Electron-transferrates

Smith, B. B. and Hynes, J. T. Electron friction and electron transferrates at metallic electrodes,... 

Removal of iron decreases the electron-transferrate from Qa to Qb by a factor of 2-3 while reconstitution with Fe, or any other metal ion investigated, restores the transfer rate. The effect of iron removal is apparently related to electrostatics rather than to the details of the electronic structure of the metal ions. Unlike Qa in a native reaction center, Qa in Ee-depleted reaction centers can become a two-electron acceptor, indicating that Qa is accessible to solvent protons when iron is absent. Even though these results indicate that iron does not play an obligatory role in electron transfer from Qa to Qb, some other possible functional or even structural role of iron in photosynthetic organisms may yet be uncovered. 

K Sigfridsson, Hansson and P Brzezinski (1995) Electrogenic light reactions in photosystem I Resolution of electron-transferrates between the iron-sulfur centers. Proc Nat Acad Sci, USA 92 3458-3462 JE Franke, L Ciesia and JT Warden (1995) Kinetics ofPsaC reduction in photosystem I. in P Mathis (ed) Photosynthesis from Light to Biosphere. Vol 2 75-78. Kluwer 27. T Hiyama and B Ke (1972) Difference spectra and extinction coefficients of P700. Biochim Biophys Acta 267 160-171... 

Stubbe, J., Nocera, O. G.. Yee. G. S. and Chang. M. C. 2003. Radical initiation in the class I ribonucleotide reductase Long rajige proton-coupled electron transferr Chem. Rev. 103 2167 2201. 

Moser, J. et al.. Surface complexation of colloidal semiconductors strongly enhances interfacial electron-transferrates, Langmuir, 7, 3012, 1991. 

Marcus, R.A. (1990). Theory of electron-transferrates across liquid-liquid interfaces [Erratum to document cited in CAl 12(24) 225352x]. J. Phys. Chem. 94, 7742. 

Fig. 14.3 Experimental ( solid lines) and simulated (open circles) voltammograms obtained when solid Fc particles are adhered to a 25 pm diameter Pt microdisk electrode in contact with [C4mim] [PFg] in the absence a) and presence (b) of 10 mM Fc. The simulated voltammogram open circles) was calculated using parameter values of iP = 0.0025 cm s , Z) = 3.0 x 10 cm s for both Fc and Fc, n= 1, a = 0.5, and an electrode area of 4.91 x 10 cm and normalized to the peak current in b) in order to demonstrate the shape and peak potential equivalence of voltammograms obtained from dissolved and adhered material. (iP, D, n, and a are standard heterogeneous electron-transferrate constants for the electrode reactions, diffusion coefficient, the number of electrons, and electron-transfer rate constant). Adapted with permission from Zhang et al.yAnal. Chem. 2003, 75, 2694-2702 [24]. Copyright 2013, American Chemical Society...

Tsionsky M, Bard AJ, Mirkin MV (1996) Scanning electrochemical microscopy.34. Potential dependence of the electron-transferrate and film formation at the liquid/liquid interface. J Phys Chem 100(45) 17881-17888... 

The current view of the exciton dissociation into free charge carriers assumes that it only occurs at the interface between donor and acceptor materials. Model calculations on pentacene/Ceo heterojunctions gave a decrease in the electron transferrate of 2 X 10 for a 3.3 A intermolecular separation that, if correct, would make longdistance electron transfer irrelevant for such materials. However, this distance... 

Peterson, R. R. and D. E. Chffel. 2006. Scanning electrochemical microscopy determination of organic soluble MPC electron-transferrates. Langmuir 22 10307-10314. 

Vehnurugan, J., Sun, R, Mirkin, M. V. Scanning electrochemical microscopy with gold nanotips The effect of electrode material on electron transferrates. J. Phys. Chem. C 2008, 113, 459-464. 

In 1988, Gray and co workers reported electron transferrates between redox centers bound in large macromolecules as a function of the distance between the redox centers [8,35]. Electron transfer between ruthenium complexes [Ru(NH3)5Hist], for example, where Hist is a histidine group in a protein, was found to increase by a factor of 10 when the complexes were 2.1 A closer. This corresponds to a = 0.91 in Equation 9.9. 

Mac, M. and Wirz, J. (1993). Deriving intrinsic electron-transferrates from nonlinear Stem-Vofiner dependencies for fluorescence quenching of aromatic molecules by inorganic anions in acetonitrile. Chem. Phys. Lett., 211(1), 20-26. 

For interfacial systems, potential functions should ideally be transferrable from the gas-phase to the condensed phase. Aqueous-mineral interfaces are not in the gas phase (although they may be close, see (7)), but both the water molecules and the atoms/ions in the substrate are in contact with an environment that is very different from their bulk environment. The easiest different environment to test, especially when comparing with electronic structure calculations, is a vacuum, so there is likely to be a great deal of information available on either the surface of the solid or the gas-phase polynuclear ion or the gas-phase aquo complex (i.e., Fe(H20)63+, C03(H20)62-). The gas-phase transfer-ability requirements on potential functions are challenging, but it is difficult to imagine constructing effective potential functions for such systems without using gas-phase systems in the construction process. This means that any water molecules used on these complexes must also transfer from the gas phase to the condensed phase. A fundamental aspect of this transferability is polarization. 

To develop further C-T complexes composed of macromolecules, it is necessary to synthesize new electron-accepting polymers with good physical and chemical properties but up to now, only a few syntheses of such polymers have been reported490-494). C-T complexes offer new application possibilities of polymers as high-conductive, heat-resistant, energy-transferrable, and charge-separable materials. 

Because electron density is a local property, electron density studies of the peptide-like molecules show that the nonspherical part of the deformation density (i.e the P]m parameters of Eq. 8) remain essentially the same for a given atom in the same environment (the peptide residue, a phenyl ring, a methyl group...) [29], The same observation was made for porphyrin ligands [30] and by Brock, Dunitz, and Hirshfeld [37] for naphthalene and anthracene type molecules. All these observations suggest that the multipole parameters are highly transferrable from one atom to a chemically similar atom in different molecules and crystals. A key question is is it possible to determine for each chemical type of a given atom a small set of pseudoatom multipole parameters, and can such parameters be used to calculate electrostatic properties of new molecules To answer this question [29], two accurate but low resolution X-ray data sets (sin 0/Xmax = 0.65 A-1) were... 

Most photosynthetic eubacteria appear to contain cyclic electron transfer pathways driven by the RCs. Electrons from the secondary acceptor of the RC are transferrred first to a quinone pool and then to the secondary donor (Cyt c) via a Cyt bic complex which stores some of the electron redox energy as potential energy in the form of a transmembrane proton gradient. Evidence for cyclic electron flow in the gram-positive line has not yet been found, but it would be surprising not to find it. 

The process depicted in Figure 17.12 of transferrring electrons from photosystem II (PSII) to photosystem I (PSI) and from water to PSII is called noncyclic electron flow. The generation of ATP by this process is called noncyclic photophosphorylation. An alternative pathway for the light reactions, called cyclic electron flow, utilizes the components of photosystem I, plastocyanin, and the cytochrome b6f complex. (Figure 17.17)... 

Above all, there is need for discussion of, and hopefully agreement on, an operational test for strong-coupling collisions. We have argued here that symmetry in the angular distribution is necessary. Nikitin specifies the need for energy equilibration, and others believe phase-space theory can be applied to charge-transfer reactions where an electron is transferr between the reactants without any momentum transfer. ... 

In summary, the body of work described above indicates that the polyproline n secondary protein structure provides an extremely effective ET pathway fliat allows electrons to be transferr over very long distances (>40 A). It is interesting to note that the small distance attenuation factors observed for these systems are of the same order of magnitude as that originally claimed by Barton and co-workers [62] in DNA-based donor-acceptor compounds. However, the specific mechanism for the efficiency of the proline-bridged ET reactions is still not understood. 

First of all one should note that in separating the motions of nuclei and transferrable electrons one has used the Born-Oppenheimer approximation which means that the electron is more rapid with respect to all remaining degrees of freedom. As far as the interaction of an electron in a donor or in an acceptor with the medium is concerned, one should bear in mind that there are various types of motions in a medium with their various characteristic times. Therefore, one should distinguish the motions which are more rapid with respect to a transferrable electron, and the motions which are slower with respect to the electron s motion. 

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