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81.
Franco I Solomon GC Schatz GC Ratner MA 《Journal of the American Chemical Society》2011,133(39):15714-15720
We present a model molecular system with an unintuitive transport-extension behavior in which the tunneling current increases with forced molecular elongation. The molecule consists of two complementary aromatic units (1,4-anthracenedione and 1,4-anthracenediol) hinged via two ether chains and attached to gold electrodes through thiol-terminated alkenes. The transport properties of the molecule as it is mechanically elongated in a single-molecule pulling setting are computationally investigated using a combination of equilibrium molecular dynamics simulations of the pulling with gDFTB computations of the transport properties in the Landauer limit. Contrary to the usual exponential decay of tunneling currents with increasing molecular length, the simulations indicate that upon elongation electronic transport along the molecule increases 10-fold. The structural origin of this inverted trend in the transport is elucidated via a local current analysis that reveals the dual role played by H-bonds in both stabilizing π-stacking for selected extensions and introducing additional electronic couplings between the complementary aromatic rings that also enhance tunneling currents across the molecule. The simulations illustrate an inverted electromechanical single-molecule switch that is based on a novel class of transport-extension behavior that can be achieved via mechanical manipulation and highlight the remarkable sensitivity of conductance measurements to the molecular conformation. 相似文献
82.
Peterson RL Himes RA Kotani H Suenobu T Tian L Siegler MA Solomon EI Fukuzumi S Karlin KD 《Journal of the American Chemical Society》2011,133(6):1702-1705
The new cupric superoxo complex [LCu(II)(O(2)(?-))](+), which possesses particularly strong O-O and Cu-O bonding, is capable of intermolecular C-H activation of the NADH analogue 1-benzyl-1,4-dihydronicotinamide (BNAH). Kinetic studies indicated a first-order dependence on both the Cu complex and BNAH with a deuterium kinetic isotope effect (KIE) of 12.1, similar to that observed for certain copper monooxygenases. 相似文献
83.
The type 1 (T1) or blue Cu (BC) proteins are a highly studied group of electron transfer (ET) active sites in bioinorganic chemistry. In this review, we cover several more recent results which extend the understanding of the geometric and electronic structure of these interesting Cu ET sites. Spectroscopic methods in tandem with density functional theory (DFT) and time dependent-DFT (TD-DFT) calculations have been used in studies of S → Se variants as well as a series of metal-varied model complexes (M = Mn2+ → Zn2+). The ligand and metal perturbations further defined the origins of the unique spectral features of BC proteins. These unique spectral features show different temperature dependencies in different T1 sites, and contrasts drawn between their behaviors define the role of the protein in tuning the geometric and electronic structure of the BC site for function. This has been termed the ‘entatic’ or ‘rack-induced’ state in bioinorganic chemistry. 相似文献
84.
This study details the electronic structure of the heme–peroxo–copper adduct {[(F8)Fe(DCHIm)]-O2-[Cu(AN)]}+ (LS(AN)) in which O2(2–) bridges the metals in a μ-1,2 or “end-on” configuration. LS(AN) is generated by addition of coordinating base to the parent complex {[(F8)Fe]-O2-[Cu(AN)]}+ (HS(AN)) in which the O2(2–) bridges the metals in an μ-η2:η2 or “side-on” mode. In addition to the structural change of the O2(2–) bridging geometry, coordination of the base changes the spin state of the heme fragment (from S = 5/2 in HS(AN) to S = 1/2 in LS(AN)) that results in an antiferromagnetically coupled diamagnetic ground state in LS(AN). The strong ligand field of the porphyrin modulates the high-spin to low-spin effect on Fe–peroxo bonding relative to nonheme complexes, which is important in the O–O bond cleavage process. On the basis of DFT calculations, the ground state of LS(AN) is dependent on the Fe–O–O–Cu dihedral angle, wherein acute angles (<~150°) yield an antiferromagnetically coupled electronic structure while more obtuse angles yield a ferromagnetic ground state. LS(AN) is diamagnetic and thus has an antiferromagnetically coupled ground state with a calculated Fe–O–O–Cu dihedral angle of 137°. The nature of the bonding in LS(AN) and the frontier molecular orbitals which lead to this magneto-structural correlation provide insight into possible spin topology contributions to O–O bond cleavage by cytochrome c oxidase. 相似文献
85.
S?ren Wohlthat Gemma C. Solomon Noel S. Hush Jeffrey R. Reimers 《Theoretical chemistry accounts》2011,130(4-6):815-828
Principles established by Shephard and Paddon-Row for optimizing and controlling intramolecular electron transport through the modulation of interfering pathways are employed to design new molecules for steady-state conduction experiments aimed at manifesting electron?Chole conduction asymmetry in a unique way. First, a review of the basic principles is presented through application to a pertinent model system in which a molecule containing donor and acceptor terminal linking groups with an internal multiple-pathway bridge is used to span two metal electrodes. Different interference patterns are produced depending on whether the through-molecule coupling pathways are symmetric or antisymmetric with respect to a topological bisecting plane, giving rise to asymmetric electron and hole conductances at the tight-binding (Hückel) level; this process is also described from a complementary molecular-orbital viewpoint. Subsequently, a new molecular system based on organic polyradicals is designed to allow such asymmetry to be realized in single-molecule conduction experiments. These polyradicals are analyzed using analogous simple models, density-functional theory (DFT) calculations of steady-state transmission, and intermediate neglect of differential overlap (INDO) calculations of intramolecular connectivity, verifying that polyradicals at low temperatures should show experimentally measureable electron?Chole conduction asymmetry. A key feature of this system is that the polyradicals form a narrow partially occupied band of orbitals that lie within and well separated from the HOMO and LUMO orbitals of the surrounding molecular scaffold, allowing for holes and electrons to be transported through the same molecular band. 相似文献
86.
Peter Vorobieff C. Randall Truman Adam M. Ragheb Gregory S. Elliott Julia K. Laystrom-Woodard Darren M. King David L. Carroll Wayne C. Solomon 《Experiments in fluids》2011,51(3):711-722
We present quantitative analysis of image sequences of multi-stream injection nozzle flows with several different injection
geometries in an experiment simulating mixing in a chemical oxygen-iodine laser. To visualize mixing, image sequences were
acquired with planar laser-induced fluorescence (PLIF) in iodine that was injected into the main flow. The injection nozzle
consisted of a slot, ejector, and injector block, with rows of ejector and injector holes along the slot length. The ejector
flow exits in an underexpanded state so that upon expanding it forces the slot and injector flows together to enhance mixing.
For this study, the diameter and geometry of ejector holes were varied to assess their effect on mixing. Two configurations
of ejector holes were used, each with two different diameters for a total of four cases with data collected at downstream
stations. We carry out a quantitative mixing analysis for these configurations, using two methods to quantify the mixing.
The first method considers the statistics of the PLIF image intensity histograms, which are bimodal for poorly-mixed flows
and have a single peak in well-mixed flows. The second method quantifies the properties of the mixing interface. Our analysis
shows that two injection schemes significantly enhance mixing by stretching the mixing interface. 相似文献
87.
88.
89.
K. Rerbal I. Solomon J.-N. Chazalviel F. Ozanam 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):61-64
We have investigated the temperature dependence of
photoluminescence in hydrogenated amorphous silicon-carbon alloys
a-Si1-xCx:H prepared by glow discharge in the low-power regime.
The radiative recombination process, due to photocarriers trapped on
band-edge states, is in competition with the thermal escape of the
photocarriers into the mobility bands. The model gives a quantitative fit
with experiment, without any adjustable parameter, provided the width of the
band-edge distribution of states is taken as the width of the conduction
band only (measured by “photo-induced infra-red spectroscopy”) and not as
the Urbach energy, as it is usually assumed. 相似文献
90.
The use of numerical models has greatly increased our understanding of the electrical and microphysical process within electrified clouds. We use the University of Washington, 1.5-dimensional thunderstorm model to examine the effects of including a runaway electron based lightning initiation mechanism. We find that this mechanism can significantly alter the electrification history of modeled storms and produce vertical electric field profiles that are very similar to those of observed storms. To cite this article: R. Solomon et al., C. R. Physique 3 (2002) 1325–1333. 相似文献