the phys. and chem. properties of org. acids with those of CCN. The results show that aerosol formate and acetate concns. range from 0.02 to 5.3 nmol m-3 and from 0.03 to 12.4 nmol m-3, resp., and that between 34 to 77% of formate and between 21 to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile org. acids are present in the gas phase, their concns. in the aerosol particles are sufficient to make them a good candidate for CCN. The results also show that org. acids may make an important contribution to the formation of CCN in some special sources such as vegetation emissions and biomass-burning. Org. acids are expected to contribute significantly to the ests. of indirect (cloud-mediated) forcing due to aerosols.
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Peng, C.; Chan, M. N.; Chan, C. K. The Hygroscopic Properties of Dicarboxylic and Multifunctional Acids: Measurements and UNIFAC Predictions. Environ. Sci. Technol. 2001, 35, 4495– 4501, DOI: 10.1021/es0107531
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The Hygroscopic Properties of Dicarboxylic and Multifunctional Acids: Measurements and UNIFAC Predictions
Peng, Changgeng; Chan, Man Nin; Chan, Chak K.
Environmental Science and Technology (2001), 35 (22), 4495-4501CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
The role of water-sol. org. compds. in regard to the hygroscopic properties of atm. aerosols has recently been the subject of many studies. In particular, low-mol.-wt. dicarboxylic acids and some multifunctional org. acids have been found or are expected to exist in atm. aerosols at urban, semiurban, rural, and remote sites. Unlike the case of their inorg. counterparts, the hygroscopic properties of org. acids have not been well characterized. In this study, the hygroscopic properties of selected water-sol. dicarboxylic acids (oxalic acid, malonic acid, succinic acid, and glutaric acid) and multifunctional acids (citric acid, DL-malic acid, and L-(+)-tartaric acid) were studied using single droplets levitated in an electrodynamic balance at 25°. The water activities of bulk samples of dil. solns. were also measured. Solute evapn. was obsd. for the dicarboxylic acids but not for the multifunctional acids. Oxalic acid, succinic acid, and glutaric acid droplets crystallize upon evapn. of water, but, except for glutaric acid droplets, do not deliquesce even at 90% relative humidity (RH). Mass transfer limitation of the deliquescence process was obsd. in glutaric acid. Neither crystn. nor deliquescence was obsd. in malonic acid, citric acid, DL-malic acid, or L-(+)-tartaric acid. Malonic acid and these three hydroxy carboxylic acids absorb water even at RHs much lower than their resp. deliquescence RH. The growth factor (Gf), defined as the ratio of the particle diam. at RH = 10% to that at RH = 90%, of oxalic acid and succinic acid was close to unity, indicating no hygroscopicity in this range. The remaining acids (malonic acid, glutaric acid, citric acid, malic acid, and tartaric acid) showed roughly similar hygroscopicity of a Gf of 1.30-1.53, which is similar to that of "more hygroscopic" aerosols in field measurements reported in the literature. A generalized equation for these four acids, Gf = (1-aw)-0.163, was developed to represent the hygroscopicity of these acids. Water activity predictions from calcns. using the UNIFAC model were found to agree with the measured water activity data to within 40% for most of the acids, but the deviations were as large as about 100% for malic acid and tartaric acid. We modified the functional group interaction parameters of the COOH-H2O, OH-H2O, and OH-COOH pairs by fitting the UNIFAC model with the measured data. The modified UNIFAC model improves the agreement of predictions and measurements to within 38% for all the acids studied.
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Kerminen, V.-M.; Ojanen, C.; Pakkanen, T.; Hillamo, R.; Aurela, M.; Meriläinen, J. Low-molecular-weight dicarboxylic acids in an urban and rural atmosphere. J. Aerosol Sci. 2000, 31, 349– 362, DOI: 10.1016/S0021-8502(99)00063-4
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Low-molecular-weight dicarboxylic acids in an urban and rural atmosphere
Kerminen, Veli-Matti; Ojanen, Christina; Pakkanen, Tuomo; Hillamo, Risto; Aurela, Minna; Merilainen, Jouni
Journal of Aerosol Science (2000), 31 (3), 349-362CODEN: JALSB7; ISSN:0021-8502. (Elsevier Science Ltd.)
Chem. of oxalic, malonic, and succinic acid was studied at the two sites representing the urban and rural conditions, and at a site intermediate between these two. The investigation was based on the particle collection with a virtual impactor and a Berner low-pressure impactor. Concns. of the three diacids displayed large seasonal amplitudes with low values in winter. Suggestive of common sources or atm. formation processes, the correlation between oxalic and malonic acid concns. was high. Both the local traffic and secondary prodn. in the long-range transported air masses seemed to be the important sources for these two acids. Contrary to oxalic and malonic acid, no enrichment at the urban site compared with the rural site was obsd. for succinic acid. The seasonal cycle of this acid resembled that of methanesulfonic acid. The most likely sources for succinic acid in our samples was the secondary prodn. in the long-range transported air, with potentially significant contribution coming from biogenic sources. The three diacids had quite different distributions over the particulate phase. Oxalic acid had a dominant accumulation mode, a clear Aitken mode at sizes below about 0.15 μm of particle diam., and modes corresponding to the sea-salt and crustal particle size ranges. Most of the malonic acid was assocd. with sea-salt particles, even though in a few samples an accumulation mode was also present. Succinic acid was distributed between the accumulation and the sea-salt particle modes, in addn. to which it frequently had quite a pronounced Aitken mode. Oxalic and succinic acids are among the orgs. that may contribute to the atm. cloud condensation nuclei prodn. Oxalic and malonic acid, and to a smaller extent succinic acid, participate in reactions occurring in sea-salt particles.
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Khwaja, H. A. Atmospheric concentrations of carboxylic acids and related compounds at a semiurban site. Atmos. Environ. 1995, 29, 127– 139, DOI: 10.1016/1352-2310(94)00211-3
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Atmospheric concentrations of carboxylic acids and related compounds at a semiurban site
Khwaja, Haider A.
Atmospheric Environment (1995), 29 (1), 127-39CODEN: AENVEQ; ISSN:1352-2310. (Elsevier)
Atm.-gas- and particle-phase carboxylic acids and related compds. were measured during Oct. 1991 in a semiurban site in northeastern US. Formic and acetic acids were present in the atm. mostly in the gaseous form with <10% in the particle phase. Concns. of formic acid and acetic acid were in the 0.80-2.5 and 0.60-3.4 ppbv range, resp. Formic acid was correlated with acetic acid (r =0.94). Diurnal variations of formic acid were similar to those of O3. This pattern is consistent with photochem. prodn. as an important source. Formic-to-acetic acid ratios <1 were recorded, likely due to an increase in acetic acid contribution from direct emissions assocd. with vehicular traffic. HCHO levels began to decrease after the mid-afternoon maxima; concns. were 0.63-3.7 ppbv. Formic, acetic, pyruvic, glyoxalic, oxalic, succinic, and malonic acids in the particle phase were identified. Aerosol carboxylic acid concns. were 26-360 ng/m3. About 80% of the carboxylic acid aerosol mass was in the size fraction <1.0 μm diam. Of the dicarboxylic acids, oxalic acid was the most abundant species, followed by succinic acid and malonic acid. Particulate total org. C exhibited a concn. range 12.6 × 103-49.9 × 103 ng/cm3. The obsd. amts. of carboxylic acids in the particle phase accounted for a small fraction of the org. C. Results indicated that photochem. processes and anthropogenic emissions such as automobile exhaust are major sources of atm. carboxylic acids.
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Chebbi, A.; Carlier, P. Atmos. Environ. 1996, 30, 4233– 4249, DOI: 10.1016/1352-2310(96)00102-1
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Carboxylic acids in the troposphere, occurrence, sources, and sinks: a review
Chebbi, A.; Carlier, P.
Atmospheric Environment (1996), 30 (24), 4233-4249CODEN: AENVEQ; ISSN:1352-2310. (Elsevier)
A review, with many refs., is given. Carboxylic acids are ubiquitous and important components of the troposphere; they are currently measured in different environments. They are thought to have several sources comprising primary biogenic and anthropogenic emissions, hydrocarbons gas-phase oxidns., and some carbonyl compds. aq.-phase oxidns. We make a synthesis of the concns. of low mol. wt. carboxylic acids in tropospheric aq. and gaseous phases and in aerosol particles for different environments. We also successively exam. the major sources of carboxylic acids and discuss their relative contribution to tropospheric concns. for various environments as well as the principal sinks of these compds.
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Martinelango, P. K.; Dasgupta, P. K.; Al-Horr, R. S. Atmos. Environ. 2007, 41, 4258– 4269, DOI: 10.1016/j.atmosenv.2006.05.085
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Atmospheric production of oxalic acid/oxalate and nitric acid/nitrate in the Tampa Bay airshed: Parallel pathways
Martinelango, P. Kalyani; Dasgupta, Purnendu K.; Al-Horr, Rida S.
Atmospheric Environment (2007), 41 (20), 4258-4269CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
Oxalic acid is the dominant dicarboxylic acid (DCA), and it constitutes up to 50% of total atm. DCAs, esp. in non-urban and marine atmospheres. A significant amt. of particulate H2Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concns. in the PM10 to PM2.5 fractions ranged from 1 to 2, with mean±sd being 1.4 ± 0.2. These results suggest that oxalate does not solely originate in the gas phase and condense into particles. Gaseous H2Ox concns. are much lower than particulate Ox concns. and are well correlated with HNO3, HCHO, and O3, supporting a photochem. origin. Of special relevance to the Bay Region Atm. Chem. Expt. (BRACE) is the extent of nitrogen deposition in the Tampa Bay estuary. Hydroxyl radical is primarily responsible for the conversion of NO2 to HNO3, the latter being much more easily deposited. Hydroxyl radical is also responsible for the aq. phase formation of oxalic acid from alkenes. Hence, we propose that an est. of ·OH can be obtained from H2Ox/Ox prodn. rate and we accordingly show that the product of total oxalate concn. and NO2 concn. approx. predicts the total nitrate concn. during the same period.
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Ma, X.; Sun, Y.; Huang, Z.; Zhang, Q.; Wang, W. A density functional theory study of the molecular interactions between a series of amides and sulfuric acid. Chemosphere 2019, 214, 781– 790, DOI: 10.1016/j.chemosphere.2018.08.152
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A density functional theory study of the molecular interactions between a series of amides and sulfuric acid
Ma, Xiaohui; Sun, Yanhui; Huang, Zixiao; Zhang, Qingzhu; Wang, Wenxing
Chemosphere (2019), 214 (), 781-790CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
Amides, a class of nitrogen-contg. org. pollutants in the atm., may affect the formation of atm. aerosols by the interactions with sulfuric acid. Here, the mol. interactions of sulfuric acid with formamide, methylformamide, DMF, acetamide, methylacetamide and dimethylacetamide was investigated by d. functional theory. Geometry optimization and Gibbs free energy calcn. were carried out at M06-2X/6-311++G(3df,3pd) level. The results indicate that the addn. of amides to H2SO4 might have a promoting effect on atm. new particle formation at 298.15 K and 1 atm. In the initial stage of new particle formation, the binding capacity of amides and sulfuric acid is stronger than ammonia, but weaker than methylamine. It is worth noting that the trans-methylacetamide could have similar capabilities of stabilizing sulfuric acid as dimethylamine. In the presence of water, amides are found to only have a weak enhancement capability on new particle formation. In addn., we can infer from evapn. rate that the small mol. clusters of formamide and sulfuric acid may be more energetically favorable than macromol. clusters.
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Hanson, D. R.; Eisele, F. L. Measurement of prenucleation molecular clusters in the NH₃, H₂SO₄, H₂O system. J. Geophys. Res.: Atmos. 2002, 107, AAC 10– 1-AAC 10-18, DOI: 10.1029/2001JD001100
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Sipilää, M.; Berndt, T.; Petäjä, T.; Brus, D.; Vanhanen, J.; Stratmann, F.; Patokoski, J.; Mauldin, R. L., 3; Hyvärinen, A.-P.; Lihavainen, H. The role of sulfuric acid in atmospheric nucleation. Science 2010, 327, 1243– 1246, DOI: 10.1126/science.1180315
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Kirkby, J.; Curtius, J.; Almeida, J.; Dunne, E.; Duplissy, J.; Ehrhart, S. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature 2011, 476, 429– 433, DOI: 10.1038/nature10343
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Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation
Kirkby, Jasper; Curtius, Joachim; Almeida, Joao; Dunne, Eimear; Duplissy, Jonathan; Ehrhart, Sebastian; Franchin, Alessandro; Gagne, Stephanie; Ickes, Luisa; Kuerten, Andreas; Kupc, Agnieszka; Metzger, Axel; Riccobono, Francesco; Rondo, Linda; Schobesberger, Siegfried; Tsagkogeorgas, Georgios; Wimmer, Daniela; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; David, Andre; Dommen, Josef; Downard, Andrew; Ehn, Mikael; Flagan, Richard C.; Haider, Stefan; Hansel, Armin; Hauser, Daniel; Jud, Werner; Junninen, Heikki; Kreissl, Fabian; Kvashin, Alexander; Laaksonen, Ari; Lehtipalo, Katrianne; Lima, Jorge; Lovejoy, Edward R.; Makhmutov, Vladimir; Mathot, Serge; Mikkilae, Jyri; Minginette, Pierre; Mogo, Sandra; Nieminen, Tuomo; Onnela, Antti; Pereira, Paulo; Petaejae, Tuukka; Schnitzhofer, Ralf; Seinfeld, John H.; Sipilae, Mikko; Stozhkov, Yuri; Stratmann, Frank; Tome, Antonio; Vanhanen, Joonas; Viisanen, Yrjo; Vrtala, Aron; Wagner, Paul E.; Walther, Hansueli; Weingartner, Ernest; Wex, Heike; Winkler, Paul M.; Carslaw, Kenneth S.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku
Nature (London, United Kingdom) (2011), 476 (7361), 429-433CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Model calcns. suggest that almost half of the global cloud condensation nuclei in the atm. boundary layer may originate from the nucleation of aerosols from trace condensable vapors, although the sensitivity of the no. of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulfuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chem. species such as ammonia. First results from the Cosmics Leaving OUtdoor Droplets (CLOUD) expt. at CERN are presented. It was found that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by vol., or less, increase the nucleation rate of sulfuric acid particles more than 100-1,000-fold. Time-resolved mol. measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia mols. Ions increase the nucleation rate by an addnl. factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair prodn. rate. Ion-induced binary nucleation of H2SO4-H2O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atm. concns. of ammonia and sulfuric acid are insufficient to account for obsd. boundary-layer nucleation.
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Elm, J.; Kubečka, J.; Besel, V.; Jääskeläinen, M. J.; Halonen, R.; Kurtén, T.; Vehkamäki, H. Modeling the formation and growth of atmospheric molecular clusters: A review. J. Aerosol Sci. 2020, 149, 105621, DOI: 10.1016/j.jaerosci.2020.105621
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Modeling the formation and growth of atmospheric molecular clusters: A review
Elm, Jonas; Kubecka, Jakub; Besel, Vitus; Jaaskelainen, Matias J.; Halonen, Roope; Kurten, Theo; Vehkamaki, Hanna
Journal of Aerosol Science (2020), 149 (), 105621CODEN: JALSB7; ISSN:0021-8502. (Elsevier Ltd.)
A review,. Mol. clusters are ubiquitous constituents of the ambient atm., that can grow into larger sizes forming new aerosol particles. The formation and growth of small clusters into aerosol particles remain one of the largest uncertainties in global climate predictions. This has made the modeling of atm. mol. clustering into an active field of research, yielding direct mol. level information about the formation mechanism. We review the present state-of-the-art quantum chem. methods and cluster distribution dynamics models that are applied to study the formation and growth of atm. mol. clusters. We outline the current challenges in applying theor. methods and the future directions to move the field forward.
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Zhang, R.; Khalizov, A.; Wang, L.; Hu, M.; Xu, W. Nucleation and Growth of Nanoparticles in the Atmosphere. Chem. Rev. 2012, 112, 1957– 2011, DOI: 10.1021/cr2001756
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Nucleation and Growth of Nanoparticles in the Atmosphere
Zhang, Renyi; Khalizov, Alexei; Wang, Lin; Hu, Min; Xu, Wen
Chemical Reviews (Washington, DC, United States) (2012), 112 (3), 1957-2011CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review which critically assesses recent findings related to nucleation and growth of atm. nanoparticles, emphasizing process understanding on a fundamental mol. level, is given. Topics discussed include: vapor nucleation overview (nucleation theories and computational approaches [classical nucleation, kinetic, and d. functional theories, mol. dynamics and Monte Carlo methods, nucleation theorem], nucleation expts. [adiabatic expansion approaches; diffusion, laminar flow, and turbulent mixing chambers; continuous generation of nucleating vapors from chem. reaction sources; exptl. results vs. nucleation theories]); atm. nanoparticle nucleation (measurements [concns. and size distribution, nanoparticle chem. compn., charged and neutral atm. clusters], lab. studies [binary nucleation of H2SO4/water; NH3 and amine-involved ternary nucleation of H2SO4/water; org. acid assisted nucleation of H2SO4/water; IOx and ion-induced nucleation; nucleating cluster chem. compn., reactivity, and thermodn.], theor./computational studies [quantum chem. calcns., mol. dynamics and Monte Carlo simulations], atm. nucleation parameterization); nanoparticle atm. growth (Kelvin [curvature] effect, condensation [H2SO4, low volatility orgs.], heterogeneous reactions [NH3, amines, aldehydes, α-dicarbonyls, alcs., other species]); numerical treatment of ambient nanoparticle nucleation and growth rates (measured, combined growth including condensation and intra-/extra-modal coagulation, nucleation rate derivation from atm. measurements); and summary and future research needs.
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Zheng, J.; Ma, Y.; Chen, M.; Zhang, Q.; Wang, L.; Khalizov, A. F. Measurement of atmospheric amines and ammonia using the high resolution time-of-flight chemical ionization mass spectrometry. Atmos. Environ. 2015, 102, 249– 259, DOI: 10.1016/j.atmosenv.2014.12.002
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Measurement of atmospheric amines and ammonia using the high resolution time-of-flight chemical ionization mass spectrometry
Zheng, Jun; Ma, Yan; Chen, Mindong; Zhang, Qi; Wang, Lin; Khalizov, Alexei F.; Yao, Lei; Wang, Zhen; Wang, Xing; Chen, Linxi
Atmospheric Environment (2015), 102 (), 249-259CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
Ammonia (NH3) and amines play important roles in the nucleation and growth of atm. aerosols. To identify the sources of these chems. in the densely populated and industrialized Yangtze River Delta region of China, we conducted measurements of NH3 and several amines, including methylamine (CH3NH2), C2-amines (C2H7N), and C3-amines (C3H9N) at a suburban site of Nanjing, China, during summer 2012. Using a high-resoln. time-of-flight chem. ionization mass spectrometer (HRToF-CIMS, Aerodyne), 1-min-averaged concns. of NH3 and amines ranged from a few parts per trillions by vol. (pptv) to dozens of ppb by vol. (ppbv). The av. ± 1σ concns. of NH3 and total amines during the measurement period were 1.7 ± 2.3 ppbv and 7.2 ± 7.4 pptv, resp. Among the amines, C2-amines were the most abundant, accounting for 54% of the total amine loading. Significant correlations between NH3 and all three types of amines (0.65 < r2 < 0.80) indicate similar emission sources. Anal. of meteorol. conditions indicated that these NH3 and amine laden air masses mainly originated from nearby industrial areas where NH3 was used for selective catalytic redn. of nitrogen oxides (NOx). The results of this work indicate that industrial emissions in Nanjing, China may have a significant impact on local and regional aerosol chem. by supplying considerable amt. of amines.
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Nair, A. A.; Yu, F. Quantification of Atmospheric Ammonia Concentrations: A Review of Its Measurement and Modeling. Atmosphere 2020, 11, 1092, DOI: 10.3390/atmos11101092
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Quantification of atmospheric ammonia concentrations: a review of its measurement and modeling
Nair, Arshad Arjunan; Yu, Fangqun
Atmosphere (2020), 11 (10), 1092CODEN: ATMOCZ; ISSN:2073-4433. (MDPI AG)
Ammonia (NH3), the most prevalent alk. gas in the atm., plays a significant role in PM2.5 formation, atm. chem., and new particle formation. This paper reviews quantification of [NH3] through measurements, satellite-remote-sensing, and modeling reported in over 500 publications towards synthesizing the current knowledge of [NH3], focusing on spatiotemporal variations, controlling processes, and quantification issues. Most measurements are through regional passive sampler networks. [NH3] hotspots are typically over agricultural regions, such as the Midwest US and the North China Plain, with elevated concns. reaching monthly avs. of 20 and 74 ppbv, resp. Topog. effects dramatically increase [NH3] over the Indo-Gangetic Plains, North India and San Joaquin Valley, US. Measurements are sparse over oceans, where [NH3] ≈ a few tens of pptv, variations of which can affect aerosol formation. Satellite remote-sensing (AIRS, CrIS, IASI, TANSO-FTS, TES) provides global [NH3] quantification in the column and at the surface since 2002. Modeling is crucial for improving understanding of NH3 chem. and transport, its spatiotemporal variations, source apportionment, exploring physicochem. mechanisms, and predicting future scenarios. GEOS-Chem (global) and FRAME (UK) models are commonly applied for this. A synergistic approach of measurements↔satellite-inference↔modeling is needed towards improved understanding of atm. ammonia, which is of concern from the standpoint of human health and the ecosystem.
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Elm, J. An Atmospheric Cluster Database Consisting of Sulfuric Acid, Bases, Organics, and Water. ACS Omega 2019, 4 (6), 10965– 10974, DOI: 10.1021/acsomega.9b00860
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An Atmospheric Cluster Database Consisting of Sulfuric Acid, Bases, Organics, and Water
Elm, Jonas
ACS Omega (2019), 4 (6), 10965-10974CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
We have collected, re-computed and compiled a database consisting of 633 unique atmospherically relevant mol. clusters contg. sulfuric acid, bases, oxidized org. compds. and water. The database comprise of strongly hydrogen bonded mol. clusters, and span both neutral, neg. charged and pos. charged clusters of atm. relevance. All the cluster structures and vibrational frequencies were re-evaluated at the ωB97X-D/6-31++G(d,p) level of theory and the single point energies were refined using a high level DLPNO-CCSD(T)/aug-cc-pVTZ calcn. The database unifies published atm. mol. clusters under a single common methodol. and serves as an efficient look-up table for mol. cluster structures and thermochem. parameters. Utilizing the database the performance of four semi-empirical methodologies (PM6, PM7, B97-3c and PBEh-3c) in calcg. the binding energies of atm. mol. clusters is assessed. The B97-3c and PBEh-3c empirically cor. DFT methods yield low errors in the binding energies compared to DLPNO-CCSD(T)/aug-cc-pVTZ ref. results and that a simple linear model can be utilized for estg. accurate binding energies based on ωB97X-D/6-31++G(d,p) results.
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Lee, S.-H.; Gordon, H.; Yu, H.; Lehtipalo, K.; Haley, R.; Li, Y.; Zhang, R. New particle formation in the atmosphere: From molecular clusters to global climate. J. Geophys. Res.: Atmos. 2019, 124, 7098– 7146, DOI: 10.1029/2018JD029356
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New Particle Formation in the Atmosphere: From Molecular Clusters to Global Climate
Lee, Shan-Hu; Gordon, Hamish; Yu, Huan; Lehtipalo, Katrianne; Haley, Ryan; Li, Yixin; Zhang, Renyi
Journal of Geophysical Research: Atmospheres (2019), 124 (13), 7098-7146CODEN: JGRDE3; ISSN:2169-8996. (Wiley-Blackwell)
New particle formation (NPF) represents the first step in the complex processes leading to formation of cloud condensation nuclei. Newly formed nanoparticles affect human health, air quality, weather, and climate. This review provides a brief history, synthesizes recent significant progresses, and outlines the challenges and future directions for research relevant to NPF. New developments include the emergence of state-of-the-art instruments that measure prenucleation clusters and newly nucleated nanoparticles down to about 1 nm; systematic lab. studies of multicomponent nucleation systems, including collaborative expts. conducted in the Cosmics Leaving Outdoor Droplets chamber at CERN; observations of NPF in different types of forests, extremely polluted urban locations, coastal sites, polar regions, and high-elevation sites; and improved nucleation theories and parameterizations to account for NPF in atm. models. The challenges include the lack of understanding of the fundamental chem. mechanisms responsible for aerosol nucleation and growth under diverse environments, the effects of SO2 and NOx on NPF, and the contribution of anthropogenic org. compds. to NPF. It is also crit. to develop instruments that can detect chem. compn. of particles from 3 to 20 nm and improve parameterizations to represent NPF over a wide range of atm. conditions of chem. precursor, temp., and humidity.
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Nahlovska, Z.; Nahlovsky, B.; Strand, T. G. Molecular Structure of Gaseous Oxalic Acid from Electron Diffraction and IR Data. Acta Chem. Scand. 1970, 24 (24), 2617– 2628, DOI: 10.3891/acta.chem.scand.24-2617
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Redington, R. L.; Redington, T. E. Infrared Matrix-Isolation Spectra of Monomeric Oxalic Acid. J. Mol. Struct. 1978, 48, 165, DOI: 10.1016/0022-2860(78)80019-2
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Back, R. A. The ultraviolet absorption spectrum of oxalic acid vapor. Can. J. Chem. 1984, 62, 1414, DOI: 10.1139/v84-241
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Nieminen, J.; Rasanen, M.; Murto, J. Matrix Isolation and ab Initio Studies of Oxalic Acid. J. Phys. Chem. 1992, 96, 5303, DOI: 10.1021/j100192a024
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Matrix-isolation and ab initio studies of oxalic acid
Nieminen, J.; Rasanen, M.; Murto, J.
Journal of Physical Chemistry (1992), 96 (13), 5303-8CODEN: JPCHAX; ISSN:0022-3654.
Rotamerization and UV photochem. decompn. of oxalic acid were studied in solid Ne, Ar, and Xe matrixes. The energies and spectra of the conformers and photoproducts were also simulated by extensive ab initio calcns. at MP2/6-31G** (energies, geometries) and MP2/4-31G* (numerical frequencies) levels. Two conformers were present in matrixes, the lowest energy species being cTc (with two intramol. H bonds) and species cTt (with only one intramol. H bond) being at ∼7 kJ mol-1 higher in energy. The uphill process cTc → cTt could be initiated by UV excitation at wavelengths of ∼270 nm. IR irradn. at wavenumbers >2000 cm-1 promoted the reverse interconversion. Full Xe arc irradn. decomps. oxalic acid in matrixes, the product yield ratio being different in different hosts. On the basis of ab initio calcns., the possible transition states for proton shifts are discussed. The calcd. vibrational spectra are given for six conformers of oxalic acid, the spectra of the obsd. conformers are assigned, and their potential energy distributions are given.
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Maçôas, E. M. S.; Fausto, R.; Pettersson, M.; Khriachtchev, L.; Rasanen, M. Infrared-Induced Rotamerization of Oxalic Acid Monomer in Argon Matrix. J. Phys. Chem. A 2000, 104, 6956, DOI: 10.1021/jp000634s
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Infrared-Induced Rotamerization of Oxalic Acid Monomer in Argon Matrix
Macoas, Ermelinda M. S.; Fausto, Rui; Pettersson, Mika; Khriachtchev, Leonid; Raesaenen, Markku
Journal of Physical Chemistry A (2000), 104 (30), 6956-6961CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
IR-induced conformational isomerization of oxalic acid monomer isolated in an argon matrix at 7.5 K was studied by IR spectroscopy. For the first time, three conformational states of this mol. were identified exptl. and their vibrational spectra are assigned. In good agreement with d. functional theory predictions, all the obsd. conformers exhibit a trans O:C-C:O axis, differing in the relative conformation of their O-C-O-H axes. In the most stable conformer (belonging to the C2h symmetry point group), two intramol. OH···O: hydrogen bonds are present. The second (Cs) most stable conformer shows a single OH···O: bond, and the third one (C2h) does not exhibit any intramol. hydrogen bond. Using narrowband tunable irradn. in the near-IR region it was possible to promote very efficiently conformer interconversions, which was followed spectroscopically.
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Godfrey, P. D.; Mirabella, M. J.; Brown, R. D. Structural Studies of Higher Energy Conformers by Millimeter-Wave Spectroscopy: Oxalic Acid. J. Phys. Chem. A 2000, 104, 258, DOI: 10.1021/jp992499t
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Structural Studies of Higher Energy Conformers by Millimeter-Wave Spectroscopy: Oxalic Acid
Godfrey, Peter D.; Mirabella, Mathew J.; Brown, Ronald D.
Journal of Physical Chemistry A (2000), 104 (2), 258-264CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
The authors have detected a polar conformer of oxalic acid and studied its structure using Stark-modulated free jet microwave spectroscopy. By comparing obsd. and ab initio predicted spectroscopic rotational consts. and deuteration isotopic substitution coordinates, the species was identified with the cis, trans, trans conformer (cTt), in which one of the carboxyl H atoms is involved in an intramol. H bond with the carbonyl O of the other carboxyl group. Stark effect measurements yielded elec. dipole moment values of μa = 2.850(6) D; μb = 1.148(3) D, μc = 0.0 D (assumed), and hence μtotal = 3.073(6) D. Ab initio calcns. at the MP2/6-311++G(d,p) level predict and expt. confirms that no other polar conformers occur in detectable concns. in the vapor at the expt. spectral search scan preexpansion temp. of 458 K. However, 2 undetectable species, one nonpolar (tTt), the other of low polarity (cTc, μ = 0.6 D) are predicted to be present in greater concns. than the obsd. species. Predicted relative stabilities of the different conformers are appreciably affected by the inclusion of Gibbs free energy corrections via the vibrational partition function. Large amplitude anharmonic vibrations, for which numerical integration of the vibrational Schrodinger equation is required for obtaining the correction, have an important influence on predicting relative stabilities of the oxalic acid conformers.
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Buemi, G. DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution. J. Phys. Org. Chem. 2009, 22, 933– 947, DOI: 10.1002/poc.1543
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DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution
Buemi, Giuseppe
Journal of Physical Organic Chemistry (2009), 22 (10), 933-947CODEN: JPOCEE; ISSN:0894-3230. (John Wiley & Sons Ltd.)
The mol. geometries of the possible conformations of formic, oxalic, glyoxylic and pyruvic acids have been fully optimized at DFT B3LYP/6-311++G(d,p) levels of calcn. in vacuum as well as in water and acetone soln. Solns. were treated according to the SCRF PCM approach but some formic acid-water and formic acid-acetone clusters as well as adducts of oxalic acid with two or four water mols. were also taken into account for testing the importance of specific solute-solvent effects. All the most stable isomers of the title compds. are characterized by weak intramol. hydrogen bonds, whose strengths (EHB) cannot be correctly estd. as stability difference between the open and chelate forms since the energy of the former isomer is, in turn, stabilized by a weak hydrogen bridge due to the formic acid moiety. Following the Rotation Barrier Method (RBM), proposed some years ago, EHB in the examd. mols. (gas phase) falls in the range of 18-22 kJ/mol for oxalic acid (9.6 kJ/mol for the c-C-t isomer), 16.8 kJ/mol for glyoxylic acid and 19.8 kJ/mol for pyruvic acid. Most of them disappear at all, or nearly at all, both in acetone and aq. soln., in consequence of the solvent effect. The frequencies of the OH and C-O stretching modes, calcd. according to the anharmonic oscillator model, are in very good agreement with the exptl. literature data, where available. Copyright © 2009 John Wiley & Sons, Ltd.
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Feller, D.; Bross, D. H.; Ruscic, B. Enthalpy of Formation of C₂H₂O₄ (Oxalic Acid) from High-Level Calculations and the Active Thermochemical Tables Approach. J. Phys. Chem. A 2019, 123, 3481– 3496, DOI: 10.1021/acs.jpca.8b12329
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Enthalpy of Formation of C2H2O4 (Oxalic Acid) from High-Level Calculations and the Active Thermochemical Tables Approach
Feller, David; Bross, David H.; Ruscic, Branko
Journal of Physical Chemistry A (2019), 123 (16), 3481-3496CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
High-level coupled cluster calcns. obtained with the Feller-Peterson-Dixon (FPD) approach and new data from the most recent version of the Active Thermochem. Tables (ATcT) are used to reassess the enthalpy of formation of gas-phase C2H2O4 (oxalic acid). The theor. value was further calibrated by comparing FPD and ATcT gas-phase enthalpies of formation for H2CO (formaldehyde) and the two low-lying conformations of C2H4O2 (syn and anti acetic acid). The FPD approach produces a theor. enthalpy of formation of gas-phase oxalic acid of -732.2 ± 4.0 kJ/mol at 298.15 K (-721.8 ± 4.0 kJ/mol at 0 K). An independently obtained ATcT value, based on reassessing the existent exptl. detns. and expanding the resulting thermochem. network with select mid-level composite theor. results, disagrees with several earlier recommendations that were based solely on exptl. detns. but is in excellent accord with the current FPD value. The inclusion of the latter in the most recent ATcT thermochem. network produces a further refined value for the gas-phase enthalpy of formation, -731.6 ± 1.2 kJ/mol at 298.15 K (-721.0 ± 1.2 kJ/mol at 0 K). The condensed-phase ATcT enthalpy of formation of oxalic acid is -829.7 ± 0.5 kJ/mol, and the resulting sublimation enthalpy is 98.1 ± 1.3 kJ/mol, both at 298.15 K.
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Chen, C.; Shyu, S.-F. Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions. Int. J. Quantum Chem. 2000, 76, 541– 551, DOI: 10.1002/(SICI)1097-461X(2000)76:4<541::AID-QUA5>3.0.CO;2-U
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Van Alsenoy, C.; Klimkowski, V. J.; Schafer, L. Ab initio studies of structural features not easily amenable to experiment: Part 37. Structural and conformational investigations of the dicarbonyls glyoxal, biacetyl and oxalic acid. J. Mol. Struct.: THEOCHEM 1984, 109, 321– 330, DOI: 10.1016/0166-1280(84)80016-0
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Mohajeri, A.; Shakerin, N. The gas-phase acidity and intramolecular hydrogen bonding in oxalic acid. J. Mol. Struct.: THEOCHEM 2004, 711, 167, DOI: 10.1016/j.theochem.2004.10.002
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The gas-phase acidity and intramolecular hydrogen bonding in oxalic acid
Mohajeri, A.; Shakerin, N.
Journal of Molecular Structure: THEOCHEM (2004), 711 (1-3), 167-172CODEN: THEODJ; ISSN:0166-1280. (Elsevier B.V.)
Ab initio calcns. at MP2/6-311++G and G2 level were carried out to study the structures and the gas-phase acidities of different conformations in oxalic acid. The gas-phase acidities (free energies of first ionization reactions) at G2 level vary from 1297.27 kJ/mol for the most acidic conformer to 1359.53 kJ/mol for the least acidic one at 298.15 K. Analyzing intramol. hydrogen bonding in different conformers, shows that the gas-phase acidity has a direct relation with hydrogen bond stabilization of both acid and its conjugated base. The results indicate that the reaction in which the acidic hydrogen is less involved and the hydrogen of its conjugated base is more involved in the intramol. hydrogen bond is the easiest deprotonation reaction. The atoms in mol. (AIM) theory has been also used to obtain the electronic charge distribution and some other related properties.
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Hermida-Ramón, J. M.; Cabaleiro-Lago, E. M.; Rodríguez-Otero, J. Computational study of the dissociation of oxalic acid in water clusters. Chem. Phys. 2004, 302, 53– 60, DOI: 10.1016/j.chemphys.2004.02.021
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Chang, J. G.; Chen, H. T.; Xu, S. C.; Lin, M. C. Computational Study on the Kinetics and Mechanisms for the Unimolecular Decomposition of Formic and Oxalic Acids. J. Phys. Chem. A 2007, 111, 6789, DOI: 10.1021/jp069036p
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Computational Study on the Kinetics and Mechanisms for the Unimolecular Decomposition of Formic and Oxalic Acids
Chang, Jee-Gong; Chen, Hsin-Tsung; Xu, Shucheng; Lin, M. C.
Journal of Physical Chemistry A (2007), 111 (29), 6789-6797CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
The kinetics and mechanisms for the unimol. decompn. reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decompn. of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate consts. for the dehydration and decarboxylation reactions are in good agreement with the exptl. data. The calcd. CO/CO2 ratio, 13.6-13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured exptl. by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramol. hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decompn. channels of oxalic acid producing CO2 + HOCOH with barriers of 33-36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temps., the latter process becomes more competitive. The rate const. predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available exptl. data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.
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Higgins, J.; Zhou, X.; Liu, R.; Huang, T. T.-S. Theoretical Study of Thermal Decomposition Mechanism of Oxalic Acid. J. Phys. Chem. A 1997, 101, 2702– 2708, DOI: 10.1021/jp9638191
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Theoretical Study of Thermal Decomposition Mechanism of Oxalic Acid
Higgins, James; Zhou, Xuefeng; Liu, Ruifeng; Huang, Thomas T.-S.
Journal of Physical Chemistry A (1997), 101 (14), 2702-2708CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
D. functional theory B3LYP/6-31G** and ab initio MP2/6-31G** and MP4(SDQ)/6-311++G** calcns. were carried out to study the structures and isomerization and decompn. mechanisms of oxalic acid. The B3LYP structures and relative energies of the rotational isomers of oxalic acid are found very similar to MP2 results, confirming that the most stable isomer is the doubly intramol. hydrogen-bonded C2h structure E1, with four other planar isomers within 6 kcal/mol. It is predicted that unimol. formation of carbon dioxide and dihydroxycarbene (DHC) from oxalic acid has an activation barrier of 31 kcal/mol and that unimol. formation of HCOOH from DHC has an activation barrier about 31 kcal/mol higher. The unimol. formation of CO2, CO and H2O from oxalic acid via a concerted transition state has an activation barrier of only 42 kcal/mol, indicating it is a more favorable unimol. decompn. channel. On the other hand, hydrogen migration from oxygen to carbon of DHC to produce HCOOH can be accomplished through a hydrogen exchange with H2O (a model for oxalic acid) with an activation barrier of less than 37 kcal/mol. Transition state theory calcns. indicate that this bimol. channel might be responsible for the rapid formation of CO2 and HCOOH in gas phase oxalic acid thermal decompn., thus confirming the proposal of Bock and Redington. With increasing temp. the unimol. channel to produce CO2, CO, and H2O might become significant.
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Medeiros, F. S.; Oliveira, K. M. T.; Canuto, S.; Chaudhuri, P. A quantum chemical investigation of the interaction of perfluoropropionic acid with monoethanolamine and sulfuric acid in the atmosphere. Comput. Theor. Chem. 2024, 1233, 114485, DOI: 10.1016/j.comptc.2024.114485
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de Oliveira, T. S.; Ghosh, A.; Chaudhuri, P. Exploring the hydrogen-bonded interactions of vanillic acid with atmospheric bases: a DFT study. Struct. Chem. 2024, 35, 1601– 1611, DOI: 10.1007/s11224-024-02307-3
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Elm, J.; Mikkelsen, K. V. Computational approaches for efficiently modelling of small atmospheric clusters. Chem. Phys. Lett. 2014, 615, 26– 29, DOI: 10.1016/j.cplett.2014.09.060
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Computational approaches for efficiently modelling of small atmospheric clusters
Elm, Jonas; Mikkelsen, Kurt V.
Chemical Physics Letters (2014), 615 (), 26-29CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
Utilizing a comprehensive test set of 205 clusters of atm. relevance, we investigate how different DFT functionals (M06-2X, PW91, ωB97X-D) and basis sets (6-311++G(3df,3pd), 6-31++G(d,p), 6-31+G(d)) affect the thermal contribution to the Gibbs free energy and single point energy. Reducing the basis set used in the geometry and frequency calcn. from 6-311++G(3df,3pd) → 6-31++G(d,p) implies a significant speed-up in computational time and only leads to small errors in the thermal contribution to the Gibbs free energy and subsequent coupled cluster single point energy calcn.
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Elm, J.; Bilde, M.; Mikkelsen, K. V. Assessment of binding energies of atmospherically relevant clusters. Phys. Chem. Chem. Phys. 2013, 15, 16442– 16445, DOI: 10.1039/c3cp52616j
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Assessment of binding energies of atmospherically relevant clusters
Elm, Jonas; Bilde, Merete; Mikkelsen, Kurt V.
Physical Chemistry Chemical Physics (2013), 15 (39), 16442-16445CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
This work assesses the binding energies of atmospherically relevant clusters contg. H2SO4, H2O, NH3 and (CH3)2NH using d. functional theory. The performance of seven DFT functionals (B3LYP, CAM-B3LYP, M06-2X, PW91, LC-PW91, PBE0 and ωB97X-D) is evaluated against high level explicitly correlated coupled cluster methods using a test set of 107 atmospherically relevant clusters. Our studies show that all the tested functionals correlate well with the coupled cluster results, but with highly varying mean abs. errors. The PBE0, CAM-B3LYP, PW91 and M06-2X functionals are found to perform similarly with errors in the range of 2.53-3.46 kcal mol-1, while the B3LYP and LC-PW91 functionals yield higher errors of 6.95 kcal mol-1 and 10.66 kcal mol-1, resp. The ωB97X-D functional gives the best est. of the binding energies with a mean abs. error as low as 2.12 kcal mol-1 over the large test set of clusters.
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Elm, J.; Bilde, M.; Mikkelsen, K. V. Assessment of Density Functional Theory in Predicting Structures and Free Energies of Reaction of Atmospheric Prenucleation Clusters. Phys. Chem. Chem. Phys. 2012, 8, 2071– 2077, DOI: 10.1021/ct300192p
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Huff, A. K.; Mackenzie, R. B.; Smith, C. J.; Leopold, K. R. A Perfluorinated Carboxylic Sulfuric Anhydride: Microwave and Computational Studies of CF₃COOSO₂OH. J. Phys. Chem. A 2019, 123, 2237– 2243, DOI: 10.1021/acs.jpca.9b00300
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A Perfluorinated Carboxylic Sulfuric Anhydride: Microwave and Computational Studies of CF3COOSO2OH
Huff, Anna K.; MacKenzie, Rebecca B.; Smith, C. J.; Leopold, Kenneth R.
Journal of Physical Chemistry A (2019), 123 (11), 2237-2243CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
Trifluoroacetic sulfuric anhydride (CF3COOSO2OH, TFASA) and its deuterated isotopologue have been obsd. by pulsed-nozzle Fourier transform microwave spectroscopy. TFASA was generated in situ in a supersonic expansion from the reaction of CF3COOH or CF3COOD with SO3. The spectrum, which was notably weaker than those of previously studied carboxylic sulfuric anhydrides, is that of a simple asym. rotor with no evidence of internal rotation of the CF3 group. Calcns. at the M06-2X/6-311++G(3df,3pd) level indicate that the title compd. is produced via a mechanism involving a concerted cycloaddn., analogous to that found for other carboxylic sulfuric anhydrides. The calcns. further show that the equil. orientation of CF3 relative to the C=O bond changes upon formation of the anhydride, indicating that any path connecting the equil. structures of CF3COOH and CF3COOSO2OH necessarily includes both cycloaddn. and internal rotation. CCSD(T)/complete basis set with double and triple extrapolation [CBS(D-T)] single-point energy calcns. at key points on the potential surface indicate that the barrier to form TFASA from a putative CF3COOH···SO3 complex is about 1.2 kcal/mol after zero-point energy corrections. This value is significantly larger than the near-zero or slightly neg. barriers previously reported for the reactions of SO3 with nonfluorinated carboxylic acids and likely accounts, at least in part, for the reduced spectral intensity. Thus, TFASA is a somewhat unique addn. to the series of carboxylic sulfuric anhydrides studied to date. Theor. values of certain structural parameters, at. charges, and vibrational frequencies also support this point of view. Despite the differences, however, this work clearly demonstrates that the reaction RCOOH + SO3 → RCOOSO2OH readily occurs in the gas phase and is not restricted to acids with hydrocarbon R groups.
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Dennington, R. D.; Keith, T. A.; Millam, J. M. GaussView 5.0.9; Gaussian Inc.: Wallingford, CT, USA, 2008.
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Kubečka, J.; Besel, V.; Kurtén, T.; Myllys, N.; Vehkamäki, H. Configurational sampling of noncovalent (atmospheric) molecular clusters: Sulfuric acid and guanidine. J. Phys. Chem. A 2019, 123, 6022– 6033, DOI: 10.1021/acs.jpca.9b03853
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Configurational Sampling of Noncovalent (Atmospheric) Molecular Clusters: Sulfuric Acid and Guanidine
Kubecka, Jakub; Besel, Vitus; Kurten, Theo; Myllys, Nanna; Vehkamaki, Hanna
Journal of Physical Chemistry A (2019), 123 (28), 6022-6033CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
We studied the configurational sampling of noncovalently bonded mol. clusters relevant to the atm. In this article, we discuss possible approaches to searching for optimal configurations and present one alternative based on systematic configurational sampling, which seems able to overcome the typical problems assocd. with searching for global min. on multidimensional potential energy surfaces. Since atm. mol. clusters are usually held together by intermol. bonds, we also present a cost-effective strategy for treating hydrogen bonding and proton transferring by using rigid mols. and ions in different protonation states and illustrate its performance on clusters contg. guanidine and sulfuric acid.
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Partanen, L.; Vehkamäki, H.; Hansen, K.; Elm, J.; Henschel, H.; Kurtén, T.; Halonen, R.; Zapadinsky, E. Effect of Conformers on Free Energies of Atmospheric Complexes. J. Phys. Chem. A 2016, 120, 8613– 8624, DOI: 10.1021/acs.jpca.6b04452
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Effect of Conformers on Free Energies of Atmospheric Complexes
Partanen, Lauri; Vehkamaki, Hanna; Hansen, Klavs; Elm, Jonas; Henschel, Henning; Kurten, Theo; Halonen, Roope; Zapadinsky, Evgeni
Journal of Physical Chemistry A (2016), 120 (43), 8613-8624CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
In this article we show how to calc. free energies for atmospherically relevant complexes when multiple conformers and/or isomers are present. We explain why the thermal averaging methods used in several published works are not correct. Based on our two sample cases, the sulfuric acid - pinic acid complex and the (H2SO4)3(NH3)3(H2O)4 cluster, we provide numerical evidence that the use of these incorrect formulas can result in errors larger than one kcal/mol. We recommend that if vibrational frequencies and thus Gibbs free energies of the individual conformers are unavailable, one should not attempt to correct for the presence of multiple conformers and instead use only the global min. conformers for both reactants and products. On the other hand, if the free energies for the conformers are calcd. for both reactants and products, their effect can be accounted for by the statistical mech. methods presented in this article.
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Fileti, E. E.; Rivelino, R.; Canuto, S. Rayleigh light scattering of hydrogen bonded clusters investigated by means of ab initio calculations. J. Phys. B: At., Mol. Opt. Phys. 2003, 36, 399– 408, DOI: 10.1088/0953-4075/36/2/319
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Rayleigh light scattering of hydrogen bonded clusters investigated by means of ab initio calculations
Fileti, Eudes E.; Rivelino, Roberto; Canuto, Sylvio
Journal of Physics B: Atomic, Molecular and Optical Physics (2003), 36 (2), 399-408CODEN: JPAPEH; ISSN:0953-4075. (Institute of Physics Publishing)
Ab initio calcns. of depolarization ratios and intensities of classically scattered light, in terms of dipole polarizabilities and polarizability anisotropies, are reported for different H bonded mol. clusters. Five different groups of org. heterodimers formed with H2O are considered: HCHO···H2O, MeHO···H2O, HCOOH···H2O, MeCN···H2O, and Me2CO···H2O, together with the H2O dimer H2O···H2O. The geometries of all complexes were optimized by the 2nd-order Moller-Plesset many-body perturbation theory (MP2), using the augmented correlation-consistent basis set with polarized valence of double-zeta quality (aug-cc-pVDZ). The calcd. av. dipole polarizabilities of the isolated mols. are in good agreement with available exptl. results. The calcns. are then extended to the complexes and, from these, the Rayleigh scattering activities and depolarization ratio changes, upon H bond formation, are obtained and analyzed. The differences in activity and depolarization for Rayleigh scattered radiation between 2 groups of isomers, (i) HCN···H2O and H2O···HCN and (ii) MeHO···H2O and MeOH···OH2, also were studied.
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Chaudhuri, P.; Canuto, S. Rayleigh scattering properties of small polyglycine molecules. J. Mol. Struct. 2006, 760, 15– 20, DOI: 10.1016/j.theochem.2005.10.039
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Rayleigh scattering properties of small polyglycine molecules
Chaudhuri, Puspitapallab; Canuto, Sylvio
Journal of Molecular Structure: THEOCHEM (2006), 760 (1-3), 15-20CODEN: THEODJ; ISSN:0166-1280. (Elsevier B.V.)
D.-functional theory calcns. of the Rayleigh optical activities of small isolated polyglycine mols. are reported. Fully extended β-sheet-like conformations of polypeptides of glycine, (Gly)n (with n = 1-5) are considered. After geometry optimizations, dipole moments and dipole polarizabilities (both the mean and the anisotropic components) are calcd. using the B3LYP and B3P86 functionals in 3 basis sets. The polarizabilities are used to analyze the Rayleigh scattering activities and depolarization ratios. The convergence of the av. dipole polarizability per monomer is analyzed. The differences in activity and depolarization for Rayleigh scattered radiation between the extended β-sheet-like and the folded α-helix-like forms of tetraglycine are analyzed and are relevant, suggesting its possible use in exptl. characterization.
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Abstract
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Figure 1
Figure 1. Structures of the five stable oxalic acid (OA) conformers, optimized using the M06–2X/6-311++G(3df,3pd) model, showing intramolecular hydrogen bonds (dotted lines) along with the relative electronic energy (ΔE_R) and relative Gibbs free energy (ΔG_R), calculated with respect to the lowest energy conformer, cTc.
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Figure 2
Figure 2. Schematic diagram of the rotational barriers for the possible interconversions among the OA conformers as obtained by the M06–2X/6-311++G(3df, 3pd) level.
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Figure 3
Figure 3. Equilibrium geometries of the stable (OA)(AM) cluster compositions optimized at the M06–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths, obtained using the present model shown in black color, while those from other models─B3LYP/aug-cc-pVDZ (6) and PW91PW91/6-311++G(3df,3pd) (7)─are shown in red and blue, respectively. The numbers in square brackets represent the relative energy differences of the conformations within each cluster composition in kcal/mol.
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Figure 4
Figure 4. Equilibrium geometries of the stable (OA)(AM)₂ cluster compositions. optimized at the M06–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths, obtained using the present model shown in black, and those from PW91PW91/6-311++G(3df,3pd) (7) in blue. The numbers in square brackets represent the relative energy differences of the conformations within each cluster composition in kcal/mol.
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Figure 5
Figure 5. Equilibrium geometries of stable (OA)(SA) cluster compositions. optimized at the MO6–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths given in angstrom. The numbers in square brackets represent the relative energy differences of the conformations in each cluster composition, in kcal/mol.
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Figure 6
Figure 6. Equilibrium geometries of the stable (OA)(SA)₂ cluster compositions. optimized at the MO6–2X/6-311++G(3df,3pd) level. The dashed lines represent the intermolecular hydrogen bonds with respective bond lengths given in angstrom. The numbers in square brackets represent the relative energy differences of the conformations in each cluster composition, in kcal/mol.
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Figure 7
Figure 7. Percentage variation of mean dipole polarizability, anisotropy of the polarizability, Rayleigh activity, and degree of depolarization for natural light in all the clusters, relative to respective OA monomers.
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Figure 8
Figure 8. Excess Rayleigh scattering intensity (Δ $R$ ) due to clustering of OA with AM and SA.
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References
This article references 84 other publications.
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  Formation and properties of hydrogen-bonded complexes of common organic oxalic acid with atmospheric nucleation precursors
  Xu, Yisheng; Nadykto, Alexey B.; Yu, Fangqun; Jiang, Lei; Wang, Wei
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  Nucleation in the Earth's atm. plays a vital role in the aerosol radiative forcing assocd. directly with the prodn. of ultrafine particles responsible for adverse public health impacts and global climate changes. The interaction of the common org. oxalic acid with the atm. nucleation precursors and trace ionic species has been investigated using the D. Functional Theory (DFT). A comprehensive study of the hydrogen-bonded complexes of oxalic acid with neutral monomers and ionic clusters of the sulfuric acid, water and ammonia, the key atm. nucleation precursors, has been carried out. Bonding of the oxalic acid with the above-mentioned neutrals was found to be moderately weak, and thus, the oxalic acid cannot stabilize the binary sulfuric acid-water and ternary sulfuric acid-ammonia clusters. The interaction of the oxalic acid with pos. ionic species is, in contrast, strong and significantly enhances stability of the clusters formed over the ions. The hydration of pos. charged (C2H2O4)(H3O+), (C2H2O4)(NH4+) and (C2H2O4)(H3O+)(H2SO4) clusters is also strong and close to that of the sulfuric acid, the key atm. nucleation precursor. These considerations lead to the logical conclusion that oxalic acid can catalyze the prodn. of pos. charged pre-nucleation clusters and, thus, its role in nucleation of pos. ions in the Earth's troposphere should be studied in further details.
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  Xu, W.; Zhang, R. Theoretical investigation of interaction of dicarboxylic acids with common aerosol nucleation precursors. J. Phys. Chem. A 2012, 116, 4539– 4550, DOI: 10.1021/jp301964u
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  Theoretical Investigation of Interaction of Dicarboxylic Acids with Common Aerosol Nucleation Precursors
  Xu, Wen; Zhang, Renyi
  Journal of Physical Chemistry A (2012), 116 (18), 4539-4550CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  Dicarboxylic acids are important products from photooxidn. of volatile org. compds. and are believed to play an important role in the formation and growth of atm. secondary org. aerosols. In this paper, the interaction of five dicarboxylic acids, i.e., oxalic acid (C2H2O4), malonic acid (C3H4O4), maleic acid (C4H4O4), phthalic acid (C8H6O4), and succinic acid (C4H6O4), with sulfuric acid and ammonia has been studied, employing quantum chem. calcns., quantum theory of atoms in mols. (QTAIM), and the natural bond orbital (NBO) anal. methods. Several levels of quantum chem. calcns. are considered, including coupled-cluster theory with single and double excitations with perturbative corrections for the triple excitations (CCSD(T)) and two d. functionals, B3LYP and PW91PW91. The free energies of formation of the heterodimer and heterotrimer clusters suggest that dicarboxylic acids can contribute to the aerosol nucleation process by binding to sulfuric acid and ammonia. In particular, the formation energies and structures of the heterotrimer clusters show that dicarboxylic acids enhance nucleation in two directions, in contrast to monocarboxylic acids.
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  Weber, K. H.; Morales, F. J.; Tao, F. Theoretical study on the structure and stabilities of molecular clusters of oxalic acid with water. J. Phys. Chem. A 2012, 116, 11601– 11617, DOI: 10.1021/jp308499f
  5
  Theoretical Study on the Structure and Stabilities of Molecular Clusters of Oxalic Acid with Water
  Weber, Kevin H.; Morales, Francisco J.; Tao, Fu-Ming
  Journal of Physical Chemistry A (2012), 116 (47), 11601-11617CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  The importance of aerosols to humankind is well-known, playing an integral role in detg. Earth's climate and influencing human health. Despite this fact, much remains unknown about the initial events of nucleation. In this work, the mol. properties of common org. atm. pollutant oxalic acid and its gas phase interactions with water have been thoroughly examd. Local min. single-point energies for the monomer conformations were calcd. at the B3LYP and MP2 level of theory with both 6-311++G(d,p) and aug-cc-pVDZ basis sets and are compared with previous works. Optimized geometries, relative energies, and free energy changes for the stable clusters of oxalic acid conformers with up to six waters were then obtained from B3LYP calcns. with 6-31+G(d) and 6-311++G(d,p) basis sets. Initially, cooperative binding is predicted to be the most important factor in nucleation, but as the clusters grow, dipole cancellations are found to play a pivotal role. The clusters of oxalic acid hydrated purely with water tend to produce extremely stable and neutral core systems. Free energies of formation and atm. implications are discussed.
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  Theoretical Study on Stable Small Clusters of Oxalic Acid with Ammonia and Water
  Weber, Kevin H.; Liu, Qian; Tao, Fu-Ming
  Journal of Physical Chemistry A (2014), 118 (8), 1451-1468CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  Thermodynamically stable small clusters of oxalic acid (CO2H)2, ammonia (NH3), and water (H2O) are studied through quantum chem. calcns. The (CO2H)2-NH3 core system with up to three waters of hydration was examd. by B3LYP d. functional theory and MP2 MO theory with the aug-cc-pVDZ basis set. The (CO2H)2-NH3 core complexes are obsd. to hydrogen bond strongly and should be found in appreciably significant concns. in the atm. Subsequent hydration of the (CO2H)2-NH3 core, however, is found to be somewhat prohibitive under ambient conditions. Relative populations of the examd. clusters are predicted and the binding patterns detailed. Atm. implications related to new particle formations are discussed.
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  Peng, X.-Q.; Liu, Y.-R.; Huang, T.; Jiang, S.; Huang, W. Interaction of gas phase oxalic acid with ammonia and its atmospheric implications. Phys. Chem. Chem. Phys. 2015, 17, 9552– 9563, DOI: 10.1039/C5CP00027K
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  Interaction of gas phase oxalic acid with ammonia and its atmospheric implications
  Peng, Xiu-Qiu; Liu, Yi-Rong; Huang, Teng; Jiang, Shuai; Huang, Wei
  Physical Chemistry Chemical Physics (2015), 17 (14), 9552-9563CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Oxalic acid is believed to play an important role in the formation and growth of atm. org. aerosols. However, as a common org. acid, the understanding of the larger clusters formed by gas phase oxalic acid with multiple ammonia mols. is incomplete. In this work, the structural characteristics and thermodn. of oxalic acid clusters with up to six ammonia mols. have been investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that oxalic acid forms relatively stable clusters with ammonia mols., and that ionization events play a key role. The analyses of the thermodn. and atm. relevance indicate that the heterodimer (H2C2O4)(NH3) shows an obvious relative concn. in the atm., and thus likely participates in new particle formation. However, with increasing no. of ammonia mols., the concn. of clusters decreases gradually. Addnl., clusters of oxalic acid with ammonia mols. are predicted to form favorably in low temp. conditions and show high Rayleigh scattering intensities.
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8. 8
  Miao, S.-K.; Jiang, S.; Chen, J.; Ma, Y.; Zhu, Y.-P.; Wen, Y. Hydration of a sulfuric acid-oxalic acid complex: acid dissociation and its atmospheric implication. RSC Adv. 2015, 5, 48638– 48646, DOI: 10.1039/C5RA06116D
  8
  Hydration of a sulfuric acid-oxalic acid complex: acid dissociation and its atmospheric implication
  Miao, Shou-Kui; Jiang, Shuai; Chen, Jiao; Ma, Yan; Zhu, Yu-Peng; Wen, Yang; Zhang, Miao-Miao; Huang, Wei
  RSC Advances (2015), 5 (60), 48638-48646CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  Oxalic acid (OA), one of the most common org. acids in the Earth's atm., is expected to enhance the nucleation and growth of nanoparticles contg. sulfuric acid (SA) and water (W); however, the details about the hydration of OA-SA are poorly understood, esp. for the larger clusters with more water mols. We have investigated the structural characteristics and thermodn. of these clusters using d. functional theory at the PW91PW91/6-311++G(3df,3pd) level. The favorable free energies of formation and obvious concns. of the OA-SA-Wn (n = 0-6) clusters at 298.15 K predict that oxalic acid can contribute to the aerosol nucleation process by binding to sulfuric acid and water until n = 6. There is strong temp. dependence for the complexes formation, and the energy order of these complexes is altered from 100 to 400 K, regardless of different cluster sizes or different isomers within the same cluster size. The lower temp. and higher relative humidity promote the formation of hydrates. Addnl., the investigation of acid dissocn. predicts that several acid-dissocd. models could coexist in the atm., specifically when more water mols. are present. Fewer waters may be needed to cause the acid dissocn., as the relative acidity of the cluster increases, which plays a key role in forming relatively stable hydrated clusters of OA-SA. Finally, the Rayleigh scattering properties of OA-SA-Wn (n = 0-6) have been systematically investigated for the first time to further discuss its atm. implication.
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9. 9
  Pavuluri, C. M.; Kawamura, K.; Mihalopoulos, N.; Swaminathan, T. Laboratory photochemical processing of aqueous aerosols: Formation and degradation of dicarboxylic acids, oxocarboxylic acids and α- dicarbonyls. Atmos. Chem. Phys. 2015, 15, 7999– 8012, DOI: 10.5194/acp-15-7999-2015
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10. 10
  Wang, G.; Cheng, C.; Meng, J.; Huang, Y.; Li, J.; Ren, Y. Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface. Atmos. Environ. 2015, 113, 169– 176, DOI: 10.1016/j.atmosenv.2015.05.013
  10
  Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface
  Wang, Gehui; Cheng, Chunlei; Meng, Jingjing; Huang, Yao; Li, Jianjun; Ren, Yanqin
  Atmospheric Environment (2015), 113 (), 169-176CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  Chem. evolution of East Asian dust during transpacific transport has been given much attention for inorg. species such as sulfate, nitrate and ammonium. However, the role of org. species during the transport has almost entirely been ignored. To understand the formation mechanism of secondary org. aerosols (SOA) on dust surfaces, this study investigated the concns. and compns. of dicarboxylic acids, keto-carboxylic acids, α-dicarbonyls and inorg. ions in size-segregated aerosols (9-stages) collected in Xi'an, central China during the two dust storm episodes in the springs of 2009 and 2011 and compared with those in nondust storm periods. During the events the ambient particulate dicarboxylic acids were 932-2240 ng m-3, which are comparable and even higher than those in nondust periods. Mol. compns. of the above SOA are similar to those in nondust periods with oxalic acid being the leading species. In the presence of the dust storms, all the above mentioned SOA species in Xi'an were predominantly enriched on the coarse particles (>2.1 μm), and oxalic acid well correlated with NO3- (R2 = 0.72, p < 0.001) rather than SO42-. This phenomenon differs greatly from the SOA in any other nondust period that is usually characterized by an enrichment of oxalic acid in fine mode and a strong correlation of oxalic acid with SO42-. We propose a formation pathway to explain these observations, in which nitric acid and/or nitrogen oxides react with dust to produce Ca(NO3)2 and form a liq. phase on the surface of dust aerosols via water vapor-absorption of Ca(NO3)2, followed by a partitioning of the gas-phase water-sol. org. precursors (e.g.,glyoxal and methylglyoxal) into the aq.-phase and a subsequent oxidn. into oxalic acid. To the best of our knowledge, we found for the first time the enrichment of glyoxal and methylglyoxal on dust surface. Our data suggest an important role of nitrate in the heterogeneous formation process of SOA on the surface of dust.
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11. 11
  Kawamura, K.; Bikkina, S. A review of dicarboxylic acids and related compounds in atmospheric424 aerosols: Molecular distributions, sources and transformation. Atmos. Res. 2016, 170, 140– 160, DOI: 10.1016/j.atmosres.2015.11.018
  11
  A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation
  Kawamura, Kimitaka; Bikkina, Srinivas
  Atmospheric Research (2016), 170 (), 140-160CODEN: ATREEW; ISSN:0169-8095. (Elsevier B.V.)
  This review aims to update our understanding on mol. distributions of water-sol. dicarboxylic acids and related compds. in atm. aerosols with a focus on their geog. variability, size distribution, sources and formation pathways. In general, mol. distributions of diacids in aerosols from the continental sites and over the open ocean waters are often characterized by the predominance of oxalic acid (C2) followed by malonic acid (C3) and/or succinic acid (C4), while those sampled over the polar regions often follow the order of C4 ≥ C2 and C3. The most abundant and ubiquitous diacid is oxalic acid, which is principally formed via atm. oxidn. of its higher homologues of long chain diacids and other pollution-derived org. precursors (e.g., olefins and arom. hydrocarbons). However, its occurrence in marine aerosols is mainly due to the transport from continental outflows (e.g., East Asian outflow during winter/spring to the North Pacific) and/or governed by photochem./aq. phase oxidn. of biogenic unsatd. fatty acids (e.g., oleic acid) and isoprene emitted from the productive open ocean waters. The long-range atm. transport of pollutants from mid latitudes to the Arctic in dark winter facilitates to accumulate the reactants prior to their intense photochem. oxidn. during springtime polar sunrise. Furthermore, the relative abundances of C2 in total diacid mass showed similar temporal trends with downward solar irradn. and ambient temps., suggesting the significance of atm. photochem. oxidn. processing. Compd.-specific isotopic analyses of oxalic acid showed the highest δ13C among diacids whereas azelaic acid showed the lowest value, corroborating the significance of atm. aging of oxalic acid. On the other hand, other diacids gave intermediate values between these two diacids, suggesting that aging of oxalic acid is assocd. with 13C enrichment.
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12. 12
  Peng, X.-Q.; Huang, T.; Miao, S.-K.; Chen, J.; Wen, H.; Feng, Y.-J. Hydration of oxalic acid–ammonia complex: atmospheric implication and Rayleigh-scattering properties. RSC Adv. 2016, 6, 46582– 47593, DOI: 10.1039/C6RA03164A
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  Zhao, H.; Zhang, Q.; Du, L. Hydrogen bonding in cyclic complexes of carboxylic acid–sulfuric acid and their atmospheric implications. RSC Adv. 2016, 6, 71733– 71743, DOI: 10.1039/C6RA16782A
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  Elm, J.; Myllys, N.; Kurtén, T. What is required for highly oxidized molecules to form clusters with sulfuric acid?. J. Phys. Chem. A 2017, 121, 4578– 4587, DOI: 10.1021/acs.jpca.7b03759
  14
  What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?
  Elm, Jonas; Myllys, Nanna; Kurten, Theo
  Journal of Physical Chemistry A (2017), 121 (23), 4578-4587CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  We have studied the specific requirements of a given neutral org. mol. to act as a stabilizer in sulfuric acid induced new particle formation. Based on an anal. of the reaction Gibbs free energies between simple functional groups and sulfuric acid, carboxylic acid groups are identified to show the strongest hydrogen bonding interaction with sulfuric acid. The free energy assocd. with the hydrogen bonding between sulfuric acid and 14 different carboxylic acids of atm. relevance reveal that the binding strength is very dependent on the ability of sulfuric acid to form an addnl. hydrogen bond via its vacant S-OH group to a γ-carbonyl group in the org. mol. Extending the anal. to monoterpene oxidn. products and further to large dimer esters, we identify the following necessary criteria for a given org. oxidn. product to efficiently stabilize sulfuric acid clustering: (1) weak or no intramol. hydrogen bonds in the isolated monomer; (2) more than two carboxylic acid groups. As a proof of concept we show that these requirements correspond to the docking of a sulfuric acid mol. between two non-interacting carboxylic acid groups in the org. mol. These findings suggests that, for a given org. oxidn. product to participate in the initial steps in new particle formation involving sulfuric acid, very distinct mol. features are required.
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15. 15
  Hu, Y.-C.; Zhang, X.-H.; Li, Q.-S.; Zhang, Y.-H.; Li, Z.-S. Effect of water on the structure and stability of hydrogen-bonded oxalic acid dimer. ChemPhyschem 2017, 18, 3375– 3383, DOI: 10.1002/cphc.201700950
  15
  Effect of Water on the Structure and Stability of Hydrogen-Bonded Oxalic Acid Dimer
  Hu, Yuan-Chun; Zhang, Xiu-Hui; Li, Quan-Song; Zhang, Yun-Hong; Li, Ze-Sheng
  ChemPhysChem (2017), 18 (23), 3375-3383CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
  As the simplest and most abundant dicarboxylic acid in the atm., oxalic acid (OA) not only plays a key role in aerosol nucleation, but also acts as a prototypical compd. for the investigation of intra- and intermol. hydrogen-bonding interactions. A systematic theor. study on the hydrated OA dimers performed by using DFT at the M06-2X/6-311++G(3df, 2p) level is discussed herein. The properties of hydrogen bonds in clusters are inspected through topol. anal. by using atoms in mols. (AIM) theory. The most stable OA dimer involves a cyclic structure with two intermol. hydrogen bonds. Calcns. show that one H2O has a slight effect on the hydrogen bonds, whereas two water mols. weaken and three water mols. break the two intermol. hydrogen bonds between OAs. Furthermore, there are no hydrogen-bond interactions between OAs in almost all stable clusters as the no. of H2O mols. increases to four and five. Addnl., ionization and isomerization of OA through water-assisted proton-transfer phenomena are obsd. in tetra- and pentahydrates. This work provides new insights into the conversion of anhyd. OA into hydrated clusters that are helpful for further understanding the atm. nucleation process and nature of hydrogen bond.
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16. 16
  Xu, J.; Finlayson-Pitts, B. J.; Gerber, R. B. Proton transfer in mixed clusters of methanesulfonic acid, methylamine, and oxalic acid: implications for atmospheric particle formation. J. Phys. Chem. A 2017, 121, 2377– 2385, DOI: 10.1021/acs.jpca.7b01223
  16
  Proton Transfer in Mixed Clusters of Methanesulfonic Acid, Methylamine, and Oxalic Acid: Implications for Atmospheric Particle Formation
  Xu, Jing; Finlayson-Pitts, Barbara J.; Gerber, R. Benny
  Journal of Physical Chemistry A (2017), 121 (12), 2377-2385CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  Understanding the properties of atm. particles made of several components is a very challenging problem. In this paper, we perform quantum chem. calcns. for small multicomponent clusters of atm. relevance that incorporate methanesulfonic acid (MSA), methylamine (MA), oxalic acid (OxA), and water (H2O). Potential correlations between theor. predictions of proton transfer in the small clusters and findings of recent expts. on formation of particles of detectable sizes (>2 nm) from the same components are studied. It is proposed that proton transfer from the acid to the amine in the 1:1 clusters correlates with expts. on particle formation in systems, such as MSA-MA and MSA-MA-OxA. In the case of OxA + MA, which has been obsd. to give few particles, proton transfer does not occur for the 1:1 cluster but does for the 2:2 cluster. Adding H2O to OxA-MA promotes the occurrence of proton transfer, and corresponding particles are slightly enhanced. The partial charge on the MA component increases by adding OxA or H2O to MSA-MA, which is correlated with enhanced particle formation compared to MSA-MA alone. Ab initio mol. dynamics simulations show that proton transfer at room temp. (T = 298 K) and high temp. (T = 500 K) is little affected compared with the equil. structure (T = 0 K). These results suggest that small cluster calcns. may be useful in predicting the formation of multicomponent particles in the atm.
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17. 17
  Chen, J.; Jiang, S.; Liu, Y.-R.; Huang, T.; Wang, C.-Y.; Miao, S.-K. Interaction of oxalic acid with dimethylamine and its atmospheric implications. RSC Adv. 2017, 7, 6374– 6388, DOI: 10.1039/C6RA27945G
  17
  Interaction of oxalic acid with dimethylamine and its atmospheric implications
  Chen, Jiao; Jiang, Shuai; Liu, Yi-Rong; Huang, Teng; Wang, Chun-Yu; Miao, Shou-Kui; Wang, Zhong-Quan; Zhang, Yang; Huang, Wei
  RSC Advances (2017), 7 (11), 6374-6388CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  Oxalic acid and dimethylamine are the most common org. acid and base in the atm., and are recognized as significant precursor species in atm. new particle formation. However, the interaction between oxalic acid and dimethylamine in the presence of hydration is not yet understood. In this study, the most stable geometric structures and thermodn. of (C2H2O4)m(CH3NHCH3)(H2O)n (m = 1-2, n = 0-4) clusters are investigated using M06-2X coupled with the 6-311+G(2d,p) basis set. A high level explicitly cor. CCSD(T)-F12/VDZ-F12 method is utilized to benchmark the d. functional theory (DFT) methods. Hydration promotes proton transfer from oxalic acid to dimethylamine for (C2H2O4)(CH3NHCH3)(H2O)n (n = 0-4) clusters, while proton transfer from oxalic acid to dimethylamine occurs without hydration for (C2H2O4)2(CH3NHCH3)(H2O)n (n = 0-4) clusters. With regards to the isomer distribution at the potential energy surface, temp. seems not to be an important parameter, since almost all of the global min. for the investigated size range dominate within the investigated temp. range, except for in the (C2H2O4)m(CH3NHCH3)(H2O)2 clusters. Under atm. conditions, the peak hydration distribution shifts from unhydrated clusters to trihydrates for the (C2H2O4)(CH3NHCH3)(H2O)n (n = 0-4) clusters, while for the (C2H2O4)2(CH3NHCH3)(H2O)n (n = 0-4) clusters, unhydrated clusters clearly dominate the cluster distribution, irresp. of whether the humidity is low or high. Finally, the formation free energies obtained from quantum calcns. are used to calc. the evapn. rates. We find that evapn. of dimethylamine is preferred compared to oxalic acid for the (C2H2O4)(CH3NHCH3)(H2O)n clusters, while the results are reversed for the (C2H2O4)2(CH3NHCH3)(H2O)n clusters.
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18. 18
  Arquero, K. D.; Xu, J.; Gerber, B.; Finlayson-Pitts, B. J. Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study. Phys. Chem. Chem. Phys. 2017, 19, 28286– 28301, DOI: 10.1039/C7CP04468B
  18
  Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study
  Arquero, Kristine D.; Xu, Jing; Gerber, R. Benny; Finlayson-Pitts, Barbara J.
  Physical Chemistry Chemical Physics (2017), 19 (41), 28286-28301CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Atm. particles affect visibility, health, and climate but the mechanisms of their formation from initial clusters and their growth to detectable particles remain largely unknown. Previous studies showed methanesulfonic acid (MSA) reactions with NH3 and amines form particles, a process enhanced by water. Results of a combined exptl./theor. study of oxalic acid (OxA) effect on particle formation and growth from the MSA reaction with trimethylamine (TMA) in the presence/absence of water are reported. Gas phase reactants were mixed in an aerosol flow reactor at 1 atm pressure and 294° K. Particle no. concns. and size distributions were measured as a function of reaction time from 0.8-12 s. The interaction of OxA with TMA with/without water did not lead to significant particle formation. When OxA was present during the MSA reaction with TMA, there was little change (≤2 times more) in particle no. concn., but particles were larger compared vs. the base case (MSA with TMA alone). However, the presence of water with MSA and TMA overwhelmed the OxA effect so that OxA has no significant impact on particle no. concn. or size. Exptl. results suggested MSA hydrate is important for particle formation and growth in the four component OxA/MSA/TMA/water system. Results were compared to earlier studies of the OxA effect on the MSA/methylamine reaction and interpreted based on theor. calcd. properties of small clusters of the components.
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19. 19
  Hong, Y.; Liu, Y.-R.; Wen, H.; Miao, S.-K.; Huang, T.; Peng, X.-Q. Interaction of oxalic acid with methylamine and its atmospheric implications. RSC Adv. 2018, 8, 7225– 7234, DOI: 10.1039/C7RA13670F
  19
  Interaction of oxalic acid with methylamine and its atmospheric implications
  Hong, Yu; Liu, Yi-Rong; Wen, Hui; Miao, Shou-Kui; Huang, Teng; Peng, Xiu-Qiu; Jiang, Shuai; Feng, Ya-Juan; Huang, Wei
  RSC Advances (2018), 8 (13), 7225-7234CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  Oxalic acid, which is one of the most common dicarboxylic acids, is expected to be an important component of atm. aerosols. However, the contribution of oxalic acid to the generation of new particles is still poorly understood. In this study, the structural characteristics and thermodn. of (C2H2O4)(CH3NH2)n (n = 1-4) were investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that clusters formed by oxalic acid and methylamine are relatively stable, and the more the atoms participating in the formation of a ring-like structure, the more stable is the cluster. In addn., via the anal. of atm. relevance, it can be revealed that clusters of (C2H2O4)(CH3NH2)n (n = 1-4) have a noteworthy concn. in the atm., which indicates that these clusters could be participating in new particle formation. Moreover, by comparison with (H2C2O4)(NH3)n (n = 1-6) species, it can be seen that oxalic acid is more readily bound to methylamine than to ammonia, which promotes nucleation or new particle formation. Finally, the Rayleigh scattering properties of clusters of (C2H2O4)(CH3NH2)n (n = 1-4) were investigated for the first time to det. their atm. implications.
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20. 20
  Boreddy, S. K. R.; Kawamura, K. Investigation on the hygroscopicity of oxalic acid and atmospherically relevant oxalate salts under sub- and supersaturated conditions. Environ. Sci.: Processes Impacts 2018, 20, 1069– 1080, DOI: 10.1039/C8EM00053K
  There is no corresponding record for this reference.
21. 21
  Lv, G.; Sun, X.; Zhang, C.; Li, M. Understanding the catalytic role of oxalic acid in SO₃ hydration to form H₂SO₄ in the atmosphere. Atmos. Chem. Phys. 2019, 19, 2833– 2844, DOI: 10.5194/acp-19-2833-2019
  21
  Understanding the catalytic role of oxalic acid in SO3 hydration to form H2SO4 in the atmosphere
  Lv, Guochun; Sun, Xiaomin; Zhang, Chenxi; Li, Mei
  Atmospheric Chemistry and Physics (2019), 19 (5), 2833-2844CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
  The hydration of SO3 plays an important role in atm. sulfuric acid formation. Some atm. species can be involved in and facilitate the reaction. In this work, using quantum chem. calcns., we show that oxalic acid, the most common dicarboxylic acid in the atm., can effectively catalyze the hydration of SO3. The energy barrier of the SO3 hydration reaction catalyzed by oxalic acid (cTt, tTt, tCt and cCt conformers) is a little higher or less than 1 kcal mol-1, which is lower than the energy barrier of 5.17 kcal mol-1 for water-catalyzed SO3 hydration. Compared with the rates of the SO3 hydration reaction catalyzed by oxalic acid and water, it can be found that in the upper troposphere the OA-catalyzed SO3 hydration can play an important role in promoting SO3 hydration. It leads us to conclude that the involvement of oxalic acid in SO3 hydration to form H2SO4 is significant in the atm.
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22. 22
  Deshmukh, D. K.; Kawamura, K.; Gupta, T.; Haque, M. M.; Zhang, Y.-L.; Singh, D. K.; Tsai, Y. I. High Loadings of Water-soluble Oxalic Acid and Related Compounds in PM2.5 Aerosols in Eastern Central India: Influence of Biomass Burning and Photochemical Processing. Aerosol Air Qual. Res. 2019, 19, 2625– 2644, DOI: 10.4209/aaqr.2019.10.0543
  There is no corresponding record for this reference.
23. 23
  Zhao, Y.; Liu, Y.-R.; Jiang, S.; Huang, T.; Wang, Z.-H.; Xu, C.-X. Volatile organic compounds enhancing sulfuric acid-based ternary homogeneous nucleation: the important role of synergistic effect. Atmos. Environ. 2020, 233, 117609, DOI: 10.1016/j.atmosenv.2020.117609
  23
  Volatile organic compounds enhancing sulfuric acid-based ternary homogeneous nucleation: The important role of synergistic effect
  Zhao, Yu; Liu, Yi-Rong; Jiang, Shuai; Huang, Teng; Wang, Zi-Hang; Xu, Cai-Xin; Feng, Ya-Juan; Huang, Wei
  Atmospheric Environment (2020), 233 (), 117609CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  New particle formation (NPF) is an important source of atm. aerosols. Sulfuric acid (SA) and water (W) are recognized as essential participating substances in the nucleation of the atm. In addn., as one of the most common org. acids, oxalic acid (OA) can improve NPF when amine such as methylamine (MA) is present. However, exploring the properties of atm. particles made up of different components is challenging and the role of volatile org. compds. in SA-based ternary homogeneous nucleation is still lacking in research. In this work, the structures and energies of (SA)x(OA)y(MA)z(W)m (0 ≤ x, y, z ≤ 3, 0 ≤ m ≤ 1) are investigated. The results indicate that it is accessible for SA to form clusters with OA and MA mols. through hydrogen bonds and proton transfer interactions. The anal. of non-covalent interactions and proton transfer reveals that ternary nucleation systems have stronger hydrogen bonds and more proton transfers than binary systems to stabilize the clusters. In terms of the thermodn. properties, the Gibbs free energies of the clusters will decrease as the addn. of SA, OA or MA mols. indicating that the synergistic effect of these three substances may be of potential in forming the initial cluster and subsequent growth processes. Moreover, the evapn. rates of clusters show that the synergistic effect of ternary clusters leads to a decrease in evapn. rate which may promote atm. nucleation.
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24. 24
  Chen, J. Theoretical analysis of sulfuric acid–dimethylamine–oxalic acid–water clusters and implications for atmospheric cluster formation. RSC Adv. 2022, 12, 22425– 22434, DOI: 10.1039/D2RA03492A
  There is no corresponding record for this reference.
25. 25
  Palmieri, F.; Estoppey, A.; House, G. L.; Lohberger, A.; Bindschedler, S.; Chain, P. S. G.; Junier, P. Oxalic acid, a molecule at the crossroads of bacterial-fungal interactions. Adv. Appl. Microbiol. 2019, 106, 49– 77, DOI: 10.1016/bs.aambs.2018.10.001
  25
  Oxalic acid, a molecule at the crossroads of bacterial-fungal interactions
  Palmieri Fabio; Estoppey Aislinn; Lohberger Andrea; Bindschedler Saskia; House Geoffrey L; Chain Patrick S G; Junier Pilar
  Advances in applied microbiology (2019), 106 (), 49-77 ISSN:0065-2164.
  Oxalic acid is the most ubiquitous and common low molecular weight organic acid produced by living organisms. Oxalic acid is produced by fungi, bacteria, plants, and animals. The aim of this review is to give an overview of current knowledge about the microbial cycling of oxalic acid through ecosystems. Here we review the production and degradation of oxalic acid, as well as its implications in the metabolism for fungi, bacteria, plants, and animals. Indeed, fungi are well known producers of oxalic acid, while bacteria are considered oxalic acid consumers. However, this framework may need to be modified, because the ability of fungi to degrade oxalic acid and the ability of bacteria to produce it, have been poorly investigated. Finally, we will highlight the role of fungi and bacteria in oxalic acid cycling in soil, plant and animal ecosystems.
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26. 26
  Rudnick, M. B.; van Veen, J. A.; de Boer, W. Oxalic acid: a signal molecule for fungus-feeding bacteria of the genus Collimonas ?. Environ. Microbiol. Rep. 2015, 7 (5), 709– 714, DOI: 10.1111/1758-2229.12290
  There is no corresponding record for this reference.
27. 27
  Hsieh, L.; Chen, C.; Wan, M.; Tsai, C.; Tsai, Y. Speciation and temporal characterization of dicarboxylic acids in PM2. 5 during a PM episode and a period of non-episodic pollution. Atmos. Environ. 2008, 42, 6836– 6850, DOI: 10.1016/j.atmosenv.2008.05.021
  There is no corresponding record for this reference.
28. 28
  Radek, M.; Savage, G. P. Oxalates in Some Indian Green Leafy Vegetables. Int. J. Food Sci. Nutr. 2008, 59, 246– 260, DOI: 10.1080/09637480701791176
  28
  Oxalates in some Indian green leafy vegetables
  Radek, M.; Savage, G. P.
  International Journal of Food Sciences and Nutrition (2008), 59 (3), 246-260CODEN: IJFNEH; ISSN:0963-7486. (Informa Healthcare)
  The sol. and total oxalate contents of 11 leafy vegetables grown in India were detd. Spinach, purple and green amaranth and colocasia contained high levels of total oxalates, which ranged from 5,138.0±37.6 mg/100 g dry matter up to 12,576.1±107.9 mg/100 g dry matter. Seven other leafy vegetables (curry, drumstick, shepu, fenugreek, coriander, radish and onion stalks) contained only insol. oxalate, which ranged from 209.0±5.0 mg/100 g dry matter to 2,774.9±18.4 mg/100 g dry matter. In vitro digestion of the samples showed that the gastric available oxalate was 10% lower than the values obtained from acid extn. and that intestinal available oxalate was 20% lower than the values obtained following hot water extn. The percentage calcium bound in the insol. oxalate fraction of the dried leafy vegetables ranged from 3.3% to 86.7% of the total calcium. Addn. of four different sources of calcium (low fat milk, whole milk, calcium carbonate and calcium sulfate) resulted in a range of 32-100% redns. of intestinal available oxalate in the mixt.
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29. 29
  Holmes, R. P.; Kennedy, M. Estimation of the Oxalate Content of Foods and Daily Oxalate Intake. Kidney Int. 2000, 57, 1662– 1667, DOI: 10.1046/j.1523-1755.2000.00010.x
  29
  Estimation of the oxalate content of foods and daily oxalate intake
  Holmes, Ross P.; Kennedy, Martha
  Kidney International (2000), 57 (4), 1662-1667CODEN: KDYIA5; ISSN:0085-2538. (Blackwell Science, Inc.)
  Background. The amt. of oxalate ingested may be an important risk factor in the development of idiopathic calcium oxalate nephrolithiasis. Reliable food tables listing the oxalate content of foods are currently not available. The aim of this research was to develop an accurate and reliable method to measure the food content of oxalate. Methods. Capillary electrophoresis (CE) and ion chromatog. (IC) were compared as direct techniques for the estn. of the oxalate content of foods. Foods were thoroughly homogenized in acid, heat extd., and clarified by centrifugation and filtration before diln. in water for anal. Five individuals consuming self-selected diets maintained food records for three days to det. their mean daily oxalate intakes. Results. Both techniques were capable of adequately measuring the oxalate in foods with a significant oxalate content. With foods of very low oxalate content (<1.8 mg/100 g), IC was more reliable than CE. The mean daily intake of oxalate by the five individuals tested was 152 ± 83 mg, ranging from 44 to 352 mg/day. Conclusions. CE appears to be the method of choice over IC for estg. the oxalate content of foods with a medium (>10 mg/100 g) to high oxalate content due to a faster anal. time and lower running costs, whereas IC may be better suited for the anal. of foods with a low oxalate content. Accurate ests. of the oxalate content of foods should permit the role of dietary oxalate in urinary oxalate excretion and stone formation to be clarified. Other factors, apart from the amt. of oxalate ingested, appear to exert a major influence over the amt. of oxalate excreted in the urine.
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30. 30
  Salgado, N.; Silva, M. A.; Figueira, M. E.; Costa, H. S.; Albuquerque, T. G. Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications. Foods 2023, 12, 3201, DOI: 10.3390/foods12173201
  There is no corresponding record for this reference.
31. 31
  Siener, R.; Seidler, A.; Hönow, R. Oxalate-rich foods. Food Sci. Technol. 2021, 41, 169– 173, DOI: 10.1590/fst.10620
  There is no corresponding record for this reference.
32. 32
  Mochizuki, T.; Kawamura, K.; Miyazaki, Y.; Wada, R.; Takahashi, Y.; Saigusa, N.; Tani, A. Secondary formation of oxalic acid and related organic species from biogenic sources in a larch forest at the northern slope of Mt. Fuji. Atmos. Environ. 2017, 166, 255– 262, DOI: 10.1016/j.atmosenv.2017.07.028
  32
  Secondary formation of oxalic acid and related organic species from biogenic sources in a larch forest at the northern slope of Mt. Fuji
  Mochizuki, Tomoki; Kawamura, Kimitaka; Miyazaki, Yuzo; Wada, Ryuichi; Takahashi, Yoshiyuki; Saigusa, Nobuko; Tani, Akira
  Atmospheric Environment (2017), 166 (), 255-262CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  To better understand the formation of water-sol. org. aerosols in the forest atm., we measured low mol. wt. (LMW) dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, unsatd. fatty acids (UFAs), and water-sol. org. carbon (WSOC) in aerosols from a Larix kaempferi forest located at the northern slope of Mt. Fuji, Japan, in summer 2012. Concns. of dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and WSOC showed maxima in daytime. Relative abundance of oxalic acid in LMW dicarboxylic acids was on av. 52% and its av. concn. was 214 ng m-3. We found that diurnal and temporal variations of oxalic acid are different from those of isoprene and α-pinene, whereas biogenic secondary org. aerosols (BSOAs) derived from isoprene and α-pinene showed similar variations with oxalic acid. The mass concn. ratios of oxalic acid/BSOAs were relatively const., although a large variation in the concns. of toluene that is an anthropogenic volatile org. compd. was obsd. These results suggest that formation of oxalic acid is assocd. with the oxidn. of isoprene and α-pinene with O3 and other oxidants in the forest atm. In addn., concns. of UFAs were obsd., for the first time, to decrease dramatically during daytime in the forest. This study demonstrates that forest ecosystem is an important source of oxalic acid and other dicarboxylic acids in the atm.
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33. 33
  Kawamura, K.; Bikkina, S. A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation. Atmos. Res. 2016, 170, 140– 160, DOI: 10.1016/j.atmosres.2015.11.018
  33
  A review of dicarboxylic acids and related compounds in atmospheric aerosols: Molecular distributions, sources and transformation
  Kawamura, Kimitaka; Bikkina, Srinivas
  Atmospheric Research (2016), 170 (), 140-160CODEN: ATREEW; ISSN:0169-8095. (Elsevier B.V.)
  This review aims to update our understanding on mol. distributions of water-sol. dicarboxylic acids and related compds. in atm. aerosols with a focus on their geog. variability, size distribution, sources and formation pathways. In general, mol. distributions of diacids in aerosols from the continental sites and over the open ocean waters are often characterized by the predominance of oxalic acid (C2) followed by malonic acid (C3) and/or succinic acid (C4), while those sampled over the polar regions often follow the order of C4 ≥ C2 and C3. The most abundant and ubiquitous diacid is oxalic acid, which is principally formed via atm. oxidn. of its higher homologues of long chain diacids and other pollution-derived org. precursors (e.g., olefins and arom. hydrocarbons). However, its occurrence in marine aerosols is mainly due to the transport from continental outflows (e.g., East Asian outflow during winter/spring to the North Pacific) and/or governed by photochem./aq. phase oxidn. of biogenic unsatd. fatty acids (e.g., oleic acid) and isoprene emitted from the productive open ocean waters. The long-range atm. transport of pollutants from mid latitudes to the Arctic in dark winter facilitates to accumulate the reactants prior to their intense photochem. oxidn. during springtime polar sunrise. Furthermore, the relative abundances of C2 in total diacid mass showed similar temporal trends with downward solar irradn. and ambient temps., suggesting the significance of atm. photochem. oxidn. processing. Compd.-specific isotopic analyses of oxalic acid showed the highest δ13C among diacids whereas azelaic acid showed the lowest value, corroborating the significance of atm. aging of oxalic acid. On the other hand, other diacids gave intermediate values between these two diacids, suggesting that aging of oxalic acid is assocd. with 13C enrichment.
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34. 34
  Claeys, M. Formation of secondary organic aerosols through photooxidation of isoprene. Science 2004, 303, 1173– 1176, DOI: 10.1126/science.1092805
  34
  Formation of Secondary Organic Aerosols Through Photooxidation of Isoprene
  Claeys, Magda; Graham, Bim; Vas, Gyorgy; Wang, Wu; Vermeylen, Reinhilde; Pashynska, Vlada; Cafmeyer, Jan; Guyon, Pascal; Andreae, Meinrat O.; Artaxo, Paulo; Maenhaut, Willy
  Science (Washington, DC, United States) (2004), 303 (5661), 1173-1176CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  Detailed org. anal. of natural aerosols from the Amazonian rain forest showed considerable quantities of previously unobserved polar org. compds. identified as a mixt. of 2 diastereoisomeric 2-methyltetrols: 2-methylthreitol and 2-methylerythritol. These polyols, which have an isoprene skeleton, can be explained by OH--initiated photooxidn. of isoprene. They have low vapor pressure, allowing them to condense onto pre-existing particles. It was estd. that photooxidn. of isoprene results in an annual global prodn. of ∼2 Tg of the polyols, a substantial fraction of the Intergovernmental Panel on Climate Change est. of 8-40 Tg/yr of secondary org. aerosol from biogenic sources.
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35. 35
  Kawamura, K.; Ikushima, K. Seasonal changes in the distribution of dicarboxylic acids in the urban atmosphere. Environ. Sci. Technol. 1993, 27, 2227– 2235, DOI: 10.1021/es00047a033
  35
  Seasonal changes in the distribution of dicarboxylic acids in the urban atmosphere
  Kawamura, Kimitaka; Ikushima, Kouichi
  Environmental Science and Technology (1993), 27 (10), 2227-35CODEN: ESTHAG; ISSN:0013-936X.
  Low-mol.-wt. dicarboxylic acids were studied in urban aerosol samples collected from Tokyo atm. in 1988-1989, by a capillary GC and GC-mass spectrometry method using a di-Bu ester derivatization technique. A homologous series of C2-C10 dicarboxylic acids were detected in the aerosols, including straight-chain satd., unsatd., branched-chain, and hydroxylated species. Mol. distributions of the diacids demonstrated that oxalic (C2) acid was the most abundant throughout the 4 seasons, followed by C3 and C4 diacids; the C2 diacid comprised 37-69% of the total diacid concns. Diacids with higher C nos. were less abundant, although C6 and C9 diacids were relatively abundant. Total concns. of diacids were 90-1370 ng/m3, which corresponded to 0.06-1.1% of the total aerosol mass. Their concns. relative to aerosol mass showed a seasonal trend with a max. in Aug. The C2-C4 diacid C normalized by aerosol total C also showed a strong seasonal change with a max. in the summer and indicated a pos. correlation with oxidant concns. Interestingly, lower diacids showed higher values for correlation coeff. (e.g., r = 0.80 for oxalic acid), suggesting a preferential prodn. of low mol. wt. dicarboxylic acids, esp., C2 diacid. Possible reaction mechanisms are discussed in relation to the preferential accumulation of lower diacids in the atm.
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36. 36
  Prenni, A. J.; DeMott, P. J.; Kreidenweis, S. M.; Sherman, D. E.; Russell, L. M.; Ming, Y. J. Phys. Chem. A 2001, 105, 11240– 11248, DOI: 10.1021/jp012427d
  36
  The effects of low molecular weight dicarboxylic acids on cloud formation
  Prenni, Anthony J.; DeMott, Paul J.; Kreidenweis, Sonia M.; Sherman, D. Eli; Russell, Lynn M.; Ming, Yi
  Journal of Physical Chemistry A (2001), 105 (50), 11240-11248CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  The ubiquitous presence of org. compds. in tropospheric particles requires that their role in aerosol/cloud interactions be accounted for in climate models. In this paper, we present studies that investigate the hygroscopic behavior of org. compds. and their efficiency as ice nuclei. Specifically, results for sol. and partially sol. dicarboxylic acids that have been obsd. in atm. aerosol are discussed. At room temp., we use a humidified tandem differential mobility analyzer (HTDMA) and a condensation particle counter interfaced with a cloud condensation nuclei counter to characterize the water uptake behavior of these acids. The HTDMA data agree quite well with modeled hygroscopic behavior. However, we find that some of the compds. retain water to very low humidities, never exhibiting efflorescence. The studies are extended to lower temps. using a continuous flow ice thermal diffusion chamber to investigate the role of these species in ice nucleation at cirrus conditions. Results suggest that ice formation occurs via homogeneous nucleation for most of these acids, and that nucleation for these acids is not as efficient as that for sulfate aerosol.
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37. 37
  Makar, P. A. The estimation of organic gas vapour pressure. Atmos. Environ. 2001, 35, 961– 974, DOI: 10.1016/S1352-2310(00)00343-5
  There is no corresponding record for this reference.
38. 38
  Limbeck, A.; Puxbaum, H.; Otter, L.; Scholes, M. C. Atmos. Environ. 2001, 35, 1853– 1862, DOI: 10.1016/S1352-2310(00)00497-0
  38
  Semivolatile behavior of dicarboxylic acids and other polar organic species at a rural background site (Nylsvley, RSA)
  Limbeck, A.; Puxbaum, H.; Otter, L.; Scholes, M. C.
  Atmospheric Environment (2001), 35 (10), 1853-1862CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.)
  In this study aerosol samples from the South African savanna were analyzed for their polar org. constituents. Samples were collected with a front/back-up filter tandem system of quartz fiber filters (dual filter strategy). In all samples (n=15) dicarboxylic acids and a variety of phthalates, aldehydes and monocarboxylic acids were obsd. Oxalic acid was the dominating compd. with an av. amt. of 79.2 ng m-3 on the front filter and 11.3 ng m-3 on the back-up filter. The presence of significant concns. of dicarboxylic acids on the back-up filter was rather unexpected. There are two possible sources to explain the presence of individual compds. on the back-up filter - particle penetration through the front filter or adsorption of compd. parts from the gas phase. Interpretation of the data indicates that the dicarboxylic acid concns. on the back-up filters appear to be caused by the adsorption of gaseous org. species. Dicarboxylic acids semivolatile behavior is evident with this results. This conclusion refutes the commonly held view that dicarboxylic acids in the atm. were assocd. with the aerosol phase only. Addnl., it was found that the distribution of dicarboxylic acids between the gas and particle phase in the atm. is not only dependent on their vapor pressures. The actual gas phase concn. appears to be more detd. by the chem. properties of the particles than by pure phys. influences. Surprisingly, malonic acid exhibits an anomaly, as it does not show a semivolatile tendency.
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39. 39
  Cheng, C.; Li, M.; Chan, C. K.; Tong, H.; Chen, C.; Chen, D.; Wu, D.; Li, L.; Wu, C.; Cheng, P. Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implications for the formation mechanism of oxalic acid. Atmos. Chem. Phys. 2017, 17 (15), 9519– 9533, DOI: 10.5194/acp-17-9519-2017
  39
  Mixing state of oxalic acid containing particles in the rural area of pearl river delta, china: implications for the formation mechanism of oxalic acid
  Cheng, Chunlei; Li, Mei; Chan, Chak K.; Tong, Haijie; Chen, Changhong; Chen, Duohong; Wu, Dui; Li, Lei; Wu, Cheng; Cheng, Peng; Gao, Wei; Huang, Zhengxu; Li, Xue; Zhang, Zhijuan; Fu, Zhong; Bi, Yanru; Zhou, Zhen
  Atmospheric Chemistry and Physics (2017), 17 (15), 9519-9533CODEN: ACPTCE; ISSN:1680-7324. (Copernicus Publications)
  The formation of oxalic acid and its mixing state in atm. particulate matter (PM) were studied using a single-particle aerosol mass spectrometer (SPAMS) in the summer and winter of 2014 in Heshan, a supersite in the rural area of the Pearl River Delta (PRD) region in China. Oxalic-acid-contg. particles accounted for 2.5 and 2.7 % in total detected ambient particles in summer and winter, resp. Oxalic acid was measured in particles classified as elemental carbon (EC), org. carbon (OC), elemental and org. carbon (ECOC), biomass burning (BB), heavy metal (HM), secondary (Sec), sodium-potassium (NaK), and dust. Oxalic acid was found predominantly mixing with sulfate and nitrate during the whole sampling period, likely due to aq.-phase reactions. In summer, oxalic-acid-contg. particle no. and ozone concn. followed a very similar trend, which may reflect the significant contribution of photochem. reactions to oxalic acid formation. The HM particles were the most abundant oxalic acid particles in summer and the diurnal variations in peak area of iron and oxalic acid show opposite trends, which suggests a possible loss of oxalic acid through the photolysis of iron oxalato-complexes during the strong photochem. activity period. In wintertime, carbonaceous particles contained a substantial amt. of oxalic acid as well as abundant carbon clusters and BB markers. The general existence of nitric acid in oxalic-acid-contg. particles indicates an acidic environment during the formation process of oxalic acid. The peak areas of nitrate, sulfate and oxalic had similar temporal change in the carbonaceous type oxalic acid particles, and the organosulfate-contg. oxalic acid particles correlated well with total oxalic acid particles during the haze episode, which suggests that the formation of oxalic acid is closely assocd. with the oxidn. of org. precursors in the aq. phase.
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40. 40
  Yu, S. Role of organic acids formic, acetic, pyruvic and/ oxalic in the formation of cloud condensation nuclei CCN: A Review. Atmos. Res. 2000, 53, 185– 217, DOI: 10.1016/S0169-8095(00)00037-5
  40
  Role of organic acids (formic, acetic, pyruvic and oxalic) in the formation of cloud condensation nuclei (CCN): a review
  Yu, S.
  Atmospheric Research (2000), 53 (4), 185-217CODEN: ATREEW; ISSN:0169-8095. (Elsevier Science B.V.)
  A review, with many refs., is given. Although it is believed that org. aerosols play a key role in cloud nucleation and make an important contribution to the cloud condensation nuclei (CCN) population, their specific species remain poorly characterized. This paper reviews the current knowledge of org. acids (mainly formic, acetic, pyruvic and oxalic acids). Without specification, org. acids in this paper refer to these four org. acids in the gas and aerosol phases. This paper analyzes the extent to which org. acids act as CCN and compares the phys. and chem. properties of org. acids with those of CCN. The results show that aerosol formate and acetate concns. range from 0.02 to 5.3 nmol m-3 and from 0.03 to 12.4 nmol m-3, resp., and that between 34 to 77% of formate and between 21 to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile org. acids are present in the gas phase, their concns. in the aerosol particles are sufficient to make them a good candidate for CCN. The results also show that org. acids may make an important contribution to the formation of CCN in some special sources such as vegetation emissions and biomass-burning. Org. acids are expected to contribute significantly to the ests. of indirect (cloud-mediated) forcing due to aerosols.
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41. 41
  Peng, C.; Chan, M. N.; Chan, C. K. The Hygroscopic Properties of Dicarboxylic and Multifunctional Acids: Measurements and UNIFAC Predictions. Environ. Sci. Technol. 2001, 35, 4495– 4501, DOI: 10.1021/es0107531
  41
  The Hygroscopic Properties of Dicarboxylic and Multifunctional Acids: Measurements and UNIFAC Predictions
  Peng, Changgeng; Chan, Man Nin; Chan, Chak K.
  Environmental Science and Technology (2001), 35 (22), 4495-4501CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
  The role of water-sol. org. compds. in regard to the hygroscopic properties of atm. aerosols has recently been the subject of many studies. In particular, low-mol.-wt. dicarboxylic acids and some multifunctional org. acids have been found or are expected to exist in atm. aerosols at urban, semiurban, rural, and remote sites. Unlike the case of their inorg. counterparts, the hygroscopic properties of org. acids have not been well characterized. In this study, the hygroscopic properties of selected water-sol. dicarboxylic acids (oxalic acid, malonic acid, succinic acid, and glutaric acid) and multifunctional acids (citric acid, DL-malic acid, and L-(+)-tartaric acid) were studied using single droplets levitated in an electrodynamic balance at 25°. The water activities of bulk samples of dil. solns. were also measured. Solute evapn. was obsd. for the dicarboxylic acids but not for the multifunctional acids. Oxalic acid, succinic acid, and glutaric acid droplets crystallize upon evapn. of water, but, except for glutaric acid droplets, do not deliquesce even at 90% relative humidity (RH). Mass transfer limitation of the deliquescence process was obsd. in glutaric acid. Neither crystn. nor deliquescence was obsd. in malonic acid, citric acid, DL-malic acid, or L-(+)-tartaric acid. Malonic acid and these three hydroxy carboxylic acids absorb water even at RHs much lower than their resp. deliquescence RH. The growth factor (Gf), defined as the ratio of the particle diam. at RH = 10% to that at RH = 90%, of oxalic acid and succinic acid was close to unity, indicating no hygroscopicity in this range. The remaining acids (malonic acid, glutaric acid, citric acid, malic acid, and tartaric acid) showed roughly similar hygroscopicity of a Gf of 1.30-1.53, which is similar to that of "more hygroscopic" aerosols in field measurements reported in the literature. A generalized equation for these four acids, Gf = (1-aw)-0.163, was developed to represent the hygroscopicity of these acids. Water activity predictions from calcns. using the UNIFAC model were found to agree with the measured water activity data to within 40% for most of the acids, but the deviations were as large as about 100% for malic acid and tartaric acid. We modified the functional group interaction parameters of the COOH-H2O, OH-H2O, and OH-COOH pairs by fitting the UNIFAC model with the measured data. The modified UNIFAC model improves the agreement of predictions and measurements to within 38% for all the acids studied.
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42. 42
  Kerminen, V.-M.; Ojanen, C.; Pakkanen, T.; Hillamo, R.; Aurela, M.; Meriläinen, J. Low-molecular-weight dicarboxylic acids in an urban and rural atmosphere. J. Aerosol Sci. 2000, 31, 349– 362, DOI: 10.1016/S0021-8502(99)00063-4
  42
  Low-molecular-weight dicarboxylic acids in an urban and rural atmosphere
  Kerminen, Veli-Matti; Ojanen, Christina; Pakkanen, Tuomo; Hillamo, Risto; Aurela, Minna; Merilainen, Jouni
  Journal of Aerosol Science (2000), 31 (3), 349-362CODEN: JALSB7; ISSN:0021-8502. (Elsevier Science Ltd.)
  Chem. of oxalic, malonic, and succinic acid was studied at the two sites representing the urban and rural conditions, and at a site intermediate between these two. The investigation was based on the particle collection with a virtual impactor and a Berner low-pressure impactor. Concns. of the three diacids displayed large seasonal amplitudes with low values in winter. Suggestive of common sources or atm. formation processes, the correlation between oxalic and malonic acid concns. was high. Both the local traffic and secondary prodn. in the long-range transported air masses seemed to be the important sources for these two acids. Contrary to oxalic and malonic acid, no enrichment at the urban site compared with the rural site was obsd. for succinic acid. The seasonal cycle of this acid resembled that of methanesulfonic acid. The most likely sources for succinic acid in our samples was the secondary prodn. in the long-range transported air, with potentially significant contribution coming from biogenic sources. The three diacids had quite different distributions over the particulate phase. Oxalic acid had a dominant accumulation mode, a clear Aitken mode at sizes below about 0.15 μm of particle diam., and modes corresponding to the sea-salt and crustal particle size ranges. Most of the malonic acid was assocd. with sea-salt particles, even though in a few samples an accumulation mode was also present. Succinic acid was distributed between the accumulation and the sea-salt particle modes, in addn. to which it frequently had quite a pronounced Aitken mode. Oxalic and succinic acids are among the orgs. that may contribute to the atm. cloud condensation nuclei prodn. Oxalic and malonic acid, and to a smaller extent succinic acid, participate in reactions occurring in sea-salt particles.
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43. 43
  Khwaja, H. A. Atmospheric concentrations of carboxylic acids and related compounds at a semiurban site. Atmos. Environ. 1995, 29, 127– 139, DOI: 10.1016/1352-2310(94)00211-3
  43
  Atmospheric concentrations of carboxylic acids and related compounds at a semiurban site
  Khwaja, Haider A.
  Atmospheric Environment (1995), 29 (1), 127-39CODEN: AENVEQ; ISSN:1352-2310. (Elsevier)
  Atm.-gas- and particle-phase carboxylic acids and related compds. were measured during Oct. 1991 in a semiurban site in northeastern US. Formic and acetic acids were present in the atm. mostly in the gaseous form with <10% in the particle phase. Concns. of formic acid and acetic acid were in the 0.80-2.5 and 0.60-3.4 ppbv range, resp. Formic acid was correlated with acetic acid (r =0.94). Diurnal variations of formic acid were similar to those of O3. This pattern is consistent with photochem. prodn. as an important source. Formic-to-acetic acid ratios <1 were recorded, likely due to an increase in acetic acid contribution from direct emissions assocd. with vehicular traffic. HCHO levels began to decrease after the mid-afternoon maxima; concns. were 0.63-3.7 ppbv. Formic, acetic, pyruvic, glyoxalic, oxalic, succinic, and malonic acids in the particle phase were identified. Aerosol carboxylic acid concns. were 26-360 ng/m3. About 80% of the carboxylic acid aerosol mass was in the size fraction <1.0 μm diam. Of the dicarboxylic acids, oxalic acid was the most abundant species, followed by succinic acid and malonic acid. Particulate total org. C exhibited a concn. range 12.6 × 103-49.9 × 103 ng/cm3. The obsd. amts. of carboxylic acids in the particle phase accounted for a small fraction of the org. C. Results indicated that photochem. processes and anthropogenic emissions such as automobile exhaust are major sources of atm. carboxylic acids.
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44. 44
  Chebbi, A.; Carlier, P. Atmos. Environ. 1996, 30, 4233– 4249, DOI: 10.1016/1352-2310(96)00102-1
  44
  Carboxylic acids in the troposphere, occurrence, sources, and sinks: a review
  Chebbi, A.; Carlier, P.
  Atmospheric Environment (1996), 30 (24), 4233-4249CODEN: AENVEQ; ISSN:1352-2310. (Elsevier)
  A review, with many refs., is given. Carboxylic acids are ubiquitous and important components of the troposphere; they are currently measured in different environments. They are thought to have several sources comprising primary biogenic and anthropogenic emissions, hydrocarbons gas-phase oxidns., and some carbonyl compds. aq.-phase oxidns. We make a synthesis of the concns. of low mol. wt. carboxylic acids in tropospheric aq. and gaseous phases and in aerosol particles for different environments. We also successively exam. the major sources of carboxylic acids and discuss their relative contribution to tropospheric concns. for various environments as well as the principal sinks of these compds.
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45. 45
  Martinelango, P. K.; Dasgupta, P. K.; Al-Horr, R. S. Atmos. Environ. 2007, 41, 4258– 4269, DOI: 10.1016/j.atmosenv.2006.05.085
  45
  Atmospheric production of oxalic acid/oxalate and nitric acid/nitrate in the Tampa Bay airshed: Parallel pathways
  Martinelango, P. Kalyani; Dasgupta, Purnendu K.; Al-Horr, Rida S.
  Atmospheric Environment (2007), 41 (20), 4258-4269CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  Oxalic acid is the dominant dicarboxylic acid (DCA), and it constitutes up to 50% of total atm. DCAs, esp. in non-urban and marine atmospheres. A significant amt. of particulate H2Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concns. in the PM10 to PM2.5 fractions ranged from 1 to 2, with mean±sd being 1.4 ± 0.2. These results suggest that oxalate does not solely originate in the gas phase and condense into particles. Gaseous H2Ox concns. are much lower than particulate Ox concns. and are well correlated with HNO3, HCHO, and O3, supporting a photochem. origin. Of special relevance to the Bay Region Atm. Chem. Expt. (BRACE) is the extent of nitrogen deposition in the Tampa Bay estuary. Hydroxyl radical is primarily responsible for the conversion of NO2 to HNO3, the latter being much more easily deposited. Hydroxyl radical is also responsible for the aq. phase formation of oxalic acid from alkenes. Hence, we propose that an est. of ·OH can be obtained from H2Ox/Ox prodn. rate and we accordingly show that the product of total oxalate concn. and NO2 concn. approx. predicts the total nitrate concn. during the same period.
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46. 46
  Ma, X.; Sun, Y.; Huang, Z.; Zhang, Q.; Wang, W. A density functional theory study of the molecular interactions between a series of amides and sulfuric acid. Chemosphere 2019, 214, 781– 790, DOI: 10.1016/j.chemosphere.2018.08.152
  46
  A density functional theory study of the molecular interactions between a series of amides and sulfuric acid
  Ma, Xiaohui; Sun, Yanhui; Huang, Zixiao; Zhang, Qingzhu; Wang, Wenxing
  Chemosphere (2019), 214 (), 781-790CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)
  Amides, a class of nitrogen-contg. org. pollutants in the atm., may affect the formation of atm. aerosols by the interactions with sulfuric acid. Here, the mol. interactions of sulfuric acid with formamide, methylformamide, DMF, acetamide, methylacetamide and dimethylacetamide was investigated by d. functional theory. Geometry optimization and Gibbs free energy calcn. were carried out at M06-2X/6-311++G(3df,3pd) level. The results indicate that the addn. of amides to H2SO4 might have a promoting effect on atm. new particle formation at 298.15 K and 1 atm. In the initial stage of new particle formation, the binding capacity of amides and sulfuric acid is stronger than ammonia, but weaker than methylamine. It is worth noting that the trans-methylacetamide could have similar capabilities of stabilizing sulfuric acid as dimethylamine. In the presence of water, amides are found to only have a weak enhancement capability on new particle formation. In addn., we can infer from evapn. rate that the small mol. clusters of formamide and sulfuric acid may be more energetically favorable than macromol. clusters.
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47. 47
  Hanson, D. R.; Eisele, F. L. Measurement of prenucleation molecular clusters in the NH₃, H₂SO₄, H₂O system. J. Geophys. Res.: Atmos. 2002, 107, AAC 10– 1-AAC 10-18, DOI: 10.1029/2001JD001100
  There is no corresponding record for this reference.
48. 48
  Sipilää, M.; Berndt, T.; Petäjä, T.; Brus, D.; Vanhanen, J.; Stratmann, F.; Patokoski, J.; Mauldin, R. L., 3; Hyvärinen, A.-P.; Lihavainen, H. The role of sulfuric acid in atmospheric nucleation. Science 2010, 327, 1243– 1246, DOI: 10.1126/science.1180315
  There is no corresponding record for this reference.
49. 49
  Kirkby, J.; Curtius, J.; Almeida, J.; Dunne, E.; Duplissy, J.; Ehrhart, S. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature 2011, 476, 429– 433, DOI: 10.1038/nature10343
  49
  Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation
  Kirkby, Jasper; Curtius, Joachim; Almeida, Joao; Dunne, Eimear; Duplissy, Jonathan; Ehrhart, Sebastian; Franchin, Alessandro; Gagne, Stephanie; Ickes, Luisa; Kuerten, Andreas; Kupc, Agnieszka; Metzger, Axel; Riccobono, Francesco; Rondo, Linda; Schobesberger, Siegfried; Tsagkogeorgas, Georgios; Wimmer, Daniela; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; David, Andre; Dommen, Josef; Downard, Andrew; Ehn, Mikael; Flagan, Richard C.; Haider, Stefan; Hansel, Armin; Hauser, Daniel; Jud, Werner; Junninen, Heikki; Kreissl, Fabian; Kvashin, Alexander; Laaksonen, Ari; Lehtipalo, Katrianne; Lima, Jorge; Lovejoy, Edward R.; Makhmutov, Vladimir; Mathot, Serge; Mikkilae, Jyri; Minginette, Pierre; Mogo, Sandra; Nieminen, Tuomo; Onnela, Antti; Pereira, Paulo; Petaejae, Tuukka; Schnitzhofer, Ralf; Seinfeld, John H.; Sipilae, Mikko; Stozhkov, Yuri; Stratmann, Frank; Tome, Antonio; Vanhanen, Joonas; Viisanen, Yrjo; Vrtala, Aron; Wagner, Paul E.; Walther, Hansueli; Weingartner, Ernest; Wex, Heike; Winkler, Paul M.; Carslaw, Kenneth S.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku
  Nature (London, United Kingdom) (2011), 476 (7361), 429-433CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Model calcns. suggest that almost half of the global cloud condensation nuclei in the atm. boundary layer may originate from the nucleation of aerosols from trace condensable vapors, although the sensitivity of the no. of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulfuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chem. species such as ammonia. First results from the Cosmics Leaving OUtdoor Droplets (CLOUD) expt. at CERN are presented. It was found that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by vol., or less, increase the nucleation rate of sulfuric acid particles more than 100-1,000-fold. Time-resolved mol. measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia mols. Ions increase the nucleation rate by an addnl. factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair prodn. rate. Ion-induced binary nucleation of H2SO4-H2O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atm. concns. of ammonia and sulfuric acid are insufficient to account for obsd. boundary-layer nucleation.
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50. 50
  Elm, J.; Kubečka, J.; Besel, V.; Jääskeläinen, M. J.; Halonen, R.; Kurtén, T.; Vehkamäki, H. Modeling the formation and growth of atmospheric molecular clusters: A review. J. Aerosol Sci. 2020, 149, 105621, DOI: 10.1016/j.jaerosci.2020.105621
  50
  Modeling the formation and growth of atmospheric molecular clusters: A review
  Elm, Jonas; Kubecka, Jakub; Besel, Vitus; Jaaskelainen, Matias J.; Halonen, Roope; Kurten, Theo; Vehkamaki, Hanna
  Journal of Aerosol Science (2020), 149 (), 105621CODEN: JALSB7; ISSN:0021-8502. (Elsevier Ltd.)
  A review,. Mol. clusters are ubiquitous constituents of the ambient atm., that can grow into larger sizes forming new aerosol particles. The formation and growth of small clusters into aerosol particles remain one of the largest uncertainties in global climate predictions. This has made the modeling of atm. mol. clustering into an active field of research, yielding direct mol. level information about the formation mechanism. We review the present state-of-the-art quantum chem. methods and cluster distribution dynamics models that are applied to study the formation and growth of atm. mol. clusters. We outline the current challenges in applying theor. methods and the future directions to move the field forward.
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51. 51
  Zhang, R.; Khalizov, A.; Wang, L.; Hu, M.; Xu, W. Nucleation and Growth of Nanoparticles in the Atmosphere. Chem. Rev. 2012, 112, 1957– 2011, DOI: 10.1021/cr2001756
  51
  Nucleation and Growth of Nanoparticles in the Atmosphere
  Zhang, Renyi; Khalizov, Alexei; Wang, Lin; Hu, Min; Xu, Wen
  Chemical Reviews (Washington, DC, United States) (2012), 112 (3), 1957-2011CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review which critically assesses recent findings related to nucleation and growth of atm. nanoparticles, emphasizing process understanding on a fundamental mol. level, is given. Topics discussed include: vapor nucleation overview (nucleation theories and computational approaches [classical nucleation, kinetic, and d. functional theories, mol. dynamics and Monte Carlo methods, nucleation theorem], nucleation expts. [adiabatic expansion approaches; diffusion, laminar flow, and turbulent mixing chambers; continuous generation of nucleating vapors from chem. reaction sources; exptl. results vs. nucleation theories]); atm. nanoparticle nucleation (measurements [concns. and size distribution, nanoparticle chem. compn., charged and neutral atm. clusters], lab. studies [binary nucleation of H2SO4/water; NH3 and amine-involved ternary nucleation of H2SO4/water; org. acid assisted nucleation of H2SO4/water; IOx and ion-induced nucleation; nucleating cluster chem. compn., reactivity, and thermodn.], theor./computational studies [quantum chem. calcns., mol. dynamics and Monte Carlo simulations], atm. nucleation parameterization); nanoparticle atm. growth (Kelvin [curvature] effect, condensation [H2SO4, low volatility orgs.], heterogeneous reactions [NH3, amines, aldehydes, α-dicarbonyls, alcs., other species]); numerical treatment of ambient nanoparticle nucleation and growth rates (measured, combined growth including condensation and intra-/extra-modal coagulation, nucleation rate derivation from atm. measurements); and summary and future research needs.
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52. 52
  Zheng, J.; Ma, Y.; Chen, M.; Zhang, Q.; Wang, L.; Khalizov, A. F. Measurement of atmospheric amines and ammonia using the high resolution time-of-flight chemical ionization mass spectrometry. Atmos. Environ. 2015, 102, 249– 259, DOI: 10.1016/j.atmosenv.2014.12.002
  52
  Measurement of atmospheric amines and ammonia using the high resolution time-of-flight chemical ionization mass spectrometry
  Zheng, Jun; Ma, Yan; Chen, Mindong; Zhang, Qi; Wang, Lin; Khalizov, Alexei F.; Yao, Lei; Wang, Zhen; Wang, Xing; Chen, Linxi
  Atmospheric Environment (2015), 102 (), 249-259CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
  Ammonia (NH3) and amines play important roles in the nucleation and growth of atm. aerosols. To identify the sources of these chems. in the densely populated and industrialized Yangtze River Delta region of China, we conducted measurements of NH3 and several amines, including methylamine (CH3NH2), C2-amines (C2H7N), and C3-amines (C3H9N) at a suburban site of Nanjing, China, during summer 2012. Using a high-resoln. time-of-flight chem. ionization mass spectrometer (HRToF-CIMS, Aerodyne), 1-min-averaged concns. of NH3 and amines ranged from a few parts per trillions by vol. (pptv) to dozens of ppb by vol. (ppbv). The av. ± 1σ concns. of NH3 and total amines during the measurement period were 1.7 ± 2.3 ppbv and 7.2 ± 7.4 pptv, resp. Among the amines, C2-amines were the most abundant, accounting for 54% of the total amine loading. Significant correlations between NH3 and all three types of amines (0.65 < r2 < 0.80) indicate similar emission sources. Anal. of meteorol. conditions indicated that these NH3 and amine laden air masses mainly originated from nearby industrial areas where NH3 was used for selective catalytic redn. of nitrogen oxides (NOx). The results of this work indicate that industrial emissions in Nanjing, China may have a significant impact on local and regional aerosol chem. by supplying considerable amt. of amines.
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53. 53
  Nair, A. A.; Yu, F. Quantification of Atmospheric Ammonia Concentrations: A Review of Its Measurement and Modeling. Atmosphere 2020, 11, 1092, DOI: 10.3390/atmos11101092
  53
  Quantification of atmospheric ammonia concentrations: a review of its measurement and modeling
  Nair, Arshad Arjunan; Yu, Fangqun
  Atmosphere (2020), 11 (10), 1092CODEN: ATMOCZ; ISSN:2073-4433. (MDPI AG)
  Ammonia (NH3), the most prevalent alk. gas in the atm., plays a significant role in PM2.5 formation, atm. chem., and new particle formation. This paper reviews quantification of [NH3] through measurements, satellite-remote-sensing, and modeling reported in over 500 publications towards synthesizing the current knowledge of [NH3], focusing on spatiotemporal variations, controlling processes, and quantification issues. Most measurements are through regional passive sampler networks. [NH3] hotspots are typically over agricultural regions, such as the Midwest US and the North China Plain, with elevated concns. reaching monthly avs. of 20 and 74 ppbv, resp. Topog. effects dramatically increase [NH3] over the Indo-Gangetic Plains, North India and San Joaquin Valley, US. Measurements are sparse over oceans, where [NH3] ≈ a few tens of pptv, variations of which can affect aerosol formation. Satellite remote-sensing (AIRS, CrIS, IASI, TANSO-FTS, TES) provides global [NH3] quantification in the column and at the surface since 2002. Modeling is crucial for improving understanding of NH3 chem. and transport, its spatiotemporal variations, source apportionment, exploring physicochem. mechanisms, and predicting future scenarios. GEOS-Chem (global) and FRAME (UK) models are commonly applied for this. A synergistic approach of measurements↔satellite-inference↔modeling is needed towards improved understanding of atm. ammonia, which is of concern from the standpoint of human health and the ecosystem.
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54. 54
  Elm, J. An Atmospheric Cluster Database Consisting of Sulfuric Acid, Bases, Organics, and Water. ACS Omega 2019, 4 (6), 10965– 10974, DOI: 10.1021/acsomega.9b00860
  54
  An Atmospheric Cluster Database Consisting of Sulfuric Acid, Bases, Organics, and Water
  Elm, Jonas
  ACS Omega (2019), 4 (6), 10965-10974CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
  We have collected, re-computed and compiled a database consisting of 633 unique atmospherically relevant mol. clusters contg. sulfuric acid, bases, oxidized org. compds. and water. The database comprise of strongly hydrogen bonded mol. clusters, and span both neutral, neg. charged and pos. charged clusters of atm. relevance. All the cluster structures and vibrational frequencies were re-evaluated at the ωB97X-D/6-31++G(d,p) level of theory and the single point energies were refined using a high level DLPNO-CCSD(T)/aug-cc-pVTZ calcn. The database unifies published atm. mol. clusters under a single common methodol. and serves as an efficient look-up table for mol. cluster structures and thermochem. parameters. Utilizing the database the performance of four semi-empirical methodologies (PM6, PM7, B97-3c and PBEh-3c) in calcg. the binding energies of atm. mol. clusters is assessed. The B97-3c and PBEh-3c empirically cor. DFT methods yield low errors in the binding energies compared to DLPNO-CCSD(T)/aug-cc-pVTZ ref. results and that a simple linear model can be utilized for estg. accurate binding energies based on ωB97X-D/6-31++G(d,p) results.
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55. 55
  Lee, S.-H.; Gordon, H.; Yu, H.; Lehtipalo, K.; Haley, R.; Li, Y.; Zhang, R. New particle formation in the atmosphere: From molecular clusters to global climate. J. Geophys. Res.: Atmos. 2019, 124, 7098– 7146, DOI: 10.1029/2018JD029356
  55
  New Particle Formation in the Atmosphere: From Molecular Clusters to Global Climate
  Lee, Shan-Hu; Gordon, Hamish; Yu, Huan; Lehtipalo, Katrianne; Haley, Ryan; Li, Yixin; Zhang, Renyi
  Journal of Geophysical Research: Atmospheres (2019), 124 (13), 7098-7146CODEN: JGRDE3; ISSN:2169-8996. (Wiley-Blackwell)
  New particle formation (NPF) represents the first step in the complex processes leading to formation of cloud condensation nuclei. Newly formed nanoparticles affect human health, air quality, weather, and climate. This review provides a brief history, synthesizes recent significant progresses, and outlines the challenges and future directions for research relevant to NPF. New developments include the emergence of state-of-the-art instruments that measure prenucleation clusters and newly nucleated nanoparticles down to about 1 nm; systematic lab. studies of multicomponent nucleation systems, including collaborative expts. conducted in the Cosmics Leaving Outdoor Droplets chamber at CERN; observations of NPF in different types of forests, extremely polluted urban locations, coastal sites, polar regions, and high-elevation sites; and improved nucleation theories and parameterizations to account for NPF in atm. models. The challenges include the lack of understanding of the fundamental chem. mechanisms responsible for aerosol nucleation and growth under diverse environments, the effects of SO2 and NOx on NPF, and the contribution of anthropogenic org. compds. to NPF. It is also crit. to develop instruments that can detect chem. compn. of particles from 3 to 20 nm and improve parameterizations to represent NPF over a wide range of atm. conditions of chem. precursor, temp., and humidity.
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56. 56
  Nahlovska, Z.; Nahlovsky, B.; Strand, T. G. Molecular Structure of Gaseous Oxalic Acid from Electron Diffraction and IR Data. Acta Chem. Scand. 1970, 24 (24), 2617– 2628, DOI: 10.3891/acta.chem.scand.24-2617
  There is no corresponding record for this reference.
57. 57
  Redington, R. L.; Redington, T. E. Infrared Matrix-Isolation Spectra of Monomeric Oxalic Acid. J. Mol. Struct. 1978, 48, 165, DOI: 10.1016/0022-2860(78)80019-2
  There is no corresponding record for this reference.
58. 58
  Back, R. A. The ultraviolet absorption spectrum of oxalic acid vapor. Can. J. Chem. 1984, 62, 1414, DOI: 10.1139/v84-241
  There is no corresponding record for this reference.
59. 59
  Nieminen, J.; Rasanen, M.; Murto, J. Matrix Isolation and ab Initio Studies of Oxalic Acid. J. Phys. Chem. 1992, 96, 5303, DOI: 10.1021/j100192a024
  59
  Matrix-isolation and ab initio studies of oxalic acid
  Nieminen, J.; Rasanen, M.; Murto, J.
  Journal of Physical Chemistry (1992), 96 (13), 5303-8CODEN: JPCHAX; ISSN:0022-3654.
  Rotamerization and UV photochem. decompn. of oxalic acid were studied in solid Ne, Ar, and Xe matrixes. The energies and spectra of the conformers and photoproducts were also simulated by extensive ab initio calcns. at MP2/6-31G** (energies, geometries) and MP2/4-31G* (numerical frequencies) levels. Two conformers were present in matrixes, the lowest energy species being cTc (with two intramol. H bonds) and species cTt (with only one intramol. H bond) being at ∼7 kJ mol-1 higher in energy. The uphill process cTc → cTt could be initiated by UV excitation at wavelengths of ∼270 nm. IR irradn. at wavenumbers >2000 cm-1 promoted the reverse interconversion. Full Xe arc irradn. decomps. oxalic acid in matrixes, the product yield ratio being different in different hosts. On the basis of ab initio calcns., the possible transition states for proton shifts are discussed. The calcd. vibrational spectra are given for six conformers of oxalic acid, the spectra of the obsd. conformers are assigned, and their potential energy distributions are given.
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60. 60
  Maçôas, E. M. S.; Fausto, R.; Pettersson, M.; Khriachtchev, L.; Rasanen, M. Infrared-Induced Rotamerization of Oxalic Acid Monomer in Argon Matrix. J. Phys. Chem. A 2000, 104, 6956, DOI: 10.1021/jp000634s
  60
  Infrared-Induced Rotamerization of Oxalic Acid Monomer in Argon Matrix
  Macoas, Ermelinda M. S.; Fausto, Rui; Pettersson, Mika; Khriachtchev, Leonid; Raesaenen, Markku
  Journal of Physical Chemistry A (2000), 104 (30), 6956-6961CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  IR-induced conformational isomerization of oxalic acid monomer isolated in an argon matrix at 7.5 K was studied by IR spectroscopy. For the first time, three conformational states of this mol. were identified exptl. and their vibrational spectra are assigned. In good agreement with d. functional theory predictions, all the obsd. conformers exhibit a trans O:C-C:O axis, differing in the relative conformation of their O-C-O-H axes. In the most stable conformer (belonging to the C2h symmetry point group), two intramol. OH···O: hydrogen bonds are present. The second (Cs) most stable conformer shows a single OH···O: bond, and the third one (C2h) does not exhibit any intramol. hydrogen bond. Using narrowband tunable irradn. in the near-IR region it was possible to promote very efficiently conformer interconversions, which was followed spectroscopically.
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61. 61
  Godfrey, P. D.; Mirabella, M. J.; Brown, R. D. Structural Studies of Higher Energy Conformers by Millimeter-Wave Spectroscopy: Oxalic Acid. J. Phys. Chem. A 2000, 104, 258, DOI: 10.1021/jp992499t
  61
  Structural Studies of Higher Energy Conformers by Millimeter-Wave Spectroscopy: Oxalic Acid
  Godfrey, Peter D.; Mirabella, Mathew J.; Brown, Ronald D.
  Journal of Physical Chemistry A (2000), 104 (2), 258-264CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  The authors have detected a polar conformer of oxalic acid and studied its structure using Stark-modulated free jet microwave spectroscopy. By comparing obsd. and ab initio predicted spectroscopic rotational consts. and deuteration isotopic substitution coordinates, the species was identified with the cis, trans, trans conformer (cTt), in which one of the carboxyl H atoms is involved in an intramol. H bond with the carbonyl O of the other carboxyl group. Stark effect measurements yielded elec. dipole moment values of μa = 2.850(6) D; μb = 1.148(3) D, μc = 0.0 D (assumed), and hence μtotal = 3.073(6) D. Ab initio calcns. at the MP2/6-311++G(d,p) level predict and expt. confirms that no other polar conformers occur in detectable concns. in the vapor at the expt. spectral search scan preexpansion temp. of 458 K. However, 2 undetectable species, one nonpolar (tTt), the other of low polarity (cTc, μ = 0.6 D) are predicted to be present in greater concns. than the obsd. species. Predicted relative stabilities of the different conformers are appreciably affected by the inclusion of Gibbs free energy corrections via the vibrational partition function. Large amplitude anharmonic vibrations, for which numerical integration of the vibrational Schrodinger equation is required for obtaining the correction, have an important influence on predicting relative stabilities of the oxalic acid conformers.
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62. 62
  Buemi, G. DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution. J. Phys. Org. Chem. 2009, 22, 933– 947, DOI: 10.1002/poc.1543
  62
  DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution
  Buemi, Giuseppe
  Journal of Physical Organic Chemistry (2009), 22 (10), 933-947CODEN: JPOCEE; ISSN:0894-3230. (John Wiley & Sons Ltd.)
  The mol. geometries of the possible conformations of formic, oxalic, glyoxylic and pyruvic acids have been fully optimized at DFT B3LYP/6-311++G(d,p) levels of calcn. in vacuum as well as in water and acetone soln. Solns. were treated according to the SCRF PCM approach but some formic acid-water and formic acid-acetone clusters as well as adducts of oxalic acid with two or four water mols. were also taken into account for testing the importance of specific solute-solvent effects. All the most stable isomers of the title compds. are characterized by weak intramol. hydrogen bonds, whose strengths (EHB) cannot be correctly estd. as stability difference between the open and chelate forms since the energy of the former isomer is, in turn, stabilized by a weak hydrogen bridge due to the formic acid moiety. Following the Rotation Barrier Method (RBM), proposed some years ago, EHB in the examd. mols. (gas phase) falls in the range of 18-22 kJ/mol for oxalic acid (9.6 kJ/mol for the c-C-t isomer), 16.8 kJ/mol for glyoxylic acid and 19.8 kJ/mol for pyruvic acid. Most of them disappear at all, or nearly at all, both in acetone and aq. soln., in consequence of the solvent effect. The frequencies of the OH and C-O stretching modes, calcd. according to the anharmonic oscillator model, are in very good agreement with the exptl. literature data, where available. Copyright © 2009 John Wiley & Sons, Ltd.
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63. 63
  Feller, D.; Bross, D. H.; Ruscic, B. Enthalpy of Formation of C₂H₂O₄ (Oxalic Acid) from High-Level Calculations and the Active Thermochemical Tables Approach. J. Phys. Chem. A 2019, 123, 3481– 3496, DOI: 10.1021/acs.jpca.8b12329
  63
  Enthalpy of Formation of C2H2O4 (Oxalic Acid) from High-Level Calculations and the Active Thermochemical Tables Approach
  Feller, David; Bross, David H.; Ruscic, Branko
  Journal of Physical Chemistry A (2019), 123 (16), 3481-3496CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  High-level coupled cluster calcns. obtained with the Feller-Peterson-Dixon (FPD) approach and new data from the most recent version of the Active Thermochem. Tables (ATcT) are used to reassess the enthalpy of formation of gas-phase C2H2O4 (oxalic acid). The theor. value was further calibrated by comparing FPD and ATcT gas-phase enthalpies of formation for H2CO (formaldehyde) and the two low-lying conformations of C2H4O2 (syn and anti acetic acid). The FPD approach produces a theor. enthalpy of formation of gas-phase oxalic acid of -732.2 ± 4.0 kJ/mol at 298.15 K (-721.8 ± 4.0 kJ/mol at 0 K). An independently obtained ATcT value, based on reassessing the existent exptl. detns. and expanding the resulting thermochem. network with select mid-level composite theor. results, disagrees with several earlier recommendations that were based solely on exptl. detns. but is in excellent accord with the current FPD value. The inclusion of the latter in the most recent ATcT thermochem. network produces a further refined value for the gas-phase enthalpy of formation, -731.6 ± 1.2 kJ/mol at 298.15 K (-721.0 ± 1.2 kJ/mol at 0 K). The condensed-phase ATcT enthalpy of formation of oxalic acid is -829.7 ± 0.5 kJ/mol, and the resulting sublimation enthalpy is 98.1 ± 1.3 kJ/mol, both at 298.15 K.
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64. 64
  Chen, C.; Shyu, S.-F. Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions. Int. J. Quantum Chem. 2000, 76, 541– 551, DOI: 10.1002/(SICI)1097-461X(2000)76:4<541::AID-QUA5>3.0.CO;2-U
  There is no corresponding record for this reference.
65. 65
  Van Alsenoy, C.; Klimkowski, V. J.; Schafer, L. Ab initio studies of structural features not easily amenable to experiment: Part 37. Structural and conformational investigations of the dicarbonyls glyoxal, biacetyl and oxalic acid. J. Mol. Struct.: THEOCHEM 1984, 109, 321– 330, DOI: 10.1016/0166-1280(84)80016-0
  There is no corresponding record for this reference.
66. 66
  Mohajeri, A.; Shakerin, N. The gas-phase acidity and intramolecular hydrogen bonding in oxalic acid. J. Mol. Struct.: THEOCHEM 2004, 711, 167, DOI: 10.1016/j.theochem.2004.10.002
  66
  The gas-phase acidity and intramolecular hydrogen bonding in oxalic acid
  Mohajeri, A.; Shakerin, N.
  Journal of Molecular Structure: THEOCHEM (2004), 711 (1-3), 167-172CODEN: THEODJ; ISSN:0166-1280. (Elsevier B.V.)
  Ab initio calcns. at MP2/6-311++G and G2 level were carried out to study the structures and the gas-phase acidities of different conformations in oxalic acid. The gas-phase acidities (free energies of first ionization reactions) at G2 level vary from 1297.27 kJ/mol for the most acidic conformer to 1359.53 kJ/mol for the least acidic one at 298.15 K. Analyzing intramol. hydrogen bonding in different conformers, shows that the gas-phase acidity has a direct relation with hydrogen bond stabilization of both acid and its conjugated base. The results indicate that the reaction in which the acidic hydrogen is less involved and the hydrogen of its conjugated base is more involved in the intramol. hydrogen bond is the easiest deprotonation reaction. The atoms in mol. (AIM) theory has been also used to obtain the electronic charge distribution and some other related properties.
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67. 67
  Hermida-Ramón, J. M.; Cabaleiro-Lago, E. M.; Rodríguez-Otero, J. Computational study of the dissociation of oxalic acid in water clusters. Chem. Phys. 2004, 302, 53– 60, DOI: 10.1016/j.chemphys.2004.02.021
  There is no corresponding record for this reference.
68. 68
  Chang, J. G.; Chen, H. T.; Xu, S. C.; Lin, M. C. Computational Study on the Kinetics and Mechanisms for the Unimolecular Decomposition of Formic and Oxalic Acids. J. Phys. Chem. A 2007, 111, 6789, DOI: 10.1021/jp069036p
  68
  Computational Study on the Kinetics and Mechanisms for the Unimolecular Decomposition of Formic and Oxalic Acids
  Chang, Jee-Gong; Chen, Hsin-Tsung; Xu, Shucheng; Lin, M. C.
  Journal of Physical Chemistry A (2007), 111 (29), 6789-6797CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  The kinetics and mechanisms for the unimol. decompn. reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decompn. of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate consts. for the dehydration and decarboxylation reactions are in good agreement with the exptl. data. The calcd. CO/CO2 ratio, 13.6-13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured exptl. by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramol. hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decompn. channels of oxalic acid producing CO2 + HOCOH with barriers of 33-36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temps., the latter process becomes more competitive. The rate const. predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available exptl. data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.
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69. 69
  Higgins, J.; Zhou, X.; Liu, R.; Huang, T. T.-S. Theoretical Study of Thermal Decomposition Mechanism of Oxalic Acid. J. Phys. Chem. A 1997, 101, 2702– 2708, DOI: 10.1021/jp9638191
  69
  Theoretical Study of Thermal Decomposition Mechanism of Oxalic Acid
  Higgins, James; Zhou, Xuefeng; Liu, Ruifeng; Huang, Thomas T.-S.
  Journal of Physical Chemistry A (1997), 101 (14), 2702-2708CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  D. functional theory B3LYP/6-31G** and ab initio MP2/6-31G** and MP4(SDQ)/6-311++G** calcns. were carried out to study the structures and isomerization and decompn. mechanisms of oxalic acid. The B3LYP structures and relative energies of the rotational isomers of oxalic acid are found very similar to MP2 results, confirming that the most stable isomer is the doubly intramol. hydrogen-bonded C2h structure E1, with four other planar isomers within 6 kcal/mol. It is predicted that unimol. formation of carbon dioxide and dihydroxycarbene (DHC) from oxalic acid has an activation barrier of 31 kcal/mol and that unimol. formation of HCOOH from DHC has an activation barrier about 31 kcal/mol higher. The unimol. formation of CO2, CO and H2O from oxalic acid via a concerted transition state has an activation barrier of only 42 kcal/mol, indicating it is a more favorable unimol. decompn. channel. On the other hand, hydrogen migration from oxygen to carbon of DHC to produce HCOOH can be accomplished through a hydrogen exchange with H2O (a model for oxalic acid) with an activation barrier of less than 37 kcal/mol. Transition state theory calcns. indicate that this bimol. channel might be responsible for the rapid formation of CO2 and HCOOH in gas phase oxalic acid thermal decompn., thus confirming the proposal of Bock and Redington. With increasing temp. the unimol. channel to produce CO2, CO, and H2O might become significant.
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70. 70
  Medeiros, F. S.; Oliveira, K. M. T.; Canuto, S.; Chaudhuri, P. A quantum chemical investigation of the interaction of perfluoropropionic acid with monoethanolamine and sulfuric acid in the atmosphere. Comput. Theor. Chem. 2024, 1233, 114485, DOI: 10.1016/j.comptc.2024.114485
  There is no corresponding record for this reference.
71. 71
  de Oliveira, T. S.; Ghosh, A.; Chaudhuri, P. Exploring the hydrogen-bonded interactions of vanillic acid with atmospheric bases: a DFT study. Struct. Chem. 2024, 35, 1601– 1611, DOI: 10.1007/s11224-024-02307-3
  There is no corresponding record for this reference.
72. 72
  Elm, J.; Mikkelsen, K. V. Computational approaches for efficiently modelling of small atmospheric clusters. Chem. Phys. Lett. 2014, 615, 26– 29, DOI: 10.1016/j.cplett.2014.09.060
  72
  Computational approaches for efficiently modelling of small atmospheric clusters
  Elm, Jonas; Mikkelsen, Kurt V.
  Chemical Physics Letters (2014), 615 (), 26-29CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
  Utilizing a comprehensive test set of 205 clusters of atm. relevance, we investigate how different DFT functionals (M06-2X, PW91, ωB97X-D) and basis sets (6-311++G(3df,3pd), 6-31++G(d,p), 6-31+G(d)) affect the thermal contribution to the Gibbs free energy and single point energy. Reducing the basis set used in the geometry and frequency calcn. from 6-311++G(3df,3pd) → 6-31++G(d,p) implies a significant speed-up in computational time and only leads to small errors in the thermal contribution to the Gibbs free energy and subsequent coupled cluster single point energy calcn.
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73. 73
  Elm, J.; Bilde, M.; Mikkelsen, K. V. Assessment of binding energies of atmospherically relevant clusters. Phys. Chem. Chem. Phys. 2013, 15, 16442– 16445, DOI: 10.1039/c3cp52616j
  73
  Assessment of binding energies of atmospherically relevant clusters
  Elm, Jonas; Bilde, Merete; Mikkelsen, Kurt V.
  Physical Chemistry Chemical Physics (2013), 15 (39), 16442-16445CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  This work assesses the binding energies of atmospherically relevant clusters contg. H2SO4, H2O, NH3 and (CH3)2NH using d. functional theory. The performance of seven DFT functionals (B3LYP, CAM-B3LYP, M06-2X, PW91, LC-PW91, PBE0 and ωB97X-D) is evaluated against high level explicitly correlated coupled cluster methods using a test set of 107 atmospherically relevant clusters. Our studies show that all the tested functionals correlate well with the coupled cluster results, but with highly varying mean abs. errors. The PBE0, CAM-B3LYP, PW91 and M06-2X functionals are found to perform similarly with errors in the range of 2.53-3.46 kcal mol-1, while the B3LYP and LC-PW91 functionals yield higher errors of 6.95 kcal mol-1 and 10.66 kcal mol-1, resp. The ωB97X-D functional gives the best est. of the binding energies with a mean abs. error as low as 2.12 kcal mol-1 over the large test set of clusters.
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74. 74
  Elm, J.; Bilde, M.; Mikkelsen, K. V. Assessment of Density Functional Theory in Predicting Structures and Free Energies of Reaction of Atmospheric Prenucleation Clusters. Phys. Chem. Chem. Phys. 2012, 8, 2071– 2077, DOI: 10.1021/ct300192p
  There is no corresponding record for this reference.
75. 75
  Huff, A. K.; Mackenzie, R. B.; Smith, C. J.; Leopold, K. R. A Perfluorinated Carboxylic Sulfuric Anhydride: Microwave and Computational Studies of CF₃COOSO₂OH. J. Phys. Chem. A 2019, 123, 2237– 2243, DOI: 10.1021/acs.jpca.9b00300
  75
  A Perfluorinated Carboxylic Sulfuric Anhydride: Microwave and Computational Studies of CF3COOSO2OH
  Huff, Anna K.; MacKenzie, Rebecca B.; Smith, C. J.; Leopold, Kenneth R.
  Journal of Physical Chemistry A (2019), 123 (11), 2237-2243CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  Trifluoroacetic sulfuric anhydride (CF3COOSO2OH, TFASA) and its deuterated isotopologue have been obsd. by pulsed-nozzle Fourier transform microwave spectroscopy. TFASA was generated in situ in a supersonic expansion from the reaction of CF3COOH or CF3COOD with SO3. The spectrum, which was notably weaker than those of previously studied carboxylic sulfuric anhydrides, is that of a simple asym. rotor with no evidence of internal rotation of the CF3 group. Calcns. at the M06-2X/6-311++G(3df,3pd) level indicate that the title compd. is produced via a mechanism involving a concerted cycloaddn., analogous to that found for other carboxylic sulfuric anhydrides. The calcns. further show that the equil. orientation of CF3 relative to the C=O bond changes upon formation of the anhydride, indicating that any path connecting the equil. structures of CF3COOH and CF3COOSO2OH necessarily includes both cycloaddn. and internal rotation. CCSD(T)/complete basis set with double and triple extrapolation [CBS(D-T)] single-point energy calcns. at key points on the potential surface indicate that the barrier to form TFASA from a putative CF3COOH···SO3 complex is about 1.2 kcal/mol after zero-point energy corrections. This value is significantly larger than the near-zero or slightly neg. barriers previously reported for the reactions of SO3 with nonfluorinated carboxylic acids and likely accounts, at least in part, for the reduced spectral intensity. Thus, TFASA is a somewhat unique addn. to the series of carboxylic sulfuric anhydrides studied to date. Theor. values of certain structural parameters, at. charges, and vibrational frequencies also support this point of view. Despite the differences, however, this work clearly demonstrates that the reaction RCOOH + SO3 → RCOOSO2OH readily occurs in the gas phase and is not restricted to acids with hydrocarbon R groups.
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76. 76
  Dennington, R. D.; Keith, T. A.; Millam, J. M. GaussView 5.0.9; Gaussian Inc.: Wallingford, CT, USA, 2008.
  There is no corresponding record for this reference.
77. 77
  Kubečka, J.; Besel, V.; Kurtén, T.; Myllys, N.; Vehkamäki, H. Configurational sampling of noncovalent (atmospheric) molecular clusters: Sulfuric acid and guanidine. J. Phys. Chem. A 2019, 123, 6022– 6033, DOI: 10.1021/acs.jpca.9b03853
  77
  Configurational Sampling of Noncovalent (Atmospheric) Molecular Clusters: Sulfuric Acid and Guanidine
  Kubecka, Jakub; Besel, Vitus; Kurten, Theo; Myllys, Nanna; Vehkamaki, Hanna
  Journal of Physical Chemistry A (2019), 123 (28), 6022-6033CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  We studied the configurational sampling of noncovalently bonded mol. clusters relevant to the atm. In this article, we discuss possible approaches to searching for optimal configurations and present one alternative based on systematic configurational sampling, which seems able to overcome the typical problems assocd. with searching for global min. on multidimensional potential energy surfaces. Since atm. mol. clusters are usually held together by intermol. bonds, we also present a cost-effective strategy for treating hydrogen bonding and proton transferring by using rigid mols. and ions in different protonation states and illustrate its performance on clusters contg. guanidine and sulfuric acid.
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78. 78
  Partanen, L.; Vehkamäki, H.; Hansen, K.; Elm, J.; Henschel, H.; Kurtén, T.; Halonen, R.; Zapadinsky, E. Effect of Conformers on Free Energies of Atmospheric Complexes. J. Phys. Chem. A 2016, 120, 8613– 8624, DOI: 10.1021/acs.jpca.6b04452
  78
  Effect of Conformers on Free Energies of Atmospheric Complexes
  Partanen, Lauri; Vehkamaki, Hanna; Hansen, Klavs; Elm, Jonas; Henschel, Henning; Kurten, Theo; Halonen, Roope; Zapadinsky, Evgeni
  Journal of Physical Chemistry A (2016), 120 (43), 8613-8624CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  In this article we show how to calc. free energies for atmospherically relevant complexes when multiple conformers and/or isomers are present. We explain why the thermal averaging methods used in several published works are not correct. Based on our two sample cases, the sulfuric acid - pinic acid complex and the (H2SO4)3(NH3)3(H2O)4 cluster, we provide numerical evidence that the use of these incorrect formulas can result in errors larger than one kcal/mol. We recommend that if vibrational frequencies and thus Gibbs free energies of the individual conformers are unavailable, one should not attempt to correct for the presence of multiple conformers and instead use only the global min. conformers for both reactants and products. On the other hand, if the free energies for the conformers are calcd. for both reactants and products, their effect can be accounted for by the statistical mech. methods presented in this article.
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79. 79
  Fileti, E. E.; Rivelino, R.; Canuto, S. Rayleigh light scattering of hydrogen bonded clusters investigated by means of ab initio calculations. J. Phys. B: At., Mol. Opt. Phys. 2003, 36, 399– 408, DOI: 10.1088/0953-4075/36/2/319
  79
  Rayleigh light scattering of hydrogen bonded clusters investigated by means of ab initio calculations
  Fileti, Eudes E.; Rivelino, Roberto; Canuto, Sylvio
  Journal of Physics B: Atomic, Molecular and Optical Physics (2003), 36 (2), 399-408CODEN: JPAPEH; ISSN:0953-4075. (Institute of Physics Publishing)
  Ab initio calcns. of depolarization ratios and intensities of classically scattered light, in terms of dipole polarizabilities and polarizability anisotropies, are reported for different H bonded mol. clusters. Five different groups of org. heterodimers formed with H2O are considered: HCHO···H2O, MeHO···H2O, HCOOH···H2O, MeCN···H2O, and Me2CO···H2O, together with the H2O dimer H2O···H2O. The geometries of all complexes were optimized by the 2nd-order Moller-Plesset many-body perturbation theory (MP2), using the augmented correlation-consistent basis set with polarized valence of double-zeta quality (aug-cc-pVDZ). The calcd. av. dipole polarizabilities of the isolated mols. are in good agreement with available exptl. results. The calcns. are then extended to the complexes and, from these, the Rayleigh scattering activities and depolarization ratio changes, upon H bond formation, are obtained and analyzed. The differences in activity and depolarization for Rayleigh scattered radiation between 2 groups of isomers, (i) HCN···H2O and H2O···HCN and (ii) MeHO···H2O and MeOH···OH2, also were studied.
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80. 80
  Chaudhuri, P.; Canuto, S. Rayleigh scattering properties of small polyglycine molecules. J. Mol. Struct. 2006, 760, 15– 20, DOI: 10.1016/j.theochem.2005.10.039
  80
  Rayleigh scattering properties of small polyglycine molecules
  Chaudhuri, Puspitapallab; Canuto, Sylvio
  Journal of Molecular Structure: THEOCHEM (2006), 760 (1-3), 15-20CODEN: THEODJ; ISSN:0166-1280. (Elsevier B.V.)
  D.-functional theory calcns. of the Rayleigh optical activities of small isolated polyglycine mols. are reported. Fully extended β-sheet-like conformations of polypeptides of glycine, (Gly)n (with n = 1-5) are considered. After geometry optimizations, dipole moments and dipole polarizabilities (both the mean and the anisotropic components) are calcd. using the B3LYP and B3P86 functionals in 3 basis sets. The polarizabilities are used to analyze the Rayleigh scattering activities and depolarization ratios. The convergence of the av. dipole polarizability per monomer is analyzed. The differences in activity and depolarization for Rayleigh scattered radiation between the extended β-sheet-like and the folded α-helix-like forms of tetraglycine are analyzed and are relevant, suggesting its possible use in exptl. characterization.
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81. 81
  da Silva, A. M.; Chakraborty, S.; Chaudhuri, P. Rayleigh light scattering from hydrogen-bonded dimers of small astrophysical molecules. Int. J. Quantum Chem. 2012, 112, 2822– 2827, DOI: 10.1002/qua.23303
  There is no corresponding record for this reference.
82. 82
  Elm, J.; Norman, P.; Bilde, M.; Mikkelsen, K. V. Computational study of the Rayleigh light scattering properties of atmospheric prenucleation clusters. Phys. Chem. Chem. Phys. 2014, 16, 10883– 10890, DOI: 10.1039/C4CP01206B
  There is no corresponding record for this reference.
83. 83
  Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H., Gaussian 16, Revision C.01; Gaussian Inc.: Wallingford, CT, USA, 2016.
  There is no corresponding record for this reference.
84. 84
  Elm, J.; Ayoubi, D.; Engsvang, M.; Jensen, A. B.; Knattrup, Y.; Kubečka, J.; Bready, C. J.; Fowler, V. R.; Harold, S. E.; Longsworth, O. M. Quantum chemical modeling of organic enhanced atmospheric nucleation: A critical review. WIREs Comput. Mol. Sci. 2023, 13 (5), e1662 DOI: 10.1002/wcms.1662
  There is no corresponding record for this reference.
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c06290.
- Containing the optimized bond lengths and bond angles of different oxalic acid conformers; the Cartesian coordinates of the optimized geometries of binary and ternary clusters of OA with AM and SA; relevant structural parameters related to hydrogen bond formation in (OA)(SA) and (OA)(SA)₂ clusters, supported by the ternary cluster images (Figure S1); successive binding free energies (ΔG_S) for the formation of various (OA)(SA)₂ ternary clusters and Boltzman-averaged values of Rayleigh scattering intensities of the OA conformers and their binary and ternatry clusters with AM and SA (PDF)
- ao4c06290_si_001.pdf (677.52 kb)
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Intermolecular Hydrogen-Bonded Interactions of Oxalic Acid Conformers with Sulfuric Acid and AmmoniaClick to copy article linkArticle link copied!

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1. Introduction

2. Computational Methods

3. Results and Discussion

3.1. Isolated Molecule of Oxalic Acid

Figure 1

Figure 2

3.2. Clusters of Oxalic Acid and Ammonia, (OA)(AM)n (n= 1,2)

Figure 3

Figure 4

3.3. Clusters of Oxalic Acid and Sulfuric Acid, (OA)(SA)n (n = 1,2)

Figure 5

Figure 6

3.4. Atmospheric Relevance of the Binding Free Energies

3.5. Interaction with Solar Radiation

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4. Conclusions

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Intermolecular Hydrogen-Bonded Interactions of Oxalic Acid Conformers with Sulfuric Acid and Ammonia
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3.2. Clusters of Oxalic Acid and Ammonia, (OA)(AM)_n (n= 1,2)

3.3. Clusters of Oxalic Acid and Sulfuric Acid, (OA)(SA)_n (n = 1,2)