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991.
Carolyn E. Lubner Jacob H. Artz David W. Mulder Aisha Oza Rachel J. Ward S. Garrett Williams Anne K. Jones John W. Peters Ivan I. Smalyukh Vivek S. Bharadwaj Paul W. King 《Chemical science》2022,13(16):4581
One of the many functions of reduction–oxidation (redox) cofactors is to mediate electron transfer in biological enzymes catalyzing redox-based chemical transformation reactions. There are numerous examples of enzymes that utilize redox cofactors to form electron transfer relays to connect catalytic sites to external electron donors and acceptors. The compositions of relays are diverse and tune transfer thermodynamics and kinetics towards the chemical reactivity of the enzyme. Diversity in relay design is exemplified among different members of hydrogenases, enzymes which catalyze reversible H2 activation, which also couple to diverse types of donor and acceptor molecules. The [FeFe]-hydrogenase I from Clostridium acetobutylicum (CaI) is a member of a large family of structurally related enzymes where interfacial electron transfer is mediated by a terminal, non-canonical, His-coordinated, [4Fe–4S] cluster. The function of His coordination was examined by comparing the biophysical properties and reactivity to a Cys substituted variant of CaI. This demonstrated that His coordination strongly affected the distal [4Fe–4S] cluster spin state, spin pairing, and spatial orientations of molecular orbitals, with a minor effect on reduction potential. The deviations in these properties by substituting His for Cys in CaI, correlated with pronounced changes in electron transfer and reactivity with the native electron donor–acceptor ferredoxin. The results demonstrate that differential coordination of the surface localized [4Fe–4S]His cluster in CaI is utilized to control intermolecular and intramolecular electron transfer where His coordination creates a physical and electronic environment that enables facile electron exchange between electron carrier molecules and the iron–sulfur cluster relay for coupling to reversible H2 activation at the catalytic site.Histidine coordination of the distal [4Fe–4S] cluster in [FeFe]-hydrogenase was demonstrated to tune the cluster spin-states, spin-pairing and surrounding molecular orbitals to enable more facile electron transfer compared to cysteine coordination. 相似文献
992.
Interactions between ions and itinerant charges govern electronic processes ranging from the redox chemistry of molecules to the conductivity of organic semiconductors, but remain an open frontier in the study of microporous materials. These interactions may strongly influence the electronic behavior of microporous materials that confine ions and charges to length scales comparable to proton-coupled electron transfer. Yet despite mounting evidence that both solvent and electrolyte influence charge transport through ion–charge interactions in metal–organic frameworks, fundamental microscopic insights are only just beginning to emerge. Here, through electrochemical analysis of two open-framework chalcogenides TMA2FeGe4S10 and TMA2ZnGe4S10, we outline the key signatures of ion-coupled charge transport in band-type and hopping-type microporous conductors. Pressed-pellet direct-current and impedance techniques reveal that solvent enhances the conductivity of both materials, but for distinct mechanistic reasons. This analysis required the development of a fitting method that provides a novel quantitative metric of concerted ion–charge motion. Taken together, these results provide chemical parameters for a general understanding of electrochemistry in nanoconfined spaces and for designing microporous conductors and electrochemical methods used to evaluate them.Interactions between ions and itinerant charges govern electronic processes ranging from the redox chemistry of molecules to the conductivity of organic semiconductors, but remain an open frontier in the study of microporous materials. 相似文献
993.
Allyson M. Buytendyk Yi Wang Jacob D. Graham Anil K. Kandalam Boggavarapu Kiran 《Molecular physics》2015,113(15-16):2095-2098
We report a joint photoelectron spectroscopic and theoretical study on the molecular anion, quinoline?. Analysis of the vibrationally resolved photoelectron spectrum found the adiabatic electron affinity, EAa(C9H7N), to be 0.16 ± 0.05 eV. These findings were supported by density functional theory calculations. Our experimental and computational results demonstrate the unusual electrophilicity for a polycyclic aromatic heterocycle. 相似文献
994.
The dynamic response caused by the sudden appearance of a flaw in materials in which square voids are distributed in a doubly periodic manner is investigated. A broad range of relative densities corresponding to cellular materials as well as to almost solid ones is considered. In the former case the materials are characterized by either bending or stretch dominated behavior, and different layouts corresponding to both these cases are examined. The flaw models a break of an intervoid ligament in a material which is subjected to a far-field tensile loading. Both cases of a first flaw in undamaged material as well as the case of a new flaw appearance in an already damaged material are addressed. 相似文献
995.
Cooperative,Reversible Self‐Assembly of Covalently Pre‐Linked Proteins into Giant Fibrous Structures
Saadyah Averick Orsolya Karcsony Jacob Mohin Xin Yong Nicholas M. Moellers Bradley F. Woodman Weipu Zhu Ryan A. Mehl Anna C. Balazs Tomasz Kowalewski Krzysztof Matyjaszewski 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(31):8188-8193
We demonstrate a simple bioconjugate polymer system that undergoes reversible self‐assembling into extended fibrous structures, reminiscent of those observed in living systems. It is comprised of green fluorescent protein (GFP) molecules linked into linear oligomeric strands through click step growth polymerization with dialkyne poly(ethylene oxide) (PEO). Confocal microscopy, atomic force microscopy, and dynamic light scattering revealed that such strands form high persistence length fibers, with lengths reaching tens of micrometers, and uniform, sub‐100 nm widths. We ascribe this remarkable and robust form of self‐assembly to the cooperativity arising from the known tendency of GFP molecules to dimerize through localized hydrophobic patches and from their covalent pre‐linking with flexible PEO. Dissipative particle dynamics simulations of a coarse‐grained model of the system revealed its tendency to form elongated fibrous aggregates, suggesting the general nature of this mode of self‐assembly. 相似文献
996.
Robert A. Kowtoniuk Tao Pei Caitlin M. DeAngelo Jacob H. Waldman Erin N. Guidry J. Michael Williams Robert M. Garbaccio Stephanie E. Barrett 《Journal of polymer science. Part A, Polymer chemistry》2014,52(10):1385-1391
l ‐Ornithine‐based poly(peptides) have been widely utilized in the field of drug delivery, however few studies have been conducted examining the details of polymerization. In this article, the effects of monomer concentration, polymerization kinetics, polymer molecular weight and monomer purity were investigated using l ‐carboxybenzyl (Cbz)‐ornithine as a model monomer. The mechanism of polymerization herein follows the normal amine mechanism to produce poly(peptides) having controlled molecular weights, known chain ends and a narrow polydispersity index (PDI). A preferred monomer concentration range was determined, which required minimal polymerization times and allowed for predictable and reproducible molecular weights with narrow PDIs. The impact of monomer purity on the polymerization was established and monomer purification conditions are reported, which produce high‐purity monomer after a single recrystallization. Additionally, the optimized polymerization conditions and monomer purification protocol were combined with a sequential monomer addition technique to produce high molecular weight poly(ornithine) with a narrow PDI and known chain ends. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1385–1391 相似文献
997.
Reynolds Jacob G. Cooke Gary A. Page Jason S. Warrant R. Wade 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(1):289-299
Journal of Radioanalytical and Nuclear Chemistry - Uranium is the most prevalent radioactive element in the 210 million liters of nuclear waste at the Hanford Site but the uranium speciation has... 相似文献
998.
Jacob M. Wahlen-Strothman Thomas M. Henderson Gustavo E. Scuseria 《Molecular physics》2018,116(2):186-193
Doubly occupied configuration interaction (DOCI), the exact diagonalisation of the Hamiltonian in the paired (seniority zero) sector of the Hilbert space, is a combinatorial cost wave function that can be very efficiently approximated by pair coupled cluster doubles (pCCD) at mean-field computational cost. As such, it is a very interesting candidate as a starting point for building the full configuration interaction (FCI) ground state eigenfunction belonging to all (not just paired) seniority sectors. The true seniority zero sector of FCI (referred to here as FCI0) includes the effect of coupling between all seniority sectors rather than just seniority zero, and is, in principle, different from DOCI. We here study the accuracy with which DOCI approximates FCI0. Using a set of small Hubbard lattices, where FCI is possible, we show that DOCI ~ FCI0 under weak correlation. However, in the strong correlation regime, the nature of the FCI0 wavefunction can change significantly, rendering DOCI and pCCD a less than ideal starting point for approximating FCI. 相似文献
999.
1000.
Shiva K. Rastogi Robert A. Rogers Justin Shi Christopher T. Brown Cindy Salinas Katherine M. Martin Jacob Armitage Christopher Dorsey Gao Chun Peter Rinaldi William J. Brittain 《Magnetic resonance in chemistry : MRC》2016,54(2):126-131
We report through‐space (TS) 19F–19F coupling for ortho‐fluoro‐substituted Z ‐azobenzenes. The magnitude of the TS‐coupling constant (TSJFF) ranged from 2.2–5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non‐bonded F–F distances (dFF) of 3.0–3.5 Å. These non‐bonded distances are significantly smaller than those determined by X‐ray crystallography or density functional theory, which argues that simple models of 19F–19F TS spin–spin coupling solely based dFF are not applicable. 1H, 13C and 19F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6‐311++G(d,p)] was used to calculate 19F chemical shifts, and the calculated values deviated 0.3–10.0 ppm compared with experimental values. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献