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Research Article
Fuel-Controlled Reassembly of Metal–Organic ArchitecturesClick to copy article linkArticle link copied!
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Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, U.K.
*E-mail: [email protected]
Abstract
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Many examples exist of biological self-assembled structures that restructure in response to external stimuli, then return to their previous state over a defined time scale, but most synthetic investigations so far have focused on systems that switch between states representing energetic minima upon stimulus application. Here we report an approach in which triphenylphosphine is used as a chemical fuel to maintain CuI-based self-assembled metallosupramolecular architectures for defined periods of time. This method was used to exert control over the threading and dethreading of the ring of a pseudorotaxane’s axle, as well as to direct the uptake and release of a guest from a metal–organic host. Management of the amount of fuel and catalyst added allowed for time-dependent regulation of product concentration.
Copyright © 2015 American Chemical Society
Synopsis
Catalyst-controlled oxidation of a ligand “fuel” allowed for metallosupramolecular structures to persist and function for defined periods of time.
Self-assembly allows for the construction of functional chemical systems with applications as diverse as catalysis, (1) gas storage, (2) molecular machinery, (3) and ion transport, (4) as well as being integral to the function of biological molecules such as proteins (5) and DNA. (6) Self-assembled complexes have been developed that can respond to stimuli such as light, (7) pH, (8) anions, (9) and electrical potential. (10) Strict self-assembly processes lead to the formation of products that are stable at equilibrium, whereby carefully designed building blocks come together to yield an energy-minimized structure. (11) In contrast, biological systems achieve greater complexity of structure and function by utilizing self-assembly in conjunction with the controlled reaction or “burning” of a reactive species or “fuel”, such as ATP, to maintain a system out of equilibrium. (12) The development of artificial chemical systems that can utilize a chemical fuel in such a way is an attractive goal because it would provide a platform for the development of new applications by providing temporal control: a sensor could be programmed to report on its analyte only when fuel was present and being consumed, or a receptor designed to bind or release a chemical signal only for the duration of fuel-burning. To date, few examples of such systems have been reported, with interest focused upon the macro- and mesoscopic scales and upon the use of biological building blocks. (13)
Here we build upon others’ recent successes (14) in demonstrating functional out-of-equilibrium systems by establishing a method that allows metal-templated supramolecular structures to reversibly rearrange during a time period when an added phosphine ligand “fuel” is undergoing catalytic “burning”. These structures can be designed to express different functions, such as rotaxane formation or guest binding, establishing our method as a platform for new applications based upon chronological control over metal-templated assembly.
Metal-templated self-assembly has proven to be a versatile method for the design of intricate supramolecular structures. (15) Copper(I) has seen wide use as a template (16) and was found to be suitable for the formation of complexes using subcomponent self-assembly, in which coordinative (N→Cu) and dynamic-covalent (C═N) linkages are constructed together. (17) The labile nature of copper(I) metal centers allows for facile ligand exchange, which is a desirable feature for the design of a fuel-controlled self-assembling system.
Pseudorotaxanes, together with other interlocked architectures, have been shown to have applications in areas as diverse as guest binding, (18) catalysis, (19) and artificial muscles. (20) Thus, a CuI-based pseudorotaxane, developed from principles established by the Leigh group, (21) was developed as a model system with which to investigate fuel-controlled self-assembly.
The combination of macrocycle 1 (22) with p-anisidine, 2-formylpyridine, and CuI led to the quantitative formation of pseudorotaxane 2 (Figure 1a). Full characterization data for 2 and all other new compounds are presented in the Supporting Information. CuI is known to form [CuN2P2]+ heteroleptic complexes preferentially when both nitrogen and phosphine ligands are present, as opposed to forming the corresponding homoleptic [CuN4]+ and [CuP4]+ complexes. (23) The addition of triphenylphosphine (PPh3) to pseudorotaxane 2 resulted in the selective displacement of bipyridine 1 to generate the heteroleptic phosphine complex 3 (Figure 1a).
Figure 1
Figure 1. Preparation of a pseudorotaxane, and its time-dependent disassembly and reassembly. (a) Synthetic scheme for the formation of 2 from p-anisidine, 2-formylpyridine, and macrocycle 1, and its subsequent conversion to 3 via addition of PPh3. (b) Structure of oxo-transfer catalyst (ReCat) used to oxidize PPh3. (c) Addition of PPh3 to 2 led to the formation of 3. Upon complete oxidation of PPh3, pseudorotaxane 2 reforms. (d) Reaction progress over time, monitored by UV–vis spectroscopy. Each arrow indicates a point at which 2 equiv of PPh3 per CuI were added. (e) Plot showing the linear increase in initial rate with increasing concentration of ReCat; points represent the averages of three runs, with error bars providing ESDs between runs.
The oxidation of phosphines is thermodynamically favorable, (24) and we hypothesized that if conditions could be developed that led to the oxidation of PPh3 to triphenylphosphine oxide (OPPh3), while leaving the components of 2 intact, PPh3 could be used as a chemical fuel to control the conversion between 2 and 3. The addition of excess of PPh3 would bring about the conversion of 2 into 3, the PPh3 would then be oxidized over a set time and, as OPPh3 is a poor ligand for copper(I), the oxidation of all PPh3 would lead to the destruction of 3, and the reformation of 2 as the system re-equilibrates. The established redox chemistry of aryl phosphines would therefore enable temporal control to be exerted over a metal–organic system via the maintenance of a transient species, moving synthetic supramolecular chemistry closer toward the complexity that has evolved in the biological sphere.
PPh3 is known to be slow to react with dioxygen, and to gain in oxidative stability once bound to a metal center. (24) Unsurprisingly, 3 was found to be air-stable; no reaction was observed between 3 and pyridine N-oxide in solution or the solid state over a period of several weeks. An oxo-transfer catalyst was therefore added to the reaction mixture in order to facilitate the oxidation of PPh3. The catalyst chosen for this purpose was ReCat (Figure 1b), which has been shown by Abu-Omar and co-workers to efficiently transfer oxygen from pyridine N-oxides to PPh3. (25) ReCat has several benefits, including rapid oxidation of PPh3 under ambient conditions (the reaction has a second order rate constant >106 L mol–1 s–1 at 293 K), (25) activity in a variety of solvents, and varying reaction rates depending on the pyridine N-oxide derivative used as the terminal oxidant.
To investigate the fuel-controlled conversion between 2 and 3, 2 (1 μmol) was dissolved in 1:1 acetonitrile/dichloromethane (0.5 mL). Upon addition of ReCat (5 mol %) and pyridine N-oxide (20 equiv) to this solution, there was no observable color change. NMR, MS, and UV–vis spectroscopy confirmed that 2 remained stable under these conditions. Upon addition of PPh3 (2 μmol) there was a rapid color change from opaque brown to clear yellow, characteristic of the formation of 3, which was confirmed by 1H NMR, mass spectrometry, and UV–vis spectroscopy. A single broad resonance corresponding to PPh3 was observed in the 31P NMR spectrum. The solution regained the dark brown color associated with 2 (Movie 1, Supporting Information) over the course of 30 s; 1H NMR analysis confirmed that this color change corresponded to the regeneration of 2 (Supporting Information, Figure S13). Further addition of PPh3 (2 μmol) caused the 1H NMR signals of 2 to disappear and those of 3 to reappear. NMR spectra also reflected the consumption of pyridine N-oxide and the production of pyridine and OPPh3. The signals for 2 progressively reappeared and those of 3 disappeared over time. UV–vis spectroscopy also provided insight into processes occurring in the reaction mixture: an increase in absorption at 340 nm was observed following the addition of PPh3 (2 equiv) to a solution of 2, assigned to the MLCT band of 3. The intensity of this absorption decayed over time as PPh3 was consumed by the oxidation reaction and 2 was reformed (Figure 1d). It was possible to perform six fuel additions to the solution before the process became difficult to follow due to the increasing concentration of OPPh3, the intensity of the signals of which obscured the other signals in both UV–vis and NMR spectra.
The rate of fuel burning could be controlled by the amount of catalyst added, with a linear relationship observed between the initial rate of the decay of 3 and catalyst concentration observed using UV–vis spectroscopy (Figure 1e). The system shown in Figure 1 thus establishes the ability to control self-assembly of 2 using a chemical fuel, although no function is achieved beyond the threading and dethreading of a pesudorotaxane.
Chemical fuels are utilized in natural systems to achieve functional ends, such as for controlling the uptake and reactivity of guests. An example of this is the ATP-regulated folding of guest proteins within chaperonins such as GroEL, where the binding of ATP within the chaperone’s cavity changes its structure and blocks the binding of substrates, ejecting them postfolding. (26) The hydrolysis of the ATP to ADP then allows for the chaperone to regain its shape and facilitate further folding events. (26) We envisaged that the dynamic system described above would allow us to build upon the well-developed foundations of static host–guest systems, to enable a guest to be released when fuel was present and rebound once the fuel was consumed; i.e., PPh3 would have a role analogous to ATP in the example described above. The new triangular Cu3L3 macrocycle 5 was thus prepared as a dynamic, self-assembling host for the fullerene C60. Macrocycle 5 formed when nickel(II)-porphyrin-containing diamine 4, 2-formylpyridine, and CuI were mixed in a 1:2:1 ratio (Figure 2a).
Figure 2
Figure 2. Uptake and release of C60 from 5. (a) Scheme depicting assembly of Cu3L3 triangle 5 upon mixing 4, 2-formylpyridine and Cu(MeCN)4OTf in DMSO, and its binding of C60. (b) Control of the disassembly of homoleptic 5 to heteroleptic 6, and its reassembly, with concomitant release and uptake of a C60 guest in a 1:1 mixture of CD3CN/DCM.
The binding of C60 by 5 was followed by NMR spectroscopy. Binding was observed both through shifts in the 1H signals of the porphyrin subunits of 5 upon addition of C60 and the appearance of a signal for the fullerene in the 13C NMR spectrum, similar to that seen for comparable host–guest systems (Supporting Information, Figures S17–18). (27) Binding was further confirmed by mass spectrometry experiments (Supporting Information, Figures S22–23). As the electronic absorption spectrum of 5 is dominated by the intense Soret bands of the porphyrin moieties at higher concentrations and the complex dissociates at higher dilutions, UV–vis absorption spectra (Supporting Information, Figure S14) did not allow for the characterization of 5 or for the quantification of its C60 affinity.
PPh3 thus served again as the system’s chemical fuel, disrupting the formation of 5 when present, and controlling the uptake and release of C60 (Figure 2b). Upon addition of PPh3 to a solution of 5, the brown color of the host–guest complex was observed to disappear, and the solution became red. NMR and mass spectra showed that the host–guest complex was no longer present, and new 1H NMR signals corresponding to heteroleptic dicopper(I) complex 6 were observed. As was observed in the case of the pseudorotaxane system shown in Figure 1, the presence of ReCat and pyridine N-oxide led the PPh3 fuel to be burned, in turn allowing the reformation of 5, which subsequently bound C60 once more. This process could also be repeated for multiple fuel addition cycles (Supporting Information, Figure S15).
The system of Figure 2 thus establishes a causal link between fuel consumption, reassembly, and the function of guest binding. Fuel is consumed in steady fashion until a threshold concentration is reached at which point a chemical event then occurs—herein, the dissassembly of a pseudorotaxane (Figure 1) or a triangular receptor (Figure 2). In biological systems, the triggered event may be used as a “reset” signal, to introduce more fuel and restart the cycle. This delay/triggered-reset behavior underpins the functioning of the biological clocks that govern such diverse phenomena as the cell cycle and circadian rhythms. (28)
The generation of a time delay is a useful property, which cannot be provided in a simple static self-assembling system. For example, addition of sufficient acid to protonate macrocycle 1 would lead to the disassembly of 2, which could be reversed by addition of a suitable base, with both steps requiring a manual signal input (i.e. the system acts as a binary switch). Our dynamic system for controlling the dethreading of 2 allows for the programming of the lifetime of the out-of-equilibrium state.
For a programmed time delay to be of use, the rate of fuel consumption must be matched to the desired delay time scale. In the case of ReCat-mediated phosphine oxidation, however, the oxidation of free PPh3 in solution occurs rapidly (t1/2 = 30 s under the conditions of Figure S1), (25) while oxidation was observed to slow upon metal coordination. We therefore sought an alternative oxo-transfer catalyst.
The alternate catalyst chosen for this purpose was MoCat (Figure 3b), a molybdenum-containing catalyst with a tetradentate salan ligand developed by White and co-workers. (29) This catalyst was chosen because (i) the rate of oxidation is influenced by the Hammett parameters of the substituents on the catalyst ligand, providing tunability; (ii) the catalyst uses DMSO as the source of oxygen to transfer to PPh3, simplifying the reaction conditions by allowing DMSO to be used as the reaction solvent and eliminating the need to add pyridine N-oxide; and (iii) most importantly for our purposes, the rate of oxidation with MoCat, with a first-order rate constant of 7.13 × 10–2 L mol–1 s–1 at 403 K, (29) is much slower than that of ReCat (first-order rate constant >106 L mol–1 s–1 at 293 K). (25)
Figure 3
Figure 3. Controlled conversion of 2 to 3 using MoCat. (a) Dethreading of macrocycle 1 from pseudorotaxane 2 upon addition of PPh3 and subsequent formation of OPPh3 using MoCat in DMSO. The excess of PPh3 must be consumed by the oxidation reaction before reformation of 2 can occur. (b) Structure of MoCat. (c) Partial 1H NMR spectra showing the decrease in concentration of PPh3 (green) over time and the increase in concentration of OPPh3 (red) upon heating 3 at 363 K with MoCat (40 mol %) in DMSO. (d) Plot of the concentrations of 2 (black) and OPPh3 (red) over time. Arrows indicate the points at which PPh3 (8 equiv) was added. The concentration of 2 remained constant at zero until the excess PPh3 had been consumed, at which point it began to increase.
To test the compatibility of MoCat with the CuI complexes of this study, MoCat (40 mol %) was added to a solution of 2 in DMSO 1 μM). No changes in the 1H NMR signals of either compound were observed after 48 h at 363 K, indicating that MoCat and 2 are stable in each others’ presence. No reaction was observed between 3 and DMSO over 48 h at 363 K in the absence of catalyst. The addition of PPh3 (2 equiv per CuI) to the reaction mixture resulted in an immediate color change of the solution from deep brown to light yellow, with 1H NMR analysis confirming the formation of 3. The solution remained unchanged when kept at room temperature, but upon heating to 363 K the color was seen to change to the dark brown of 2 over the course of several hours. NMR and MS experiments confirmed the reformation of 2 and the formation of OPPh3 (Figure 3c). As with ReCat, the conversion could be repeated following multiple additions of fuel to the system, with 12 cycles being possible with no notable decrease in the rate of oxidation of PPh3 by MoCat.
To investigate the ability of the PPh3 fuel to control the concentration of 2 over a prolonged period, excess PPh3 (8 equiv per CuI) was added to 2. The conversion to 3 proceeded cleanly, as before, but the concentration of 2 now remained at a steady state even as the concentration of OPPh3 grew. As the free PPh3 in solution was consumed, 3 remained stable, with 2 only being observed once there was no free PPh3 left in solution (Figure 3d). This system thus incorporates an effective time delay, with the lifetime of 3 within the system depending only upon the amount of fuel present and the rate at which it is consumed.
Conclusions
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The addition and oxidation of PPh3 has thus been used to regulate the timing of responses within complex metallosupramolecular systems: the threading and dethreading of a pseudorotaxane, and the uptake and release of a fullerene guest from a macrocyclic host. The rates of these processes could be controlled both through the choice and concentration of the oxo-transfer catalyst employed, as well as the amount of phosphine fuel present.
The above methods allow time-dependent control over guest binding and rotaxane formation and has the potential to be coupled to yet more complex responses, such as those exhibited by molecular machines. (30) The ability to incorporate time delays into complex molecular systems is of importance in the context of designing intricate responses, as highlighted by examples both in natural systems, such as the delicate orchestration of the myriad individual events of the cell cycle, (31) and in the artificial information-processing systems that make up digital computers, whose signals must be passed in the correct temporal order. (32) Future work will aim to utilize the temporal control demonstrated here in order to develop more complex applications within systems chemistry. (33)
Methods
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Fuel-Controlled Dethreading of 2 Using ReCat
2 (10 mg, 1 μmol) was dissolved in 1:1 CD3CN/CD2Cl2 (0.5 mL) in a NMR tube. Pyridine N-oxide (1.93 mg, 0.2 mmol) and ReCat (5 mol %) were added, and the solution was sonicated for 5 min. Triphenylphosphine (5.31 mg, 2 μmol) was added and the tube was shaken and sonicated to ensure complete mixing. The reaction was kept at 298 K and monitored by NMR until complete oxidation of the PPh3 had occurred, at which point a further 2 equiv of PPh3 was added. This process was repeated seven further times, beyond which the reaction became difficult to follow by NMR.
Fuel-Controlled Release of C60 from 5 using ReCat
C60⊂5 (4 mg, 1 μmol) was dissolved in 1:1 CD3CN/CD2Cl2 (0.5 mL) in a NMR tube. Pyridine N-oxide (1.93 mg, 0.2 mmol) and ReCat (5 mol %) were added, and the solution was sonicated for 5 min. Triphenylphosphine (5.31 mg, 2 μmol) was added and the tube was shaken and sonicated to ensure complete mixing. The reaction was kept at room temperature and monitored by NMR until complete oxidation of the PPh3 had occurred, at which point a further 2 equiv of PPh3 was added. This process was repeated seven further times, beyond which the reaction became difficult to follow by NMR.
Fuel-Controlled Dethreading of 2 Using MoCat
2 (10 mg, 10 μmol) was dissolved in DMSO-d6 (0.5 mL) in a NMR tube. MoCat (50 mol %) was added and the mixture was sonicated for 10 min. Triphenylphosphine (5.31 mg, 20 μmol) was added. The tube was heated at 363 K and the reaction process was monitored by measuring NMR spectra every 30 min.
Supporting Information
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscentsci.5b00279.
Synthetic procedures and spectroscopic data for all newly reported compounds; experimental procedures for the fuel-burning systems reported in Figures 1–3 (PDF)
Movie 1 (AVI)
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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
References
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- 6Watson, J. D.; Crick, F. H. C. Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid Nature 1953, 171 (4356) 737– 738 DOI: 10.1038/171737a0Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG2cXivVGktA%253D%253D&md5=66b78cf4b12c8c5ced56ff75a9468f35Molecular structure of nucleic acids. A structure for deoxyribose nucleic acidWatson, J. D.; Crick, F. H. C.Nature (London, United Kingdom) (1953), 171 (), 737-8CODEN: NATUAS; ISSN:0028-0836.W. and C. propose a new structure for the Na salt of deoxyribose nucleic acid. This structure, which loosely resembles Furberg's model No. 1 (C.A. 47, 9924g), has 2 helical polynucleotide chains each coiled around the same axis but whose sequence of atoms runs in opposite directions. The chains are held together by H-bonding between purine and pyrimidine bases, a purine of 1 chain bonded to a pyrimidine of the other. Full details will be published elsewhere.
- 7Han, M.; Michel, R.; He, B.; Chen, Y.-S.; Stalke, D.; John, M.; Clever, G. H. Light-Triggered Guest Uptake and Release by a Photochromic Coordination Cage Angew. Chem., Int. Ed. 2013, 52 (4) 1319– 1323 DOI: 10.1002/anie.201207373Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslKmsrrO&md5=bc159f4a3916e7df60ada9ab5e59d6c9Light-Triggered Guest Uptake and Release by a Photochromic Coordination CageHan, Muxin; Michel, Reent; He, Bice; Chen, Yu-Sheng; Stalke, Dietmar; John, Michael; Clever, Guido H.Angewandte Chemie, International Edition (2013), 52 (4), 1319-1323CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors have shown that a photochromic coordination cage, which quant. self-assembles from four ligands based on a dithienylethene photoswitch can be smoothly interconverted between a structurally flexible form open-ring form and a rigid form closed-ring form by irradn. with UV or white light, resp. The assocd. modulation of the affinity for anionic guests might find applications in fields such as supramol. catalysis, drug delivery and functional constructs that are based on the control by external stimuli such as switchable receptors and mol. machine.
- 8Busschaert, N.; Elmes, R. B. P.; Czech, D. D.; Wu, X.; Kirby, I. L.; Peck, E. M.; Hendzel, K. D.; Shaw, S. K.; Chan, B.; Smith, B. D.; Jolliffe, K. A.; Gale, P. A. Thiosquaramides: pH Switchable Anion Transporters Chem. Sci. 2014, 5 (9) 3617– 3626 DOI: 10.1039/C4SC01629GGoogle Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVOitbvF&md5=0dd7287935fa4e769a39d4e1456d7d5bThiosquaramides: pH switchable anion transportersBusschaert, Nathalie; Elmes, Robert B. P.; Czech, Dawid D.; Wu, Xin; Kirby, Isabelle L.; Peck, Evan M.; Hendzel, Kevin D.; Shaw, Scott K.; Chan, Bun; Smith, Bradley D.; Jolliffe, Katrina A.; Gale, Philip A.Chemical Science (2014), 5 (9), 3617-3626CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)The transport of anions across cellular membranes is an important biol. function governed by specialised proteins. In recent years, many small mols. have emerged that mimick the anion transport behavior of these proteins, but only a few of these synthetic mols. also display the gating/switching behavior seen in biol. systems. A small series of thiosquaramides was synthesized and their pH-dependent chloride binding and anion transport behavior was investigated using 1H NMR titrns., single crystal X-ray diffraction and a variety of vesicle-based techniques. Spectrophotometric titrns. and DFT calcns. revealed that the thiosquaramides are significantly more acidic than their oxosquaramide analogs, with pKa values between 4.0 and 9.0. This led to the observation that at pH 7.2 the anion transport ability of the thiosquaramides is fully switched OFF due to deprotonation of the receptor, but is completely switched ON at lower pH.
- 9Riddell, I. A.; Smulders, M. M. J.; Clegg, J. K.; Hristova, Y. R.; Breiner, B.; Thoburn, J. D.; Nitschke, J. R. Anion-Induced Reconstitution of a Self-assembling System to Express a Chloride-Binding Co10L15 Pentagonal Prism Nat. Chem. 2012, 4 (9) 751– 756 DOI: 10.1038/nchem.1407Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFCgs7jN&md5=7edf2577c8d380b17b2cd0775b88f5a1Anion-induced reconstitution of a self-assembling system to express a chloride-binding Co10L15 pentagonal prismRiddell, Imogen A.; Smulders, Maarten M. J.; Clegg, Jack K.; Hristova, Yana R.; Breiner, Boris; Thoburn, John D.; Nitschke, Jonathan R.Nature Chemistry (2012), 4 (9), 751-756CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Biochem. systems are adaptable, capable of reconstitution at all levels to achieve the functions assocd. with life. Synthetic chem. systems are more limited in their ability to reorganize to achieve new functions; they can reconfigure to bind an added substrate (template effect) or one binding event may modulate a receptor's affinity for a second substrate (allosteric effect). Here the authors describe a synthetic chem. system that is capable of structural reconstitution on receipt of one anionic signal (perchlorate) to create a tight binding pocket for another anion (chloride). A decanuclear cobalt(II) complex [Cl- ⊂ Co10L15](ClO4)19 (L = 6,6'-bis[(4-methylphenyl)iminomethyl]-3,3'-bipyridine) was prepd. by the reaction of p-toluidine and 6,6'-diformyl-3,3'-bipyridine and Co(ClO4)2, whereas a tetranuclear complex [Co4L6](OTf)8 results when Co(OTf)2 is used as the cobalt(II) source. The tetranuclear complex is converted to the decanuclear complex upon addn. of LiClO4. The decanuclear complex acts as a receptor for halides, N3-, OCN- and SCN-. The complex, barrel-like structure of the chloride receptor is templated by five perchlorate anions. This second-order templation phenomenon allows chem. networks to be envisaged that express more complex responses to chem. signals than is currently feasible.
- 10Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S. D.; Goddard, W. A.; Ho, C.-M.; Stoddart, J. F. Linear Artificial Molecular Muscles J. Am. Chem. Soc. 2005, 127 (27) 9745– 9759 DOI: 10.1021/ja051088pGoogle Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltV2nt78%253D&md5=932ec813923ded0ac0f59f1825e8f5bdLinear Artificial Molecular MusclesLiu, Yi; Flood, Amar H.; Bonvallet, Paul A.; Vignon, Scott A.; Northrop, Brian H.; Tseng, Hsian-Rong; Jeppesen, Jan O.; Huang, Tony J.; Brough, Branden; Baller, Marko; Magonov, Sergei; Solares, Santiago D.; Goddard, William A.; Ho, Chih-Ming; Stoddart, J. FraserJournal of the American Chemical Society (2005), 127 (27), 9745-9759CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two switchable, palindromically constituted bistable [3]rotaxanes have been designed and synthesized with a pair of mech. mobile rings encircling a single dumbbell. These designs are reminiscent of a "mol. muscle" for the purposes of amplifying and harnessing mol. mech. motions. The location of the two cyclobis(paraquat-p-phenylene) (CBPQT4+) rings can be controlled to be on either tetrathiafulvalene (TTF) or naphthalene (NP) stations, either chem. (1H NMR spectroscopy) or electrochem. (cyclic voltammetry), such that switching of inter-ring distances from 4.2 to 1.4 nm mimics the contraction and extension of skeletal muscle, albeit on a shorter length scale. Fast scan-rate cyclic voltammetry at low temps. reveals stepwise oxidns. and movements of one-half of the [3]rotaxane and then of the other, a process that appears to be concerted at room temp. The active form of the bistable [3]rotaxane bears disulfide tethers attached covalently to both of the CBPQT4+ ring components for the purpose of its self-assembly onto a gold surface. An array of flexible microcantilever beams, each coated on one side with a monolayer of 6 billion of the active bistable [3]rotaxane mols., undergoes controllable and reversible bending up and down when it is exposed to the synchronous addn. of aq. chem. oxidants and reductants. The beam bending is correlated with flexing of the surface-bound mol. muscles, whereas a monolayer of the dumbbell alone is inactive under the same conditions. This observation supports the hypothesis that the cumulative nanoscale movements within surface-bound "mol. muscles" can be harnessed to perform larger-scale mech. work.
- 11Lindsey, J. S. Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives: A Review New. J. Chem. 1991, 15, 153– 180Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXitValu70%253D&md5=ea2ac7c2790242ba600f08e8f4e4aa8cSelf-assembly in synthetic routes to molecular devices. Biological principles and chemical perspectives: a reviewLindsey, Jonathan S.New Journal of Chemistry (1991), 15 (2-3), 153-80CODEN: NJCHE5; ISSN:1144-0546.A review with many refs. summarizing the concepts, limitations, and paradigms of biol. self-assembly processes, then surveying covalent self-assembly processes in the synthesis of 3-dimensional mols. and ordered assemblies. Self-assembly as a soln. to the synthesis problems of mol. electronics is considered.
- 12(a) Mitchison, T.; Kirschner, M. Dynamic Instability of Microtubule Growth Nature 1984, 312 (5991) 237– 242 DOI: 10.1038/312237a0Google Scholar12ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhvF2jsQ%253D%253D&md5=2c8244aca07fd3b65f76da5580cf6c48Dynamic instability of microtubule growthMitchison, Tim; Kirschner, MarcNature (London, United Kingdom) (1984), 312 (5991), 237-42CODEN: NATUAS; ISSN:0028-0836.Microtubules placed in a tubulin soln. just about the steady-state concn. of 14 μM showed a steady increase in length with no change in no. of microtubules. At lower tubulin concns. (7.5 μM), the no. of microtubules decreased with time, whereas the mean length of microtubules still increased somewhat. Axonemes could nucleate growth of microtubules well below the steady-state concn. of tubulin. At steady state (14 μM tubulin), when the net polymer mass remained const., a steady increase in mean microtubule length still occurred, whereas the no. of microtubules decreased steadily. This was attributed to depolymn. of some microtubules, which provided tubulin monomers for growth of other microtubules. The transition of microtubules between growing and shrinking phases was evidently rare. Possibly growing microtubules have GTP-liganded caps, whereas shrinking ones do not. A new model for microtubule assembly is proposed based on these findings.(b) Flaherty, K. M.; DeLuca-Flaherty, C.; McKay, D. B. Three-Dimensional Structure of the ATPase Fragment of a 70K Heat-Shock Cognate Protein Nature 1990, 346 (6285) 623– 628 DOI: 10.1038/346623a0Google Scholar12bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXlsVOqtbc%253D&md5=4b5978279abd701d2f53253aa59b3d26Three-dimensional structure of the ATPase fragment of a 70k heat-shock cognate proteinFlaherty, Kevin M.; DeLuca-Flaherty, Camille; McKay, David B.Nature (London, United Kingdom) (1990), 346 (6285), 623-8CODEN: NATUAS; ISSN:0028-0836.The 3-dimensional structure of the N-terminal 44K ATPase fragment of the 70K bovine heat-shock cognate protein has been solved to a resoln. of 2.2 Å. The ATPase fragment has 2 structural lobes with a deep cleft between them; ATP binds at the base of the cleft. Surprisingly, the nucleotide-binding core of the ATPase fragment has a tertiary structure similar to that of hexokinase, although the remainder of the structures of the 2 proteins are completely dissimilar, suggesting that both the phosphotransferase mechanism and the substrate-induced conformational change intrinsic to the hexokinases may be used by the 70K heat shock-related proteins. Crystal structure parameters are reported.(c) Vale, R. D. The Molecular Motor Toolbox for Intracellular Transport Cell 2003, 112 (4) 467– 480 DOI: 10.1016/S0092-8674(03)00111-9Google Scholar12chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXhs1SnsLo%253D&md5=621a970c2349aba1d594dcf76f516e43The molecular motor toolbox for intracellular transportVale, Ronald D.Cell (Cambridge, MA, United States) (2003), 112 (4), 467-480CODEN: CELLB5; ISSN:0092-8674. (Cell Press)A review. Eukaryotic cells create internal order by using protein motors to transport mols. and organelles along cytoskeletal tracks. Recent genomic and functional studies suggest that 5 cargo-carrying motors emerged in primitive eukaryotes and have been widely used throughout evolution. The complexity of these "toolbox" motors expanded in higher eukaryotes through gene duplication, alternative splicing, and the addn. of assocd. subunits, which enabled new cargoes to be transported. Remarkably, fungi, parasites, plants, and animals have distinct subsets of toolbox motors in their genomes, suggesting an underlying diversity of strategies for intracellular transport.
- 13(a) Hermans, T. M.; Frauenrath, H.; Stellacci, F. Droplets Out of Equilibrium Science 2013, 341 (6143) 243– 244 DOI: 10.1126/science.1241793Google ScholarThere is no corresponding record for this reference.(b) Grzybowski, B. A.; Stone, H. A.; Whitesides, G. M. Dynamic Self-Assembly of Magnetized, Millimetre-Sized Objects Rotating at a Liquid-Air Interface Nature 2000, 405 (6790) 1033– 1036 DOI: 10.1038/35016528Google ScholarThere is no corresponding record for this reference.(c) Fialkowski, M.; Bishop, K. J. M.; Klajn, R.; Smoukov, S. K.; Campbell, C. J.; Grzybowski, B. A. Principles and Implementations of Dissipative (Dynamic) Self-Assembly J. Phys. Chem. B 2006, 110 (6) 2482– 2496 DOI: 10.1021/jp054153qGoogle Scholar13chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvVSqsw%253D%253D&md5=5cd81063fd8698ec8e0c7bf3963a1fa1Principles and Implementations of Dissipative (Dynamic) Self-AssemblyFialkowski, Marcin; Bishop, Kyle J. M.; Klajn, Rafal; Smoukov, Stoyan K.; Campbell, Christopher J.; Grzybowski, Bartosz A.Journal of Physical Chemistry B (2006), 110 (6), 2482-2496CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)A review. Dynamic self-assembly (DySA) processes occurring outside of thermodn. equil. underlie many forms of adaptive and intelligent behaviors in natural systems. Relatively little, however, is known about the principles that govern DySA and the ways in which it can be extended to artificial ensembles. This article discusses recent advances in both the theory and the practice of nonequil. self-assembly. It is argued that a union of ideas from thermodn. and dynamic systems' theory can provide a general description of DySA. In parallel, heuristic design rules can be used to construct DySA systems of increasing complexities based on a variety of suitable interactions/potentials on length scales from nanoscopic to macroscopic. Applications of these rules to MHD DySA are also discussed.(d) Weitz, M.; Kim, J.; Kapsner, K.; Winfree, E.; Franco, E.; Simmel, F. C. Diversity in the Dynamical Behaviour of a Compartmentalized Programmable Biochemical Oscillator Nat. Chem. 2014, 6 (4) 295– 302 DOI: 10.1038/nchem.1869Google Scholar13dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXisFOjtbs%253D&md5=bc290cb6326fadb156dcb85af3eb587fDiversity in the dynamical behaviour of a compartmentalized programmable biochemical oscillatorWeitz, Maximilian; Kim, Jongmin; Kapsner, Korbinian; Winfree, Erik; Franco, Elisa; Simmel, Friedrich C.Nature Chemistry (2014), 6 (4), 295-302CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)In vitro compartmentalization of biochem. reaction networks is a crucial step towards engineering artificial cell-scale devices and systems. At this scale the dynamics of mol. systems becomes stochastic, which introduces several engineering challenges and opportunities. Here we study a programmable transcriptional oscillator system that is compartmentalized into microemulsion droplets with vols. between 33 fl and 16 pl. Simultaneous measurement of large populations of droplets reveals major variations in the amplitude, frequency and damping of the oscillations. Variability increases for smaller droplets and depends on the operating point of the oscillator. Rather than reflecting the stochastic kinetics of the chem. reaction network itself, the variability can be attributed to the statistical variation of reactant concns. created during their partitioning into droplets. We anticipate that robustness to partitioning variability will be a crit. challenge for engineering cell-scale systems, and that highly parallel time-series acquisition from microemulsion droplets will become a key tool for characterization of stochastic circuit function.
- 14(a) Boekhoven, J.; Brizard, A. M.; Kowlgi, K. N. K.; Koper, G. J. M.; Eelkema, R.; van Esch, J. H. Dissipative Self-Assembly of a Molecular Gelator by Using a Chemical Fuel Angew. Chem., Int. Ed. 2010, 49 (28) 4825– 4828 DOI: 10.1002/anie.201001511Google Scholar14ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXotVCguro%253D&md5=2ae7a93948a9966b3ed0cbcb56d447fdDissipative Self-Assembly of a Molecular Gelator by Using a Chemical FuelBoekhoven, Job; Brizard, Aurelie M.; Kowlgi, Krishna N. K.; Koper, Ger J. M.; Eelkema, Rienk; van Esch, Jan H.Angewandte Chemie, International Edition (2010), 49 (28), 4825-4828, S4825/1-S4825/4CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We present a synthetic dissipative self-assembly fibrous network that uses chem. fuel as an energy source. A gelator precursor is converted into a gelator by reaction with a chem. fuel, thus leading to self-assembly. Hydrolysis of gelator leads to energy dissipation and disassembly of the formed structures.(b) Debnath, S.; Roy, S.; Ulijn, R. V. Peptide Nanofibers with Dynamic Instability through Nonequilibrium Biocatalytic Assembly J. Am. Chem. Soc. 2013, 135 (45) 16789– 16792 DOI: 10.1021/ja4086353Google Scholar14bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1KktLrL&md5=2428ddda2ec544c177fe562a4c60fa62Peptide Nanofibers with Dynamic Instability through Nonequilibrium Biocatalytic AssemblyDebnath, Sisir; Roy, Sangita; Ulijn, Rein V.Journal of the American Chemical Society (2013), 135 (45), 16789-16792CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We demonstrate the formation of supramol. peptide nanofibers that display dynamic instability; i.e., they are formed by competing assembly and disassembly reactions, where assembly is favored away from equil. The systems are based on competitive catalytic transacylation and hydrolysis, producing a self-assembling arom. peptide amphiphile from amino acid precursors that temporarily exceeds the crit. gelation concn., until the competing hydrolytic reaction takes over. Anal. by at. force microscopy shows consecutive nanofiber formation and shortening. The process results in macroscopically observable temporary hydrogelation, which may be repeated upon refueling the system with further addn. of the chem. activated amino acid precursor. Nonequil. nanostructures open up opportunities for mimicry of the behavior of dynamic gels found in natural systems and provide components for future adaptive nanotechnologies.(c) Dambenieks, A. K.; Vu, P. H. Q.; Fyles, T. M. Dissipative Assembly of a Membrane Transport System Chem. Sci. 2014, 5 (9) 3396– 3403 DOI: 10.1039/C4SC01258EGoogle Scholar14chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1amtr3M&md5=5047aa074337cb2395276a92596df01cDissipative assembly of a membrane transport systemDambenieks, A. K.; Vu, P. H. Q.; Fyles, T. M.Chemical Science (2014), 5 (9), 3396-3403CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A membrane system consisting of a transport-inactive thiol-terminated oligoester and a channel-forming amine-terminated thioester is subject to kinetic control though the provision of a chem. fuel. Intermol. thioester exchange occurs rapidly between the fuel and the inactive thiol to produce the channel-forming species. Spontaneous intramol. degrdn. of the active compd. with release of a lactam occurs more slowly to reform the inactive thiol. The system can cycle from transport inactive to active and back via injection of the fuel. Such behavior is consistent with dissipative assembly of the ion-channel function of the system.(d) Semenov, S. N.; Wong, A. S. Y.; van der Made, R. M.; Postma, S. G. J.; Groen, J.; van Roekel, H. W. H.; de Greef, T. F. A.; Huck, W. T. S. Rational Design of Functional and Tunable Oscillating Enzymatic Networks Nat. Chem. 2015, 7 (2) 160– 165 DOI: 10.1038/nchem.2142Google Scholar14dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmtFSgsQ%253D%253D&md5=e5010fdd61b6a845eb70077cfebb232fRational design of functional and tunable oscillating enzymatic networksSemenov, Sergey N.; Wong, Albert S. Y.; van der Made, R. Martijn; Postma, Sjoerd G. J.; Groen, Joost; van Roekel, Hendrik W. H.; de Greef, Tom F. A.; Huck, Wilhelm T. S.Nature Chemistry (2015), 7 (2), 160-165CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Life is sustained by complex systems operating far from equil. and consisting of a multitude of enzymic reaction networks. The operating principles of biol.'s regulatory networks are known, but the in vitro assembly of out-of-equil. enzymic reaction networks proved challenging, limiting the development of synthetic systems showing autonomous behavior. Here, the authors present a strategy for the rational design of programmable functional reaction networks that exhibit dynamic behavior. A network built around autoactivation and delayed neg. feedback of the enzyme trypsin is capable of producing sustained oscillating concns. of active trypsin for over 65 h. Other functions, such as amplification, analog-to-digital conversion and periodic control over equil. systems, were obtained by linking multiple network modules in microfluidic flow reactors. The methodol. developed here provides a general framework to construct dissipative, tunable and robust (bio)chem. reaction networks.(e) Ragazzon, G.; Baroncini, M.; Silvi, S.; Venturi, M.; Credi, A. Light-Powered Autonomous and Directional Molecular Motion of a Dissipative Self-assembling System Nat. Nanotechnol. 2014, 10 (1) 70– 75 DOI: 10.1038/nnano.2014.260Google ScholarThere is no corresponding record for this reference.(f) Cheng, C.; McGonigal, P. R.; Liu, W.-G.; Li, H.; Vermeulen, N. A.; Ke, C.; Frasconi, M.; Stern, C. L.; Goddard III, W. A.; Stoddart, J. F. Energetically Demanding Transport in a Supramolecular Assembly J. Am. Chem. Soc. 2014, 136 (42) 14702– 14705 DOI: 10.1021/ja508615fGoogle ScholarThere is no corresponding record for this reference.
- 15(a) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Supramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional Ensembles Chem. Rev. 2011, 111 (11) 6810– 6918 DOI: 10.1021/cr200077mGoogle Scholar15ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVOnsrbP&md5=720bcf4d887a36411c6382d3b50278ceSupramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional EnsemblesChakrabarty, Rajesh; Mukherjee, Partha Sarathi; Stang, Peter J.Chemical Reviews (Washington, DC, United States) (2011), 111 (11), 6810-6918CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. This review focuses on the journey of early coordination-driven self-assembly paradigms to more complex and discrete 2D and 3D supramol. ensembles over the past decade. The authors begin with a discussion of various approaches that have been developed by different groups to assemble finite supramol. architectures. The subsequent sections contain detailed discussions on the synthesis of discrete 2D and 3D systems and their functionalizations and applications.(b) Beves, J. E.; Blight, B. A.; Campbell, C. J.; Leigh, D. A.; McBurney, R. T. Strategies and Tactics for the Metal-Directed Synthesis of Rotaxanes, Knots, Catenanes, and Higher Order Links Angew. Chem., Int. Ed. 2011, 50 (40) 9260– 9327 DOI: 10.1002/anie.201007963Google Scholar15bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFylsrrL&md5=3378dd02bc055d958e42af9408a0eba5Strategies and Tactics for the Metal-Directed Synthesis of Rotaxanes, Knots, Catenanes, and Higher Order LinksBeves, Jonathon E.; Blight, Barry A.; Campbell, Christopher J.; Leigh, David A.; McBurney, Roy T.Angewandte Chemie, International Edition (2011), 50 (40), 9260-9327CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. More than a quarter of a century after the 1st metal template synthesis of a [2]catenane in Strasbourg, there now exists a plethora of strategies available for the construction of mech. bonded and entwined mol. level structures. Catenanes, rotaxanes, knots and Borromean rings have all been successfully accessed by methods in which metal ions play a pivotal role. Originally metal ions were used solely for their coordination chem.; acting either to gather and position the building blocks such that subsequent reactions generated the interlocked products or by being an integral part of the rings or stoppers of the interlocked assembly. Recently the role of the metal has evolved to encompass catalysis: the metal ions not only organize the building blocks in an entwined or threaded arrangement but also actively promote the reaction that covalently captures the interlocked structure. This Review outlines the diverse strategies that currently exist for forming mech. bonded mol. structures with metal ions and details the tactics that the chemist can use for creating cross-over points, maximizing the yield of interlocked over noninterlocked products, and the reactions-of-choice for the covalent capture of threaded and entwined intermediates.(c) Cook, T. R.; Stang, P. J. Recent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via Coordination Chem. Rev. 2015, 115, 7001– 7045 DOI: 10.1021/cr5005666Google Scholar15chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlsVGltL4%253D&md5=3d246d2007812392beb0d5e43113d7afRecent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via CoordinationCook, Timothy R.; Stang, Peter J.Chemical Reviews (Washington, DC, United States) (2015), 115 (15), 7001-7045CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review.
- 16Dietrich-Buchecker, C. O.; Sauvage, J.-P. A Synthetic Molecular Trefoil Knot Angew. Chem., Int. Ed. Engl. 1989, 28 (2) 189– 192 DOI: 10.1002/anie.198901891Google ScholarThere is no corresponding record for this reference.
- 17Nitschke, J. R. Construction, Substitution, and Sorting of Metallo-organic Structures via Subcomponent Self-Assembly Acc. Chem. Res. 2007, 40 (2) 103– 112 DOI: 10.1021/ar068185nGoogle Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtV2gt7jE&md5=3d5687d98ceec631838a8f8408205719Construction, Substitution, and Sorting of Metallo-organic Structures via Subcomponent Self-AssemblyNitschke, Jonathan R.Accounts of Chemical Research (2007), 40 (2), 103-112CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. Subcomponent self-assembly allows the construction of complex architectures from simple building blocks via formation of covalent bonds around metal templates. Since both covalent and coordinative bonds are formed reversibly, a wealth of rearrangement reactions is possible involving substitution at both intraligand (often C:N) and metal-ligand (N → metal) bonds. If the possibilities latent within a set of subcomponents and metal ions are understood, one may also select specific structures from among dynamic libraries of products. The parallel prepn. of structures from nonorthogonal mixts. of subcomponents is also possible, as is the direction of subcomponents to specific sites within product structures.
- 18Lee, S.; Chen, C.-H.; Flood, A. H. A Pentagonal Cyanostar Macrocycle with Cyanostilbene CH Donors Binds Anions and Forms Dialkylphosphate [3]Rotaxanes Nat. Chem. 2013, 5 (8) 704– 710 DOI: 10.1038/nchem.1668Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsFSgs7g%253D&md5=0dc7b420189c616d10b1e9a709f533f2A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanesLee, Semin; Chen, Chun-Hsing; Flood, Amar H.Nature Chemistry (2013), 5 (8), 704-710CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Since the discovery of crown ethers, macrocycles were recognized as powerful platforms for supramol. chem. Although their nos. and variations are now legion, macrocycles that are simple to make using high-yielding reactions in one pot and on the multigram scale are rare. Here the authors present such a discovery obtained during the creation of a C5-sym. cyanostilbene campestarene' macrocycle, cyanostar, that employs Knoevenagel condensations in the prepn. of its cyanostilbene repeat unit. In the solid state, cyanostars form π-stacked dimers constituted of chiral P and M enantiomers. The electropos. central cavity stabilizes anions with CH hydrogen-bonding units that are activated by electron-withdrawing cyano groups. In soln., the cyanostar shows high-affinity binding as 2:1 sandwich complexes, log β2 ≈ 12 and ΔG ≈ -70 kJ mol-1, of large anions (BF4-, ClO4- and PF6-) usually considered weakly coordinating. The cyanostar's size preference gave an unprecedented [3]rotaxane templated around a dialkylphosphate.
- 19Berná, J.; Alajarín, M.; Orenes, R.-A. Azodicarboxamides as Template Binding Motifs for the Building of Hydrogen-Bonded Molecular Shuttles J. Am. Chem. Soc. 2010, 132 (31) 10741– 10747 DOI: 10.1021/ja101151tGoogle Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXptFWkt7Y%253D&md5=85c89c7f2c6cfe08a81253d6a239a74fAzodicarboxamides as Template Binding Motifs for the Building of Hydrogen-Bonded Molecular ShuttlesBerna, Jose; Alajarin, Mateo; Orenes, Raul-AngelJournal of the American Chemical Society (2010), 132 (31), 10741-10747CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Azodicarboxamides (R2NCON=NCONR2) act as new templates for the assembly of unprecedented azo-functionalized hydrogen-bond-assembled [2]rotaxanes. Also, these binding sites can be reversibly and efficiently interconverted with their hydrazo forms through a hydrogenation-dehydrogenation strategy of the nitrogen-nitrogen bond. This novel chem. switchable control element was implemented in stimuli-responsive mol. shuttles that work through a reversible azo/hydrazo interconversion, producing large amplitude net positional changes with a good discrimination between the binding sites of the macrocycle in both states of the shuttle. These mol. shuttles are able to operate by two different mechanisms: in a discrete mode through two reversible and independent chem. events and, importantly, in a continuous regime through a catalyzed ester bond formation reaction in which the shuttle acts as an organocatalyst. In this latter, the incorporation of both states of the shuttle into this simple chem. reaction network promotes a dynamic translocation of the macrocycle between two nitrogen and carbon-based stations of the thread allowing an energetically uphill esterification process to take place.
- 20Bruns, C. J.; Stoddart, J. F. Rotaxane-Based Molecular Muscles Acc. Chem. Res. 2014, 47 (7) 2186– 2199 DOI: 10.1021/ar500138uGoogle Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXptVWrtbw%253D&md5=b751f692350fbc0675990ccf349d10ceRotaxane-Based Molecular MusclesBruns, Carson J.; Stoddart, J. FraserAccounts of Chemical Research (2014), 47 (7), 2186-2199CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. More than two decades of investigating the chem. of bistable mech. interlocked mols. (MIMs), such as rotaxanes and catenanes, has led to the advent of numerous mol. switches that express controlled translational or circumrotational movement on the nanoscale. Directed motion at this scale is an essential feature of many biomol. assemblies known as mol. machines, which carry out essential life-sustaining functions of the cell. It follows that the use of bistable MIMs as artificial mol. machines (AMMs) has been long anticipated. This objective is rarely achieved, however, because of challenges assocd. with coupling the directed motions of mech. switches with other systems on which they can perform work. A natural source of inspiration for designing AMMs is muscle tissue, since it is a material that relies on the hierarchical organization of mol. machines (myosin) and filaments (actin) to produce the force and motion that underpin locomotion, circulation, digestion, and many other essential life processes in humans and other animals. Muscle is characterized at both microscopic and macroscopic length scales by its ability to generate forces that vary the distance between two points at the expense of chem. energy. Artificial muscles that mimic this ability are highly sought for applications involving the transduction of mech. energy. Rotaxane-based mol. switches are excellent candidates for artificial muscles because their architectures intrinsically possess movable filamentous mol. components. In this Account, we describe (i) the different types of rotaxane "mol. muscle" architectures that express contractile and extensile motion, (ii) the mol. recognition motifs and corresponding stimuli that have been used to actuate them, and (iii) the progress made on integrating and scaling up these motions for potential applications. We identify three types of rotaxane muscles, namely, "daisy chain", "press", and "cage" rotaxanes, and discuss their mech. actuation driven by ions, pH, light, solvents, and redox stimuli. Different applications of these rotaxane-based mol. muscles are possible at various length scales. On a mol. level, they have been harnessed to create adjustable receptors and to control electronic communication between chem. species. On the mesoscale, they have been incorporated into artificial muscle materials that amplify their concerted motions and forces, making future applications at macroscopic length scales look feasible. We emphasize how rotaxanes constitute a remarkably versatile platform for directing force and motion, owing to the wide range of stimuli that can be used to actuate them and their diverse modes of mech. switching as dictated by the stereochem. of their mech. bonds, i.e., their mechanostereochem. We hope that this Account will serve as an exposition that sets the stage for new applications and materials that exploit the capabilities of rotaxanes to transduce mech. energy and help in paving the path going forward to genuine AMMs.
- 21Campbell, C. J.; Leigh, D. A.; Vitorica-Yrezabal, I. J.; Woltering, S. L. A Simple and Highly Effective Ligand System for the Copper(I)-Mediated Assembly of Rotaxanes Angew. Chem., Int. Ed. 2014, 53 (50) 13771– 13774 DOI: 10.1002/anie.201407817Google ScholarThere is no corresponding record for this reference.
- 22Berná, J.; Crowley, J. D.; Goldup, S. M.; Hänni, K. D.; Lee, A.-L.; Leigh, D. A. A Catalytic Palladium Active-Metal Template Pathway to [2]Rotaxanes Angew. Chem., Int. Ed. 2007, 46 (30) 5709– 5713 DOI: 10.1002/anie.200701678Google ScholarThere is no corresponding record for this reference.
- 23(a) Jardine, F. H.; Vohra, A. G.; Young, F. J. Copper(I) Ntrato and Nitrate Complexes J. Inorg. Nucl. Chem. 1971, 33 (9) 2941– 2945 DOI: 10.1016/0022-1902(71)80056-8Google Scholar23ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3MXltlKltro%253D&md5=b0349bce8138fcd76e7cb84ed6ae296aCopper(I) nitrato and nitrate complexesJardine, F. H.; Vohra, A. G.; Young, F. J.Journal of Inorganic and Nuclear Chemistry (1971), 33 (9), 2941-5CODEN: JINCAO; ISSN:0022-1902.Complexes of the type CuNO3(ZPh3)3 (Z = P, As, Sb) were prepd. and converted into CuNO3(ZPh3)(biL) (where biL = 1,10-phenanthroline, 2,2'-biquinoline, 2-(2-pyridyl)quinoline, and 2,2'-bipyridine). Under mild conditions CuNO3(PPh3)3 also forms the ionic complexes [Cu(PPh3)2(biL)]NO2 when reacted with these ligands. The tertiary arsine and stibine complexes can be converted into [Cu(biL)2]NO3 complexes by reacting them with excess bidentate ligand.(b) Kaeser, A.; Mohankumar, M.; Mohanraj, J.; Monti, F.; Holler, M.; Cid, J.-J.; Moudam, O.; Nierengarten, I.; Karmazin-Brelot, L.; Duhayon, C.; Delavaux-Nicot, B.; Armaroli, N.; Nierengarten, J.-F. Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine Ligands Inorg. Chem. 2013, 52 (20) 12140– 12151 DOI: 10.1021/ic4020042Google Scholar23bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGrs7nK&md5=940e12636184a3e4e12435e32a7ca043Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine LigandsKaeser, Adrien; Mohankumar, Meera; Mohanraj, John; Monti, Filippo; Holler, Michel; Cid, Juan-Jose; Moudam, Omar; Nierengarten, Iwona; Karmazin-Brelot, Lydia; Duhayon, Carine; Delavaux-Nicot, Beatrice; Armaroli, Nicola; Nierengarten, Jean-FrancoisInorganic Chemistry (2013), 52 (20), 12140-12151CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)Prepn. of [Cu(NN)(PP)]+ derivs. was systematically studied starting from two libraries of phenanthroline (NN) derivs. and bis-phosphine (PP) ligands, namely, (A) 1,10-phenanthroline (phen), neocuproine (2,9-dimethyl-1,10-phenanthroline, dmp), bathophenanthroline (4,7-diphenyl-1,10-phenanthroline, Bphen), 2,9-diphenethyl-1,10-phenanthroline (dpep), and 2,9-diphenyl-1,10-phenanthroline (dpp); (B) bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)benzene (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppFc), and bis[(2-diphenylphosphino)phenyl] ether (POP). Whatever the bis-phosphine ligand, stable heteroleptic [Cu(NN)(PP)]+ complexes were obtained from the 2,9-unsubstituted-1,10-phenanthroline ligands (phen and Bphen). By contrast, heteroleptic complexes obtained from dmp and dpep are stable in the solid state, but a dynamic ligand exchange reaction is systematically obsd. in soln., and the homoleptic/heteroleptic ratio is highly dependent on the bis-phosphine ligand. Detailed anal. revealed that the ligand exchange dynamic equil. is mainly influenced by the relative thermodn. stability of different possible complexes. Finally, in the case of dpp, only homoleptic complexes were obtained whatever the bis-phosphine ligand. Obviously, steric effects resulting from the presence of the bulky Ph rings on the dpp ligand destabilize the heteroleptic [Cu(NN)(PP)]+ complexes. In addn. to the remarkable thermodn. stability of [Cu(dpp)2]BF4, this neg. steric effect drives the dynamic complexation scenario toward almost exclusive formation of homoleptic [Cu-(NN)2]+ and [Cu-(PP)2]+ complexes. This work provides definitive rationalization of the stability of [Cu(NN)(PP)]+ complexes, marking the way for future developments in this field.
- 24Holm, R. H.; Donahue, J. P. A Thermodynamic Scale for Oxygen Atom Transfer Reactions Polyhedron 1993, 12 (6) 571– 589 DOI: 10.1016/S0277-5387(00)84972-4Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXisVajsb0%253D&md5=ebbec091c8107b77154d709487ba52c6A thermodynamic scale for oxygen atom transfer reactionsHolm, R. H.; Donahue, James P.Polyhedron (1993), 12 (6), 571-89CODEN: PLYHDE; ISSN:0277-5387.An extensive compilation of data on thermodn. (enthalpy and free energy) of oxo transfer reactions; bond energies were also considered,.
- 25McPherson, L. D.; Drees, M.; Khan, S. I.; Strassner, T.; Abu-Omar, M. M. Multielectron Atom Transfer Reactions of Perchlorate and Other Substrates Catalyzed by Rhenium Oxazoline and Thiazoline Complexes: Reaction Kinetics, Mechanisms, and Density Functional Theory Calculations Inorg. Chem. 2004, 43 (13) 4036– 4050 DOI: 10.1021/ic0498945Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXksVeisL0%253D&md5=d61c829a059ed43fff403b95fddc311aMultielectron Atom Transfer Reactions of Perchlorate and Other Substrates Catalyzed by Rhenium Oxazoline and Thiazoline Complexes: Reaction Kinetics, Mechanisms, and Density Functional Theory CalculationsMcPherson, Lee D.; Drees, Markus; Khan, Saeed I.; Strassner, Thomas; Abu-Omar, Mahdi M.Inorganic Chemistry (2004), 43 (13), 4036-4050CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)The title complexes, the Re(O)L2(Solv)+ complexes (L = hoz, 2-(2'-hydroxyphenyl)-2-oxazoline(-) or thoz, 2-(2'-hydroxyphenyl)-2-thiazoline(-); Solv = H2O or CH3CN), are effective catalysts for the following fundamental oxo transfer reaction between closed shell mols.: XO + Y → X + YO. Among suitable oxygen acceptors (Y's) are org. thioethers and phosphines, and among suitable oxo donors (XO's) are pyridine N-oxide (PyO), t-BuOOH, and inorg. oxyanions. One of the remarkable features of these catalysts is their high kinetic competency in effecting perchlorate redn. by pure atom transfer. Oxo transfer to rhenium(V) proceeds cleanly to afford the cationic dioxorhenium(VII) complex Re(O)2L2+ in a two-step mechanism, rapid substrate (XO) coordination to give the precursor adduct cis-ReV(O)(OX)L2+ followed by oxygen atom transfer (OAT) as the rate detg. step. Electronic variations with PyO derivs. demonstrated that electron-withdrawing substituents accelerate the rate of ReVII(O)2L2+ formation from the precursor adduct cis-ReV(O)(OX)L2+. The activation parameters for OAT with picoline N-oxide and chlorate have been measured; the entropic barrier to oxo transfer is essentially zero. The potential energy surface for the reaction of Re(O)(hoz)2(OH2)+ with PyO was defined, and all pertinent intermediates and transition states along the reaction pathway were located by d. functional theory (DFT) calcns. (B3LYP/6-31G*). In the second half of the catalytic cycle, Re(O)2L2+ reacts with oxygen acceptors (Y's) in second-order reactions with associative transition states. The rate of OAT to substrates spans a remarkable range of 0.1-106 L mol-1 s-1, and the substrate reactivity order is Ph3P > dialkyl sulfides > alkyl aryl sulfides > Ph2S ∼ DMSO, which demonstrates electrophilic oxo transfer. Competing deactivation and inhibitory pathways as well as their relevant kinetics are also reported.
- 26(a) Saibil, H. Chaperone Machines for Protein Folding, Unfolding and Disaggregation Nat. Rev. Mol. Cell Biol. 2013, 14 (10) 630– 642 DOI: 10.1038/nrm3658Google Scholar26ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVeisrvF&md5=67ad948e3c1bacac4fb0b21b4a84c077Chaperone machines for protein folding, unfolding and disaggregationSaibil, HelenNature Reviews Molecular Cell Biology (2013), 14 (10), 630-642CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)A review. Mol. chaperones are diverse families of multidomain proteins that have evolved to assist nascent proteins to reach their native fold, protect subunits from heat shock during the assembly of complexes, prevent protein aggregation or mediate targeted unfolding and disassembly. Their increased expression in response to stress is a key factor in the health of the cell and longevity of an organism. Unlike enzymes with their precise and finely tuned active sites, chaperones are heavy-duty mol. machines that operate on a wide range of substrates. The structural basis of their mechanism of action is being unraveled (in particular for the heat shock proteins HSP60, HSP70, HSP90 and HSP100) and typically involves massive displacements of 20-30 kDa domains over distances of 20-50 Å and rotations of up to 100°.(b) Xu, Z.; Horwich, A. L.; Sigler, P. B. The Crystal Structure of the Asymmetric GroEL-GroES-(ADP)7 Chaperonin Complex Nature 1997, 388 (6644) 741– 750 DOI: 10.1038/41944Google Scholar26bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXls1GltLo%253D&md5=34087d9539ef63ba088f6775aa5ee841The crystal structure of the asymmetric GroEL-GroES-(ADP)7 chaperonin complexXu, Zhaohui; Horwich, Arthur L.; Sigler, Paul B.Nature (London) (1997), 388 (6644), 741-750CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)Chaperonins assist protein folding with the consumption of ATP. They exist as multi-subunits protein assemblies comprising rings of subunits stacked back to back. In Escherichia coli, asym. intermediates of GroEL are formed with the co-chaperonin GroES and nucleotides bound only to one of the seven-subunit rings (the cis ring) and not to the opposing ring (the trans ring). The structure of the GroEL-GroES-(ADP)7 complex reveals how large en bloc movements of the cis ring's intermediate and apical domains enable bound GroES to stabilize a folding chamber with ADP confined to the cis ring. Elevation and twist of the apical domains double the vol. of the central cavity and bury hydrophobic peptide-binding residues in the interface with GroES, as well as between GroEL subunits, leaving a hydrophilic cavity lining that is conducive to protein folding. An inward tilt of the cis equatorial domain causes an outward tilt in the trans ring that opposes the binding of a second GroES. When combined with new functional results, this neg. allosteric mechanism suggests a model for an ATP-driven folding cycle that requires a double toroid.(c) Wang, J.; Chen, L. Domain Motions in GroEL upon Binding of an Oligopeptide J. Mol. Biol. 2003, 334 (3) 489– 499 DOI: 10.1016/j.jmb.2003.09.074Google ScholarThere is no corresponding record for this reference.
- 27(a) Kishi, N.; Li, Z.; Yoza, K.; Akita, M.; Yoshizawa, M. An M2L4 Molecular Capsule with an Anthracene Shell: Encapsulation of Large Guests up to 1 nm J. Am. Chem. Soc. 2011, 133 (30) 11438– 11441 DOI: 10.1021/ja2037029Google Scholar27ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXosFymu7w%253D&md5=7a863b7469695496769cff841905244cAn M2L4 Molecular Capsule with an Anthracene Shell: Encapsulation of Large Guests up to 1 nmKishi, Norifumi; Li, Zhiou; Yoza, Kenji; Akita, Munetaka; Yoshizawa, MichitoJournal of the American Chemical Society (2011), 133 (30), 11438-11441CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A new M2L4 mol. capsule with an arom. shell (I) was prepd. using two Pd(II) ions and four bisanthracene ligands. The self-assembled capsule possesses a cavity with a diam. of ∼1 nm that can encapsulate medium-sized spherical and planar mols. as well as a very large mol. (C60) in quant. yields. The encapsulated guests are fully segregated and shielded from the external environment by the large anthracene panels.(b) Wood, D. M.; Meng, W.; Ronson, T. K.; Stefankiewicz, A. R.; Sanders, J. K. M.; Nitschke, J. R. Guest-Induced Transformation of a Porphyrin-Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene Receptor Angew. Chem., Int. Ed. 2015, 54 (13) 3988– 3992 DOI: 10.1002/anie.201411985Google Scholar27bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksVCru7k%253D&md5=ea01ec3dc7f7a3139489b2a811024193Guest-Induced Transformation of a Porphyrin-Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene ReceptorWood, Daniel M.; Meng, Wenjing; Ronson, Tanya K.; Stefankiewicz, Artur R.; Sanders, Jeremy K. M.; Nitschke, Jonathan R.Angewandte Chemie, International Edition (2015), 54 (13), 3988-3992CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The combination of a bent diamino(nickel(II) porphyrin) with 2-formylpyridine and FeII yielded an FeII4L6 cage. Upon treatment with the fullerenes C60 or C70, this cage was found to transform into a new host-guest complex incorporating three FeII centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsatn. at one of the FeII centers as the result of the incommensurate metal-to-ligand ratio, which enabled the prepn. of a heterometallic cone-shaped CuIFeII2L4 adduct of C60 or C70.
- 28(a) Nigg, E. A. Cyclin-dependent Protein Kinases: Key Regulators of the Eukaryotic Cell Cycle BioEssays 1995, 17 (6) 471– 480 DOI: 10.1002/bies.950170603Google ScholarThere is no corresponding record for this reference.(b) Bloom, J.; Cross, F. R. Multiple Levels of Cyclin Specificity in Cell-cycle Control Nat. Rev. Mol. Cell Biol. 2007, 8 (2) 149– 160 DOI: 10.1038/nrm2105Google Scholar28bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXotFKmuw%253D%253D&md5=72e7e2fbc11d6613035cdca1c084815dMultiple levels of cyclin specificity in cell-cycle controlBloom, Joanna; Cross, Frederick R.Nature Reviews Molecular Cell Biology (2007), 8 (2), 149-160CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)A review. Cyclins regulate the cell cycle by binding to and activating cyclin-dependent kinases (Cdks). Phosphorylation of specific targets by cyclin-Cdk complexes sets in motion different processes that drive the cell cycle in a timely manner. In budding yeast, a single Cdk is activated by multiple cyclins. The ability of these cyclins to target specific proteins and to initiate different cell cycle events might, in some cases, reflect the timing of the expression of the cyclins; in others, it might reflect intrinsic properties of the cyclins that render them better suited to target particular proteins.(c) Hut, R. A.; Beersma, D. G. M. Evolution of Time-Keeping Mechanisms: Early Emergence and Adaptation to Photoperiod Philos. Trans. R. Soc., B 2011, 366 (1574) 2141– 2154 DOI: 10.1098/rstb.2010.0409Google Scholar28chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3MnitFGitg%253D%253D&md5=c4a3cdf0d021081ec77209237949e855Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiodHut R A; Beersma D G MPhilosophical transactions of the Royal Society of London. Series B, Biological sciences (2011), 366 (1574), 2141-54 ISSN:.Virtually all species have developed cellular oscillations and mechanisms that synchronize these cellular oscillations to environmental cycles. Such environmental cycles in biotic (e.g. food availability and predation risk) or abiotic (e.g. temperature and light) factors may occur on a daily, annual or tidal time scale. Internal timing mechanisms may facilitate behavioural or physiological adaptation to such changes in environmental conditions. These timing mechanisms commonly involve an internal molecular oscillator (a 'clock') that is synchronized ('entrained') to the environmental cycle by receptor mechanisms responding to relevant environmental signals ('Zeitgeber', i.e. German for time-giver). To understand the evolution of such timing mechanisms, we have to understand the mechanisms leading to selective advantage. Although major advances have been made in our understanding of the physiological and molecular mechanisms driving internal cycles (proximate questions), studies identifying mechanisms of natural selection on clock systems (ultimate questions) are rather limited. Here, we discuss the selective advantage of a circadian system and how its adaptation to day length variation may have a functional role in optimizing seasonal timing. We discuss various cases where selective advantages of circadian timing mechanisms have been shown and cases where temporarily loss of circadian timing may cause selective advantage. We suggest an explanation for why a circadian timing system has emerged in primitive life forms like cyanobacteria and we evaluate a possible molecular mechanism that enabled these bacteria to adapt to seasonal variation in day length. We further discuss how the role of the circadian system in photoperiodic time measurement may explain differential selection pressures on circadian period when species are exposed to changing climatic conditions (e.g. global warming) or when they expand their geographical range to different latitudes or altitudes.
- 29Whiteoak, C. J.; Britovsek, G. J. P.; Gibson, V. C.; White, A. J. P. Electronic Effects in Oxo Transfer Reactions Catalysed by Salan Molybdenum(VI) cis-dioxo Complexes Dalton. Trans. 2009, 13, 2337– 2344 DOI: 10.1039/b820754bGoogle ScholarThere is no corresponding record for this reference.
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- 33(a) Ludlow, R. F.; Otto, S. Systems chemistry Chem. Soc. Rev. 2008, 37 (1) 101– 108 DOI: 10.1039/B611921MGoogle Scholar33ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXmtVWhtQ%253D%253D&md5=151c83f30396538fccc0ea2f9c016d26Systems chemistryLudlow, R. Frederick; Otto, SijbrenChemical Society Reviews (2008), 37 (1), 101-108CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A tutorial review. The study of complex mixts. of interacting synthetic mols. has historically not received much attention from chemists, even though research into complexity is well established in the neighboring fields. However, with the huge recent interest in systems biol. and the availability of modern anal. techniques this situation is likely to change. In this tutorial review we discuss some of the incentives for developing systems chem. and we highlight the pioneering work in which mol. networks are making a splash. A distinction is made between networks under thermodn. and kinetic control. The former include dynamic combinatorial libraries while the latter involve pseudo-dynamic combinatorial libraries, oscillating reactions and networks of autocatalytic and replicating compds. These studies provide fundamental insights into the organizational principles of mol. networks and how these give rise to emergent properties such as amplification and feedback loops, and may eventually shed light on the origin of life. The knowledge obtained from the study of mol. networks should ultimately enable us to engineer new systems with properties and functions unlike any conventional materials.(b) Whitesides, G. M.; Ismagilov, R. F. Complexity in Chemistry Science 1999, 284 (5411) 89– 92 DOI: 10.1126/science.284.5411.89Google Scholar33bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXitlCns7Y%253D&md5=0ee023c01ca62e8e3466c193212c9b76Complexity in chemistryWhitesides, George M.; Ismagilov, Rustem F.Science (Washington, D. C.) (1999), 284 (5411), 89-92CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Chem. has usually represented complicated processes with simple and linear approxns. However, there is an ongoing trend towards complexity. New types of problems are stimulating the move towards the study of nonlinear process which are highly sensitive to conditions. Genomics and proteomics have encouraged research on complex systems.
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Abstract
Figure 1
Figure 1. Preparation of a pseudorotaxane, and its time-dependent disassembly and reassembly. (a) Synthetic scheme for the formation of 2 from p-anisidine, 2-formylpyridine, and macrocycle 1, and its subsequent conversion to 3 via addition of PPh3. (b) Structure of oxo-transfer catalyst (ReCat) used to oxidize PPh3. (c) Addition of PPh3 to 2 led to the formation of 3. Upon complete oxidation of PPh3, pseudorotaxane 2 reforms. (d) Reaction progress over time, monitored by UV–vis spectroscopy. Each arrow indicates a point at which 2 equiv of PPh3 per CuI were added. (e) Plot showing the linear increase in initial rate with increasing concentration of ReCat; points represent the averages of three runs, with error bars providing ESDs between runs.
Figure 2
Figure 2. Uptake and release of C60 from 5. (a) Scheme depicting assembly of Cu3L3 triangle 5 upon mixing 4, 2-formylpyridine and Cu(MeCN)4OTf in DMSO, and its binding of C60. (b) Control of the disassembly of homoleptic 5 to heteroleptic 6, and its reassembly, with concomitant release and uptake of a C60 guest in a 1:1 mixture of CD3CN/DCM.
Figure 3
Figure 3. Controlled conversion of 2 to 3 using MoCat. (a) Dethreading of macrocycle 1 from pseudorotaxane 2 upon addition of PPh3 and subsequent formation of OPPh3 using MoCat in DMSO. The excess of PPh3 must be consumed by the oxidation reaction before reformation of 2 can occur. (b) Structure of MoCat. (c) Partial 1H NMR spectra showing the decrease in concentration of PPh3 (green) over time and the increase in concentration of OPPh3 (red) upon heating 3 at 363 K with MoCat (40 mol %) in DMSO. (d) Plot of the concentrations of 2 (black) and OPPh3 (red) over time. Arrows indicate the points at which PPh3 (8 equiv) was added. The concentration of 2 remained constant at zero until the excess PPh3 had been consumed, at which point it began to increase.
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- 5Anfinsen, C. B. Principles that Govern the Folding of Protein Chains Science 1973, 181 (4096) 223– 230 DOI: 10.1126/science.181.4096.2235https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3sXkvVygtbc%253D&md5=5ffae70d46719288cad91f56bd56e489Principles that govern the folding of protein chainsAnfinsen, Christian B.Science (Washington, DC, United States) (1973), 181 (4096), 223-30CODEN: SCIEAS; ISSN:0036-8075.A review with 51 refs. on protein conformation. The Nobel Prize lecture summarizing the author's investigations on the nature of the process that controls the folding of polypeptide chains into a unique three-dimensional protein. Studies with RNase and staphylococcal nuclease are esp. emphasized.
- 6Watson, J. D.; Crick, F. H. C. Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid Nature 1953, 171 (4356) 737– 738 DOI: 10.1038/171737a06https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG2cXivVGktA%253D%253D&md5=66b78cf4b12c8c5ced56ff75a9468f35Molecular structure of nucleic acids. A structure for deoxyribose nucleic acidWatson, J. D.; Crick, F. H. C.Nature (London, United Kingdom) (1953), 171 (), 737-8CODEN: NATUAS; ISSN:0028-0836.W. and C. propose a new structure for the Na salt of deoxyribose nucleic acid. This structure, which loosely resembles Furberg's model No. 1 (C.A. 47, 9924g), has 2 helical polynucleotide chains each coiled around the same axis but whose sequence of atoms runs in opposite directions. The chains are held together by H-bonding between purine and pyrimidine bases, a purine of 1 chain bonded to a pyrimidine of the other. Full details will be published elsewhere.
- 7Han, M.; Michel, R.; He, B.; Chen, Y.-S.; Stalke, D.; John, M.; Clever, G. H. Light-Triggered Guest Uptake and Release by a Photochromic Coordination Cage Angew. Chem., Int. Ed. 2013, 52 (4) 1319– 1323 DOI: 10.1002/anie.2012073737https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslKmsrrO&md5=bc159f4a3916e7df60ada9ab5e59d6c9Light-Triggered Guest Uptake and Release by a Photochromic Coordination CageHan, Muxin; Michel, Reent; He, Bice; Chen, Yu-Sheng; Stalke, Dietmar; John, Michael; Clever, Guido H.Angewandte Chemie, International Edition (2013), 52 (4), 1319-1323CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors have shown that a photochromic coordination cage, which quant. self-assembles from four ligands based on a dithienylethene photoswitch can be smoothly interconverted between a structurally flexible form open-ring form and a rigid form closed-ring form by irradn. with UV or white light, resp. The assocd. modulation of the affinity for anionic guests might find applications in fields such as supramol. catalysis, drug delivery and functional constructs that are based on the control by external stimuli such as switchable receptors and mol. machine.
- 8Busschaert, N.; Elmes, R. B. P.; Czech, D. D.; Wu, X.; Kirby, I. L.; Peck, E. M.; Hendzel, K. D.; Shaw, S. K.; Chan, B.; Smith, B. D.; Jolliffe, K. A.; Gale, P. A. Thiosquaramides: pH Switchable Anion Transporters Chem. Sci. 2014, 5 (9) 3617– 3626 DOI: 10.1039/C4SC01629G8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVOitbvF&md5=0dd7287935fa4e769a39d4e1456d7d5bThiosquaramides: pH switchable anion transportersBusschaert, Nathalie; Elmes, Robert B. P.; Czech, Dawid D.; Wu, Xin; Kirby, Isabelle L.; Peck, Evan M.; Hendzel, Kevin D.; Shaw, Scott K.; Chan, Bun; Smith, Bradley D.; Jolliffe, Katrina A.; Gale, Philip A.Chemical Science (2014), 5 (9), 3617-3626CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)The transport of anions across cellular membranes is an important biol. function governed by specialised proteins. In recent years, many small mols. have emerged that mimick the anion transport behavior of these proteins, but only a few of these synthetic mols. also display the gating/switching behavior seen in biol. systems. A small series of thiosquaramides was synthesized and their pH-dependent chloride binding and anion transport behavior was investigated using 1H NMR titrns., single crystal X-ray diffraction and a variety of vesicle-based techniques. Spectrophotometric titrns. and DFT calcns. revealed that the thiosquaramides are significantly more acidic than their oxosquaramide analogs, with pKa values between 4.0 and 9.0. This led to the observation that at pH 7.2 the anion transport ability of the thiosquaramides is fully switched OFF due to deprotonation of the receptor, but is completely switched ON at lower pH.
- 9Riddell, I. A.; Smulders, M. M. J.; Clegg, J. K.; Hristova, Y. R.; Breiner, B.; Thoburn, J. D.; Nitschke, J. R. Anion-Induced Reconstitution of a Self-assembling System to Express a Chloride-Binding Co10L15 Pentagonal Prism Nat. Chem. 2012, 4 (9) 751– 756 DOI: 10.1038/nchem.14079https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFCgs7jN&md5=7edf2577c8d380b17b2cd0775b88f5a1Anion-induced reconstitution of a self-assembling system to express a chloride-binding Co10L15 pentagonal prismRiddell, Imogen A.; Smulders, Maarten M. J.; Clegg, Jack K.; Hristova, Yana R.; Breiner, Boris; Thoburn, John D.; Nitschke, Jonathan R.Nature Chemistry (2012), 4 (9), 751-756CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Biochem. systems are adaptable, capable of reconstitution at all levels to achieve the functions assocd. with life. Synthetic chem. systems are more limited in their ability to reorganize to achieve new functions; they can reconfigure to bind an added substrate (template effect) or one binding event may modulate a receptor's affinity for a second substrate (allosteric effect). Here the authors describe a synthetic chem. system that is capable of structural reconstitution on receipt of one anionic signal (perchlorate) to create a tight binding pocket for another anion (chloride). A decanuclear cobalt(II) complex [Cl- ⊂ Co10L15](ClO4)19 (L = 6,6'-bis[(4-methylphenyl)iminomethyl]-3,3'-bipyridine) was prepd. by the reaction of p-toluidine and 6,6'-diformyl-3,3'-bipyridine and Co(ClO4)2, whereas a tetranuclear complex [Co4L6](OTf)8 results when Co(OTf)2 is used as the cobalt(II) source. The tetranuclear complex is converted to the decanuclear complex upon addn. of LiClO4. The decanuclear complex acts as a receptor for halides, N3-, OCN- and SCN-. The complex, barrel-like structure of the chloride receptor is templated by five perchlorate anions. This second-order templation phenomenon allows chem. networks to be envisaged that express more complex responses to chem. signals than is currently feasible.
- 10Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; Magonov, S.; Solares, S. D.; Goddard, W. A.; Ho, C.-M.; Stoddart, J. F. Linear Artificial Molecular Muscles J. Am. Chem. Soc. 2005, 127 (27) 9745– 9759 DOI: 10.1021/ja051088p10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltV2nt78%253D&md5=932ec813923ded0ac0f59f1825e8f5bdLinear Artificial Molecular MusclesLiu, Yi; Flood, Amar H.; Bonvallet, Paul A.; Vignon, Scott A.; Northrop, Brian H.; Tseng, Hsian-Rong; Jeppesen, Jan O.; Huang, Tony J.; Brough, Branden; Baller, Marko; Magonov, Sergei; Solares, Santiago D.; Goddard, William A.; Ho, Chih-Ming; Stoddart, J. FraserJournal of the American Chemical Society (2005), 127 (27), 9745-9759CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two switchable, palindromically constituted bistable [3]rotaxanes have been designed and synthesized with a pair of mech. mobile rings encircling a single dumbbell. These designs are reminiscent of a "mol. muscle" for the purposes of amplifying and harnessing mol. mech. motions. The location of the two cyclobis(paraquat-p-phenylene) (CBPQT4+) rings can be controlled to be on either tetrathiafulvalene (TTF) or naphthalene (NP) stations, either chem. (1H NMR spectroscopy) or electrochem. (cyclic voltammetry), such that switching of inter-ring distances from 4.2 to 1.4 nm mimics the contraction and extension of skeletal muscle, albeit on a shorter length scale. Fast scan-rate cyclic voltammetry at low temps. reveals stepwise oxidns. and movements of one-half of the [3]rotaxane and then of the other, a process that appears to be concerted at room temp. The active form of the bistable [3]rotaxane bears disulfide tethers attached covalently to both of the CBPQT4+ ring components for the purpose of its self-assembly onto a gold surface. An array of flexible microcantilever beams, each coated on one side with a monolayer of 6 billion of the active bistable [3]rotaxane mols., undergoes controllable and reversible bending up and down when it is exposed to the synchronous addn. of aq. chem. oxidants and reductants. The beam bending is correlated with flexing of the surface-bound mol. muscles, whereas a monolayer of the dumbbell alone is inactive under the same conditions. This observation supports the hypothesis that the cumulative nanoscale movements within surface-bound "mol. muscles" can be harnessed to perform larger-scale mech. work.
- 11Lindsey, J. S. Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives: A Review New. J. Chem. 1991, 15, 153– 18011https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXitValu70%253D&md5=ea2ac7c2790242ba600f08e8f4e4aa8cSelf-assembly in synthetic routes to molecular devices. Biological principles and chemical perspectives: a reviewLindsey, Jonathan S.New Journal of Chemistry (1991), 15 (2-3), 153-80CODEN: NJCHE5; ISSN:1144-0546.A review with many refs. summarizing the concepts, limitations, and paradigms of biol. self-assembly processes, then surveying covalent self-assembly processes in the synthesis of 3-dimensional mols. and ordered assemblies. Self-assembly as a soln. to the synthesis problems of mol. electronics is considered.
- 12(a) Mitchison, T.; Kirschner, M. Dynamic Instability of Microtubule Growth Nature 1984, 312 (5991) 237– 242 DOI: 10.1038/312237a012ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhvF2jsQ%253D%253D&md5=2c8244aca07fd3b65f76da5580cf6c48Dynamic instability of microtubule growthMitchison, Tim; Kirschner, MarcNature (London, United Kingdom) (1984), 312 (5991), 237-42CODEN: NATUAS; ISSN:0028-0836.Microtubules placed in a tubulin soln. just about the steady-state concn. of 14 μM showed a steady increase in length with no change in no. of microtubules. At lower tubulin concns. (7.5 μM), the no. of microtubules decreased with time, whereas the mean length of microtubules still increased somewhat. Axonemes could nucleate growth of microtubules well below the steady-state concn. of tubulin. At steady state (14 μM tubulin), when the net polymer mass remained const., a steady increase in mean microtubule length still occurred, whereas the no. of microtubules decreased steadily. This was attributed to depolymn. of some microtubules, which provided tubulin monomers for growth of other microtubules. The transition of microtubules between growing and shrinking phases was evidently rare. Possibly growing microtubules have GTP-liganded caps, whereas shrinking ones do not. A new model for microtubule assembly is proposed based on these findings.(b) Flaherty, K. M.; DeLuca-Flaherty, C.; McKay, D. B. Three-Dimensional Structure of the ATPase Fragment of a 70K Heat-Shock Cognate Protein Nature 1990, 346 (6285) 623– 628 DOI: 10.1038/346623a012bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXlsVOqtbc%253D&md5=4b5978279abd701d2f53253aa59b3d26Three-dimensional structure of the ATPase fragment of a 70k heat-shock cognate proteinFlaherty, Kevin M.; DeLuca-Flaherty, Camille; McKay, David B.Nature (London, United Kingdom) (1990), 346 (6285), 623-8CODEN: NATUAS; ISSN:0028-0836.The 3-dimensional structure of the N-terminal 44K ATPase fragment of the 70K bovine heat-shock cognate protein has been solved to a resoln. of 2.2 Å. The ATPase fragment has 2 structural lobes with a deep cleft between them; ATP binds at the base of the cleft. Surprisingly, the nucleotide-binding core of the ATPase fragment has a tertiary structure similar to that of hexokinase, although the remainder of the structures of the 2 proteins are completely dissimilar, suggesting that both the phosphotransferase mechanism and the substrate-induced conformational change intrinsic to the hexokinases may be used by the 70K heat shock-related proteins. Crystal structure parameters are reported.(c) Vale, R. D. The Molecular Motor Toolbox for Intracellular Transport Cell 2003, 112 (4) 467– 480 DOI: 10.1016/S0092-8674(03)00111-912chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXhs1SnsLo%253D&md5=621a970c2349aba1d594dcf76f516e43The molecular motor toolbox for intracellular transportVale, Ronald D.Cell (Cambridge, MA, United States) (2003), 112 (4), 467-480CODEN: CELLB5; ISSN:0092-8674. (Cell Press)A review. Eukaryotic cells create internal order by using protein motors to transport mols. and organelles along cytoskeletal tracks. Recent genomic and functional studies suggest that 5 cargo-carrying motors emerged in primitive eukaryotes and have been widely used throughout evolution. The complexity of these "toolbox" motors expanded in higher eukaryotes through gene duplication, alternative splicing, and the addn. of assocd. subunits, which enabled new cargoes to be transported. Remarkably, fungi, parasites, plants, and animals have distinct subsets of toolbox motors in their genomes, suggesting an underlying diversity of strategies for intracellular transport.
- 13(a) Hermans, T. M.; Frauenrath, H.; Stellacci, F. Droplets Out of Equilibrium Science 2013, 341 (6143) 243– 244 DOI: 10.1126/science.1241793There is no corresponding record for this reference.(b) Grzybowski, B. A.; Stone, H. A.; Whitesides, G. M. Dynamic Self-Assembly of Magnetized, Millimetre-Sized Objects Rotating at a Liquid-Air Interface Nature 2000, 405 (6790) 1033– 1036 DOI: 10.1038/35016528There is no corresponding record for this reference.(c) Fialkowski, M.; Bishop, K. J. M.; Klajn, R.; Smoukov, S. K.; Campbell, C. J.; Grzybowski, B. A. Principles and Implementations of Dissipative (Dynamic) Self-Assembly J. Phys. Chem. B 2006, 110 (6) 2482– 2496 DOI: 10.1021/jp054153q13chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvVSqsw%253D%253D&md5=5cd81063fd8698ec8e0c7bf3963a1fa1Principles and Implementations of Dissipative (Dynamic) Self-AssemblyFialkowski, Marcin; Bishop, Kyle J. M.; Klajn, Rafal; Smoukov, Stoyan K.; Campbell, Christopher J.; Grzybowski, Bartosz A.Journal of Physical Chemistry B (2006), 110 (6), 2482-2496CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)A review. Dynamic self-assembly (DySA) processes occurring outside of thermodn. equil. underlie many forms of adaptive and intelligent behaviors in natural systems. Relatively little, however, is known about the principles that govern DySA and the ways in which it can be extended to artificial ensembles. This article discusses recent advances in both the theory and the practice of nonequil. self-assembly. It is argued that a union of ideas from thermodn. and dynamic systems' theory can provide a general description of DySA. In parallel, heuristic design rules can be used to construct DySA systems of increasing complexities based on a variety of suitable interactions/potentials on length scales from nanoscopic to macroscopic. Applications of these rules to MHD DySA are also discussed.(d) Weitz, M.; Kim, J.; Kapsner, K.; Winfree, E.; Franco, E.; Simmel, F. C. Diversity in the Dynamical Behaviour of a Compartmentalized Programmable Biochemical Oscillator Nat. Chem. 2014, 6 (4) 295– 302 DOI: 10.1038/nchem.186913dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXisFOjtbs%253D&md5=bc290cb6326fadb156dcb85af3eb587fDiversity in the dynamical behaviour of a compartmentalized programmable biochemical oscillatorWeitz, Maximilian; Kim, Jongmin; Kapsner, Korbinian; Winfree, Erik; Franco, Elisa; Simmel, Friedrich C.Nature Chemistry (2014), 6 (4), 295-302CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)In vitro compartmentalization of biochem. reaction networks is a crucial step towards engineering artificial cell-scale devices and systems. At this scale the dynamics of mol. systems becomes stochastic, which introduces several engineering challenges and opportunities. Here we study a programmable transcriptional oscillator system that is compartmentalized into microemulsion droplets with vols. between 33 fl and 16 pl. Simultaneous measurement of large populations of droplets reveals major variations in the amplitude, frequency and damping of the oscillations. Variability increases for smaller droplets and depends on the operating point of the oscillator. Rather than reflecting the stochastic kinetics of the chem. reaction network itself, the variability can be attributed to the statistical variation of reactant concns. created during their partitioning into droplets. We anticipate that robustness to partitioning variability will be a crit. challenge for engineering cell-scale systems, and that highly parallel time-series acquisition from microemulsion droplets will become a key tool for characterization of stochastic circuit function.
- 14(a) Boekhoven, J.; Brizard, A. M.; Kowlgi, K. N. K.; Koper, G. J. M.; Eelkema, R.; van Esch, J. H. Dissipative Self-Assembly of a Molecular Gelator by Using a Chemical Fuel Angew. Chem., Int. Ed. 2010, 49 (28) 4825– 4828 DOI: 10.1002/anie.20100151114ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXotVCguro%253D&md5=2ae7a93948a9966b3ed0cbcb56d447fdDissipative Self-Assembly of a Molecular Gelator by Using a Chemical FuelBoekhoven, Job; Brizard, Aurelie M.; Kowlgi, Krishna N. K.; Koper, Ger J. M.; Eelkema, Rienk; van Esch, Jan H.Angewandte Chemie, International Edition (2010), 49 (28), 4825-4828, S4825/1-S4825/4CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)We present a synthetic dissipative self-assembly fibrous network that uses chem. fuel as an energy source. A gelator precursor is converted into a gelator by reaction with a chem. fuel, thus leading to self-assembly. Hydrolysis of gelator leads to energy dissipation and disassembly of the formed structures.(b) Debnath, S.; Roy, S.; Ulijn, R. V. Peptide Nanofibers with Dynamic Instability through Nonequilibrium Biocatalytic Assembly J. Am. Chem. Soc. 2013, 135 (45) 16789– 16792 DOI: 10.1021/ja408635314bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1KktLrL&md5=2428ddda2ec544c177fe562a4c60fa62Peptide Nanofibers with Dynamic Instability through Nonequilibrium Biocatalytic AssemblyDebnath, Sisir; Roy, Sangita; Ulijn, Rein V.Journal of the American Chemical Society (2013), 135 (45), 16789-16792CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)We demonstrate the formation of supramol. peptide nanofibers that display dynamic instability; i.e., they are formed by competing assembly and disassembly reactions, where assembly is favored away from equil. The systems are based on competitive catalytic transacylation and hydrolysis, producing a self-assembling arom. peptide amphiphile from amino acid precursors that temporarily exceeds the crit. gelation concn., until the competing hydrolytic reaction takes over. Anal. by at. force microscopy shows consecutive nanofiber formation and shortening. The process results in macroscopically observable temporary hydrogelation, which may be repeated upon refueling the system with further addn. of the chem. activated amino acid precursor. Nonequil. nanostructures open up opportunities for mimicry of the behavior of dynamic gels found in natural systems and provide components for future adaptive nanotechnologies.(c) Dambenieks, A. K.; Vu, P. H. Q.; Fyles, T. M. Dissipative Assembly of a Membrane Transport System Chem. Sci. 2014, 5 (9) 3396– 3403 DOI: 10.1039/C4SC01258E14chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1amtr3M&md5=5047aa074337cb2395276a92596df01cDissipative assembly of a membrane transport systemDambenieks, A. K.; Vu, P. H. Q.; Fyles, T. M.Chemical Science (2014), 5 (9), 3396-3403CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)A membrane system consisting of a transport-inactive thiol-terminated oligoester and a channel-forming amine-terminated thioester is subject to kinetic control though the provision of a chem. fuel. Intermol. thioester exchange occurs rapidly between the fuel and the inactive thiol to produce the channel-forming species. Spontaneous intramol. degrdn. of the active compd. with release of a lactam occurs more slowly to reform the inactive thiol. The system can cycle from transport inactive to active and back via injection of the fuel. Such behavior is consistent with dissipative assembly of the ion-channel function of the system.(d) Semenov, S. N.; Wong, A. S. Y.; van der Made, R. M.; Postma, S. G. J.; Groen, J.; van Roekel, H. W. H.; de Greef, T. F. A.; Huck, W. T. S. Rational Design of Functional and Tunable Oscillating Enzymatic Networks Nat. Chem. 2015, 7 (2) 160– 165 DOI: 10.1038/nchem.214214dhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXmtFSgsQ%253D%253D&md5=e5010fdd61b6a845eb70077cfebb232fRational design of functional and tunable oscillating enzymatic networksSemenov, Sergey N.; Wong, Albert S. Y.; van der Made, R. Martijn; Postma, Sjoerd G. J.; Groen, Joost; van Roekel, Hendrik W. H.; de Greef, Tom F. A.; Huck, Wilhelm T. S.Nature Chemistry (2015), 7 (2), 160-165CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Life is sustained by complex systems operating far from equil. and consisting of a multitude of enzymic reaction networks. The operating principles of biol.'s regulatory networks are known, but the in vitro assembly of out-of-equil. enzymic reaction networks proved challenging, limiting the development of synthetic systems showing autonomous behavior. Here, the authors present a strategy for the rational design of programmable functional reaction networks that exhibit dynamic behavior. A network built around autoactivation and delayed neg. feedback of the enzyme trypsin is capable of producing sustained oscillating concns. of active trypsin for over 65 h. Other functions, such as amplification, analog-to-digital conversion and periodic control over equil. systems, were obtained by linking multiple network modules in microfluidic flow reactors. The methodol. developed here provides a general framework to construct dissipative, tunable and robust (bio)chem. reaction networks.(e) Ragazzon, G.; Baroncini, M.; Silvi, S.; Venturi, M.; Credi, A. Light-Powered Autonomous and Directional Molecular Motion of a Dissipative Self-assembling System Nat. Nanotechnol. 2014, 10 (1) 70– 75 DOI: 10.1038/nnano.2014.260There is no corresponding record for this reference.(f) Cheng, C.; McGonigal, P. R.; Liu, W.-G.; Li, H.; Vermeulen, N. A.; Ke, C.; Frasconi, M.; Stern, C. L.; Goddard III, W. A.; Stoddart, J. F. Energetically Demanding Transport in a Supramolecular Assembly J. Am. Chem. Soc. 2014, 136 (42) 14702– 14705 DOI: 10.1021/ja508615fThere is no corresponding record for this reference.
- 15(a) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Supramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional Ensembles Chem. Rev. 2011, 111 (11) 6810– 6918 DOI: 10.1021/cr200077m15ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVOnsrbP&md5=720bcf4d887a36411c6382d3b50278ceSupramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional EnsemblesChakrabarty, Rajesh; Mukherjee, Partha Sarathi; Stang, Peter J.Chemical Reviews (Washington, DC, United States) (2011), 111 (11), 6810-6918CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. This review focuses on the journey of early coordination-driven self-assembly paradigms to more complex and discrete 2D and 3D supramol. ensembles over the past decade. The authors begin with a discussion of various approaches that have been developed by different groups to assemble finite supramol. architectures. The subsequent sections contain detailed discussions on the synthesis of discrete 2D and 3D systems and their functionalizations and applications.(b) Beves, J. E.; Blight, B. A.; Campbell, C. J.; Leigh, D. A.; McBurney, R. T. Strategies and Tactics for the Metal-Directed Synthesis of Rotaxanes, Knots, Catenanes, and Higher Order Links Angew. Chem., Int. Ed. 2011, 50 (40) 9260– 9327 DOI: 10.1002/anie.20100796315bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtFylsrrL&md5=3378dd02bc055d958e42af9408a0eba5Strategies and Tactics for the Metal-Directed Synthesis of Rotaxanes, Knots, Catenanes, and Higher Order LinksBeves, Jonathon E.; Blight, Barry A.; Campbell, Christopher J.; Leigh, David A.; McBurney, Roy T.Angewandte Chemie, International Edition (2011), 50 (40), 9260-9327CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. More than a quarter of a century after the 1st metal template synthesis of a [2]catenane in Strasbourg, there now exists a plethora of strategies available for the construction of mech. bonded and entwined mol. level structures. Catenanes, rotaxanes, knots and Borromean rings have all been successfully accessed by methods in which metal ions play a pivotal role. Originally metal ions were used solely for their coordination chem.; acting either to gather and position the building blocks such that subsequent reactions generated the interlocked products or by being an integral part of the rings or stoppers of the interlocked assembly. Recently the role of the metal has evolved to encompass catalysis: the metal ions not only organize the building blocks in an entwined or threaded arrangement but also actively promote the reaction that covalently captures the interlocked structure. This Review outlines the diverse strategies that currently exist for forming mech. bonded mol. structures with metal ions and details the tactics that the chemist can use for creating cross-over points, maximizing the yield of interlocked over noninterlocked products, and the reactions-of-choice for the covalent capture of threaded and entwined intermediates.(c) Cook, T. R.; Stang, P. J. Recent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via Coordination Chem. Rev. 2015, 115, 7001– 7045 DOI: 10.1021/cr500566615chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXlsVGltL4%253D&md5=3d246d2007812392beb0d5e43113d7afRecent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via CoordinationCook, Timothy R.; Stang, Peter J.Chemical Reviews (Washington, DC, United States) (2015), 115 (15), 7001-7045CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review.
- 16Dietrich-Buchecker, C. O.; Sauvage, J.-P. A Synthetic Molecular Trefoil Knot Angew. Chem., Int. Ed. Engl. 1989, 28 (2) 189– 192 DOI: 10.1002/anie.198901891There is no corresponding record for this reference.
- 17Nitschke, J. R. Construction, Substitution, and Sorting of Metallo-organic Structures via Subcomponent Self-Assembly Acc. Chem. Res. 2007, 40 (2) 103– 112 DOI: 10.1021/ar068185n17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtV2gt7jE&md5=3d5687d98ceec631838a8f8408205719Construction, Substitution, and Sorting of Metallo-organic Structures via Subcomponent Self-AssemblyNitschke, Jonathan R.Accounts of Chemical Research (2007), 40 (2), 103-112CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. Subcomponent self-assembly allows the construction of complex architectures from simple building blocks via formation of covalent bonds around metal templates. Since both covalent and coordinative bonds are formed reversibly, a wealth of rearrangement reactions is possible involving substitution at both intraligand (often C:N) and metal-ligand (N → metal) bonds. If the possibilities latent within a set of subcomponents and metal ions are understood, one may also select specific structures from among dynamic libraries of products. The parallel prepn. of structures from nonorthogonal mixts. of subcomponents is also possible, as is the direction of subcomponents to specific sites within product structures.
- 18Lee, S.; Chen, C.-H.; Flood, A. H. A Pentagonal Cyanostar Macrocycle with Cyanostilbene CH Donors Binds Anions and Forms Dialkylphosphate [3]Rotaxanes Nat. Chem. 2013, 5 (8) 704– 710 DOI: 10.1038/nchem.166818https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsFSgs7g%253D&md5=0dc7b420189c616d10b1e9a709f533f2A pentagonal cyanostar macrocycle with cyanostilbene CH donors binds anions and forms dialkylphosphate [3]rotaxanesLee, Semin; Chen, Chun-Hsing; Flood, Amar H.Nature Chemistry (2013), 5 (8), 704-710CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)Since the discovery of crown ethers, macrocycles were recognized as powerful platforms for supramol. chem. Although their nos. and variations are now legion, macrocycles that are simple to make using high-yielding reactions in one pot and on the multigram scale are rare. Here the authors present such a discovery obtained during the creation of a C5-sym. cyanostilbene campestarene' macrocycle, cyanostar, that employs Knoevenagel condensations in the prepn. of its cyanostilbene repeat unit. In the solid state, cyanostars form π-stacked dimers constituted of chiral P and M enantiomers. The electropos. central cavity stabilizes anions with CH hydrogen-bonding units that are activated by electron-withdrawing cyano groups. In soln., the cyanostar shows high-affinity binding as 2:1 sandwich complexes, log β2 ≈ 12 and ΔG ≈ -70 kJ mol-1, of large anions (BF4-, ClO4- and PF6-) usually considered weakly coordinating. The cyanostar's size preference gave an unprecedented [3]rotaxane templated around a dialkylphosphate.
- 19Berná, J.; Alajarín, M.; Orenes, R.-A. Azodicarboxamides as Template Binding Motifs for the Building of Hydrogen-Bonded Molecular Shuttles J. Am. Chem. Soc. 2010, 132 (31) 10741– 10747 DOI: 10.1021/ja101151t19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXptFWkt7Y%253D&md5=85c89c7f2c6cfe08a81253d6a239a74fAzodicarboxamides as Template Binding Motifs for the Building of Hydrogen-Bonded Molecular ShuttlesBerna, Jose; Alajarin, Mateo; Orenes, Raul-AngelJournal of the American Chemical Society (2010), 132 (31), 10741-10747CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Azodicarboxamides (R2NCON=NCONR2) act as new templates for the assembly of unprecedented azo-functionalized hydrogen-bond-assembled [2]rotaxanes. Also, these binding sites can be reversibly and efficiently interconverted with their hydrazo forms through a hydrogenation-dehydrogenation strategy of the nitrogen-nitrogen bond. This novel chem. switchable control element was implemented in stimuli-responsive mol. shuttles that work through a reversible azo/hydrazo interconversion, producing large amplitude net positional changes with a good discrimination between the binding sites of the macrocycle in both states of the shuttle. These mol. shuttles are able to operate by two different mechanisms: in a discrete mode through two reversible and independent chem. events and, importantly, in a continuous regime through a catalyzed ester bond formation reaction in which the shuttle acts as an organocatalyst. In this latter, the incorporation of both states of the shuttle into this simple chem. reaction network promotes a dynamic translocation of the macrocycle between two nitrogen and carbon-based stations of the thread allowing an energetically uphill esterification process to take place.
- 20Bruns, C. J.; Stoddart, J. F. Rotaxane-Based Molecular Muscles Acc. Chem. Res. 2014, 47 (7) 2186– 2199 DOI: 10.1021/ar500138u20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXptVWrtbw%253D&md5=b751f692350fbc0675990ccf349d10ceRotaxane-Based Molecular MusclesBruns, Carson J.; Stoddart, J. FraserAccounts of Chemical Research (2014), 47 (7), 2186-2199CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. More than two decades of investigating the chem. of bistable mech. interlocked mols. (MIMs), such as rotaxanes and catenanes, has led to the advent of numerous mol. switches that express controlled translational or circumrotational movement on the nanoscale. Directed motion at this scale is an essential feature of many biomol. assemblies known as mol. machines, which carry out essential life-sustaining functions of the cell. It follows that the use of bistable MIMs as artificial mol. machines (AMMs) has been long anticipated. This objective is rarely achieved, however, because of challenges assocd. with coupling the directed motions of mech. switches with other systems on which they can perform work. A natural source of inspiration for designing AMMs is muscle tissue, since it is a material that relies on the hierarchical organization of mol. machines (myosin) and filaments (actin) to produce the force and motion that underpin locomotion, circulation, digestion, and many other essential life processes in humans and other animals. Muscle is characterized at both microscopic and macroscopic length scales by its ability to generate forces that vary the distance between two points at the expense of chem. energy. Artificial muscles that mimic this ability are highly sought for applications involving the transduction of mech. energy. Rotaxane-based mol. switches are excellent candidates for artificial muscles because their architectures intrinsically possess movable filamentous mol. components. In this Account, we describe (i) the different types of rotaxane "mol. muscle" architectures that express contractile and extensile motion, (ii) the mol. recognition motifs and corresponding stimuli that have been used to actuate them, and (iii) the progress made on integrating and scaling up these motions for potential applications. We identify three types of rotaxane muscles, namely, "daisy chain", "press", and "cage" rotaxanes, and discuss their mech. actuation driven by ions, pH, light, solvents, and redox stimuli. Different applications of these rotaxane-based mol. muscles are possible at various length scales. On a mol. level, they have been harnessed to create adjustable receptors and to control electronic communication between chem. species. On the mesoscale, they have been incorporated into artificial muscle materials that amplify their concerted motions and forces, making future applications at macroscopic length scales look feasible. We emphasize how rotaxanes constitute a remarkably versatile platform for directing force and motion, owing to the wide range of stimuli that can be used to actuate them and their diverse modes of mech. switching as dictated by the stereochem. of their mech. bonds, i.e., their mechanostereochem. We hope that this Account will serve as an exposition that sets the stage for new applications and materials that exploit the capabilities of rotaxanes to transduce mech. energy and help in paving the path going forward to genuine AMMs.
- 21Campbell, C. J.; Leigh, D. A.; Vitorica-Yrezabal, I. J.; Woltering, S. L. A Simple and Highly Effective Ligand System for the Copper(I)-Mediated Assembly of Rotaxanes Angew. Chem., Int. Ed. 2014, 53 (50) 13771– 13774 DOI: 10.1002/anie.201407817There is no corresponding record for this reference.
- 22Berná, J.; Crowley, J. D.; Goldup, S. M.; Hänni, K. D.; Lee, A.-L.; Leigh, D. A. A Catalytic Palladium Active-Metal Template Pathway to [2]Rotaxanes Angew. Chem., Int. Ed. 2007, 46 (30) 5709– 5713 DOI: 10.1002/anie.200701678There is no corresponding record for this reference.
- 23(a) Jardine, F. H.; Vohra, A. G.; Young, F. J. Copper(I) Ntrato and Nitrate Complexes J. Inorg. Nucl. Chem. 1971, 33 (9) 2941– 2945 DOI: 10.1016/0022-1902(71)80056-823ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3MXltlKltro%253D&md5=b0349bce8138fcd76e7cb84ed6ae296aCopper(I) nitrato and nitrate complexesJardine, F. H.; Vohra, A. G.; Young, F. J.Journal of Inorganic and Nuclear Chemistry (1971), 33 (9), 2941-5CODEN: JINCAO; ISSN:0022-1902.Complexes of the type CuNO3(ZPh3)3 (Z = P, As, Sb) were prepd. and converted into CuNO3(ZPh3)(biL) (where biL = 1,10-phenanthroline, 2,2'-biquinoline, 2-(2-pyridyl)quinoline, and 2,2'-bipyridine). Under mild conditions CuNO3(PPh3)3 also forms the ionic complexes [Cu(PPh3)2(biL)]NO2 when reacted with these ligands. The tertiary arsine and stibine complexes can be converted into [Cu(biL)2]NO3 complexes by reacting them with excess bidentate ligand.(b) Kaeser, A.; Mohankumar, M.; Mohanraj, J.; Monti, F.; Holler, M.; Cid, J.-J.; Moudam, O.; Nierengarten, I.; Karmazin-Brelot, L.; Duhayon, C.; Delavaux-Nicot, B.; Armaroli, N.; Nierengarten, J.-F. Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine Ligands Inorg. Chem. 2013, 52 (20) 12140– 12151 DOI: 10.1021/ic402004223bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsFGrs7nK&md5=940e12636184a3e4e12435e32a7ca043Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine LigandsKaeser, Adrien; Mohankumar, Meera; Mohanraj, John; Monti, Filippo; Holler, Michel; Cid, Juan-Jose; Moudam, Omar; Nierengarten, Iwona; Karmazin-Brelot, Lydia; Duhayon, Carine; Delavaux-Nicot, Beatrice; Armaroli, Nicola; Nierengarten, Jean-FrancoisInorganic Chemistry (2013), 52 (20), 12140-12151CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)Prepn. of [Cu(NN)(PP)]+ derivs. was systematically studied starting from two libraries of phenanthroline (NN) derivs. and bis-phosphine (PP) ligands, namely, (A) 1,10-phenanthroline (phen), neocuproine (2,9-dimethyl-1,10-phenanthroline, dmp), bathophenanthroline (4,7-diphenyl-1,10-phenanthroline, Bphen), 2,9-diphenethyl-1,10-phenanthroline (dpep), and 2,9-diphenyl-1,10-phenanthroline (dpp); (B) bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)benzene (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppFc), and bis[(2-diphenylphosphino)phenyl] ether (POP). Whatever the bis-phosphine ligand, stable heteroleptic [Cu(NN)(PP)]+ complexes were obtained from the 2,9-unsubstituted-1,10-phenanthroline ligands (phen and Bphen). By contrast, heteroleptic complexes obtained from dmp and dpep are stable in the solid state, but a dynamic ligand exchange reaction is systematically obsd. in soln., and the homoleptic/heteroleptic ratio is highly dependent on the bis-phosphine ligand. Detailed anal. revealed that the ligand exchange dynamic equil. is mainly influenced by the relative thermodn. stability of different possible complexes. Finally, in the case of dpp, only homoleptic complexes were obtained whatever the bis-phosphine ligand. Obviously, steric effects resulting from the presence of the bulky Ph rings on the dpp ligand destabilize the heteroleptic [Cu(NN)(PP)]+ complexes. In addn. to the remarkable thermodn. stability of [Cu(dpp)2]BF4, this neg. steric effect drives the dynamic complexation scenario toward almost exclusive formation of homoleptic [Cu-(NN)2]+ and [Cu-(PP)2]+ complexes. This work provides definitive rationalization of the stability of [Cu(NN)(PP)]+ complexes, marking the way for future developments in this field.
- 24Holm, R. H.; Donahue, J. P. A Thermodynamic Scale for Oxygen Atom Transfer Reactions Polyhedron 1993, 12 (6) 571– 589 DOI: 10.1016/S0277-5387(00)84972-424https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXisVajsb0%253D&md5=ebbec091c8107b77154d709487ba52c6A thermodynamic scale for oxygen atom transfer reactionsHolm, R. H.; Donahue, James P.Polyhedron (1993), 12 (6), 571-89CODEN: PLYHDE; ISSN:0277-5387.An extensive compilation of data on thermodn. (enthalpy and free energy) of oxo transfer reactions; bond energies were also considered,.
- 25McPherson, L. D.; Drees, M.; Khan, S. I.; Strassner, T.; Abu-Omar, M. M. Multielectron Atom Transfer Reactions of Perchlorate and Other Substrates Catalyzed by Rhenium Oxazoline and Thiazoline Complexes: Reaction Kinetics, Mechanisms, and Density Functional Theory Calculations Inorg. Chem. 2004, 43 (13) 4036– 4050 DOI: 10.1021/ic049894525https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXksVeisL0%253D&md5=d61c829a059ed43fff403b95fddc311aMultielectron Atom Transfer Reactions of Perchlorate and Other Substrates Catalyzed by Rhenium Oxazoline and Thiazoline Complexes: Reaction Kinetics, Mechanisms, and Density Functional Theory CalculationsMcPherson, Lee D.; Drees, Markus; Khan, Saeed I.; Strassner, Thomas; Abu-Omar, Mahdi M.Inorganic Chemistry (2004), 43 (13), 4036-4050CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)The title complexes, the Re(O)L2(Solv)+ complexes (L = hoz, 2-(2'-hydroxyphenyl)-2-oxazoline(-) or thoz, 2-(2'-hydroxyphenyl)-2-thiazoline(-); Solv = H2O or CH3CN), are effective catalysts for the following fundamental oxo transfer reaction between closed shell mols.: XO + Y → X + YO. Among suitable oxygen acceptors (Y's) are org. thioethers and phosphines, and among suitable oxo donors (XO's) are pyridine N-oxide (PyO), t-BuOOH, and inorg. oxyanions. One of the remarkable features of these catalysts is their high kinetic competency in effecting perchlorate redn. by pure atom transfer. Oxo transfer to rhenium(V) proceeds cleanly to afford the cationic dioxorhenium(VII) complex Re(O)2L2+ in a two-step mechanism, rapid substrate (XO) coordination to give the precursor adduct cis-ReV(O)(OX)L2+ followed by oxygen atom transfer (OAT) as the rate detg. step. Electronic variations with PyO derivs. demonstrated that electron-withdrawing substituents accelerate the rate of ReVII(O)2L2+ formation from the precursor adduct cis-ReV(O)(OX)L2+. The activation parameters for OAT with picoline N-oxide and chlorate have been measured; the entropic barrier to oxo transfer is essentially zero. The potential energy surface for the reaction of Re(O)(hoz)2(OH2)+ with PyO was defined, and all pertinent intermediates and transition states along the reaction pathway were located by d. functional theory (DFT) calcns. (B3LYP/6-31G*). In the second half of the catalytic cycle, Re(O)2L2+ reacts with oxygen acceptors (Y's) in second-order reactions with associative transition states. The rate of OAT to substrates spans a remarkable range of 0.1-106 L mol-1 s-1, and the substrate reactivity order is Ph3P > dialkyl sulfides > alkyl aryl sulfides > Ph2S ∼ DMSO, which demonstrates electrophilic oxo transfer. Competing deactivation and inhibitory pathways as well as their relevant kinetics are also reported.
- 26(a) Saibil, H. Chaperone Machines for Protein Folding, Unfolding and Disaggregation Nat. Rev. Mol. Cell Biol. 2013, 14 (10) 630– 642 DOI: 10.1038/nrm365826ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVeisrvF&md5=67ad948e3c1bacac4fb0b21b4a84c077Chaperone machines for protein folding, unfolding and disaggregationSaibil, HelenNature Reviews Molecular Cell Biology (2013), 14 (10), 630-642CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)A review. Mol. chaperones are diverse families of multidomain proteins that have evolved to assist nascent proteins to reach their native fold, protect subunits from heat shock during the assembly of complexes, prevent protein aggregation or mediate targeted unfolding and disassembly. Their increased expression in response to stress is a key factor in the health of the cell and longevity of an organism. Unlike enzymes with their precise and finely tuned active sites, chaperones are heavy-duty mol. machines that operate on a wide range of substrates. The structural basis of their mechanism of action is being unraveled (in particular for the heat shock proteins HSP60, HSP70, HSP90 and HSP100) and typically involves massive displacements of 20-30 kDa domains over distances of 20-50 Å and rotations of up to 100°.(b) Xu, Z.; Horwich, A. L.; Sigler, P. B. The Crystal Structure of the Asymmetric GroEL-GroES-(ADP)7 Chaperonin Complex Nature 1997, 388 (6644) 741– 750 DOI: 10.1038/4194426bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXls1GltLo%253D&md5=34087d9539ef63ba088f6775aa5ee841The crystal structure of the asymmetric GroEL-GroES-(ADP)7 chaperonin complexXu, Zhaohui; Horwich, Arthur L.; Sigler, Paul B.Nature (London) (1997), 388 (6644), 741-750CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)Chaperonins assist protein folding with the consumption of ATP. They exist as multi-subunits protein assemblies comprising rings of subunits stacked back to back. In Escherichia coli, asym. intermediates of GroEL are formed with the co-chaperonin GroES and nucleotides bound only to one of the seven-subunit rings (the cis ring) and not to the opposing ring (the trans ring). The structure of the GroEL-GroES-(ADP)7 complex reveals how large en bloc movements of the cis ring's intermediate and apical domains enable bound GroES to stabilize a folding chamber with ADP confined to the cis ring. Elevation and twist of the apical domains double the vol. of the central cavity and bury hydrophobic peptide-binding residues in the interface with GroES, as well as between GroEL subunits, leaving a hydrophilic cavity lining that is conducive to protein folding. An inward tilt of the cis equatorial domain causes an outward tilt in the trans ring that opposes the binding of a second GroES. When combined with new functional results, this neg. allosteric mechanism suggests a model for an ATP-driven folding cycle that requires a double toroid.(c) Wang, J.; Chen, L. Domain Motions in GroEL upon Binding of an Oligopeptide J. Mol. Biol. 2003, 334 (3) 489– 499 DOI: 10.1016/j.jmb.2003.09.074There is no corresponding record for this reference.
- 27(a) Kishi, N.; Li, Z.; Yoza, K.; Akita, M.; Yoshizawa, M. An M2L4 Molecular Capsule with an Anthracene Shell: Encapsulation of Large Guests up to 1 nm J. Am. Chem. Soc. 2011, 133 (30) 11438– 11441 DOI: 10.1021/ja203702927ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXosFymu7w%253D&md5=7a863b7469695496769cff841905244cAn M2L4 Molecular Capsule with an Anthracene Shell: Encapsulation of Large Guests up to 1 nmKishi, Norifumi; Li, Zhiou; Yoza, Kenji; Akita, Munetaka; Yoshizawa, MichitoJournal of the American Chemical Society (2011), 133 (30), 11438-11441CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A new M2L4 mol. capsule with an arom. shell (I) was prepd. using two Pd(II) ions and four bisanthracene ligands. The self-assembled capsule possesses a cavity with a diam. of ∼1 nm that can encapsulate medium-sized spherical and planar mols. as well as a very large mol. (C60) in quant. yields. The encapsulated guests are fully segregated and shielded from the external environment by the large anthracene panels.(b) Wood, D. M.; Meng, W.; Ronson, T. K.; Stefankiewicz, A. R.; Sanders, J. K. M.; Nitschke, J. R. Guest-Induced Transformation of a Porphyrin-Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene Receptor Angew. Chem., Int. Ed. 2015, 54 (13) 3988– 3992 DOI: 10.1002/anie.20141198527bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXksVCru7k%253D&md5=ea01ec3dc7f7a3139489b2a811024193Guest-Induced Transformation of a Porphyrin-Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene ReceptorWood, Daniel M.; Meng, Wenjing; Ronson, Tanya K.; Stefankiewicz, Artur R.; Sanders, Jeremy K. M.; Nitschke, Jonathan R.Angewandte Chemie, International Edition (2015), 54 (13), 3988-3992CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The combination of a bent diamino(nickel(II) porphyrin) with 2-formylpyridine and FeII yielded an FeII4L6 cage. Upon treatment with the fullerenes C60 or C70, this cage was found to transform into a new host-guest complex incorporating three FeII centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsatn. at one of the FeII centers as the result of the incommensurate metal-to-ligand ratio, which enabled the prepn. of a heterometallic cone-shaped CuIFeII2L4 adduct of C60 or C70.
- 28(a) Nigg, E. A. Cyclin-dependent Protein Kinases: Key Regulators of the Eukaryotic Cell Cycle BioEssays 1995, 17 (6) 471– 480 DOI: 10.1002/bies.950170603There is no corresponding record for this reference.(b) Bloom, J.; Cross, F. R. Multiple Levels of Cyclin Specificity in Cell-cycle Control Nat. Rev. Mol. Cell Biol. 2007, 8 (2) 149– 160 DOI: 10.1038/nrm210528bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXotFKmuw%253D%253D&md5=72e7e2fbc11d6613035cdca1c084815dMultiple levels of cyclin specificity in cell-cycle controlBloom, Joanna; Cross, Frederick R.Nature Reviews Molecular Cell Biology (2007), 8 (2), 149-160CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)A review. Cyclins regulate the cell cycle by binding to and activating cyclin-dependent kinases (Cdks). Phosphorylation of specific targets by cyclin-Cdk complexes sets in motion different processes that drive the cell cycle in a timely manner. In budding yeast, a single Cdk is activated by multiple cyclins. The ability of these cyclins to target specific proteins and to initiate different cell cycle events might, in some cases, reflect the timing of the expression of the cyclins; in others, it might reflect intrinsic properties of the cyclins that render them better suited to target particular proteins.(c) Hut, R. A.; Beersma, D. G. M. Evolution of Time-Keeping Mechanisms: Early Emergence and Adaptation to Photoperiod Philos. Trans. R. Soc., B 2011, 366 (1574) 2141– 2154 DOI: 10.1098/rstb.2010.040928chttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3MnitFGitg%253D%253D&md5=c4a3cdf0d021081ec77209237949e855Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiodHut R A; Beersma D G MPhilosophical transactions of the Royal Society of London. Series B, Biological sciences (2011), 366 (1574), 2141-54 ISSN:.Virtually all species have developed cellular oscillations and mechanisms that synchronize these cellular oscillations to environmental cycles. Such environmental cycles in biotic (e.g. food availability and predation risk) or abiotic (e.g. temperature and light) factors may occur on a daily, annual or tidal time scale. Internal timing mechanisms may facilitate behavioural or physiological adaptation to such changes in environmental conditions. These timing mechanisms commonly involve an internal molecular oscillator (a 'clock') that is synchronized ('entrained') to the environmental cycle by receptor mechanisms responding to relevant environmental signals ('Zeitgeber', i.e. German for time-giver). To understand the evolution of such timing mechanisms, we have to understand the mechanisms leading to selective advantage. Although major advances have been made in our understanding of the physiological and molecular mechanisms driving internal cycles (proximate questions), studies identifying mechanisms of natural selection on clock systems (ultimate questions) are rather limited. Here, we discuss the selective advantage of a circadian system and how its adaptation to day length variation may have a functional role in optimizing seasonal timing. We discuss various cases where selective advantages of circadian timing mechanisms have been shown and cases where temporarily loss of circadian timing may cause selective advantage. We suggest an explanation for why a circadian timing system has emerged in primitive life forms like cyanobacteria and we evaluate a possible molecular mechanism that enabled these bacteria to adapt to seasonal variation in day length. We further discuss how the role of the circadian system in photoperiodic time measurement may explain differential selection pressures on circadian period when species are exposed to changing climatic conditions (e.g. global warming) or when they expand their geographical range to different latitudes or altitudes.
- 29Whiteoak, C. J.; Britovsek, G. J. P.; Gibson, V. C.; White, A. J. P. Electronic Effects in Oxo Transfer Reactions Catalysed by Salan Molybdenum(VI) cis-dioxo Complexes Dalton. Trans. 2009, 13, 2337– 2344 DOI: 10.1039/b820754bThere is no corresponding record for this reference.
- 30(a) Ballardini, R.; Balzani, V.; Credi, A.; Gandolfi, M. T.; Venturi, M. Artificial Molecular-Level Machines: Which Energy To Make Them Work? Acc. Chem. Res. 2001, 34 (6), 445− 455.There is no corresponding record for this reference.(b) Coskun, A.; Banaszak, M.; Astumian, R. D.; Stoddart, J. F.; Grzybowski, B. A. Great Expectations: Can Artificial Molecular Machines Deliver on Their Promise? Chem. Soc. Rev. 2012, 41 (1) 19– 30 DOI: 10.1039/C1CS15262A30bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFKntrjN&md5=90c437fa644e77a30ac1bbe4f01404b2Great expectations: can artificial molecular machines deliver on their promise?Coskun, Ali; Banaszak, Michal; Astumian, R. Dean; Stoddart, J. Fraser; Grzybowski, Bartosz A.Chemical Society Reviews (2012), 41 (1), 19-30CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A review. The development and fabrication of mech. devices powered by artificial mol. machines is one of the contemporary goals of nanoscience. Before this goal can be realized, however, we must learn how to control the coupling/uncoupling to the environment of individual switchable mols., and also how to integrate these bistable mols. into organized, hierarchical assemblies that can perform significant work on their immediate environment at nano-, micro- and macroscopic levels. In this tutorial review, we seek to draw an all-important distinction between artificial mol. switches which are now ten a penny-or a dime a dozen-in the chem. literature and artificial mol. machines which are few and far between despite the ubiquitous presence of their naturally occurring counterparts in living systems. At the single mol. level, a prevailing perspective as to how machine-like characteristics may be achieved focuses on harnessing, rather than competing with, the ineluctable effects of thermal noise. At the macroscopic level, one of the major challenges inherent to the construction of machine-like assemblies lies in our ability to control the spatial ordering of switchable mols.-e.g., into linear chains and then into muscle-like bundles-and to influence the cross-talk between their switching kinetics. In this regard, situations where all the bistable mols. switch synchronously appear desirable for maximizing mech. power generated. On the other hand, when the bistable mols. switch "out of phase," the assemblies could develop intricate spatial or spatiotemporal patterns. Assembling and controlling synergistically artificial mol. machines housed in highly interactive and robust architectural domains heralds a game-changer for chem. synthesis and a defining moment for nanofabrication.
- 31Elledge, S. J. Cell Cycle Checkpoints: Preventing an Identity Crisis Science 1996, 274 (5293) 1664– 1672 DOI: 10.1126/science.274.5293.166431https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XntlyktL0%253D&md5=285d04939bf2887ffa8ef36282cd9c54Cell cycle checkpoints: preventing an identity crisisElledge, Stephen J.Science (Washington, D. C.) (1996), 274 (5293), 1664-1671CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)A review with 72 refs. Cell cycle checkpoints are regulatory pathways that control the order and timing of cell cycle transitions and ensure that crit. events such as DNA replication and chromosome segregation are completed with high fidelity. In addn., checkpoints respond to damage by arresting the cell cycle to provide time for repair and by inducing transcription of genes that facilitate repair. Checkpoint loss results in genomic instability and has been implicated in the evolution of normal cells into cancer cells. Recent advances have revealed signal transduction pathways that transmit checkpoint signals in response to DNA damage, replication blocks, and spindle damage. Checkpoint pathways have components shared among all eukaryotes, underscoring the conservation of cell cycle regulatory machinery.
- 32Patterson, D. A.; Hennessy, J. L. Computer Organization and Design: The Hardware/Software Interface, 5th ed.; Morgan Kaufmann: Burlington, MA, 2013.There is no corresponding record for this reference.
- 33(a) Ludlow, R. F.; Otto, S. Systems chemistry Chem. Soc. Rev. 2008, 37 (1) 101– 108 DOI: 10.1039/B611921M33ahttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXmtVWhtQ%253D%253D&md5=151c83f30396538fccc0ea2f9c016d26Systems chemistryLudlow, R. Frederick; Otto, SijbrenChemical Society Reviews (2008), 37 (1), 101-108CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A tutorial review. The study of complex mixts. of interacting synthetic mols. has historically not received much attention from chemists, even though research into complexity is well established in the neighboring fields. However, with the huge recent interest in systems biol. and the availability of modern anal. techniques this situation is likely to change. In this tutorial review we discuss some of the incentives for developing systems chem. and we highlight the pioneering work in which mol. networks are making a splash. A distinction is made between networks under thermodn. and kinetic control. The former include dynamic combinatorial libraries while the latter involve pseudo-dynamic combinatorial libraries, oscillating reactions and networks of autocatalytic and replicating compds. These studies provide fundamental insights into the organizational principles of mol. networks and how these give rise to emergent properties such as amplification and feedback loops, and may eventually shed light on the origin of life. The knowledge obtained from the study of mol. networks should ultimately enable us to engineer new systems with properties and functions unlike any conventional materials.(b) Whitesides, G. M.; Ismagilov, R. F. Complexity in Chemistry Science 1999, 284 (5411) 89– 92 DOI: 10.1126/science.284.5411.8933bhttps://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXitlCns7Y%253D&md5=0ee023c01ca62e8e3466c193212c9b76Complexity in chemistryWhitesides, George M.; Ismagilov, Rustem F.Science (Washington, D. C.) (1999), 284 (5411), 89-92CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Chem. has usually represented complicated processes with simple and linear approxns. However, there is an ongoing trend towards complexity. New types of problems are stimulating the move towards the study of nonlinear process which are highly sensitive to conditions. Genomics and proteomics have encouraged research on complex systems.
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscentsci.5b00279.
Synthetic procedures and spectroscopic data for all newly reported compounds; experimental procedures for the fuel-burning systems reported in Figures 1–3 (PDF)
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