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Melamine Barbiturate as a Light-Induced Nanostructured Supramolecular Material for a Bioinspired Oxygen and Organic Radical Trap and Stabilization
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Melamine Barbiturate as a Light-Induced Nanostructured Supramolecular Material for a Bioinspired Oxygen and Organic Radical Trap and Stabilization
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  • Alexandra A. Timralieva
    Alexandra A. Timralieva
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    More by Alexandra A. Timralieva
  • Ivan V. Moskalenko
    Ivan V. Moskalenko
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
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  • Pavel V. Nesterov
    Pavel V. Nesterov
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
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  • Vladimir V. Shilovskikh
    Vladimir V. Shilovskikh
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
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  • Alexander S. Novikov
    Alexander S. Novikov
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
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  • Elizaveta A. Konstantinova
    Elizaveta A. Konstantinova
    Physics Department, M. V. Lomonosov Moscow State University, Leninskie Gory 1/2, Moscow 119991, Russia
    Institute of Nano-, Bio-, Information, Cognitive and Socio-humanistic Sciences and Technologies, Moscow Institute of Physics and Technology, Dolgoprudny 141701 Moscow Region, Russia
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  • Alexander I. Kokorin
    Alexander I. Kokorin
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygin st. 4, Moscow 119991, Russia
    Plekhanov Russian University of Economics, Stremyannyi per. 36, Moscow 115093, Russia
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  • Ekaterina V. Skorb*
    Ekaterina V. Skorb
    Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-0888-1693
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ACS Omega

Cite this: ACS Omega 2023, 8, 9, 8276–8284
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https://doi.org/10.1021/acsomega.2c06510
Published February 22, 2023

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Abstract

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Use of coantioxidant systems is a prospective way to increase the effectiveness of antioxidant species in tissue repair and regeneration. In this paper, we introduce a novel scheme of a reactive oxygen species (ROS) trap and neutralization during self-assembly of supramolecular melamine barbiturate material. The performed reaction chain mimics the biological process of ROS generation in key stages and enables one to obtain stable hydroperoxyl and organic radicals in a melamine barbiturate structure. Melamine barbiturate also neutralizes hydroxyl radicals, and the effectiveness of the radical trap is controlled with ROS scavenger incorporation. The number of radicals dramatically increases during light-inducing and depends on pH. The proposed scheme of the ROS trap and neutralization opens a way to the use of supramolecular assemblies as a component of coantioxidant systems and a source of organic radicals.

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Introduction

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Bioinspired material design has been a great trend in tissue engineering for at least a decade. (1−4) One crucial aspect of tissue engineering is oxygen delivery or production that requires novel derivatives of previously known functional materials. (5) Several metal–organic frameworks are considered to trap oxygen due to their high porosity and specific surface area. (6−8) Some layered perovskites show the same function but without oxygen release. (9,10) Bioinspired materials that mimic biological systems’ functions or composition release oxygen under mild conditions, which is a great advantage of these materials. (11)
A wide range of nanostructured biomaterials for tissue repair tends to respond only under external stimuli. (12) Some of them respond in the presence of O-centered radicals and turn into the activated state. (13,14) On the other hand, O2 delivery is often associated with undesired O-centered radicals’ increase in the tissue, which requires antioxidant incorporation. (15)
O-centered radicals are a class of an oxygen-bearing species that commonly are extremely active. They play an important role in a wide range of biological processes, e.g., aging and age-dependent diseases. (16) Both radical and nonradical oxygen derivatives can promote oxidizing. This class of substances is called reactive oxygen species (ROS), also called oxygen free radicals. This class includes both radical and nonradical substances. The first group includes superoxide (O2•–), hydroxyl (HO•), peroxyl (ROO•), and hydroperoxyl (HO2•) radicals. The second one consists of hydrogen peroxide (H2O2), lipid hydroperoxide (ROOH), hypochlorous acid (HOCl), ozone (O3), and singlet oxygen (1O2). (17)
The oxidizing function is not the same for O-centered radicals. The hydroperoxyl radical HO2• greatly contributes to oxidation stress in living systems, while its conjugated base, superoxide O2•–, is inactivate as an oxidizing initiator. (18) HO2• initiates the lipid peroxidation of polyunsaturated fatty acids with the formation of unstable and reactive fatty acid molecules, which contribute to membrane and tissue damage. (19) HO2• contribution increases the rate constant of polyunsaturated fatty acid oxidation. (20)
However, HO2• is an important part of coantioxidant systems as it regenerates antioxidant agents such as nitroxides, phenols, amines, and quinones due to the fast hydrogen atom transfer (HAT). (21−23) This approach, combined with antioxidant nanoparticle synthesis, enables the increase of antioxidant activity by several times. (24) A wide range of nanoparticles that produces antioxidant enzymes has been synthesized, but the question of HO2• radical stability has still remained open. (25) One prospective way of stabilizing radicals is a noncovalent approach, e.g., the applicability of supramolecular materials as organic radical cages. (26,27) In previous studies, we had presented melamine barbiturate (M-B) supramolecular assembly as a nanostructured material that traps O-centered radicals and shows significant radical activity. (28,29)
Here, we present an M-B behavior study in the presence of ROS and ROS scavengers to specify the radical’s trap and stabilization function. Surprisingly, the process of melamine barbiturate assembly almost mimics ROS formation in the mitochondria and its further neutralization in the cytoplasm.
We propose melamine barbiturate as a novel material for hydroperoxyl radical trap for the purposes of stable radical storage and antioxidant regeneration. Besides, we show that melamine barbiturate can prevent the oxidation action of hydrogen peroxide and hydroxyl radical through organic radical formation in the M-B structure. Furthermore, light-induced radicals expand and the pH control of radical number is performed.

Results and Discussion

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According to the performed density functional theory (DFT) calculations, (28,29) one radical center likely links up the O-centered radicals. The previously proposed O2•– is in equilibrium with its protonated form HO2• in the aqueous medium. However, M-B crystalline aggregates go through thermal processing, and then their radical activity is measured. Heterogeneous uptake and stabilization are typical for HO2• radicals in a nonaqueous medium. (30) Here, we present a batch of reactions for hydroperoxyl generation in M-B without corrections on O2•– formation.
The HO2• radical can regenerate antioxidants such as phenols. Tocopherol as a methylated phenol is one of the active compounds of the vitamin E group that occurs in plasma to prevent membrane damage by ROS. (31) Hydroperoxyl and hydroxyl radicals form in the mitochondria during incomplete oxygen reduction and further reaction chain with superoxide dismutase (SOD) and Fe2+ ions (Figure 1a). (32) HO2• and HO• radicals relocate in the plasma via the mitochondrial electron transport chain and attack −OH and −CH3 functional groups of the tocopherol correspondingly (Figure 1b). As a result, both ROS are neutralized, and two organic radicals appear. In a real biological system, tocopherol stays as a radical and no more acts as an antioxidant, so its antioxidant activity is limited at all. The question of antioxidant activity control and increase stays open in the case of lipid membrane repair.

Figure 1

Figure 1. Reactive oxygen species production in mitochondria (a), and its neutralization by vitamin E in the cytoplasm (b). Bioinspired way of HO2• generation and HO• neutralization by barbituric acid (c), and HO2• trap and stabilization into the melamine barbiturate structure (d). Radical trap and formation depend on pH and light irradiation: EPR kinetic curves of the melamine barbiturate system under light irradiation at 298 K as a function of pH values (e).

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However, tocopherol radicals can be regenerated via fast hydrogen atom transfer (HAT) from initial HO2• radicals. (33) For this purpose, a source of stable hydroperoxyl radicals is needed. We applied the performed scheme of ROS generation and neutralization to the M-B assembly process, and several similar key stages were indicated.
Barbituric acid (BA) as a single component shows no electron paramagnetic resonance signal, and a weak signal is observed during UV-light irradiation. Thus, we considered that light-inducing can be an essential stimulus for radical generation as was stated for a wide range of nanomaterials. (34,35) UV-light irradiation promotes oxygen transition from the triplet state to the singlet state, while compounds with the carbonyl group in the excited state present in the reaction medium. (36,37) BA has three carbonyl groups and easily goes into the excited state, so singlet oxygen formation is highly probable. (38) The reaction of BA with the formed singlet oxygen can theoretically go via two BA sites (Figure S1, top). It is thermodynamically preferable that singlet oxygen as a strong oxidizer takes the proton off the −CH2. Energy is required, and a heating of up to 120 °C can cover it during the experiment. It is in good accordance with X-ray diffraction data of M-B, which show deprotonated BA molecules in the structure. (39) The same calculations were conducted for melamine (M) oxidation and reactions with triplet oxygen (Figure S1, bottom). These reactions also are not energetically favorable.
Thus, BA produces an active HO2• radical via the reaction chain with oxygen under light irradiation (Figure 1c), and this stage matches mitochondrial hydroperoxyl radical generation. An important difference is that BA produces no HO• radicals, and we decided to artificially add it to the M-B assembly.
When BA reacts with melamine (M), the hydroperoxyl radical is not stabilized yet and can act as an oxidizer via HAT
RH+HO2•→R•+H2O2
(1)
We calculated HAT of M and BA with both hydroperoxyl and hydroxyl radicals, in comparison. The HAT of M and BA via HO2• is thermodynamically unfavorable at 298 K, while three reactions with HO• have significant negative ΔG values (Figure S2). Thus, the hydroperoxyl radical stays nonactive in M-B (Figure S2).
Figure 1d shows that there are stable hydroperoxyl radicals and organic radicals −CH• at BA molecules in the M-B assembly. We consider that not only the −CH• radical can occur in M-B but also −C• if BA is deprotonated during the assembly. This stage is similar to ROS neutralization in the plasma. Despite the rigidity of HO2• in M-B, it can become active in the presence of other agents. Thus, we propose using M-B as the regenerating agent for antioxidant systems.
However, the question of the controllable increase of the HO2• radical number still remains significant. As was confirmed in previous research, the M-B radical activity depends on pH values. At first, we decided to determine the optimal conditions for M-B formation. EPR measurements were conducted for M-B samples prepared at five different pH values. As an example, Figure S3 presents the experimental EPR spectra of M-B recorded at 298 K before and after 20 min of light irradiation prepared at pH 3.9 and 6.2 and also a sample of M-B + 2.0% H2O2. One can see that there are at least two radical centers in the M-B complex, whose nature has been presumably discussed in refs (28,29). Symbols R1, R||, and R2 in Figure S3 show line positions of two stable free radicals, most likely HO2• (R⊥, R||) and C• (R2), probably CH• centers, in BA correspondingly. The samples were irradiated by UV light during 25 min, and the ratio of the total radical signal intensity after and before irradiation was calculated for each sample. The radical signal intensity increases by about 2 times in cases of pH = 6.2 and 5.1 (Figure 1e). This effect is related most likely to the protonation and deprotonation of functional groups of melamine (M) and barbituric acid (BA) and the locked site for singlet oxygen attack. For further research, pH = 6.2 was considered the most preferable condition as it almost matches the pH value of the M-B suspension after complete formation, and no extra treatment is required.
It should be noted that EPR line intensities sufficiently change under illumination (Figure S3). Indeed, it is evidently seen that the intensity of the R2 line noticeably increases in the case of spectra (b) and (d) in comparison with spectra (a) and (c) in parallel to the amplitude of the whole spectrum. Therefore, we may conclude that UV–vis light irradiation results in the generation of new C• radicals in the M-BA system.
DFT calculations showed that HO• preferably reacts with the −CH2 site of BA via HAT. Theoretically, it means that M-B can convert HO• into H2O during M-B treatment with the hydroxyl radical source. As has been mentioned before, EPR spectra show that there are two radical centers in M-B. The first type of such a center is definitely the HO2• radical. The second one likely links up C-centered radicals, most probably, CH• of BA. Thus, HO• treatment of M-B should increase the total radical activity due to the CH• expansion, which is in agreement with EPR data.
To confirm this statement, we obtained M-B samples prepared from solutions of M and BA containing 2 wt % H2O2 as a source of hydroxyl radicals. To check the effect of hydroxyl radicals, we conducted experiments with 0.05 wt % sodium benzoate as the HO• scavenger. The control experiment with sodium benzoate was also performed. The suspensions of M-B were centrifuged, the precipitates were dried at 120 °C and rewashed with deionized water, and the procedure was repeated three times to remove traces of H2O2 and sodium benzoate.
The obtained crystalline aggregates show changes in the M-B morphology (Figure 2). Bright-field optical microscopy images demonstrate that the size distribution of M-B remains almost the same, but the shape changes. In the case of pure M-B and the adding of sodium benzoate, aggregates show an eight-star shape with strong twinning from the center. Sodium benzoate presence leads to a high increase of surface defects. Two samples of M-B that formed in the presence of H2O2 are also aggregates with strong twinning. The main difference is the rose-like shape consisting of thin platelets. Platelets become thinner, to 1 μm thickness, from the bottom of the aggregate to its top. Each platelet is represented by a single crystal. M-B formed in the presence of sodium benzoate consists of a hexagonal prism with triangular pyramidal head single crystals also as pure M-B aggregates.

Figure 2

Figure 2. Melamine barbiturate (a), M-B formed in the presence of sodium benzoate (b), H2O2 (c), H2O2 and sodium benzoate (d): bright-field, FITC channel fluorescence, polarized light optical microscopy, and scanning electron microscopy (from left to right).

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MB aggregates show distinct anisotropy in cross-polarized light. In general, separate single crystals exhibit uniform extinction when rotated in polarized light. The light extinction has a radially radiant form, which indicates the presence of a clear crystallization center. This makes it possible to attribute the formation of such aggregates to systems with nucleation control and high nucleation energy relative to that of the stationary growth process. (40)
All samples show luminescence at 517 nm under light irradiation (495 nm, FITC channel). Pure M-B has a weak luminescence with a raise at the edges of single crystals. Luminescence becomes stronger when M-B forms in the presence of sodium benzoate, and the maximum is observed at both the edges and surface defects of aggregates. We associate the luminescence of M-B with radical contribution to the π-system and electron localization. (41) Surface binding of luminescence is considered to depend on the number of radicals taken up by surface defects.
In the case of H2O2, luminescence is also pronounced mostly on the edges of platelets where the number of defects is the most. When we add sodium benzoate to H2O2, the formed M-B shows a dramatic increase of luminescence among all of the aggregates. We also see that the luminescence strengthens at the edges of each platelet. The number of platelets is significantly more than for the M-B formed in the presence of only H2O2. Often, we also observe the increase of defects on the M-B surface in the case of small aggregates like it occurs when we add only sodium benzoate.
Four samples were analyzed by X-ray powder diffraction (XRD) in comparison to initial compounds (Figure S4). No traces of M, BA, and sodium benzoate fractions are observed. For all M-B samples, we obtained similar reflex patterns, but the plane (002) extremely increases in the case of sodium benzoate addition. According to the previous study, sodium benzoate can be incorporated into the structure of M-B with the mentioned increase in interplanar spacing.
Figure S4A also shows that a little reflex appears in the case of H2O2 addition. We suppose that some structural changes can occur; however, the intensity of the reflex is too small to correctly interpret it. The calculated crystallinity values decrease to 87.1 and 63.0% for pure M-B and M-B formed in the presence of H2O2, respectively. Amorphous phases are 29.1 and 32.4% for M-B formed with only sodium benzoate and both sodium benzoate and H2O2, respectively. It seems that sodium benzoate promotes overgrowth of M-B and, as a result, a decrease in crystallinity.
To assess whether sodium benzoate incorporates into the M-B structure, we modeled several associates via DFT calculations, and values of Gibbs free energy change during associates’ formation of M, B, H2O2, and benzoate anion were obtained (Figure 3). Formation of melamine and benzoate anion associates (M-Benz) such as structures 3 and 4 is less thermodynamically favorable than BA-Benz (structures 1, 2). During BA-Benz formation, it was observed that the hydrogen atom transfers from the N–H bond of BA to the −COO– functional group. M-B-Benz trimers (structures 5, 6) also form with a decrease in the Gibbs free energy in contrast to melamine barbiturate dimers and trimers (structures 14, 15, 16). The benzoate anion association with BA via a hydrogen bond (structure 5) is more thermodynamically favorable for trimers.

Figure 3

Figure 3. Change of Gibbs free energy during associate formation of M, B with the benzoate anion (a), H2O2 (b), and both benzoate anion and H2O2 in contrast to melamine barbiturate dimers and trimers (c).

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The H2O2 hypothetically can associate with BA in two ways (structures 7, 8), and structure 8 is the least thermodynamically favorable. H2O2 association with M (structure 9) occurs preferably than with BA. H2O2 association with the M-B dimer (structure 10) is thermodynamically favorable, and H2O2 coordinates preferably to M than to BA. H2O2 association with M-B trimers (structures 11, 12, 13) is thermodynamically favorable. Note that despite numerous attempts to obtain an equilibrium structure 12, corresponding to the supramolecular associate of BA with the benzoate anion, as a result of geometry optimization, an associate 12′, corresponding to the barbiturate anion and benzoic acid, was always obtained (see the attached animation of the geometry optimization steps for one of the attempts, in which BA and the benzoate anion in the starting geometry are spaced by 3 Å). H2O2 coordination to M in B–M–B (structure 13) leads to a significant gain in the Gibbs free energy of formation in contrast to all other calculated associates. According to DFT calculations, H2O2 and sodium benzoate possibly associate with M and BA during melamine barbiturate formation in experiments performed above. DFT calculation results correspond to XRD data that sodium benzoate likely temporarily incorporates into the M-B structure. Molecular dynamics simulations show that M-BenZ and BA-BenZ associates exist and the M-BA dimer seems more stable and has a longer life period (Figure S5). Moreover, BA-BenZ dimers have a longer life period than M-BenZ dimers, but the interaction between barbituric acid and sodium benzoate can go only after melamine barbiturate formation as this interaction is less preferable. Breaking of barbituric acid and benzoate anion interaction through the washing of the process and explains the defects. Molecular dynamics simulation also shows that M–Na dimers exist but have a much smaller period of life. However, it seems that BA-Na does not exist in the solution or has a negligible period of life (Figure S6). The stability of M-B and H2O2 associates casts a doubt, but microscopy images confirm that the growth of M-B crystals is blocked for one axis.
We recorded four M-B samples using EPR to assess whether the radical’s chemical redox activity also changes. One can see from Figure 4a that the type of the EPR spectrum shape is similar in all cases of studied samples, while their amplitudes and integral intensities differ much initially and also after light irradiation as shown by their their kinetic curves (Figure 4b). Characteristic EPR parameters such as g-values g⊥ and g|| as well as the line width ΔH⊥ were estimated and are shown in Figure 4a. Both sodium benzoate and H2O2 revealed a strong effect on the concentration of the created stable radicals. Measured total concentrations were performed (Figure 4c). M-B samples formed in the presence of H2O2, sodium benzoate, and both reagents show an increase in the number of spins almost in 3 orders in contrast to the pure M-B sample. Considering the accuracy, we see that the M-B formed with both reagents shows almost the same increase of spin amount as the M-B formed with H2O2.

Figure 4

Figure 4. (Panel a) EPR spectra of M-B samples formed in the presence of H2O2 (a) and sodium benzoate (b) before and after 20 min of light irradiation (*) at T = 298 K. (Panel b) Kinetic curves at 298 K under light irradiation of M-B samples obtained in the presence of H2O2 (a), sodium benzoate (b), and both H2O2 and sodium benzoate (c). (Panel c) Total concentration of spins in the dark at T = 298 K in M-B samples obtained at pH = 6.2.

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We associate the difference with targeted activation of specific radical centers via sodium benzoate and hydrogen peroxide. H2O2 seems to increase the amount of stable CH• radicals according to the scheme shown above, while hydrogen peroxide decomposes into HO• radicals. Sodium benzoate likely increases the amount of both stable CH• and HO2• radicals. As was shown by microscopy methods, sodium benzoate increases the overgrowth of M-B and surface defects’ appearance. It leads to an increase in the triplet oxygen number near the nucleation center and further trapped HO2•. Expansion of two stable radicals explains the strong effect on the spin concentration, but it limits with the singlet oxygen formation stage.
However, sodium benzoate reduces the decomposition of H2O2 and weakens the effect of HAT between HO• radicals and BA molecules. It explains the smaller gain in the spin concentration than we expected for M-B samples formed in the presence of both sodium benzoate and H2O2. UV–Vis light illumination intensifies HAT that was blocked before and explains the difference in kinetic curves.

Conclusions

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In this study, we performed a nanostructured supramolecular melamine barbiturate assembly for bioinspired radical trap, neutralization, and stabilization. The melamine barbiturate supramolecular assembly generates hydroperoxyl radicals via a light-induced reaction chain. The HO2• radical remains stable in the M-B structure and seems to be activated as an antioxidant regenerator. An equilibrium between the hydroperoxyl radical and the superoxide radical can occur, and the presence of two conjugated radicals in M-B is probable. Moreover, the superoxide radical is also considered an effective oxidant regenerator as well as a hydroperoxyl radical. (42)
Barbituric acid is oxidized with CH• radicals’ formation that are stabilized into melamine barbiturate. Besides, oxidation of barbituric acid involves a singlet oxygen and neutralizes it as well. Thus, melamine barbiturate traps HO2• radicals and generates CH• radicals.
We show that addition of reactive oxygen species such as H2O2 leads to a significant increase in radical activity. Melamine barbiturate neutralizes HO• radicals via hydrogen atom transfer with the increase in CH• radicals.
Addition of sodium benzoate intensively promotes HO2• radical trapping even while H2O2 and HO• radicals are neutralized. Besides, the amount of spin increases by 1.4 times during UV–vis light irradiation.
Thus, in this study, we show a novel scheme of ROS stabilization and neutralization with supramolecular materials for antioxidant activity increase. The performed reaction chains mimic biological processes such as mitochondrial ROS generation and their neutralization in key stages.

Experimental Section

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Materials

Melamine (M), barbituric acid (BA), and sodium benzoate were purchased from Sigma-Aldrich, and hydrogen peroxide (H2O2) was purchased from Lenreactiv. The chemicals were used without further purification: BA (C4H4N2O3, 99.0%, Sigma-Aldrich), M (C3H6N6, 99.0%, Sigma-Aldrich), sodium benzoate (C6H5COONa, 99.0%, Sigma-Aldrich), and H2O2 (35%, Lenreactiv). Deionized water (18 MΩ·cm2/cm) was used as a solvent.

Synthesis

Stock 20 mm solutions of M and BA in water were prepared in advance to obtain four samples. Solutions were mixed and vigorously stirred in a 1:1 volumetric ratio to obtain a pure M-B suspension. The suspension was centrifuged, and the precipitate was dried at 120 °C and rewashed with deionized water; this procedure was repeated three times to remove traces of initial compounds. Sodium benzoate powder was weighed to get 0.05 wt % in solution. Each stock solution was mixed with sodium benzoate powder and heated until powder dissolution. Solutions of M and BA with sodium benzoate were mixed, and the suspension was proceeded according to the above-mentioned protocol. First, 35% H2O2 was mixed with each stock solution to obtain solutions of M and BA in 2% H2O2. Solutions were mixed to obtain a suspension, and the following steps were the same as mentioned previously. Then, 35% H2O2 was diluted in 8.75 times; sodium benzoate was added to get a 0.1 wt % solution, and it was heated until powder dissolution. The obtained solution was mixed with each stock M and BA solution in a 1:1 volumetric ratio, and solutions of M and BA in H2O2 with sodium benzoate were mixed. Further steps were performed according to the procedure mentioned before.

Microscopy and Microanalysis

All of the prepared powders were investigated by means of optical and scanning electron microscopies. Microimages were acquired using a Zeiss Axio Imager.A2m. A Tescan Vega 3 scanning electron microscope equipped with an Oxford x-act energy-dispersive X-ray spectrometer was used for imaging and microanalysis. Operating conditions were as follows: 5 kV accelerating voltage, 100 s dwell time per spectrum. All data were processed using Oxford Aztec One software. Image analysis was performed using ImageJ software.

XRD

Powder diffraction data of M-BA, M-BA-Benz, M-BA-H2O2, M-BA-Benz-H2O2, and reference M, BA, and Benz were collected by means of D2 PHASER (Bruker) with Cu Kα radiation from the 5 to 60° angular range with a 0.02 step size and 1 s resonance time. Phase analysis was carried out using the software package Eva (Bruker) utilizing the ICSD crystal database (PDF4+).

EPR Measurements

The EPR spectra were recorded at room temperature with a Bruker spectrometer ELEXSYS-E500 (X-band, sensitivity up to 1010 spin/G). For investigating the photoactivity and behavior of paramagnetic centers (PCs), the samples were illuminated directly in the cavity of the spectrometer with the use of a 50 W high-pressure mercury lamp. The concentration of PCs was evaluated using a CuCl2·2H2O monocrystal with a known number of spins as the standard. The EPR spectra simulation permitting determination of g-factor values of radicals was carried out with the use of the EasySpin MATLAB toolbox. EPR spectra analysis was carried out using a computer program package developed by Prof. A. Kh. Vorob′ev (Chemistry Department, M. Lomonosov Moscow State University) and kindly provided to us.

Quantum Chemical Computations

The full geometry optimization of all model structures was carried out at the B3LYP-d3/def2-SVP level of theory utilizing the ORCA 5.0.3 program package. (43) Spin-restricted approximation for structures with closed electron shells and the unrestricted approach for structures with open electron shells have been employed. The RIJCOSX approximation utilizing the def2-SVP/C auxiliary basis set was employed. (44,45) The convergence tolerances for geometry optimization were energy change = 5.0 × 10–6 Eh, maximal gradient = 3.0 × 10–4 Eh/Bohr, RMS gradient = 1.0 × 10–4 Eh/Bohr, maximal displacement = 4.0 × 10–3 Bohr, and RMS displacement = 2.0 × 10–3 Bohr. The couple perturbed self-consistent field (CPSCF) equations were solved using the conjugated gradient (CG) method with convergence tolerance on a residual of 1.0 × 10–6 Eh. The Hessian matrices were calculated for all optimized model structures to prove the location of correct stationary points on the potential energy surfaces (no imaginary frequencies were found in all cases) and to estimate the thermodynamic properties (viz. enthalpy, entropy, and Gibbs free energy) for all model systems at 298.15 K and 1 atm.

Molecular Dynamics Simulations

MD simulations of M-BA association with Rh6G were performed utilizing the GROMACS program package (46) for topology preparation and OpenMM (47) for calculation. Interatomic interactions were described by the OPLS-AA/CM1A force field, (48) with topology and charges generated by LigParGen. (49−51) For the water model, the rigid nonpolarizable TIP3P (52) model was used. The cutoff for nonbonded and long-range interactions was 1.2 nm. For the calculation of long-range Coulomb interactions, the particle-mesh Ewald method was used. (53) Energy minimization was performed with the steepest descent algorithm. Simulations were performed in the NPT ensemble at T = 300 K and P = 1 atm in the cubic unit cell (∼85 × 85 × 85 Å3). The integration time step for trajectories’ calculations was 2 fs, and for relaxation, it was 0.5 fs. Radial distribution functions, spatial distribution functions, and dimer existence autocorrelation functions were calculated from the resulting trajectories using the TRAVIS program package. (54)

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c06510.

  • Additional animation for illustration of geometry optimization steps for barbituric acid and benzoate anion adduct, in which barbituric acid and benzoate anion in the starting geometry are spaced by 3 Å (MP4)

  • Additional figures for illustration of pathways of M and BA oxidation via oxygen; corresponding calculated Gibbs free energies of reactions and equilibrium constants; HAT from BA and M to hydroperoxyl and hydroxyl radicals; corresponding calculated Gibbs free energies of reactions; and XRD data of four M-B samples (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Alexandra A. Timralieva - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    • Ivan V. Moskalenko - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    • Pavel V. Nesterov - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    • Vladimir V. Shilovskikh - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    • Alexander S. Novikov - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia
    • Elizaveta A. Konstantinova - Physics Department, M. V. Lomonosov Moscow State University, Leninskie Gory 1/2, Moscow 119991, Russia;  Institute of Nano-, Bio-, Information, Cognitive and Socio-humanistic Sciences and Technologies, Moscow Institute of Physics and Technology, Dolgoprudny 141701 Moscow Region, Russia
    • Alexander I. Kokorin - Infochemistry Scientific Center of ITMO University, Lomonosova str. 9, St. Petersburg 191002, Russia;  N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygin st. 4, Moscow 119991, Russia;  Plekhanov Russian University of Economics, Stremyannyi per. 36, Moscow 115093, Russia
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The work was carried out with the support of the Ministry of Science and Higher Education of the Russian Federation (agreement No 075-15-2021-1349) and was performed partially within the framework of the Program of Fundamental Research of the Russian Federation (Reg. No. 122040500068-0). Priority 2030 is acknowledged for infrastructural support.

References

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This article references 54 other publications.

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    ACS Nano (2018), 12 (6), 5417-5426CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
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    ACS Nano (2021), 15 (1), 419-433CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Chronic blood transfusions are used to alleviate anemic symptoms in thalassemia and sickle cell anemia patients but can eventually result in iron overload (IO) and subsequently lead to severe oxidative stress in cells and tissues. Deferoxamine (DFO) is clin. approved to treat transfusional IO, but the use of the iron chelator is hindered by nonspecific toxicity and poor pharmacokinetic (PK) properties in humans, resulting in the need to administer the drug via long-term infusion regimens that can often lead to poor patient compliance. Herein, a nanochelator system that uses the characteristic IO physiol. environment to dissoc. was prepd. through the incorporation of DFO and reactive oxygen species (ROS)-sensitive thioketal groups into an α-cyclodextrin-based polyrotaxane platform (rPR-DFO). ROS-induced dissocn. of this nanochelator (ca. 10 nm) into constructs averaging 2 nm in diam. significantly increased urine and fecal elimination of excess iron in vivo. In addn. to significantly improved PK properties, rPR-DFO was well-tolerated in mice and no adverse side effects were noted in single high dose or multiple dose acute toxicity studies. The overall features of rPR-DFO as a promising system for iron chelation therapy can be attributed to a combination of the nanochelator's improved PK, favorable distribution to the liver, and ROS-induced dissocn. properties into constructs <6 nm for faster renal elimination. This ROS-responsive nanochelator design may serve as a promising alternative for safely prolonging the circulation of DFO and more rapidly eliminating iron chelates from the body in iron chelation therapy regimens requiring repeated dosing of nanochelators.
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  15. 15
    Willemen, N. G. A.; Hassan, S.; Gurian, M.; Li, J.; Allijn, I. E.; Shin, S. R.; Leijten, J. Oxygen-Releasing Biomaterials: Current Challenges and Future Applications. Trends Biotechnol. 2021, 39, 1144– 1159,  DOI: 10.1016/j.tibtech.2021.01.007
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    15
    Oxygen-Releasing Biomaterials: Current Challenges and Future Applications
    Willemen, Niels G. A.; Hassan, Shabir; Gurian, Melvin; Li, Jinghang; Allijn, Iris E.; Shin, Su Ryon; Leijten, Jeroen
    Trends in Biotechnology (2021), 39 (11), 1144-1159CODEN: TRBIDM; ISSN:0167-7799. (Elsevier Ltd.)
    A review. Oxygen is essential for the survival, function, and fate of mammalian cells. Oxygen tension controls cellular behavior via metabolic programming, which in turn controls tissue regeneration, stem cell differentiation, drug metab., and numerous pathologies. Thus, oxygen-releasing biomaterials represent a novel and unique strategy to gain control over a variety of in vivo processes. Consequently, numerous oxygen-generating or carrying materials have been developed in recent years, which offer innovative solns. in the field of drug efficiency, regenerative medicine, and engineered living systems. In this review, we discuss the latest trends, highlight current challenges and solns., and provide a future perspective on the field of oxygen-releasing materials.
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  16. 16
    Giorgi, C.; Marchi, S.; Simoes, I. C. M.; Ren, Z.; Morciano, G.; Perrone, M.; Patalas-Krawczyk, P.; Borchard, S.; Jędrak, P.; Pierzynowska, K.; Szymański, J.; Wang, D. Q.; Portincasa, P.; Węgrzyn, G.; Zischka, H.; Dobrzyn, P.; Bonora, M.; Duszynski, J.; Rimessi, A.; Karkucinska-Wieckowska, A. Mitochondria and Reactive Oxygen Species in Aging and Age-Related Diseases. Int. Rev. Cell Mol. Biol. 2018, 340, 209– 344,  DOI: 10.1016/bs.ircmb.2018.05.006
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    Mitochondria and reactive oxygen species in aging and age-related diseases
    Giorgi, Carlotta; Marchi, Saverio; Simoes, Ines C. M.; Ren, Ziyu; Morciano, Giampaolo; Perrone, Mariasole; Patalas-Krawczyk, Paulina; Borchard, Sabine; Jedrak, Paulina; Pierzynowska, Karolina; Szymanski, Jedrzej; Wang, David Q.; Portincasa, Piero; Wegrzyn, Grzegorz; Zischka, Hans; Dobrzyn, Pawel; Bonora, Massimo; Duszynski, Jerzy; Rimessi, Alessandro; Karkucinska-Wieckowska, Agnieszka; Dobrzyn, Agnieszka; Szabadkai, Gyorgy; Zavan, Barbara; Oliveira, Paulo J.; Sardao, Vilma A.; Pinton, Paolo; Wieckowski, Mariusz R.
    International Review of Cell and Molecular Biology (2018), 340 (), 209-344CODEN: IRCMAH; ISSN:1937-6448. (Elsevier Inc.)
    A review. Aging has been linked to several degenerative processes that, through the accumula- tion of mol. and cellular damage, can progressively lead to cell dysfunction and organ failure. Human aging is linked with a higher risk for individuals to develop cancer, neurodegenerative, cardiovascular, and metabolic disorders. The understanding of the mol. basis of aging and assocd. diseases has been one major challenge of sci- entific research over the last decades. Mitochondria, the center of oxidative metab. and principal site of reactive oxygen species (ROS) prodn., are crucial both in health and in pathogenesis of many diseases. Redox signaling is important for the modulation of cell functions and several studies indicate a dual role for ROS in cell physiol. In fact, high concns. of ROS are pathogenic and can cause severe damage to cell and organelle membranes, DNA, and proteins. On the other hand, moderate amts. of ROS are essential for the maintenance of several biol. processes, including gene expression. In this review, we provide an update regarding the key roles of ROS-mitochondria cross talk in different fundamental physiol. or pathol. situations accompanying aging and highlighting that mitochondria!. ROS may be a decisive target in clin. practice.
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  17. 17
    Sies, H.; Belousov, Vv.; Chandel, N. S.; Davies, M. J.; Jones, D. P.; Mann, G. E.; Murphy, M. P.; Yamamoto, M.; Winterbourn, C. Defining Roles of Specific Reactive Oxygen Species (ROS) in Cell Biology and Physiology. Nat. Rev. Mol. Cell Biol. 2022, 23, 499– 515,  DOI: 10.1038/s41580-022-00456-z
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    17
    Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology
    Sies, Helmut; Belousov, Vsevolod V.; Chandel, Navdeep S.; Davies, Michael J.; Jones, Dean P.; Mann, Giovanni E.; Murphy, Michael P.; Yamamoto, Masayuki; Winterbourn, Christine
    Nature Reviews Molecular Cell Biology (2022), 23 (7), 499-515CODEN: NRMCBP; ISSN:1471-0072. (Nature Portfolio)
    A review. Abstr.: 'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant mols. with vastly different properties and biol. functions that range from signaling to causing cell damage. Consequently, the description of oxidants needs to be chem. precise to translate research on their biol. effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues assocd. with identifying the physiol. roles of oxidants, focusing on H2O2 and O2.-. We also advocate for greater precision in measurement of H2O2, O2.- and other oxidants, along with more specific identification of their signaling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signaling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiol. O2 levels should be maintained in cell culture to better mimic in vivo redox reactions assocd. with specific cell types. Use of precise definitions and anal. tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biol.
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  18. 18
    Foret, M. K.; Lincoln, R.; do Carmo, S.; Cuello, A. C.; Cosa, G. Connecting the “Dots”: From Free Radical Lipid Autoxidation to Cell Pathology and Disease. Chem. Rev. 2020, 120, 12757– 12787,  DOI: 10.1021/acs.chemrev.0c00761
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    18
    Connecting the "Dots": From Free Radical Lipid Autoxidation to Cell Pathology and Disease
    Foret, Morgan K.; Lincoln, Richard; Do Carmo, Sonia; Cuello, A. Claudio; Cosa, Gonzalo
    Chemical Reviews (Washington, DC, United States) (2020), 120 (23), 12757-12787CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Our understanding of lipid peroxidn. in biol. and medicine is rapidly evolving, as it is increasingly implicated in various diseases but also recognized as a key part of normal cell function, signaling, and death (ferroptosis). Not surprisingly, the root and consequences of lipid peroxidn. have garnered increasing attention from multiple disciplines in recent years. Here we "connect the dots" between the fundamental chem. underpinning the cascade reactions of lipid peroxidn. (enzymic or free radical), the reactive nature of the products formed (lipid-derived electrophiles), and the biol. targets and mechanisms assocd. with these products that culminate in cellular responses. We addnl. bring light to the use of highly sensitive, fluorescence-based methodologies. Stemming from the foundational concepts in chem. and biol., these methodologies enable visualizing and quantifying each reaction in the cascade in a cellular and ultimately tissue context, toward deciphering the connections between the chem. and physiol. of lipid peroxidn. The review offers a platform in which the chem. and biomedical research communities can access a comprehensive summary of fundamental concepts regarding lipid peroxidn., exptl. tools for the study of such processes, as well as the recent discoveries by leading investigators with an emphasis on significant open questions.
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    Panov, A. Perhydroxyl Radical (HO2•) as Inducer of the Isoprostane Lipid Peroxidation in Mitochondria. Mol. Biol. 2018, 52, 295– 305,  DOI: 10.1134/S0026893318020097
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    19
    Perhydroxyl Radical (HO2•) as Inducer of the Isoprostane Lipid Peroxidation in Mitochondria
    Panov, A.
    Molecular Biology (Moscow, Russian Federation, English Edition) (2018), 52 (3), 295-305CODEN: MOLBBJ; ISSN:0026-8933. (Pleiades Publishing, Ltd.)
    A review. The nonenzymic isoprostane pathway of lipid peroxidn. of polyunsatd. fatty acids results in formation of products, termed isoprostanes, which have very large positional and stereo isomerism, possess various biol. activities, produce adducts with proteins, and thus contribute to pathogeneses of the agedependent diseases. However, it was unclear what mechanism drives this type of lipid autoxidn., and why the products have very large isomerism. We propose a mechanism when perhydroxyl radicals (HO2•) react with polyunsatd. fatty acids in the hydrophobic milieu of membranes. In the membrane HO2• initiates a chain of reactions with formation first H2O2, which undergoes homolytic fission producing two •OH radicals, thus very rapidly abstracting three H atoms from a polyunsatd. fatty acid. As a result, the HO2• mol. is converted to two mols. of water, and the mol. of a polyunsatd. fatty acid loses two double bonds, becomes highly unstable and undergoes peroxidn. and random intramol. re-arrangements causing a very large isomerism of the final products. The extremely high reactivity of •HO2 with polyunsatd. fatty acids is the cause of very subtle and slow accumulation of damages in the membrane and membrane assocd. proteins, even though the concn. of •HO2 relative to superoxide radical may be very low.
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  20. 20
    Soloviev, M.; Moskalenko, I.; Pliss, E. Quantum Chemical Evaluation of the Role of HO2· Radicals in the Kinetics of the Methyl Linoleate Oxidation in Micelles. React. Kinet., Mech. Catal. 2019, 127, 561– 581,  DOI: 10.1007/s11144-019-01613-w
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    20
    Quantum chemical evaluation of the role of HO2· radicals in the kinetics of the methyl linoleate oxidation in micelles
    Soloviev, Mikhail; Moskalenko, Ivan; Pliss, Eugene
    Reaction Kinetics, Mechanisms and Catalysis (2019), 127 (2), 561-581CODEN: RKMCAJ; ISSN:1878-5190. (Springer)
    The process of lipid peroxidn. (LPO) plays an extremely important role in the human body due to the fact that its uncontrolled development can lead to oxidative stress and a no. of serious diseases. The traditional approach to the anal. of the mechanism and kinetics of LPO is based on the well-known ideas that emerged from the study of radical-chain oxidn. of hydrocarbons in a homogeneous medium. However, the distinctive feature of LPO is that this process is heterogeneous and the processes of diffusion of active intermediates between the aq. and hydrocarbon phases should play a significant role in it. In the present work, an attempt has been made to theor. est. the contribution of these processes to the oxidn. kinetics of model substances used in practice in the study of LPO. In the course of the calcns., a quantum chem. and kinetic anal. of the role of hydroperoxyl radical in the radical-chain mechanism of oxidn. of Me linoleate in micelles was carried out. The mol. dynamics method shows the important role of changing the dynamic rigidity of a hydrocarbon fragment of a chain during the formation of a peroxyl radical and hydroperoxyl group during the oxidn. of a substrate in a heterogeneous medium. Quantum chem. calcns. of the thermodn. of reactions involving HO2· radicals and the effects of their solvation made it possible to est. the kinetic consts. of the reaction rates. Using kinetic modeling, their relative contribution to the oxidn. kinetics was revealed. In this case, it is possible to explain a no. of anomalies assocd. with the oxidn. of polyunsatd. fatty acids and their esters in micelles compared with their oxidn. in a homogeneous hydrocarbon medium.
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  21. 21
    Harrison, K. A.; Haidasz, E. A.; Griesser, M.; Pratt, D. A. Inhibition of Hydrocarbon Autoxidation by Nitroxide-Catalyzed Cross-Dismutation of Hydroperoxyl and Alkylperoxyl Radicals. Chem. Sci. 2018, 9, 6068– 6079,  DOI: 10.1039/C8SC01575A
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    21
    Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals
    Harrison, Kareem A.; Haidasz, Evan A.; Griesser, Markus; Pratt, Derek A.
    Chemical Science (2018), 9 (28), 6068-6079CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Nitroxides are putative intermediates in the accepted reaction mechanisms of the diarylamine and hindered amine antioxidants that are universally added to preserve synthetic and natural hydrocarbon-based materials. New methodol. which enables monitoring of hydrocarbon autoxidns. at low rates of radical generation has revealed that diarylnitroxides and hindered nitroxides are far better inhibitors of unsatd. hydrocarbon autoxidn. than their precursor amines, implying intervention of a different mechanism. Exptl. and computational investigations suggest that the nitroxides catalyze the cross-dismutation of hydroperoxyl and alkylperoxyl radicals to yield O2 and a hydroperoxide, thereby halting the autoxidn. chain reaction. The hydroperoxyl radicals - key players in hydrocarbon combustion, but essentially unknown in autoxidn. - are proposed to derive from a tunneling-enhanced intramol. (1,4-) hydrogen-atom transfer/elimination sequence from oxygenated radical addn. intermediates. These insights suggest that nitroxides are preferred additives for the protection of hydrocarbon-based materials from autoxidn. since they exhibit catalytic activity under conditions where their precursor amines are less effective and/or inefficiently converted to nitroxides in situ.
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  22. 22
    Guo, Y.; Baschieri, A.; Mollica, F.; Valgimigli, L.; Cedrowski, J.; Litwinienko, G.; Amorati, R. Hydrogen Atom Transfer from HOO. to Ortho-Quinones Explains the Antioxidant Activity of Polydopamine. Angew. Chem., Int. Ed. 2021, 60, 15220– 15224,  DOI: 10.1002/anie.202101033
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    Hydrogen Atom Transfer from HOO. to ortho-Quinones Explains the Antioxidant Activity of Polydopamine
    Guo, Yafang; Baschieri, Andrea; Mollica, Fabio; Valgimigli, Luca; Cedrowski, Jakub; Litwinienko, Grzegorz; Amorati, Riccardo
    Angewandte Chemie, International Edition (2021), 60 (28), 15220-15224CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well-known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidn. of lipid substrates) in the presence of hydroperoxyl radicals (HOO.). The key reaction explaining this peculiar antioxidant activity is the redn. of the ortho-quinone moieties present in PDA by the reaction with HOO.. This reaction occurs via a H-atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5-di-tert-butyl-1,2-benzoquinone) with HOO. (k=1.5x107 and 1.1x105 M-1 s-1 in PhCl and MeCN). The chem. disclosed herein is an important step to rationalize the redox-mediated bioactivity of melanins and of quinones.
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    Baschieri, A.; Valgimigli, L.; Gabbanini, S.; Dilabio, G. A.; Romero-Montalvo, E.; Amorati, R. Extremely Fast Hydrogen Atom Transfer between Nitroxides and HOO· Radicals and Implication for Catalytic Coantioxidant Systems. J. Am. Chem. Soc. 2018, 140, 10354– 10362,  DOI: 10.1021/jacs.8b06336
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    23
    Extremely Fast Hydrogen Atom Transfer between Nitroxides and HOO· Radicals and Implication for Catalytic Coantioxidant Systems
    Baschieri, Andrea; Valgimigli, Luca; Gabbanini, Simone; DiLabio, Gino A.; Romero-Montalvo, Eduardo; Amorati, Riccardo
    Journal of the American Chemical Society (2018), 140 (32), 10354-10362CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We report a novel coantioxidant system based on TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) that, in biol. relevant model systems, rapidly converts chain-carrying alkylperoxyl radicals to HOO·. Extremely efficient quenching of HOO· by TEMPO blocks the oxidative chain. Rate consts. in chlorobenzene were measured to be 1.1 × 109 M-1 s-1 for the reductive reaction TEMPO + HOO· → TEMPOH + O2 and 5.0 × 107 M-1 s-1 for the oxidative reaction TEMPOH + HOO· → TEMPO + H2O2. These rate consts. are significantly higher than that assocd. with the reaction of HOO· with α-tocopherol, Nature's best lipid sol. antioxidant (k = 1.6 × 106 M-1 s-1). These data show that in the presence of ROO·-to-HOO· chain-transfer agents, which are common in lipophilic environments, the TEMPO/TEMPOH couple protects org. mols. from oxidn. by establishing an efficient reductive catalytic cycle. This catalytic cycle provides a new understanding of the efficacy of the antioxidant capability of TEMPO in nonaq. systems and its potential to act as a chemoprotective against radical damage.
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    Astete, C. E.; Dolliver, D.; Whaley, M.; Khachatryan, L.; Sabliov, C. M. Antioxidant Poly(Lactic-Co-Glycolic) Acid Nanoparticles Made with α-Tocopherol-Ascorbic Acid Surfactant. ACS Nano 2011, 5, 9313– 9325,  DOI: 10.1021/nn102845t
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    Antioxidant Poly(lactic-co-glycolic) Acid Nanoparticles Made with α-Tocopherol-Ascorbic Acid Surfactant
    Astete, Carlos E.; Dolliver, Debra; Whaley, Meocha; Khachatryan, Lavrent; Sabliov, Cristina M.
    ACS Nano (2011), 5 (12), 9313-9325CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The goal of the study was to synthesize a surfactant made of α-tocopherol (vitamin E) and ascorbic acid (vitamin C) of antioxidant properties dubbed as EC, and to use this surfactant to make poly(lactic-co-glycolic) acid (PLGA) nanoparticles. Self-assembled EC nanostructures and PLGA-EC nanoparticles were made by nanopptn., and their phys. properties (size, size distribution, morphol.) were studied at different salt concns., surfactant concns., and polymer/surfactant ratios. EC surfactant was shown to form self-assembled nanostructures in water with a size of 22 to 138 nm in the presence of sodium chloride, or 12 to 31 nm when synthesis was carried out in sodium bicarbonate. Polymeric PLGA-EC nanoparticles presented a size of 90 to 126 nm for 40% to 120% mass ratio PLGA to surfactant. For the same mass ratios, the PLGA-Span80 formed particles measured 155 to 216 nm. Span 80 formed bilayers, whereas EC formed monolayers at the interfaces. PLGA-EC nanoparticles and EC showed antioxidant activity based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay measurements using UV and EPR techniques, antioxidant activity which is not characteristic to com. available Span80. The thiobarbituric acid reactive substances (TBARS) assay for lipid peroxidn. showed that PLGA nanoparticles with EC performed better as antioxidants than the EC nanoassembly or the free vitamin C. Nanoparticles were readily internalized by HepG2 cells and were localized in the cytoplasm. The newly synthesized EC surfactant was therefore found successful in forming uniform, small size polymeric nanoparticles of intrinsic antioxidant properties.
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    Jalilov, A. S.; Nilewski, L. G.; Berka, V.; Zhang, C.; Yakovenko, A. A.; Wu, G.; Kent, T. A.; Tsai, A. L.; Tour, J. M. Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic. ACS Nano 2017, 11, 2024– 2032,  DOI: 10.1021/acsnano.6b08211
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    Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic
    Jalilov, Almaz S.; Nilewski, Lizanne G.; Berka, Vladimir; Zhang, Chenhao; Yakovenko, Andrey A.; Wu, Gang; Kent, Thomas A.; Tsai, Ah-Lim; Tour, James M.
    ACS Nano (2017), 11 (2), 2024-2032CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Here we show that the active portion of a graphitic nanoparticle can be mimicked by a perylene diimide (PDI) to explain the otherwise elusive biol. and electrocatalytic activity of the nanoparticle construct. Development of mol. analogs that mimic the antioxidant properties of oxidized graphenes, in this case the poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs), will afford important insights into the highly efficient activity of PEG-HCCs and their graphitic analogs. PEGylated perylene diimides (PEGn-PDI) serve as well-defined mol. analogs of PEG-HCCs and oxidized graphenes in general, and their antioxidant and superoxide dismutase-like (SOD-like) properties were studied. PEGn-PDIs have two reversible redn. peaks which are more pos. than the oxidn. peak of superoxide (O2•-). This is similar to the redn. peak of the HCCs. Thus, as with PEG-HCCs, PEGn-PDIs are also strong single-electron oxidants of O2•-. Furthermore, reduced PEGn-PDI, PEGn-PDI•- in the presence of protons, was shown to reduce O2•- to H2O2 to complete the catalytic cycle in this SOD analog. The kinetics of the conversion of O2•- to O2 by PEG8-PDI was measured using freeze-trap EPR expts. to provide a turnover no. of 133 s-1, the similarity in kinetics further supports that PEG8-PDI is a true SOD mimetic. Finally, PDIs can be used as catalysts in the electrochem. oxygen redn. reaction in water, which proceeds by a two-electron process with the prodn. of H2O2, mimicking graphene oxide nanoparticles that are otherwise difficult to study spectroscopically.
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    Huang, B.; Mao, L.; Shi, X.; Yang, H. B. Recent Advances and Perspectives on Supramolecular Radical Cages. Chem. Sci. 2021, 12, 13648– 13663,  DOI: 10.1039/D1SC01618K
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    Recent advances and perspectives on supramolecular radical cages
    Huang, Bin; Mao, Lijun; Shi, Xueliang; Yang, Hai-Bo
    Chemical Science (2021), 12 (41), 13648-13663CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    A review. Supramol. radical chem. has been emerging as a cutting-edge interdisciplinary field of traditional supramol. chem. and radical chem. in recent years. The purpose of such a fundamental research field is to combine traditional supramol. chem. and radical chem. together, and take the benefit of both to eventually create new mols. and materials. Recently, supramol. radical cages have been becoming one of the most frontier and challenging research focuses in the field of supramol. chem. In this Perspective, we give a brief introduction to org. radical chem., supramol. chem., and the emerging supramol. radical chem. along with their history and application. Subsequently, we turn to the main part of this topic: supramol. radical cages. The design and synthesis of supramol. cages consisting of redox-active building blocks and radical centers are summarized. The host-guest interactions between supramol. (radical) cages and org. radicals are also surveyed. Some interesting properties and applications of supramol. radical cages such as their unique spin-spin interactions and intriguing confinement effects in radical-mediated/catalyzed reactions are comprehensively discussed and highlighted in the main text. The purpose of this Perspective is to help students and researchers understand the development of supramol. radical cages, and potentially to stimulate innovation and creativity and infuse new energy into the fields of traditional supramol. chem. and radical chem. as well as supramol. radical chem.
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    Tang, B.; Zhao, J.; Xu, J. F.; Zhang, X. Tuning the Stability of Organic Radicals: From Covalent Approaches to Non-Covalent Approaches. Chem. Sci. 2020, 11, 1192– 1204,  DOI: 10.1039/C9SC06143F
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    Tuning the stability of organic radicals: from covalent approaches to non-covalent approaches
    Tang, Bohan; Zhao, Jiantao; Xu, Jiang-Fei; Zhang, Xi
    Chemical Science (2020), 11 (5), 1192-1204CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    A review. Org. radicals are important species with single electrons. Because of their open-shell structure, they are widely used in functional materials, such as spin probes, magnetic materials and optoelectronic materials. Owing to the high reactivity of single electrons, they often serve as a key intermediate in org. synthesis. Therefore, tuning the stability of radicals is crucial for their functions. Herein, we summarize covalent and non-covalent approaches to tune the stability of org. radicals through steric effects and tuning the delocalization of spin d. Covalent approaches can tune the stability of radicals effectively and non-covalent approaches benefit from dynamicity and reversibility. It is anticipated that the further development of covalent and non-covalent approaches, as well as the interplay between them, may push the fields forward by enriching new radical materials and radical mediated reactions.
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    Shilovskikh, V. V.; Timralieva, A. A.; Belogub, E. V.; Konstantinova, E. A.; Kokorin, A. I.; Skorb, E. V. Radical Activity of Binary Melamine-Based Hydrogen-Bonded Self-Assemblies. Appl. Magn. Reson. 2020, 51, 939– 949,  DOI: 10.1007/s00723-020-01254-6
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    Radical Activity of Binary Melamine-Based Hydrogen-Bonded Self-Assemblies
    Shilovskikh, Vladimir V.; Timralieva, Alexandra A.; Belogub, Elena V.; Konstantinova, Elizaveta A.; Kokorin, Alexander I.; Skorb, Ekaterina V.
    Applied Magnetic Resonance (2020), 51 (9-10), 939-949CODEN: APMREI; ISSN:0937-9347. (Springer-Verlag GmbH)
    Melamine cyanurate and melamine barbiturate self-assembled materials were prepd. and studied by the ESR spectroscopy, optical and SEM, X-ray powder diffraction (XRD). Both optical and electron microscopy show the formation of microscale cryst. particles possessing complex layered structures with a highly stable appearance. Both assemblies tend to form twinned crystals, which in the barbiturate case leads to multiple twinning in every particle. Optical microscopy shows high anisotropy and birefringence of both materials. XRD data represent a high crystallinity of melamine barbiturate and much lower for melamine cyanurate. Studied materials reveal the ability to incorporate radicals that correlate with their crystal structure quality. It is attributed to the structure-dependent stabilization of active radical superoxide species in structure voids or defects. In the example of melamine barbiturate, it is shown that the no. of active paramagnetic centers increases at ca. 22% when a substance is irradiated with UV + Vis light. It reaches satn. in approx. 20 min, whereas only ca. 14% decrease was obsd. in a week.
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    Shilovskikh, V. V.; Timralieva, A. A.; Nesterov, P. V.; Novikov, A. S.; Sitnikov, P. A.; Konstantinova, E. A.; Kokorin, A. I.; Skorb, E. V. Melamine–Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material. Chem. – Eur. J. 2020, 26, 16603– 16610,  DOI: 10.1002/chem.202002947
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    Melamine-Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material
    Shilovskikh, Vladimir V.; Timralieva, Alexandra A.; Nesterov, Pavel V.; Novikov, Alexander S.; Sitnikov, Petr A.; Konstantinova, Elizaveta A.; Kokorin, Alexander I.; Skorb, Ekaterina V.
    Chemistry - A European Journal (2020), 26 (70), 16603-16610CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In the last two decades, a large no. of self-assembled materials were synthesized and they have already found their way into large-scale industry and science. Hydrogen-bond-based supramol. adducts are found to have unique properties and to be perfect host structures for trapping target mols. or ions. Such chem. systems are believed to resemble living matter and can substitute a living cell in a no. of cases. Herein, a report on an org. material based on supramol. assembly of barbituric acid and melamine is presented. Surprisingly, the structure is found to host and stabilize radicals under mild conditions allowing its use for biol. applications. The no. of free radicals is found to be easily tuned by changing the pH of the environment and it increases when exposed to light up to a satn. level. We describe a prepn. method as well as stability properties of melamine-barbiturate self-assembly, potentiometric titrn., and hydrogen ions adsorption data and EPR spectra concerning the composite.
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    Ivatt, P. D.; Evans, M. J.; Lewis, A. C. Suppression of Surface Ozone by an Aerosol-Inhibited Photochemical Ozone Regime. Nat. Geosci. 2022, 15, 536– 540,  DOI: 10.1038/s41561-022-00972-9
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    Suppression of surface ozone by an aerosol-inhibited photochemical ozone regime
    Ivatt, Peter D.; Evans, Mathew J.; Lewis, Alastair C.
    Nature Geoscience (2022), 15 (7), 536-540CODEN: NGAEBU; ISSN:1752-0894. (Nature Portfolio)
    Atm. ozone (O3) is a pollutant produced through chem. chain reactions where volatile org. compds. (VOCs), carbon monoxide and methane are oxidized in the presence of oxides of nitrogen (NOx). For decades, the controlling chain termination step has been used to sep. regions into either 'NOx limited' (peroxyl-radical self-reactions dominate) or 'VOC limited' (hydroxyl radical (OH) + nitrogen dioxide (NO2) reaction dominates). The controlling regime would then guide policies for reducing emissions and so O3 concns. Using a chem. transport model, we show that a third 'aerosol inhibited' regime exists, where reactive uptake of hydroperoxyl radicals (HO2) onto aerosol particles dominates. In 1970, 2% of the Northern Hemisphere population lived in an aerosol-inhibited regime, but by 2014 this had increased to 21%; 60% more than lived in a VOC-limited regime. Aerosol-inhibited chem. suppressed surface O3 concns. in North America and Europe in the 1970s and is currently suppressing surface O3 over Asia. This third photochem. O3 regime leads to potential trade-off tensions between reducing particle pollution in Asia (a key current health policy and priority) and increasing surface O3, should O3 precursors emissions not be reduced in tandem.
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    Sena, L. A.; Chandel, N. S. Physiological Roles of Mitochondrial Reactive Oxygen Species. Mol. Cell 2012, 48, 158– 167,  DOI: 10.1016/j.molcel.2012.09.025
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    Physiological Roles of Mitochondrial Reactive Oxygen Species
    Sena, Laura A.; Chandel, Navdeep S.
    Molecular Cell (2012), 48 (2), 158-167CODEN: MOCEFL; ISSN:1097-2765. (Elsevier Inc.)
    A review. Historically, mitochondrial reactive oxygen species (mROS) were thought to exclusively cause cellular damage and lack a physiol. function. Accumulation of ROS and oxidative damage have been linked to multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. Thus, mROS were originally envisioned as a necessary evil of oxidative metab., a product of an imperfect system. Yet few biol. systems possess such flagrant imperfections, thanks to the persistent optimization of evolution, and it appears that oxidative metab. is no different. More and more evidence suggests that mROS are crit. for healthy cell function. In this Review, we discuss this evidence following some background on the generation and regulation of mROS.
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    Dröge, W. Free Radicals in the Physiological Control of Cell Function. Physiol. Rev. 2002, 82, 47– 95,  DOI: 10.1152/physrev.00018.2001
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    Free radicals in the physiological control of cell function
    Droge, Wulf
    Physiological Reviews (2002), 82 (1), 47-95CODEN: PHREA7; ISSN:0031-9333. (American Physiological Society)
    A review. At high concns., free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concns., however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis.". Higher organisms, however, have evolved the use of NO and ROS also as signaling mols. for other physiol. functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin prodn., and signal transduction from membrane receptors in various physiol. processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, resp. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amts. of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metab. An excessive and/or sustained increase in ROS prodn. has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addn., free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 yr ago by Harman (J Gerontol 11: 208-300, 1956). There is growing evidence that aging involves, in addn., progressive changes in free radical-mediated regulatory processes that result in altered gene expression.
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    Cedrowski, J.; Litwinienko, G.; Baschieri, A.; Amorati, R. Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer. Chem. – Eur. J. 2016, 22, 16441– 16445,  DOI: 10.1002/chem.201603722
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    Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer
    Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo
    Chemistry - A European Journal (2016), 22 (46), 16441-16445CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Hydroperoxyl (HOO.) and alkylperoxyl (ROO.) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analog of α-tocopherol (TOH), but HOO., unlike ROO., is able to regenerate TOH by a fast H-atom transfer: TO.+HOO.→TOH+O2. The kinetic solvent effect on the H-atom transfer from TOH to HOO. is much stronger than that obsd. for ROO. because noncovalent interactions with polar solvents (Solv···HOO.) destabilize the transition state.
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    Chong, Y.; Ge, C.; Fang, G.; Tian, X.; Ma, X.; Wen, T.; Wamer, W. G.; Chen, C.; Chai, Z.; Yin, J. J. Crossover between Anti- and Pro-Oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light. ACS Nano 2016, 10, 8690– 8699,  DOI: 10.1021/acsnano.6b04061
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    Crossover between Anti- and Pro-oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light
    Chong, Yu; Ge, Cuicui; Fang, Ge; Tian, Xin; Ma, Xiaochuan; Wen, Tao; Wamer, Wayne G.; Chen, Chunying; Chai, Zhifang; Yin, Jun-Jie
    ACS Nano (2016), 10 (9), 8690-8699CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Graphene quantum dots (GQDs), zero-dimensional carbon materials displaying excellent luminescence properties, show great promise for medical applications such as imaging, drug delivery, biosensors, and novel therapeutics. A deeper understanding of how the properties of GQDs interact with biol. systems is essential for these applications. Our work demonstrates that GQDs can efficiently scavenge a no. of free radicals and thereby protect cells against oxidative damage. However, upon exposure to blue light, GQDs exhibit significant phototoxicity through increasing intracellular reactive oxygen species (ROS) levels and reducing cell viability, attributable to the generation of free radicals under light excitation. We confirm that light-induced formation of ROS originates from the electron-hole pair and, more importantly, reveal that singlet oxygen is generated by photoexcited GQDs via both energy-transfer and electron-transfer pathways. Moreover, upon light excitation, GQDs accelerate the oxidn. of non-enzymic anti-oxidants and promote lipid peroxidn., contributing to the phototoxicity of GQDs. Our results reveal that GQDs can display both anti- and pro-oxidant activities, depending upon light exposure, which will be useful in guiding the safe application and development of potential anticancer/antibacterial applications for GQDs.
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    Li, Y.; Zhang, W.; Niu, J.; Chen, Y. Mechanism of Photogenerated Reactive Oxygen Species and Correlation with the Antibacterial Properties of Engineered Metal-Oxide Nanoparticles. ACS Nano 2012, 6, 5164– 5173,  DOI: 10.1021/nn300934k
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    Mechanism of Photogenerated Reactive Oxygen Species and Correlation with the Antibacterial Properties of Engineered Metal-Oxide Nanoparticles
    Li, Yang; Zhang, Wen; Niu, Junfeng; Chen, Yongsheng
    ACS Nano (2012), 6 (6), 5164-5173CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Oxidative stress induced by reactive oxygen species (ROS) is one of the most important antibacterial mechanisms of engineered nanoparticles (NPs). To elucidate the ROS generation mechanisms, we investigated the ROS prodn. kinetics of seven selected metal-oxide NPs and their bulk counterparts under UV irradn. (365 nm). The results show that different metal oxides had distinct photogenerated ROS kinetics. Particularly, TiO2 nanoparticles and ZnO nanoparticles generated three types of ROS (superoxide radical, hydroxyl radical, and singlet oxygen), whereas other metal oxides generated only one or two types or did not generate any type of ROS. Moreover, NPs yielded more ROS than their bulk counterparts likely due to larger surface areas of NPs providing more absorption sites for UV irradn. The ROS generation mechanism was elucidated by comparing the electronic structures (i.e., band edge energy levels) of the metal oxides with the redox potentials of various ROS generation, which correctly interpreted the ROS generation of most metal oxides. To develop a quant. relationship between oxidative stress and antibacterial activity of NPs, we examd. the viability of E. coli cells in aq. suspensions of NPs under UV irradn., and a linear correlation was found between the av. concn. of total ROS and the bacterial survival rates (R2 = 0.84). Although some NPs (i.e., ZnO and CuO nanoparticles) released toxic ions that partially contributed to their antibacterial activity, this correlation quant. linked ROS prodn. capability of NPs to their antibacterial activity as well as shed light on the applications of metal-oxide NPs as potential antibacterial agents.
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    Cilento, G.; Adam, W. From free radicals to electronically excited species. Free Radical Biol. Med. 1995, 19, 103– 114,  DOI: 10.1016/0891-5849(95)00002-F
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    From free radicals to electronically excited species
    Cilento, Giuseppe; Adam, Waldemar
    Free Radical Biology & Medicine (1995), 19 (1), 103-14CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
    A review with 86 refs. Biol./medicinally important compds., when metabolized, can generate free radicals from which electronically excited products, often in the triplet state, are generated. Peroxidases are particularly apt to catalyze such processes, which usually entail oxidns. by electron transfer. In the latter case, the chemiluminescence may derive from peroxy and alloxyl radicals or excited states derived from dioxetanes. Besides peroxidases, prostaglandin-H synthase and lipoxygenase may catalyze the formation of excited carbonyls. The pronounced similarity in the chem. behavior and reactivity of radicals and excited species derives in part from the bλradical nature of the latter. Usually in analyzing the biol. effects of xenobiotics, only radicals and/or reactive ground state products have been considered. However, in such processes the generation of excited species is possible, which should be tested for by direct and/or sensitized emission or by photochem. transformation.
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    Miyamoto, S.; Martinez, G. R.; Medeiros, M. H. G.; di Mascio, P. Singlet Molecular Oxygen Generated by Biological Hydroperoxides. J. Photochem. Photobiol. B 2014, 139, 24– 33,  DOI: 10.1016/j.jphotobiol.2014.03.028
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    Singlet molecular oxygen generated by biological hydroperoxides
    Miyamoto, Sayuri; Martinez, Glaucia R.; Medeiros, Marisa H. G.; Di Mascio, Paolo
    Journal of Photochemistry and Photobiology, B: Biology (2014), 139 (), 24-33CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
    A review. The chem. behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chem. generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the prodn. of excited carbonyl species and singlet mol. oxygen in the mechanism of generation of chemiluminescence in biol. system. In particular, attention has been focused on the potential generation of singlet mol. oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet mol. oxygen from reactions involving the decompn. of biol. relevant hydroperoxides, esp. from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chem. aspects related to the mechanism of singlet mol. oxygen generation from different biol. hydroperoxides.
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    Delchev, V. B.; Ivanova, I. P. Theoretical Study of the Excited-State Reaction Paths of the OH and NH Dissociation Processes in Barbituric Acid. Monatsh. Chem. 2012, 143, 1141– 1150,  DOI: 10.1007/s00706-012-0766-9
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    Theoretical study of the excited-state reaction paths of the OH and NH dissociation processes in barbituric acid
    Delchev, Vassil B.; Ivanova, Iva P.
    Monatshefte fuer Chemie (2012), 143 (8), 1141-1150CODEN: MOCMB7; ISSN:0026-9247. (SpringerWienNewYork)
    We studied the OH and NH dissocn. mechanisms of eight tautomers of barbituric acid via excited states. The theor. research was performed at the TD DFT level of theory (B3LYP). It was found that all mechanisms pass through the repulsive 1πσ* excited state whose excited-state reaction paths showed conical intersections S0-S1. Some OH dissocn. mechanisms showed barrierless 1πσ* reaction paths which indicate an ultrafast relaxation of the 1πσ* excited states to the ground state. The study of the NH dissocn. mechanisms revealed that almost all 1πσ* reaction paths show low energy barriers and min. before the conical intersections S0-S1.
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    Nesterov, P. V.; Shilovskikh, V. V.; Sokolov, A. D.; Gurzhiy, V. V.; Novikov, A. S.; Timralieva, A. A.; Belogub, Ev.; Kondratyuk, N. D.; Orekhov, N. D.; Skorb, E. V. Encapsulation of Rhodamine 6G Dye Molecules for Affecting Symmetry of Supramolecular Crystals of Melamine-Barbiturate. Symmetry 2021, 13, 1119,  DOI: 10.3390/sym13071119
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    Encapsulation of Rhodamine 6G Dye Molecules for Affecting Symmetry of Supramolecular Crystals of Melamine-Barbiturate
    Nesterov, Pavel V.; Shilovskikh, Vladimir V.; Sokolov, Alexander D.; Gurzhiy, Vladislav V.; Novikov, Alexander S.; Timralieva, Alexandra A.; Belogub, Elena V.; Kondratyuk, Nikolay D.; Orekhov, Nikita D.; Skorb, Ekaterina V.
    Symmetry (2021), 13 (7), 1119CODEN: SYMMAM; ISSN:2073-8994. (MDPI AG)
    Supramol. org. systems can be used as a host for the encapsulation of small org. mols. Here, we chose melamine barbiturate as a robust system capable of supramol. assembly and the Rhodamine 6G dye entrapment as a guest mol. The encapsulation of the dye was investigated by UV-visible spectroscopy, SEM and optical fluorescent microscopy while the insight into the crystal structure of the system was obtained by single crystal and powder XRD. For investigation of the system's properties on a mol. level, the DFT and Classical Mol. Dynamics methods were utilized. Surprisingly, both theor. and exptl. data show not only the successful encapsulation of Rhodamine 6G mols. inside the supramol. assembly, but also that inclusion of such mols. leads to the drastic improvement in the org. crystal shape. The melamine barbiturate in presence of the Rhodamine 6G mols. tend to form crystals with lesser degree of twinning and higher symmetry in shape than the ones without dye mols.
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    Orekhov, N.; Kondratyuk, N.; Logunov, M.; Timralieva, A.; Shilovskikh, V.; Skorb, E. V. Insights into the Early Stages of Melamine Cyanurate Nucleation from Aqueous Solution. Cryst. Growth Des. 2021, 21, 1984– 1992,  DOI: 10.1021/acs.cgd.0c01285
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    Insights into the Early Stages of Melamine Cyanurate Nucleation from Aqueous Solution
    Orekhov, Nikita; Kondratyuk, Nikolay; Logunov, Mikhail; Timralieva, Alexandra; Shilovskikh, Vladimir; Skorb, Ekaterina V.
    Crystal Growth & Design (2021), 21 (4), 1984-1992CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    From computational and exptl. approaches, mol.-level insights into melamine cyanurate (M-CA) self-assembly in aq. soln. are provided and corresponding mechanisms of aggregation identified. Small M-CA mol. complexes possibly are stabilized predominantly via arom. π-π-stacking rather than by formation of H bonds. Variation of the [M]/[CA] component concn. ratio results in a smooth change in the structure of the crit. nuclei from more disordered in the excess of M to more crystal-like in the excess of CA. This behavior can indicate that the process of M-CA nucleation in aq. solns. could be altered between classical and nonclassical mechanisms depending on the local [M]/[CA] concn. ratio, which could be prospective for the programmable design of functional supramol. materials.
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    Abdurahman, A.; Hele, T. J. H.; Gu, Q.; Zhang, J.; Peng, Q.; Zhang, M.; Friend, R. H.; Li, F.; Evans, E. W. Understanding the Luminescent Nature of Organic Radicals for Efficient Doublet Emitters and Pure-Red Light-Emitting Diodes. Nat. Mater. 2020, 19, 1224– 1229,  DOI: 10.1038/s41563-020-0705-9
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    Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes
    Abdurahman, Alim; Hele, Timothy J. H.; Gu, Qinying; Zhang, Jiangbin; Peng, Qiming; Zhang, Ming; Friend, Richard H.; Li, Feng; Evans, Emrys W.
    Nature Materials (2020), 19 (11), 1224-1229CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
    The doublet-spin nature of radical emitters is advantageous for applications in org. light-emitting diodes, as it avoids the formation of triplet excitons that limit the electroluminescence efficiency of non-radical emitters. However, radicals generally show low optical absorption and photoluminescence yields. Here we explain the poor optical properties of radicals based on alternant hydrocarbons, and establish design rules to increase the absorption and luminescence yields for donor-acceptor-type radicals. We show that non-alternant systems are necessary to lift the degeneracy of the lowest energy orbital excitations; moreover, intensity borrowing from an intense high-lying transition by the low-energy charge-transfer excitation enhances the oscillator strength of the emitter. We apply these rules to design tris(2,4,6-trichlorophenyl)methyl-pyridoindolyl derivs. with a high photoluminescence quantum yield (>90%). Org. light-emitting diodes based on these mols. showed a pure-red emission with an over 12% external quantum efficiency. These insights may be beneficial for the rational design and discovery of highly luminescent doublet emitters.
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    Bedard, L.; Young, M. J.; Hall, D.; Paul, T.; Ingold, K. U. Quantitative Studies on the Peroxidation of Human Low-Density Lipoprotein Initiated by Superoxide and by Charged and Neutral Alkylperoxyl Radicals. J. Am. Chem. Soc. 2001, 123, 12439– 12448,  DOI: 10.1021/ja011076d
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    Quantitative Studies on the Peroxidation of Human Low-Density Lipoprotein Initiated by Superoxide and by Charged and Neutral Alkylperoxyl Radicals
    Bedard, Leanne; Young, Mary Jane; Hall, David; Paul, Thomas; Ingold, K. U.
    Journal of the American Chemical Society (2001), 123 (50), 12439-12448CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Rates of peroxidn. of human LDL and rates of consumption of the LDL's α-tocopherol (TocH) have been measured at 37 °C. Peroxidn. was initiated by radicals generated in the aerated aq. phase at known rates by thermal decompn. of appropriate precursors: superoxide (O2•-/HOO•) from a hyponitrite and alkylperoxyls (ROO•, two pos. charged, one neg. charged and one neutral) from azo compds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidn. (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidn. was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-contg. LDL at pH's from 7.6 to 6.5 and peroxidn. was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidn. was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidn. rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiol. relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiol. important alkylperoxyls. Rates of LDL peroxidn. initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidn. of fresh LDL occurring via H-atom abstraction from TocH by HOO• to form the Toc• radical and termination by reaction of O2•- with Toc•, a process that occurs partly by addn. leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH.
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    Neese, F.; Wiley, J. The ORCA Program System. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2012, 2, 73– 78,  DOI: 10.1002/wcms.81
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  • Abstract

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    Figure 1

    Figure 1. Reactive oxygen species production in mitochondria (a), and its neutralization by vitamin E in the cytoplasm (b). Bioinspired way of HO2• generation and HO• neutralization by barbituric acid (c), and HO2• trap and stabilization into the melamine barbiturate structure (d). Radical trap and formation depend on pH and light irradiation: EPR kinetic curves of the melamine barbiturate system under light irradiation at 298 K as a function of pH values (e).

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    Figure 2

    Figure 2. Melamine barbiturate (a), M-B formed in the presence of sodium benzoate (b), H2O2 (c), H2O2 and sodium benzoate (d): bright-field, FITC channel fluorescence, polarized light optical microscopy, and scanning electron microscopy (from left to right).

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    Figure 3

    Figure 3. Change of Gibbs free energy during associate formation of M, B with the benzoate anion (a), H2O2 (b), and both benzoate anion and H2O2 in contrast to melamine barbiturate dimers and trimers (c).

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    Figure 4

    Figure 4. (Panel a) EPR spectra of M-B samples formed in the presence of H2O2 (a) and sodium benzoate (b) before and after 20 min of light irradiation (*) at T = 298 K. (Panel b) Kinetic curves at 298 K under light irradiation of M-B samples obtained in the presence of H2O2 (a), sodium benzoate (b), and both H2O2 and sodium benzoate (c). (Panel c) Total concentration of spins in the dark at T = 298 K in M-B samples obtained at pH = 6.2.

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      Wang, Yi; Xu, Yuanhang; Zhai, Weijie; Zhang, Zhinan; Liu, Yuhong; Cheng, Shujie; Zhang, Hongyu
      Nature Communications (2022), 13 (1), 5056CODEN: NCAOBW; ISSN:2041-1723. (Nature Portfolio)
      It is a great challenge to achieve robustly bonded, fully covered, and nanoscaled coating on the surface of electrospun nanofibers. Herein, we develop a controllable, facile, and versatile strategy to in-situ grow superlubricated nano-skin (SLNS) on the single electrospun nanofiber. Specifically, zwitterionic polymer chains are generated from the nanofiber subsurface in an inside-out way, which consequently form a robust network interpenetrating with the polymeric chains of the nanofiber matrix. The nanofibers with SLNS are superlubricated with the coeff. of friction (COF) lower than 0.025, which is about 16-fold of redn. than the original nanofibers. The time-COF plot is very stable after 12, 000 cycles of friction test, and no abrasion is obsd. Addnl., the developed nanofibrous membranes possess favorable tensile property and biocompatibility. Furthermore, the nanofibrous membranes with SLNS achieve prevention of post-operative adhesion, which is confirmed in both rat tendon adhesion model and abdominal adhesion model. Compared with clin.-used antiadhesive membranes such as Interceed and DK-film, our nanofibrous membranes are not only more effective but also have the advantage of lower prodn. cost. Therefore, this study demonstrates a potential of the superlubricated nanofibrous membranes in-situ grown based on a SLNS strategy for achieving prevention of post-operative adhesion in clinics.
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    4. 4
      Fernandes, M. M.; Correia, D. M.; Ribeiro, C.; Castro, N.; Correia, V.; Lanceros-Mendez, S. Bioinspired Three-Dimensional Magnetoactive Scaffolds for Bone Tissue Engineering. ACS Appl. Mater. Interfaces 2019, 11, 45265– 45275,  DOI: 10.1021/acsami.9b14001
      4
      Bioinspired Three-Dimensional Magnetoactive Scaffolds for Bone Tissue Engineering
      Fernandes, Margarida M.; Correia, Daniela M.; Ribeiro, Clarisse; Castro, Nelson; Correia, Vitor; Lanceros-Mendez, Senentxu
      ACS Applied Materials & Interfaces (2019), 11 (48), 45265-45275CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Bone tissue repair strategies are gaining increasing relevance due to the growing incidence of bone disorders worldwide. Biochem. stimulation is the most commonly used strategy for cell regeneration, while the application of phys. cues, including magnetic, mech., or elec. fields, is a promising, however, scarcely investigated field. This work reports on novel magnetoactive three-dimensional (3D) porous scaffolds suitable for effective proliferation of osteoblasts in a biomimetic microenvironment. This phys. active microenvironment is developed through the bone-mimicking structure of the scaffold combined with the phys. stimuli provided by a magnetic custom-made bioreactor on a magnetoresponsive scaffold. Scaffolds are obtained through the development of nanocomposites comprised of a piezoelec. polymer, poly(vinylidene fluoride) (PVDF), and magnetostrictive particles of CoFe2O4, using a solvent casting method guided by the overlapping of nylon template structures with three different fiber diam. sizes (60, 80, and 120 μm), thus generating 3D scaffolds with different pore sizes. The magnetoactive composites show a structure very similar to trabecular bone with pore sizes that range from 5 to 20 μm, owing to the inherent process of crystn. of PVDF with the nanoparticles (NPs), interconnected with bigger pores, formed after removing the nylon templates. It is found that the materials crystallize in the electroactive β-phase of PVDF and promote the proliferation of preosteoblasts through the application of magnetic stimuli. This phenomenon is attributed to both local magnetomech. and magnetoelec. response of the scaffolds, which induce a proper cellular mechano- and electro-transduction process.
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    5. 5
      Li, Y.; Lou, N.; Xu, D.; Pan, C.; Lu, X.; Gan, L. Oxygen-Delivery Materials: Synthesis of an Open-Cage Fullerene Derivative Suitable for Encapsulation of H2O2 and O2. Angew. Chem. 2018, 130, 14340– 14344,  DOI: 10.1002/ange.201808926
      There is no corresponding record for this reference.
    6. 6
      Lyu, J.; Zhang, X.; Chen, Z.; Anderson, R.; Wang, X.; Wasson, M. C.; Bai, P.; Guo, X.; Islamoglu, T.; Gómez-Gualdrón, D. A.; Farha, O. K. Modular Synthesis of Highly Porous Zr-MOFs Assembled from Simple Building Blocks for Oxygen Storage. ACS Appl. Mater. Interfaces 2019, 11, 42179– 42185,  DOI: 10.1021/acsami.9b14439
      6
      Modular Synthesis of Highly Porous Zr-MOFs Assembled from Simple Building Blocks for Oxygen Storage
      Lyu, Jiafei; Zhang, Xuan; Chen, Zhijie; Anderson, Ryther; Wang, Xingjie; Wasson, Megan C.; Bai, Peng; Guo, Xianghai; Islamoglu, Timur; Gomez-Gualdron, Diego A.; Farha, Omar K.
      ACS Applied Materials & Interfaces (2019), 11 (45), 42179-42185CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The last decade has witnessed significant advances in the scale-up synthesis of metal-org. frameworks (MOFs) using com. available and affordable org. linkers. However, the synthesis of MOFs using elongated and/or multitopic linkers to access MOFs with large pore vol. and/or various topologies can often be challenging due to multistep org. syntheses involved for linker prepn. In this report, a modular MOF synthesis strategy is developed by utilizing the coordination and covalent bonds formation in one-pot strategy where monoacid-based ligands reacted to form ditopic ligands, which then assembled into a three-dimensional MOF with Zr6 clusters. Chem. stability of the resulting materials was significantly enhanced through converting the imine bond into robust linkage via cycloaddn. with phenylacetylene. Oxygen storage capacities of the MOFs were measured, and enhanced volumetric O2 uptake was obsd. for the stabilized MOF, NU-401-Q.
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    7. 7
      DeCoste, J. B.; Weston, M. H.; Fuller, P. E.; Tovar, T. M.; Peterson, G. W.; LeVan, M. D.; Farha, O. K. Metal-Organic Frameworks for Oxygen Storage. Angew. Chem., Int. Ed. 2014, 53, 14092– 14095,  DOI: 10.1002/anie.201408464
      7
      Metal-organic frameworks for oxygen storage
      DeCoste Jared B; Weston Mitchell H; Fuller Patrick E; Tovar Trenton M; Peterson Gregory W; LeVan M Douglas; Farha Omar K
      Angewandte Chemie (International ed. in English) (2014), 53 (51), 14092-5 ISSN:.
      We present a systematic study of metal-organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10,000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST-1 (Cu-BTC) and NU-125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST-1 and NU-125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU-125 has an increased excess capacity for oxygen of 237% and 98%, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.
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    8. 8
      Moghadam, P. Z.; Islamoglu, T.; Goswami, S.; Exley, J.; Fantham, M.; Kaminski, C. F.; Snurr, R. Q.; Farha, O. K.; Fairen-Jimenez, D. Computer-Aided Discovery of a Metal-Organic Framework with Superior Oxygen Uptake. Nat. Commun. 2018, 9, 1378  DOI: 10.1038/s41467-018-03892-8
      8
      Computer-aided discovery of a metal-organic framework with superior oxygen uptake
      Moghadam Peyman Z; Fantham Marcus; Kaminski Clemens F; Fairen-Jimenez David; Islamoglu Timur; Goswami Subhadip; Farha Omar K; Exley Jason; Snurr Randall Q; Farha Omar K; Farha Omar K
      Nature communications (2018), 9 (1), 1378 ISSN:.
      Current advances in materials science have resulted in the rapid emergence of thousands of functional adsorbent materials in recent years. This clearly creates multiple opportunities for their potential application, but it also creates the following challenge: how does one identify the most promising structures, among the thousands of possibilities, for a particular application? Here, we present a case of computer-aided material discovery, in which we complete the full cycle from computational screening of metal-organic framework materials for oxygen storage, to identification, synthesis and measurement of oxygen adsorption in the top-ranked structure. We introduce an interactive visualization concept to analyze over 1000 unique structure-property plots in five dimensions and delimit the relationships between structural properties and oxygen adsorption performance at different pressures for 2932 already-synthesized structures. We also report a world-record holding material for oxygen storage, UMCM-152, which delivers 22.5% more oxygen than the best known material to date, to the best of our knowledge.
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    9. 9
      Kalapsazova, M. L.; Kostov, K. L.; Kukeva, R. R.; Zhecheva, E. N.; Stoyanova, R. K. Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides. J. Phys. Chem. Lett. 2021, 12, 7804– 7811,  DOI: 10.1021/acs.jpclett.1c01982
      9
      Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides
      Kalapsazova, Mariya L.; Kostov, Krassimir L.; Kukeva, Rositsa R.; Zhecheva, Ekaterina N.; Stoyanova, Radostina K.
      Journal of Physical Chemistry Letters (2021), 12 (32), 7804-7811CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      To double the energy d. of lithium- and sodium-ion batteries there is a need to activate simultaneously cationic and anionic redox reactions at the intercalation-type electrodes. In contrast to the cationic redox activity, the oxygen redox activity enforces an enhancement in the surface reactivity of the oxides leading to their poor reversibility and cycling stability. Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-storage materials as an efficient buffer supplying and receiving oxygen during alkali ion intercalation. As a proof-of-concept, the study is focused on CeO2 as a modifier of sodium nickel-manganese oxide with a three-layer sequence, P3-Na2/3Ni1/2Mn1/2O2. The CeO2-modified P3-Na2/3Ni1/2Mn1/2O2 displays a drastic increase in the reversible capacity following the order Na+ intercalation < Li+ intercalation < Li+,Na+ cointercalation.
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    10. 10
      Klimkowicz, A.; Świerczek, K.; Rzasa, T.; Takasaki, A.; Dabrowski, B. Oxygen Storage Properties and Catalytic Activity of Layer-Ordered Perovskites BaY1- XGdxMn2O5+δ. Solid State Ionics 2016, 288, 43– 47,  DOI: 10.1016/j.ssi.2016.01.038
      10
      Oxygen storage properties and catalytic activity of layer-ordered perovskites BaY1 - xGdxMn2O5 + δ
      Klimkowicz, A.; Swierczek, K.; Rzasa, T.; Takasaki, A.; Dabrowski, B.
      Solid State Ionics (2016), 288 (), 43-47CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
      Crystal structure, oxygen storage-related and preliminary anaerobic methane combustion studies were conducted for BaY1-xGdxMn2O5+δ (0, 0.25, 0.5, 0.75 and 1) series of oxides prepd. by a sol-gel method. All samples were found to possess layered-type A-site cation ordering, with the unit cell vol. linearly dependent on the av. radius of Y1- xGdx for both the reduced and the oxidized materials. The oxygen content in the temp. range of 400 °C-600 °C indicates change on the order of 1 at. mole, occurring when the sample's surrounding atm. was changed from air to 5 vol.% H2 in Ar. The time dependence of the redn. shows activated character on temp., with an activation energy, which seems to be related to the oxygen diffusion in the bulk of the materials. Initial data concerning methane combustion in oxygen-free conditions show promising catalytic activity of BaYMn2O6 at elevated temps.
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    11. 11
      Fu, X.; Ohta, S.; Kawakatsu, T.; Kamihira, M.; Sakai, Y.; Ito, T. Bioinspired Perfluorocarbon-Based Oxygen Carriers with Concave Shape and Deformable Shell. Adv. Mater. Technol. 2022, 7, 2100573  DOI: 10.1002/admt.202100573
      11
      Bioinspired Perfluorocarbon-Based Oxygen Carriers with Concave Shape and Deformable Shell
      Fu, Xiaoting; Ohta, Seiichi; Kawakatsu, Takahiro; Kamihira, Masamichi; Sakai, Yasuyuki; Ito, Taichi
      Advanced Materials Technologies (Weinheim, Germany) (2022), 7 (3), 2100573CODEN: AMTDCM; ISSN:2365-709X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Human red blood cells (hRBCs) possess a unique biconcave structure with a highly deformable cell membrane and condensed cytosol Hb for oxygen delivery. Inspired by hRBCs, novel deformable core-shell particles are developed as perfluorocarbon-based oxygen carriers (OCs), called "cDFCs" (concave-shaped deformable PFC-based OCs), using the Shirasu porous glass (SPG) membrane emulsification technique. cDFCs have a perfluorooctyl bromide core of high oxygen soly. and poly(lactide-co-caprolactone) shell, which is thin and highly deformable. They have an optical equiv. diam. of 7.9 ± 2.5 μm and a unique concave shape. Owing to their low Youngs modulus (93 kPa) and their diam. and shape, they successfully pass through a 4.5-μm-gap silicon microchannel as a blood capillary model. Enhanced oxygen supply to multiple layered cells is demonstrated under hypoxic conditions, indicating their efficiency as OCs. cDFCs are new potential OCs in tissue engineering and blood substitution in the future.
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    12. 12
      Gelmi, A.; Schutt, C. E. Stimuli-Responsive Biomaterials: Scaffolds for Stem Cell Control. Adv. Healthcare Mater. 2021, 10, 2001125  DOI: 10.1002/adhm.202001125
      12
      Stimuli-Responsive Biomaterials: Scaffolds for Stem Cell Control
      Gelmi, Amy; Schutt, Carolyn E.
      Advanced Healthcare Materials (2021), 10 (1), 2001125CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Stem cell fate is closely intertwined with microenvironmental and endogenous cues within the body. Recapitulating this dynamic environment ex vivo can be achieved through engineered biomaterials which can respond to exogenous stimulation (including light, elec. stimulation, ultrasound, and magnetic fields) to deliver temporal and spatial cues to stem cells. These stimuli-responsive biomaterials can be integrated into scaffolds to investigate stem cell response in vitro and in vivo, and offer many pathways of cellular manipulation: biochem. cues, scaffold property changes, drug release, mech. stress, and elec. signaling. The aim of this review is to assess and discuss the current state of exogenous stimuli-responsive biomaterials, and their application in multipotent stem cell control. Future perspectives in utilizing these biomaterials for personalized tissue engineering and directing organoid models are also discussed.
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    13. 13
      Lv, W.; Xu, J.; Wang, X.; Li, X.; Xu, Q.; Xin, H. Bioengineered Boronic Ester Modified Dextran Polymer Nanoparticles as Reactive Oxygen Species Responsive Nanocarrier for Ischemic Stroke Treatment. ACS Nano 2018, 12, 5417– 5426,  DOI: 10.1021/acsnano.8b00477
      13
      Bioengineered Boronic Ester Modified Dextran Polymer Nanoparticles as Reactive Oxygen Species Responsive Nanocarrier for Ischemic Stroke Treatment
      Lv, Wei; Xu, Jianpei; Wang, Xiaoqi; Li, Xinrui; Xu, Qunwei; Xin, Hongliang
      ACS Nano (2018), 12 (6), 5417-5426CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Ischemic stroke is a leading cause of long-term disability and death worldwide. Current drug delivery vehicles for the treatment of ischemic stroke are less than satisfactory, in large part due to their short circulation lives, lack of specific targeting to the ischemic site, and poor controllability of drug release. In light of the upregulation of reactive oxygen species (ROS) in the ischemic neuron, we herein developed a bioengineered ROS-responsive nanocarrier for stroke-specific delivery of a neuroprotective agent, NR2B9C, against ischemic brain damage. The nanocarrier is composed of a dextran polymer core modified with ROS-responsive boronic ester and a red blood cell (RBC) membrane shell with stroke homing peptide (SHp) inserted. These targeted "core-shell" nanoparticles (designated as SHp-RBC-NP) could thus have controlled release of NR2B9C triggered by high intracellular ROS in ischemic neurons after homing to ischemic brain tissues. The potential of the SHp-RBC-NP for ischemic stroke therapy was systematically evaluated in vitro and in rat models of middle cerebral artery occlusion (MCAO). In vitro results showed that the SHp-RBC-NP had great protective effects on glutamate-induced cytotoxicity in PC-12 cells. In vivo pharmacokinetic (PK) and pharmacodynamic (PD) testing further demonstrated that the bioengineered nanoparticles can drastically prolong the systemic circulation of NR2B9C, enhance the active targeting of the ischemic area in the MCAO rats, and reduce ischemic brain damage.
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    14. 14
      Liu, Z.; Simchick, G. A.; Qiao, J.; Ashcraft, M. M.; Cui, S.; Nagy, T.; Zhao, Q.; Xiong, M. P. Reactive Oxygen Species-Triggered Dissociation of a Polyrotaxane-Based Nanochelator for Enhanced Clearance of Systemic and Hepatic Iron. ACS Nano 2021, 15, 419– 433,  DOI: 10.1021/acsnano.0c01083
      14
      Reactive Oxygen Species-Triggered Dissociation of a Polyrotaxane-Based Nanochelator for Enhanced Clearance of Systemic and Hepatic Iron
      Liu, Zhi; Simchick, Gregory A.; Qiao, Jing; Ashcraft, Morgan M.; Cui, Shuolin; Nagy, Tamas; Zhao, Qun; Xiong, May P.
      ACS Nano (2021), 15 (1), 419-433CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Chronic blood transfusions are used to alleviate anemic symptoms in thalassemia and sickle cell anemia patients but can eventually result in iron overload (IO) and subsequently lead to severe oxidative stress in cells and tissues. Deferoxamine (DFO) is clin. approved to treat transfusional IO, but the use of the iron chelator is hindered by nonspecific toxicity and poor pharmacokinetic (PK) properties in humans, resulting in the need to administer the drug via long-term infusion regimens that can often lead to poor patient compliance. Herein, a nanochelator system that uses the characteristic IO physiol. environment to dissoc. was prepd. through the incorporation of DFO and reactive oxygen species (ROS)-sensitive thioketal groups into an α-cyclodextrin-based polyrotaxane platform (rPR-DFO). ROS-induced dissocn. of this nanochelator (ca. 10 nm) into constructs averaging 2 nm in diam. significantly increased urine and fecal elimination of excess iron in vivo. In addn. to significantly improved PK properties, rPR-DFO was well-tolerated in mice and no adverse side effects were noted in single high dose or multiple dose acute toxicity studies. The overall features of rPR-DFO as a promising system for iron chelation therapy can be attributed to a combination of the nanochelator's improved PK, favorable distribution to the liver, and ROS-induced dissocn. properties into constructs <6 nm for faster renal elimination. This ROS-responsive nanochelator design may serve as a promising alternative for safely prolonging the circulation of DFO and more rapidly eliminating iron chelates from the body in iron chelation therapy regimens requiring repeated dosing of nanochelators.
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    15. 15
      Willemen, N. G. A.; Hassan, S.; Gurian, M.; Li, J.; Allijn, I. E.; Shin, S. R.; Leijten, J. Oxygen-Releasing Biomaterials: Current Challenges and Future Applications. Trends Biotechnol. 2021, 39, 1144– 1159,  DOI: 10.1016/j.tibtech.2021.01.007
      15
      Oxygen-Releasing Biomaterials: Current Challenges and Future Applications
      Willemen, Niels G. A.; Hassan, Shabir; Gurian, Melvin; Li, Jinghang; Allijn, Iris E.; Shin, Su Ryon; Leijten, Jeroen
      Trends in Biotechnology (2021), 39 (11), 1144-1159CODEN: TRBIDM; ISSN:0167-7799. (Elsevier Ltd.)
      A review. Oxygen is essential for the survival, function, and fate of mammalian cells. Oxygen tension controls cellular behavior via metabolic programming, which in turn controls tissue regeneration, stem cell differentiation, drug metab., and numerous pathologies. Thus, oxygen-releasing biomaterials represent a novel and unique strategy to gain control over a variety of in vivo processes. Consequently, numerous oxygen-generating or carrying materials have been developed in recent years, which offer innovative solns. in the field of drug efficiency, regenerative medicine, and engineered living systems. In this review, we discuss the latest trends, highlight current challenges and solns., and provide a future perspective on the field of oxygen-releasing materials.
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    16. 16
      Giorgi, C.; Marchi, S.; Simoes, I. C. M.; Ren, Z.; Morciano, G.; Perrone, M.; Patalas-Krawczyk, P.; Borchard, S.; Jędrak, P.; Pierzynowska, K.; Szymański, J.; Wang, D. Q.; Portincasa, P.; Węgrzyn, G.; Zischka, H.; Dobrzyn, P.; Bonora, M.; Duszynski, J.; Rimessi, A.; Karkucinska-Wieckowska, A. Mitochondria and Reactive Oxygen Species in Aging and Age-Related Diseases. Int. Rev. Cell Mol. Biol. 2018, 340, 209– 344,  DOI: 10.1016/bs.ircmb.2018.05.006
      16
      Mitochondria and reactive oxygen species in aging and age-related diseases
      Giorgi, Carlotta; Marchi, Saverio; Simoes, Ines C. M.; Ren, Ziyu; Morciano, Giampaolo; Perrone, Mariasole; Patalas-Krawczyk, Paulina; Borchard, Sabine; Jedrak, Paulina; Pierzynowska, Karolina; Szymanski, Jedrzej; Wang, David Q.; Portincasa, Piero; Wegrzyn, Grzegorz; Zischka, Hans; Dobrzyn, Pawel; Bonora, Massimo; Duszynski, Jerzy; Rimessi, Alessandro; Karkucinska-Wieckowska, Agnieszka; Dobrzyn, Agnieszka; Szabadkai, Gyorgy; Zavan, Barbara; Oliveira, Paulo J.; Sardao, Vilma A.; Pinton, Paolo; Wieckowski, Mariusz R.
      International Review of Cell and Molecular Biology (2018), 340 (), 209-344CODEN: IRCMAH; ISSN:1937-6448. (Elsevier Inc.)
      A review. Aging has been linked to several degenerative processes that, through the accumula- tion of mol. and cellular damage, can progressively lead to cell dysfunction and organ failure. Human aging is linked with a higher risk for individuals to develop cancer, neurodegenerative, cardiovascular, and metabolic disorders. The understanding of the mol. basis of aging and assocd. diseases has been one major challenge of sci- entific research over the last decades. Mitochondria, the center of oxidative metab. and principal site of reactive oxygen species (ROS) prodn., are crucial both in health and in pathogenesis of many diseases. Redox signaling is important for the modulation of cell functions and several studies indicate a dual role for ROS in cell physiol. In fact, high concns. of ROS are pathogenic and can cause severe damage to cell and organelle membranes, DNA, and proteins. On the other hand, moderate amts. of ROS are essential for the maintenance of several biol. processes, including gene expression. In this review, we provide an update regarding the key roles of ROS-mitochondria cross talk in different fundamental physiol. or pathol. situations accompanying aging and highlighting that mitochondria!. ROS may be a decisive target in clin. practice.
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    17. 17
      Sies, H.; Belousov, Vv.; Chandel, N. S.; Davies, M. J.; Jones, D. P.; Mann, G. E.; Murphy, M. P.; Yamamoto, M.; Winterbourn, C. Defining Roles of Specific Reactive Oxygen Species (ROS) in Cell Biology and Physiology. Nat. Rev. Mol. Cell Biol. 2022, 23, 499– 515,  DOI: 10.1038/s41580-022-00456-z
      17
      Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology
      Sies, Helmut; Belousov, Vsevolod V.; Chandel, Navdeep S.; Davies, Michael J.; Jones, Dean P.; Mann, Giovanni E.; Murphy, Michael P.; Yamamoto, Masayuki; Winterbourn, Christine
      Nature Reviews Molecular Cell Biology (2022), 23 (7), 499-515CODEN: NRMCBP; ISSN:1471-0072. (Nature Portfolio)
      A review. Abstr.: 'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant mols. with vastly different properties and biol. functions that range from signaling to causing cell damage. Consequently, the description of oxidants needs to be chem. precise to translate research on their biol. effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues assocd. with identifying the physiol. roles of oxidants, focusing on H2O2 and O2.-. We also advocate for greater precision in measurement of H2O2, O2.- and other oxidants, along with more specific identification of their signaling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signaling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiol. O2 levels should be maintained in cell culture to better mimic in vivo redox reactions assocd. with specific cell types. Use of precise definitions and anal. tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biol.
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    18. 18
      Foret, M. K.; Lincoln, R.; do Carmo, S.; Cuello, A. C.; Cosa, G. Connecting the “Dots”: From Free Radical Lipid Autoxidation to Cell Pathology and Disease. Chem. Rev. 2020, 120, 12757– 12787,  DOI: 10.1021/acs.chemrev.0c00761
      18
      Connecting the "Dots": From Free Radical Lipid Autoxidation to Cell Pathology and Disease
      Foret, Morgan K.; Lincoln, Richard; Do Carmo, Sonia; Cuello, A. Claudio; Cosa, Gonzalo
      Chemical Reviews (Washington, DC, United States) (2020), 120 (23), 12757-12787CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Our understanding of lipid peroxidn. in biol. and medicine is rapidly evolving, as it is increasingly implicated in various diseases but also recognized as a key part of normal cell function, signaling, and death (ferroptosis). Not surprisingly, the root and consequences of lipid peroxidn. have garnered increasing attention from multiple disciplines in recent years. Here we "connect the dots" between the fundamental chem. underpinning the cascade reactions of lipid peroxidn. (enzymic or free radical), the reactive nature of the products formed (lipid-derived electrophiles), and the biol. targets and mechanisms assocd. with these products that culminate in cellular responses. We addnl. bring light to the use of highly sensitive, fluorescence-based methodologies. Stemming from the foundational concepts in chem. and biol., these methodologies enable visualizing and quantifying each reaction in the cascade in a cellular and ultimately tissue context, toward deciphering the connections between the chem. and physiol. of lipid peroxidn. The review offers a platform in which the chem. and biomedical research communities can access a comprehensive summary of fundamental concepts regarding lipid peroxidn., exptl. tools for the study of such processes, as well as the recent discoveries by leading investigators with an emphasis on significant open questions.
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    19. 19
      Panov, A. Perhydroxyl Radical (HO2•) as Inducer of the Isoprostane Lipid Peroxidation in Mitochondria. Mol. Biol. 2018, 52, 295– 305,  DOI: 10.1134/S0026893318020097
      19
      Perhydroxyl Radical (HO2•) as Inducer of the Isoprostane Lipid Peroxidation in Mitochondria
      Panov, A.
      Molecular Biology (Moscow, Russian Federation, English Edition) (2018), 52 (3), 295-305CODEN: MOLBBJ; ISSN:0026-8933. (Pleiades Publishing, Ltd.)
      A review. The nonenzymic isoprostane pathway of lipid peroxidn. of polyunsatd. fatty acids results in formation of products, termed isoprostanes, which have very large positional and stereo isomerism, possess various biol. activities, produce adducts with proteins, and thus contribute to pathogeneses of the agedependent diseases. However, it was unclear what mechanism drives this type of lipid autoxidn., and why the products have very large isomerism. We propose a mechanism when perhydroxyl radicals (HO2•) react with polyunsatd. fatty acids in the hydrophobic milieu of membranes. In the membrane HO2• initiates a chain of reactions with formation first H2O2, which undergoes homolytic fission producing two •OH radicals, thus very rapidly abstracting three H atoms from a polyunsatd. fatty acid. As a result, the HO2• mol. is converted to two mols. of water, and the mol. of a polyunsatd. fatty acid loses two double bonds, becomes highly unstable and undergoes peroxidn. and random intramol. re-arrangements causing a very large isomerism of the final products. The extremely high reactivity of •HO2 with polyunsatd. fatty acids is the cause of very subtle and slow accumulation of damages in the membrane and membrane assocd. proteins, even though the concn. of •HO2 relative to superoxide radical may be very low.
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    20. 20
      Soloviev, M.; Moskalenko, I.; Pliss, E. Quantum Chemical Evaluation of the Role of HO2· Radicals in the Kinetics of the Methyl Linoleate Oxidation in Micelles. React. Kinet., Mech. Catal. 2019, 127, 561– 581,  DOI: 10.1007/s11144-019-01613-w
      20
      Quantum chemical evaluation of the role of HO2· radicals in the kinetics of the methyl linoleate oxidation in micelles
      Soloviev, Mikhail; Moskalenko, Ivan; Pliss, Eugene
      Reaction Kinetics, Mechanisms and Catalysis (2019), 127 (2), 561-581CODEN: RKMCAJ; ISSN:1878-5190. (Springer)
      The process of lipid peroxidn. (LPO) plays an extremely important role in the human body due to the fact that its uncontrolled development can lead to oxidative stress and a no. of serious diseases. The traditional approach to the anal. of the mechanism and kinetics of LPO is based on the well-known ideas that emerged from the study of radical-chain oxidn. of hydrocarbons in a homogeneous medium. However, the distinctive feature of LPO is that this process is heterogeneous and the processes of diffusion of active intermediates between the aq. and hydrocarbon phases should play a significant role in it. In the present work, an attempt has been made to theor. est. the contribution of these processes to the oxidn. kinetics of model substances used in practice in the study of LPO. In the course of the calcns., a quantum chem. and kinetic anal. of the role of hydroperoxyl radical in the radical-chain mechanism of oxidn. of Me linoleate in micelles was carried out. The mol. dynamics method shows the important role of changing the dynamic rigidity of a hydrocarbon fragment of a chain during the formation of a peroxyl radical and hydroperoxyl group during the oxidn. of a substrate in a heterogeneous medium. Quantum chem. calcns. of the thermodn. of reactions involving HO2· radicals and the effects of their solvation made it possible to est. the kinetic consts. of the reaction rates. Using kinetic modeling, their relative contribution to the oxidn. kinetics was revealed. In this case, it is possible to explain a no. of anomalies assocd. with the oxidn. of polyunsatd. fatty acids and their esters in micelles compared with their oxidn. in a homogeneous hydrocarbon medium.
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    21. 21
      Harrison, K. A.; Haidasz, E. A.; Griesser, M.; Pratt, D. A. Inhibition of Hydrocarbon Autoxidation by Nitroxide-Catalyzed Cross-Dismutation of Hydroperoxyl and Alkylperoxyl Radicals. Chem. Sci. 2018, 9, 6068– 6079,  DOI: 10.1039/C8SC01575A
      21
      Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals
      Harrison, Kareem A.; Haidasz, Evan A.; Griesser, Markus; Pratt, Derek A.
      Chemical Science (2018), 9 (28), 6068-6079CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Nitroxides are putative intermediates in the accepted reaction mechanisms of the diarylamine and hindered amine antioxidants that are universally added to preserve synthetic and natural hydrocarbon-based materials. New methodol. which enables monitoring of hydrocarbon autoxidns. at low rates of radical generation has revealed that diarylnitroxides and hindered nitroxides are far better inhibitors of unsatd. hydrocarbon autoxidn. than their precursor amines, implying intervention of a different mechanism. Exptl. and computational investigations suggest that the nitroxides catalyze the cross-dismutation of hydroperoxyl and alkylperoxyl radicals to yield O2 and a hydroperoxide, thereby halting the autoxidn. chain reaction. The hydroperoxyl radicals - key players in hydrocarbon combustion, but essentially unknown in autoxidn. - are proposed to derive from a tunneling-enhanced intramol. (1,4-) hydrogen-atom transfer/elimination sequence from oxygenated radical addn. intermediates. These insights suggest that nitroxides are preferred additives for the protection of hydrocarbon-based materials from autoxidn. since they exhibit catalytic activity under conditions where their precursor amines are less effective and/or inefficiently converted to nitroxides in situ.
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    22. 22
      Guo, Y.; Baschieri, A.; Mollica, F.; Valgimigli, L.; Cedrowski, J.; Litwinienko, G.; Amorati, R. Hydrogen Atom Transfer from HOO. to Ortho-Quinones Explains the Antioxidant Activity of Polydopamine. Angew. Chem., Int. Ed. 2021, 60, 15220– 15224,  DOI: 10.1002/anie.202101033
      22
      Hydrogen Atom Transfer from HOO. to ortho-Quinones Explains the Antioxidant Activity of Polydopamine
      Guo, Yafang; Baschieri, Andrea; Mollica, Fabio; Valgimigli, Luca; Cedrowski, Jakub; Litwinienko, Grzegorz; Amorati, Riccardo
      Angewandte Chemie, International Edition (2021), 60 (28), 15220-15224CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well-known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO., typically formed during autoxidn. of lipid substrates) in the presence of hydroperoxyl radicals (HOO.). The key reaction explaining this peculiar antioxidant activity is the redn. of the ortho-quinone moieties present in PDA by the reaction with HOO.. This reaction occurs via a H-atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5-di-tert-butyl-1,2-benzoquinone) with HOO. (k=1.5x107 and 1.1x105 M-1 s-1 in PhCl and MeCN). The chem. disclosed herein is an important step to rationalize the redox-mediated bioactivity of melanins and of quinones.
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    23. 23
      Baschieri, A.; Valgimigli, L.; Gabbanini, S.; Dilabio, G. A.; Romero-Montalvo, E.; Amorati, R. Extremely Fast Hydrogen Atom Transfer between Nitroxides and HOO· Radicals and Implication for Catalytic Coantioxidant Systems. J. Am. Chem. Soc. 2018, 140, 10354– 10362,  DOI: 10.1021/jacs.8b06336
      23
      Extremely Fast Hydrogen Atom Transfer between Nitroxides and HOO· Radicals and Implication for Catalytic Coantioxidant Systems
      Baschieri, Andrea; Valgimigli, Luca; Gabbanini, Simone; DiLabio, Gino A.; Romero-Montalvo, Eduardo; Amorati, Riccardo
      Journal of the American Chemical Society (2018), 140 (32), 10354-10362CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We report a novel coantioxidant system based on TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) that, in biol. relevant model systems, rapidly converts chain-carrying alkylperoxyl radicals to HOO·. Extremely efficient quenching of HOO· by TEMPO blocks the oxidative chain. Rate consts. in chlorobenzene were measured to be 1.1 × 109 M-1 s-1 for the reductive reaction TEMPO + HOO· → TEMPOH + O2 and 5.0 × 107 M-1 s-1 for the oxidative reaction TEMPOH + HOO· → TEMPO + H2O2. These rate consts. are significantly higher than that assocd. with the reaction of HOO· with α-tocopherol, Nature's best lipid sol. antioxidant (k = 1.6 × 106 M-1 s-1). These data show that in the presence of ROO·-to-HOO· chain-transfer agents, which are common in lipophilic environments, the TEMPO/TEMPOH couple protects org. mols. from oxidn. by establishing an efficient reductive catalytic cycle. This catalytic cycle provides a new understanding of the efficacy of the antioxidant capability of TEMPO in nonaq. systems and its potential to act as a chemoprotective against radical damage.
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    24. 24
      Astete, C. E.; Dolliver, D.; Whaley, M.; Khachatryan, L.; Sabliov, C. M. Antioxidant Poly(Lactic-Co-Glycolic) Acid Nanoparticles Made with α-Tocopherol-Ascorbic Acid Surfactant. ACS Nano 2011, 5, 9313– 9325,  DOI: 10.1021/nn102845t
      24
      Antioxidant Poly(lactic-co-glycolic) Acid Nanoparticles Made with α-Tocopherol-Ascorbic Acid Surfactant
      Astete, Carlos E.; Dolliver, Debra; Whaley, Meocha; Khachatryan, Lavrent; Sabliov, Cristina M.
      ACS Nano (2011), 5 (12), 9313-9325CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The goal of the study was to synthesize a surfactant made of α-tocopherol (vitamin E) and ascorbic acid (vitamin C) of antioxidant properties dubbed as EC, and to use this surfactant to make poly(lactic-co-glycolic) acid (PLGA) nanoparticles. Self-assembled EC nanostructures and PLGA-EC nanoparticles were made by nanopptn., and their phys. properties (size, size distribution, morphol.) were studied at different salt concns., surfactant concns., and polymer/surfactant ratios. EC surfactant was shown to form self-assembled nanostructures in water with a size of 22 to 138 nm in the presence of sodium chloride, or 12 to 31 nm when synthesis was carried out in sodium bicarbonate. Polymeric PLGA-EC nanoparticles presented a size of 90 to 126 nm for 40% to 120% mass ratio PLGA to surfactant. For the same mass ratios, the PLGA-Span80 formed particles measured 155 to 216 nm. Span 80 formed bilayers, whereas EC formed monolayers at the interfaces. PLGA-EC nanoparticles and EC showed antioxidant activity based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay measurements using UV and EPR techniques, antioxidant activity which is not characteristic to com. available Span80. The thiobarbituric acid reactive substances (TBARS) assay for lipid peroxidn. showed that PLGA nanoparticles with EC performed better as antioxidants than the EC nanoassembly or the free vitamin C. Nanoparticles were readily internalized by HepG2 cells and were localized in the cytoplasm. The newly synthesized EC surfactant was therefore found successful in forming uniform, small size polymeric nanoparticles of intrinsic antioxidant properties.
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    25. 25
      Jalilov, A. S.; Nilewski, L. G.; Berka, V.; Zhang, C.; Yakovenko, A. A.; Wu, G.; Kent, T. A.; Tsai, A. L.; Tour, J. M. Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic. ACS Nano 2017, 11, 2024– 2032,  DOI: 10.1021/acsnano.6b08211
      25
      Perylene Diimide as a Precise Graphene-like Superoxide Dismutase Mimetic
      Jalilov, Almaz S.; Nilewski, Lizanne G.; Berka, Vladimir; Zhang, Chenhao; Yakovenko, Andrey A.; Wu, Gang; Kent, Thomas A.; Tsai, Ah-Lim; Tour, James M.
      ACS Nano (2017), 11 (2), 2024-2032CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Here we show that the active portion of a graphitic nanoparticle can be mimicked by a perylene diimide (PDI) to explain the otherwise elusive biol. and electrocatalytic activity of the nanoparticle construct. Development of mol. analogs that mimic the antioxidant properties of oxidized graphenes, in this case the poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs), will afford important insights into the highly efficient activity of PEG-HCCs and their graphitic analogs. PEGylated perylene diimides (PEGn-PDI) serve as well-defined mol. analogs of PEG-HCCs and oxidized graphenes in general, and their antioxidant and superoxide dismutase-like (SOD-like) properties were studied. PEGn-PDIs have two reversible redn. peaks which are more pos. than the oxidn. peak of superoxide (O2•-). This is similar to the redn. peak of the HCCs. Thus, as with PEG-HCCs, PEGn-PDIs are also strong single-electron oxidants of O2•-. Furthermore, reduced PEGn-PDI, PEGn-PDI•- in the presence of protons, was shown to reduce O2•- to H2O2 to complete the catalytic cycle in this SOD analog. The kinetics of the conversion of O2•- to O2 by PEG8-PDI was measured using freeze-trap EPR expts. to provide a turnover no. of 133 s-1, the similarity in kinetics further supports that PEG8-PDI is a true SOD mimetic. Finally, PDIs can be used as catalysts in the electrochem. oxygen redn. reaction in water, which proceeds by a two-electron process with the prodn. of H2O2, mimicking graphene oxide nanoparticles that are otherwise difficult to study spectroscopically.
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    26. 26
      Huang, B.; Mao, L.; Shi, X.; Yang, H. B. Recent Advances and Perspectives on Supramolecular Radical Cages. Chem. Sci. 2021, 12, 13648– 13663,  DOI: 10.1039/D1SC01618K
      26
      Recent advances and perspectives on supramolecular radical cages
      Huang, Bin; Mao, Lijun; Shi, Xueliang; Yang, Hai-Bo
      Chemical Science (2021), 12 (41), 13648-13663CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      A review. Supramol. radical chem. has been emerging as a cutting-edge interdisciplinary field of traditional supramol. chem. and radical chem. in recent years. The purpose of such a fundamental research field is to combine traditional supramol. chem. and radical chem. together, and take the benefit of both to eventually create new mols. and materials. Recently, supramol. radical cages have been becoming one of the most frontier and challenging research focuses in the field of supramol. chem. In this Perspective, we give a brief introduction to org. radical chem., supramol. chem., and the emerging supramol. radical chem. along with their history and application. Subsequently, we turn to the main part of this topic: supramol. radical cages. The design and synthesis of supramol. cages consisting of redox-active building blocks and radical centers are summarized. The host-guest interactions between supramol. (radical) cages and org. radicals are also surveyed. Some interesting properties and applications of supramol. radical cages such as their unique spin-spin interactions and intriguing confinement effects in radical-mediated/catalyzed reactions are comprehensively discussed and highlighted in the main text. The purpose of this Perspective is to help students and researchers understand the development of supramol. radical cages, and potentially to stimulate innovation and creativity and infuse new energy into the fields of traditional supramol. chem. and radical chem. as well as supramol. radical chem.
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    27. 27
      Tang, B.; Zhao, J.; Xu, J. F.; Zhang, X. Tuning the Stability of Organic Radicals: From Covalent Approaches to Non-Covalent Approaches. Chem. Sci. 2020, 11, 1192– 1204,  DOI: 10.1039/C9SC06143F
      27
      Tuning the stability of organic radicals: from covalent approaches to non-covalent approaches
      Tang, Bohan; Zhao, Jiantao; Xu, Jiang-Fei; Zhang, Xi
      Chemical Science (2020), 11 (5), 1192-1204CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      A review. Org. radicals are important species with single electrons. Because of their open-shell structure, they are widely used in functional materials, such as spin probes, magnetic materials and optoelectronic materials. Owing to the high reactivity of single electrons, they often serve as a key intermediate in org. synthesis. Therefore, tuning the stability of radicals is crucial for their functions. Herein, we summarize covalent and non-covalent approaches to tune the stability of org. radicals through steric effects and tuning the delocalization of spin d. Covalent approaches can tune the stability of radicals effectively and non-covalent approaches benefit from dynamicity and reversibility. It is anticipated that the further development of covalent and non-covalent approaches, as well as the interplay between them, may push the fields forward by enriching new radical materials and radical mediated reactions.
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    28. 28
      Shilovskikh, V. V.; Timralieva, A. A.; Belogub, E. V.; Konstantinova, E. A.; Kokorin, A. I.; Skorb, E. V. Radical Activity of Binary Melamine-Based Hydrogen-Bonded Self-Assemblies. Appl. Magn. Reson. 2020, 51, 939– 949,  DOI: 10.1007/s00723-020-01254-6
      28
      Radical Activity of Binary Melamine-Based Hydrogen-Bonded Self-Assemblies
      Shilovskikh, Vladimir V.; Timralieva, Alexandra A.; Belogub, Elena V.; Konstantinova, Elizaveta A.; Kokorin, Alexander I.; Skorb, Ekaterina V.
      Applied Magnetic Resonance (2020), 51 (9-10), 939-949CODEN: APMREI; ISSN:0937-9347. (Springer-Verlag GmbH)
      Melamine cyanurate and melamine barbiturate self-assembled materials were prepd. and studied by the ESR spectroscopy, optical and SEM, X-ray powder diffraction (XRD). Both optical and electron microscopy show the formation of microscale cryst. particles possessing complex layered structures with a highly stable appearance. Both assemblies tend to form twinned crystals, which in the barbiturate case leads to multiple twinning in every particle. Optical microscopy shows high anisotropy and birefringence of both materials. XRD data represent a high crystallinity of melamine barbiturate and much lower for melamine cyanurate. Studied materials reveal the ability to incorporate radicals that correlate with their crystal structure quality. It is attributed to the structure-dependent stabilization of active radical superoxide species in structure voids or defects. In the example of melamine barbiturate, it is shown that the no. of active paramagnetic centers increases at ca. 22% when a substance is irradiated with UV + Vis light. It reaches satn. in approx. 20 min, whereas only ca. 14% decrease was obsd. in a week.
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    29. 29
      Shilovskikh, V. V.; Timralieva, A. A.; Nesterov, P. V.; Novikov, A. S.; Sitnikov, P. A.; Konstantinova, E. A.; Kokorin, A. I.; Skorb, E. V. Melamine–Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material. Chem. – Eur. J. 2020, 26, 16603– 16610,  DOI: 10.1002/chem.202002947
      29
      Melamine-Barbiturate Supramolecular Assembly as a pH-Dependent Organic Radical Trap Material
      Shilovskikh, Vladimir V.; Timralieva, Alexandra A.; Nesterov, Pavel V.; Novikov, Alexander S.; Sitnikov, Petr A.; Konstantinova, Elizaveta A.; Kokorin, Alexander I.; Skorb, Ekaterina V.
      Chemistry - A European Journal (2020), 26 (70), 16603-16610CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In the last two decades, a large no. of self-assembled materials were synthesized and they have already found their way into large-scale industry and science. Hydrogen-bond-based supramol. adducts are found to have unique properties and to be perfect host structures for trapping target mols. or ions. Such chem. systems are believed to resemble living matter and can substitute a living cell in a no. of cases. Herein, a report on an org. material based on supramol. assembly of barbituric acid and melamine is presented. Surprisingly, the structure is found to host and stabilize radicals under mild conditions allowing its use for biol. applications. The no. of free radicals is found to be easily tuned by changing the pH of the environment and it increases when exposed to light up to a satn. level. We describe a prepn. method as well as stability properties of melamine-barbiturate self-assembly, potentiometric titrn., and hydrogen ions adsorption data and EPR spectra concerning the composite.
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    30. 30
      Ivatt, P. D.; Evans, M. J.; Lewis, A. C. Suppression of Surface Ozone by an Aerosol-Inhibited Photochemical Ozone Regime. Nat. Geosci. 2022, 15, 536– 540,  DOI: 10.1038/s41561-022-00972-9
      30
      Suppression of surface ozone by an aerosol-inhibited photochemical ozone regime
      Ivatt, Peter D.; Evans, Mathew J.; Lewis, Alastair C.
      Nature Geoscience (2022), 15 (7), 536-540CODEN: NGAEBU; ISSN:1752-0894. (Nature Portfolio)
      Atm. ozone (O3) is a pollutant produced through chem. chain reactions where volatile org. compds. (VOCs), carbon monoxide and methane are oxidized in the presence of oxides of nitrogen (NOx). For decades, the controlling chain termination step has been used to sep. regions into either 'NOx limited' (peroxyl-radical self-reactions dominate) or 'VOC limited' (hydroxyl radical (OH) + nitrogen dioxide (NO2) reaction dominates). The controlling regime would then guide policies for reducing emissions and so O3 concns. Using a chem. transport model, we show that a third 'aerosol inhibited' regime exists, where reactive uptake of hydroperoxyl radicals (HO2) onto aerosol particles dominates. In 1970, 2% of the Northern Hemisphere population lived in an aerosol-inhibited regime, but by 2014 this had increased to 21%; 60% more than lived in a VOC-limited regime. Aerosol-inhibited chem. suppressed surface O3 concns. in North America and Europe in the 1970s and is currently suppressing surface O3 over Asia. This third photochem. O3 regime leads to potential trade-off tensions between reducing particle pollution in Asia (a key current health policy and priority) and increasing surface O3, should O3 precursors emissions not be reduced in tandem.
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    31. 31
      Sena, L. A.; Chandel, N. S. Physiological Roles of Mitochondrial Reactive Oxygen Species. Mol. Cell 2012, 48, 158– 167,  DOI: 10.1016/j.molcel.2012.09.025
      31
      Physiological Roles of Mitochondrial Reactive Oxygen Species
      Sena, Laura A.; Chandel, Navdeep S.
      Molecular Cell (2012), 48 (2), 158-167CODEN: MOCEFL; ISSN:1097-2765. (Elsevier Inc.)
      A review. Historically, mitochondrial reactive oxygen species (mROS) were thought to exclusively cause cellular damage and lack a physiol. function. Accumulation of ROS and oxidative damage have been linked to multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. Thus, mROS were originally envisioned as a necessary evil of oxidative metab., a product of an imperfect system. Yet few biol. systems possess such flagrant imperfections, thanks to the persistent optimization of evolution, and it appears that oxidative metab. is no different. More and more evidence suggests that mROS are crit. for healthy cell function. In this Review, we discuss this evidence following some background on the generation and regulation of mROS.
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    32. 32
      Dröge, W. Free Radicals in the Physiological Control of Cell Function. Physiol. Rev. 2002, 82, 47– 95,  DOI: 10.1152/physrev.00018.2001
      32
      Free radicals in the physiological control of cell function
      Droge, Wulf
      Physiological Reviews (2002), 82 (1), 47-95CODEN: PHREA7; ISSN:0031-9333. (American Physiological Society)
      A review. At high concns., free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concns., however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis.". Higher organisms, however, have evolved the use of NO and ROS also as signaling mols. for other physiol. functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin prodn., and signal transduction from membrane receptors in various physiol. processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, resp. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amts. of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metab. An excessive and/or sustained increase in ROS prodn. has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addn., free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 yr ago by Harman (J Gerontol 11: 208-300, 1956). There is growing evidence that aging involves, in addn., progressive changes in free radical-mediated regulatory processes that result in altered gene expression.
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    33. 33
      Cedrowski, J.; Litwinienko, G.; Baschieri, A.; Amorati, R. Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer. Chem. – Eur. J. 2016, 22, 16441– 16445,  DOI: 10.1002/chem.201603722
      33
      Hydroperoxyl Radicals (HOO.): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer
      Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo
      Chemistry - A European Journal (2016), 22 (46), 16441-16445CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Hydroperoxyl (HOO.) and alkylperoxyl (ROO.) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analog of α-tocopherol (TOH), but HOO., unlike ROO., is able to regenerate TOH by a fast H-atom transfer: TO.+HOO.→TOH+O2. The kinetic solvent effect on the H-atom transfer from TOH to HOO. is much stronger than that obsd. for ROO. because noncovalent interactions with polar solvents (Solv···HOO.) destabilize the transition state.
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    34. 34
      Chong, Y.; Ge, C.; Fang, G.; Tian, X.; Ma, X.; Wen, T.; Wamer, W. G.; Chen, C.; Chai, Z.; Yin, J. J. Crossover between Anti- and Pro-Oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light. ACS Nano 2016, 10, 8690– 8699,  DOI: 10.1021/acsnano.6b04061
      34
      Crossover between Anti- and Pro-oxidant Activities of Graphene Quantum Dots in the Absence or Presence of Light
      Chong, Yu; Ge, Cuicui; Fang, Ge; Tian, Xin; Ma, Xiaochuan; Wen, Tao; Wamer, Wayne G.; Chen, Chunying; Chai, Zhifang; Yin, Jun-Jie
      ACS Nano (2016), 10 (9), 8690-8699CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Graphene quantum dots (GQDs), zero-dimensional carbon materials displaying excellent luminescence properties, show great promise for medical applications such as imaging, drug delivery, biosensors, and novel therapeutics. A deeper understanding of how the properties of GQDs interact with biol. systems is essential for these applications. Our work demonstrates that GQDs can efficiently scavenge a no. of free radicals and thereby protect cells against oxidative damage. However, upon exposure to blue light, GQDs exhibit significant phototoxicity through increasing intracellular reactive oxygen species (ROS) levels and reducing cell viability, attributable to the generation of free radicals under light excitation. We confirm that light-induced formation of ROS originates from the electron-hole pair and, more importantly, reveal that singlet oxygen is generated by photoexcited GQDs via both energy-transfer and electron-transfer pathways. Moreover, upon light excitation, GQDs accelerate the oxidn. of non-enzymic anti-oxidants and promote lipid peroxidn., contributing to the phototoxicity of GQDs. Our results reveal that GQDs can display both anti- and pro-oxidant activities, depending upon light exposure, which will be useful in guiding the safe application and development of potential anticancer/antibacterial applications for GQDs.
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    35. 35
      Li, Y.; Zhang, W.; Niu, J.; Chen, Y. Mechanism of Photogenerated Reactive Oxygen Species and Correlation with the Antibacterial Properties of Engineered Metal-Oxide Nanoparticles. ACS Nano 2012, 6, 5164– 5173,  DOI: 10.1021/nn300934k
      35
      Mechanism of Photogenerated Reactive Oxygen Species and Correlation with the Antibacterial Properties of Engineered Metal-Oxide Nanoparticles
      Li, Yang; Zhang, Wen; Niu, Junfeng; Chen, Yongsheng
      ACS Nano (2012), 6 (6), 5164-5173CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Oxidative stress induced by reactive oxygen species (ROS) is one of the most important antibacterial mechanisms of engineered nanoparticles (NPs). To elucidate the ROS generation mechanisms, we investigated the ROS prodn. kinetics of seven selected metal-oxide NPs and their bulk counterparts under UV irradn. (365 nm). The results show that different metal oxides had distinct photogenerated ROS kinetics. Particularly, TiO2 nanoparticles and ZnO nanoparticles generated three types of ROS (superoxide radical, hydroxyl radical, and singlet oxygen), whereas other metal oxides generated only one or two types or did not generate any type of ROS. Moreover, NPs yielded more ROS than their bulk counterparts likely due to larger surface areas of NPs providing more absorption sites for UV irradn. The ROS generation mechanism was elucidated by comparing the electronic structures (i.e., band edge energy levels) of the metal oxides with the redox potentials of various ROS generation, which correctly interpreted the ROS generation of most metal oxides. To develop a quant. relationship between oxidative stress and antibacterial activity of NPs, we examd. the viability of E. coli cells in aq. suspensions of NPs under UV irradn., and a linear correlation was found between the av. concn. of total ROS and the bacterial survival rates (R2 = 0.84). Although some NPs (i.e., ZnO and CuO nanoparticles) released toxic ions that partially contributed to their antibacterial activity, this correlation quant. linked ROS prodn. capability of NPs to their antibacterial activity as well as shed light on the applications of metal-oxide NPs as potential antibacterial agents.
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    36. 36
      Cilento, G.; Adam, W. From free radicals to electronically excited species. Free Radical Biol. Med. 1995, 19, 103– 114,  DOI: 10.1016/0891-5849(95)00002-F
      36
      From free radicals to electronically excited species
      Cilento, Giuseppe; Adam, Waldemar
      Free Radical Biology & Medicine (1995), 19 (1), 103-14CODEN: FRBMEH; ISSN:0891-5849. (Elsevier)
      A review with 86 refs. Biol./medicinally important compds., when metabolized, can generate free radicals from which electronically excited products, often in the triplet state, are generated. Peroxidases are particularly apt to catalyze such processes, which usually entail oxidns. by electron transfer. In the latter case, the chemiluminescence may derive from peroxy and alloxyl radicals or excited states derived from dioxetanes. Besides peroxidases, prostaglandin-H synthase and lipoxygenase may catalyze the formation of excited carbonyls. The pronounced similarity in the chem. behavior and reactivity of radicals and excited species derives in part from the bλradical nature of the latter. Usually in analyzing the biol. effects of xenobiotics, only radicals and/or reactive ground state products have been considered. However, in such processes the generation of excited species is possible, which should be tested for by direct and/or sensitized emission or by photochem. transformation.
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    37. 37
      Miyamoto, S.; Martinez, G. R.; Medeiros, M. H. G.; di Mascio, P. Singlet Molecular Oxygen Generated by Biological Hydroperoxides. J. Photochem. Photobiol. B 2014, 139, 24– 33,  DOI: 10.1016/j.jphotobiol.2014.03.028
      37
      Singlet molecular oxygen generated by biological hydroperoxides
      Miyamoto, Sayuri; Martinez, Glaucia R.; Medeiros, Marisa H. G.; Di Mascio, Paolo
      Journal of Photochemistry and Photobiology, B: Biology (2014), 139 (), 24-33CODEN: JPPBEG; ISSN:1011-1344. (Elsevier B.V.)
      A review. The chem. behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chem. generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the prodn. of excited carbonyl species and singlet mol. oxygen in the mechanism of generation of chemiluminescence in biol. system. In particular, attention has been focused on the potential generation of singlet mol. oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet mol. oxygen from reactions involving the decompn. of biol. relevant hydroperoxides, esp. from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chem. aspects related to the mechanism of singlet mol. oxygen generation from different biol. hydroperoxides.
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    38. 38
      Delchev, V. B.; Ivanova, I. P. Theoretical Study of the Excited-State Reaction Paths of the OH and NH Dissociation Processes in Barbituric Acid. Monatsh. Chem. 2012, 143, 1141– 1150,  DOI: 10.1007/s00706-012-0766-9
      38
      Theoretical study of the excited-state reaction paths of the OH and NH dissociation processes in barbituric acid
      Delchev, Vassil B.; Ivanova, Iva P.
      Monatshefte fuer Chemie (2012), 143 (8), 1141-1150CODEN: MOCMB7; ISSN:0026-9247. (SpringerWienNewYork)
      We studied the OH and NH dissocn. mechanisms of eight tautomers of barbituric acid via excited states. The theor. research was performed at the TD DFT level of theory (B3LYP). It was found that all mechanisms pass through the repulsive 1πσ* excited state whose excited-state reaction paths showed conical intersections S0-S1. Some OH dissocn. mechanisms showed barrierless 1πσ* reaction paths which indicate an ultrafast relaxation of the 1πσ* excited states to the ground state. The study of the NH dissocn. mechanisms revealed that almost all 1πσ* reaction paths show low energy barriers and min. before the conical intersections S0-S1.
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    39. 39
      Nesterov, P. V.; Shilovskikh, V. V.; Sokolov, A. D.; Gurzhiy, V. V.; Novikov, A. S.; Timralieva, A. A.; Belogub, Ev.; Kondratyuk, N. D.; Orekhov, N. D.; Skorb, E. V. Encapsulation of Rhodamine 6G Dye Molecules for Affecting Symmetry of Supramolecular Crystals of Melamine-Barbiturate. Symmetry 2021, 13, 1119,  DOI: 10.3390/sym13071119
      39
      Encapsulation of Rhodamine 6G Dye Molecules for Affecting Symmetry of Supramolecular Crystals of Melamine-Barbiturate
      Nesterov, Pavel V.; Shilovskikh, Vladimir V.; Sokolov, Alexander D.; Gurzhiy, Vladislav V.; Novikov, Alexander S.; Timralieva, Alexandra A.; Belogub, Elena V.; Kondratyuk, Nikolay D.; Orekhov, Nikita D.; Skorb, Ekaterina V.
      Symmetry (2021), 13 (7), 1119CODEN: SYMMAM; ISSN:2073-8994. (MDPI AG)
      Supramol. org. systems can be used as a host for the encapsulation of small org. mols. Here, we chose melamine barbiturate as a robust system capable of supramol. assembly and the Rhodamine 6G dye entrapment as a guest mol. The encapsulation of the dye was investigated by UV-visible spectroscopy, SEM and optical fluorescent microscopy while the insight into the crystal structure of the system was obtained by single crystal and powder XRD. For investigation of the system's properties on a mol. level, the DFT and Classical Mol. Dynamics methods were utilized. Surprisingly, both theor. and exptl. data show not only the successful encapsulation of Rhodamine 6G mols. inside the supramol. assembly, but also that inclusion of such mols. leads to the drastic improvement in the org. crystal shape. The melamine barbiturate in presence of the Rhodamine 6G mols. tend to form crystals with lesser degree of twinning and higher symmetry in shape than the ones without dye mols.
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    40. 40
      Orekhov, N.; Kondratyuk, N.; Logunov, M.; Timralieva, A.; Shilovskikh, V.; Skorb, E. V. Insights into the Early Stages of Melamine Cyanurate Nucleation from Aqueous Solution. Cryst. Growth Des. 2021, 21, 1984– 1992,  DOI: 10.1021/acs.cgd.0c01285
      40
      Insights into the Early Stages of Melamine Cyanurate Nucleation from Aqueous Solution
      Orekhov, Nikita; Kondratyuk, Nikolay; Logunov, Mikhail; Timralieva, Alexandra; Shilovskikh, Vladimir; Skorb, Ekaterina V.
      Crystal Growth & Design (2021), 21 (4), 1984-1992CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      From computational and exptl. approaches, mol.-level insights into melamine cyanurate (M-CA) self-assembly in aq. soln. are provided and corresponding mechanisms of aggregation identified. Small M-CA mol. complexes possibly are stabilized predominantly via arom. π-π-stacking rather than by formation of H bonds. Variation of the [M]/[CA] component concn. ratio results in a smooth change in the structure of the crit. nuclei from more disordered in the excess of M to more crystal-like in the excess of CA. This behavior can indicate that the process of M-CA nucleation in aq. solns. could be altered between classical and nonclassical mechanisms depending on the local [M]/[CA] concn. ratio, which could be prospective for the programmable design of functional supramol. materials.
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    41. 41
      Abdurahman, A.; Hele, T. J. H.; Gu, Q.; Zhang, J.; Peng, Q.; Zhang, M.; Friend, R. H.; Li, F.; Evans, E. W. Understanding the Luminescent Nature of Organic Radicals for Efficient Doublet Emitters and Pure-Red Light-Emitting Diodes. Nat. Mater. 2020, 19, 1224– 1229,  DOI: 10.1038/s41563-020-0705-9
      41
      Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes
      Abdurahman, Alim; Hele, Timothy J. H.; Gu, Qinying; Zhang, Jiangbin; Peng, Qiming; Zhang, Ming; Friend, Richard H.; Li, Feng; Evans, Emrys W.
      Nature Materials (2020), 19 (11), 1224-1229CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
      The doublet-spin nature of radical emitters is advantageous for applications in org. light-emitting diodes, as it avoids the formation of triplet excitons that limit the electroluminescence efficiency of non-radical emitters. However, radicals generally show low optical absorption and photoluminescence yields. Here we explain the poor optical properties of radicals based on alternant hydrocarbons, and establish design rules to increase the absorption and luminescence yields for donor-acceptor-type radicals. We show that non-alternant systems are necessary to lift the degeneracy of the lowest energy orbital excitations; moreover, intensity borrowing from an intense high-lying transition by the low-energy charge-transfer excitation enhances the oscillator strength of the emitter. We apply these rules to design tris(2,4,6-trichlorophenyl)methyl-pyridoindolyl derivs. with a high photoluminescence quantum yield (>90%). Org. light-emitting diodes based on these mols. showed a pure-red emission with an over 12% external quantum efficiency. These insights may be beneficial for the rational design and discovery of highly luminescent doublet emitters.
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    42. 42
      Bedard, L.; Young, M. J.; Hall, D.; Paul, T.; Ingold, K. U. Quantitative Studies on the Peroxidation of Human Low-Density Lipoprotein Initiated by Superoxide and by Charged and Neutral Alkylperoxyl Radicals. J. Am. Chem. Soc. 2001, 123, 12439– 12448,  DOI: 10.1021/ja011076d
      42
      Quantitative Studies on the Peroxidation of Human Low-Density Lipoprotein Initiated by Superoxide and by Charged and Neutral Alkylperoxyl Radicals
      Bedard, Leanne; Young, Mary Jane; Hall, David; Paul, Thomas; Ingold, K. U.
      Journal of the American Chemical Society (2001), 123 (50), 12439-12448CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Rates of peroxidn. of human LDL and rates of consumption of the LDL's α-tocopherol (TocH) have been measured at 37 °C. Peroxidn. was initiated by radicals generated in the aerated aq. phase at known rates by thermal decompn. of appropriate precursors: superoxide (O2•-/HOO•) from a hyponitrite and alkylperoxyls (ROO•, two pos. charged, one neg. charged and one neutral) from azo compds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidn. (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidn. was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-contg. LDL at pH's from 7.6 to 6.5 and peroxidn. was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidn. was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidn. rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiol. relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiol. important alkylperoxyls. Rates of LDL peroxidn. initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidn. of fresh LDL occurring via H-atom abstraction from TocH by HOO• to form the Toc• radical and termination by reaction of O2•- with Toc•, a process that occurs partly by addn. leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH.
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    43. 43
      Neese, F.; Wiley, J. The ORCA Program System. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2012, 2, 73– 78,  DOI: 10.1002/wcms.81
      43
      The ORCA program system
      Neese, Frank
      Wiley Interdisciplinary Reviews: Computational Molecular Science (2012), 2 (1), 73-78CODEN: WIRCAH; ISSN:1759-0884. (Wiley-Blackwell)
      A review. ORCA is a general-purpose quantum chem. program package that features virtually all modern electronic structure methods (d. functional theory, many-body perturbation and coupled cluster theories, and multireference and semiempirical methods). It is designed with the aim of generality, extendibility, efficiency, and user friendliness. Its main field of application is larger mols., transition metal complexes, and their spectroscopic properties. ORCA uses std. Gaussian basis functions and is fully parallelized. The article provides an overview of its current possibilities and documents its efficiency.
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    44. 44
      Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U.; Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient, Approximate and Parallel Hartree-Fock and Hybrid DFT Calculations. A ‘Chain-of-Spheres’ Algorithm for the Hartree-Fock Exchange. Chem. Phys. 2009, 356, 98– 109,  DOI: 10.1016/j.chemphys.2008.10.036
      44
      Efficient, approximate and parallel Hartree-Fock and hybrid DFT calculations. A 'chain-of-spheres' algorithm for the Hartree-Fock exchange
      Neese, Frank; Wennmohs, Frank; Hansen, Andreas; Becker, Ute
      Chemical Physics (2009), 356 (1-3), 98-109CODEN: CMPHC2; ISSN:0301-0104. (Elsevier B.V.)
      In this paper, the possibility is explored to speed up Hartree-Fock and hybrid d. functional calcns. by forming the Coulomb and exchange parts of the Fock matrix by different approxns. For the Coulomb part the previously introduced Split-RI-J variant of the well-known d. fitting' approxn. is used. The exchange part is formed by semi-numerical integration techniques that are closely related to Friesner's pioneering pseudo-spectral approach. Our potentially linear scaling realization of this algorithm is called the 'chain-of-spheres exchange' (COSX). A combination of semi-numerical integration and d. fitting is also proposed. Both Split-RI-J and COSX scale very well with the highest angular momentum in the basis sets. It is shown that for extended basis sets speed-ups of up to two orders of magnitude compared to traditional implementations can be obtained in this way. Total energies are reproduced with an av. error of <0.3 kcal/mol as detd. from extended test calcns. with various basis sets on a set of 26 mols. with 20-200 atoms and up to 2000 basis functions. Reaction energies agree to within 0.2 kcal/mol (Hartree-Fock) or 0.05 kcal/mol (hybrid DFT) with the canonical values. The COSX algorithm parallelizes with a speedup of 8.6 obsd. for 10 processes. Min. energy geometries differ by less than 0.3 pm in the bond distances and 0.5° in the bond angles from their canonical values. These developments enable highly efficient and accurate SCF calcns. including nonlocal Hartree-Fock exchange for large mols. In combination with the RI-MP2 method and large basis sets, second-order many body perturbation energies can be obtained for medium sized mols. with unprecedented efficiency. The algorithms are implemented into the ORCA electronic structure system.
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    45. 45
      Neese, F. An Improvement of the Resolution of the Identity Approximation for the Formation of the Coulomb Matrix. J. Comput. Chem. 2003, 24, 1740– 1747,  DOI: 10.1002/jcc.10318
      45
      An improvement of the resolution of the identity approximation for the formation of the Coulomb matrix
      Neese, Frank
      Journal of Computational Chemistry (2003), 24 (14), 1740-1747CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
      A straightforward modification of the resoln. of the identity (RI) approxn. to the Coulomb interaction is described. In the limit of basis sets that are dominated by high angular momentum functions the obsd. speedups in realistic test systems reach a factor of 2 compared to the std. RI algorithm, and a factor of up to 300 compared to the std. algorithm to form the Coulomb matrix. More moderate savings on the order of 0-20% are obtained for the more commonly used smaller basis sets. A series of test calcns. is reported to illustrate the efficiency of the algorithm.
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    46. 46
      Berendsen, H.J.C.; van der Spoel, D.; van Drunen, R. GROMACS: A message-passing parallel molecular dynamics implementation. Comput. Phys. Commun. 1995, 91, 43– 56,  DOI: 10.1016/0010-4655(95)00042-E
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      GROMACS: A message-passing parallel molecular dynamics implementation
      Berendsen, H. J. C.; van der Spoel, D.; van Drunen, R.
      Computer Physics Communications (1995), 91 (1-3), 43-56CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier)
      A parallel message-passing implementation of a mol. dynamics (MD) program that is useful for bio(macro)mols. in aq. environment is described. The software has been developed for a custom-designed 32-processor ring GROMACS (Groningen MAchine for Chem. Simulation) with communication to and from left and right neighbors, but can run on any parallel system onto which a a ring of processors can be mapped and which supports PVM-like block send and receive calls. The GROMACS software consists of a preprocessor, a parallel MD and energy minimization program that can use an arbitrary no. of processors (including one), an optional monitor, and several anal. tools. The programs are written in ANSI C and available by ftp (information: [email protected]). The functionality is based on the GROMOS (Groningen Mol. Simulation) package (van Gunsteren and Berendsen, 1987; BIOMOS B.V., Nijenborgh 4, 9747 AG Groningen). Conversion programs between GROMOS and GROMACS formats are included.The MD program can handle rectangular periodic boundary conditions with temp. and pressure scaling. The interactions that can be handled without modification are variable non-bonded pair interactions with Coulomb and Lennard-Jones or Buckingham potentials, using a twin-range cut-off based on charge groups, and fixed bonded interactions of either harmonic or constraint type for bonds and bond angles and either periodic or cosine power series interactions for dihedral angles. Special forces can be added to groups of particles (for non-equil. dynamics or for position restraining) or between particles (for distance restraints). The parallelism is based on particle decompn. Interprocessor communication is largely limited to position and force distribution over the ring once per time step.
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    47. 47
      Eastman, P.; Swails, J.; Chodera, J. D.; McGibbon, R. T.; Zhao, Y.; Beauchamp, K. A.; Wang, L. P.; Simmonett, A. C.; Harrigan, M. P.; Stern, C. D.; Wiewiora, R. P.; Brooks, B. R.; Pande, V. S. OpenMM 7: Rapid Development of High Performance Algorithms for Molecular Dynamics. PLoS Comput. Biol. 2017, 13, e1005659  DOI: 10.1371/journal.pcbi.1005659
      47
      OpenMM 7: Rapid development of high performance algorithms for molecular dynamics
      Eastman, Peter; Swails, Jason; Chodera, John D.; McGibbon, Robert T.; Zhao, Yutong; Beauchamp, Kyle A.; Wang, Lee-Ping; Simmonett, Andrew C.; Harrigan, Matthew P.; Stern, Chaya D.; Wiewiora, Rafal P.; Brooks, Bernard R.; Pande, Vijay S.
      PLoS Computational Biology (2017), 13 (7), e1005659/1-e1005659/17CODEN: PCBLBG; ISSN:1553-7358. (Public Library of Science)
      OpenMM is a mol. dynamics simulation toolkit with a unique focus on extensibility. It allows users to easily add new features, including forces with novel functional forms, new integration algorithms, and new simulation protocols. Those features automatically work on all supported hardware types (including both CPUs and GPUs) and perform well on all of them. In many cases they require minimal coding, just a math. description of the desired function. They also require no modification to OpenMM itself and can be distributed independently of OpenMM. This makes it an ideal tool for researchers developing new simulation methods, and also allows those new methods to be immediately available to the larger community.
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    48. 48
      Jorgensen, W. L.; Maxwell, D. S.; Tirado-Rives, J. Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J. Am. Chem. Soc. 1996, 118, 11225– 11236,  DOI: 10.1021/ja9621760
      48
      Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids
      Jorgensen, William L.; Maxwell, David S.; Tirado-Rives, Julian
      Journal of the American Chemical Society (1996), 118 (45), 11225-11236CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The parametrization and testing of the OPLS all-atom force field for org. mols. and peptides are described. Parameters for both torsional and nonbonded energetics have been derived, while the bond stretching and angle bending parameters have been adopted mostly from the AMBER all-atom force field. The torsional parameters were detd. by fitting to rotational energy profiles obtained from ab initio MO calcns. at the RHF/6-31G*//RHF/6-31G* level for more than 50 org. mols. and ions. The quality of the fits was high with av. errors for conformational energies of less than 0.2 kcal/mol. The force-field results for mol. structures are also demonstrated to closely match the ab initio predictions. The nonbonded parameters were developed in conjunction with Monte Carlo statistical mechanics simulations by computing thermodn. and structural properties for 34 pure org. liqs. including alkanes, alkenes, alcs., ethers, acetals, thiols, sulfides, disulfides, aldehydes, ketones, and amides. Av. errors in comparison with exptl. data are 2% for heats of vaporization and densities. The Monte Carlo simulations included sampling all internal and intermol. degrees of freedom. It is found that such non-polar and monofunctional systems do not show significant condensed-phase effects on internal energies in going from the gas phase to the pure liqs.
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    49. 49
      Jorgensen, W. L.; Tirado-Rives, J. Potential energy functions for atomic-level simulations of water and organic and biomolecular systems. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 6665– 6670,  DOI: 10.1073/pnas.0408037102
      49
      Potential energy functions for atomic-level simulations of water and organic and biomolecular systems
      Jorgensen, William L.; Tirado-Rives, Julian
      Proceedings of the National Academy of Sciences of the United States of America (2005), 102 (19), 6665-6670CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      A review. An overview is provided on the development and status of potential energy functions that are used in at.-level statistical mechanics and mol. dynamics simulations of water and of org. and biomol. systems. Some topics that are considered are the form of force fields, their parameterization and performance, simulations of org. liqs., computation of free energies of hydration, universal extension for org. mols., and choice of at. charges. The discussion of water models covers some history, performance issues, and special topics such as nuclear quantum effects.
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    50. 50
      Dodda, L. S.; Vilseck, J. Z.; Tirado-Rives, J.; Jorgensen, W. L. 1.14*CM1A-LBCC: Localized bond-charge corrected CM1A charges for condensed-phase simulations. J. Phys. Chem. B 2017, 121, 3864– 3870,  DOI: 10.1021/acs.jpcb.7b00272
      50
      1.14*CM1A-LBCC: Localized Bond-Charge Corrected CM1A Charges for Condensed-Phase Simulations
      Dodda, Leela S.; Vilseck, Jonah Z.; Tirado-Rives, Julian; Jorgensen, William L.
      Journal of Physical Chemistry B (2017), 121 (15), 3864-3870CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      The quality of the 1.14*CM1A and 1.20*CM5 charge models was evaluated for calcns. of free energies of hydration. For a set of 426 neutral mols., 1.14*CM1A and 1.20*CM5 yield MADs of 1.26 and 1.21 kcal/mol, resp. The 1.14*CM1A charges, which can be readily obtained for large systems, exhibit large deviations only for a subset of functional groups. The results for these cases were systematically improved using localized bond-charge corrections (LBCC) by which offsetting adjustments are made to the partial charges for atoms in specified bond types. Only 19 LBCCs were needed to yield 1.14*CM1A-LBCC charges that reduce the errors for the 426 ΔGhyd values to only 0.61 kcal/mol. The modified charge method was also tested in computation of heats of vaporization and densities for pure org. liqs., yielding av. errors of 1.40 kcal/mol and 0.024 g/cm3, similar to those for 1.14*CM1A.
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    51. 51
      Dodda, L. S.; De Vaca, I. C.; Tirado-Rives, J.; Jorgensen, W. L. LigParGen web server: An automatic OPLS-AA parameter generator for organic ligands. Nucleic Acids Res. 2017, 45, W331– W336,  DOI: 10.1093/nar/gkx312
      51
      LigParGen web server: an automatic OPLS-AA parameter generator for organic ligands
      Dodda, Leela S.; Cabeza de Vaca, Israel; Tirado-Rives, Julian; Jorgensen, William L.
      Nucleic Acids Research (2017), 45 (W1), W331-W336CODEN: NARHAD; ISSN:1362-4962. (Oxford University Press)
      The accurate calcn. of protein/nucleic acid- ligand interactions or condensed phase properties by force field-based methods require a precise description of the energetics of intermol. interactions. Despite the progress made in force fields, small mol. parameterization remains an open problem due to the magnitude of the chem. space; the most crit. issue is the estn. of a balanced set of at. charges with the ability to reproduce exptl. properties. The LigParGen web server provides an intuitive interface for generating OPLS-AA/1.14*CM1A(-LBCC) force field parameters for org. ligands, in the formats of commonly used mol. dynamics and Monte Carlo simulation packages. This server has high value for researchers interested in studying any phenomena based on intermol. interactions with ligands via mol. mechanics simulations.
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    52. 52
      Jorgensen, W. L.; Chandrasekhar, J.; Madura, J. D.; Impey, R. W.; Klein, M. L. Comparison of simple potential functions for simulating liquid water. J. Chem. Phys. 1983, 79, 926– 935,  DOI: 10.1063/1.445869
      52
      Comparison of simple potential functions for simulating liquid water
      Jorgensen, William L.; Chandrasekhar, Jayaraman; Madura, Jeffry D.; Impey, Roger W.; Klein, Michael L.
      Journal of Chemical Physics (1983), 79 (2), 926-35CODEN: JCPSA6; ISSN:0021-9606.
      Classical Monte Carlo simulations were carried out for liq. H2O in the NPT ensemble at 25° and 1 atm using 6 of the simpler intermol. potential functions for the dimer. Comparisons were made with exptl. thermodn. and structural data including the neutron diffraction results of Thiessen and Narten (1982). The computed densities and potential energies agree with expt. except for the original Bernal-Fowler model, which yields an 18% overest. of the d. and poor structural results. The discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons were made for the self-diffusion coeffs. obtained from mol. dynamics simulations.
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    53. 53
      Essmann, U.; Perera, L.; Berkowitz, M. L.; Darden, T.; Lee, H.; Pedersen, L. G. A smooth particle mesh Ewald method. J. Chem. Phys. 1995, 103, 8577– 8593,  DOI: 10.1063/1.470117
      53
      A smooth particle mesh Ewald method
      Essmann, Ulrich; Perera, Lalith; Berkowitz, Max L.; Darden, Tom; Lee, Hsing; Pedersen, Lee G.
      Journal of Chemical Physics (1995), 103 (19), 8577-93CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The previously developed particle mesh Ewald method is reformulated in terms of efficient B-spline interpolation of the structure factors. This reformulation allows a natural extension of the method to potentials of the form 1/rp with p ≥ 1. Furthermore, efficient calcn. of the virial tensor follows. Use of B-splines in the place of Lagrange interpolation leads to analytic gradients as well as a significant improvement in the accuracy. The authors demonstrate that arbitrary accuracy can be achieved, independent of system size N, at a cost that scales as N log(N). For biomol. systems with many thousands of atoms and this method permits the use of Ewald summation at a computational cost comparable to that of a simple truncation method of 10 Å or less.
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    54. 54
      Brehm, M.; Kirchner, B. TRAVIS-A free analyzer and visualizer for monte carlo and molecular dynamics trajectories. J. Chem. Inf. Model. 2011, 51, 2007– 2023,  DOI: 10.1021/ci200217w
      54
      TRAVIS - A Free Analyzer and Visualizer for Monte Carlo and Molecular Dynamics Trajectories
      Brehm, Martin; Kirchner, Barbara
      Journal of Chemical Information and Modeling (2011), 51 (8), 2007-2023CODEN: JCISD8; ISSN:1549-9596. (American Chemical Society)
      We present TRAVIS ("TRajectory Analyzer and VISualizer"), a free program package for analyzing and visualizing Monte Carlo and mol. dynamics trajectories. The aim of TRAVIS is to collect as many analyses as possible in one program, creating a powerful tool and making it unnecessary to use many different programs for evaluating simulations. This should greatly rationalize and simplify the work-flow of analyzing trajectories. TRAVIS is written in C++, open-source free-ware and licensed under the terms of the GNU General Public License (GPLv3). It is easy to install (platform independent, no external libraries) and easy to use. In this article, we present some of the algorithms that are implemented in TRAVIS - many of them widely known for a long time, but some of them also to appear in literature for the first time. All shown analyses only require a std. MD trajectory as input data.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c06510.

    • Additional animation for illustration of geometry optimization steps for barbituric acid and benzoate anion adduct, in which barbituric acid and benzoate anion in the starting geometry are spaced by 3 Å (MP4)

    • Additional figures for illustration of pathways of M and BA oxidation via oxygen; corresponding calculated Gibbs free energies of reactions and equilibrium constants; HAT from BA and M to hydroperoxyl and hydroxyl radicals; corresponding calculated Gibbs free energies of reactions; and XRD data of four M-B samples (PDF)


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