Dispersity electron transfer kinetics

Ideally, PFV requires a film of active molecules (monolayer or submonolayer) that behave independently of each other and homogeneously with regard to their electrochemical and catalytic properties. Interactions between centres in neighbouring molecules are naturally minimised by the surrounding polypeptide and ensure that PFV is relatively free from complications induced by intermolecular interactions of the type that frequently distort the voltammetry of surface-confined small molecules. Usually, however, peak widths are larger than expected due to inhomogeneity (dispersion). The activity of enzyme molecules with dispersed and poor interfacial electron-transfer kinetics (low will distort the voltammogram and complicate analysis. 

The kinetics of the oxidation of [Ru(bpy)3] by Tl " ", catalyzed by Ru02 a H20 dispersed in HNO3 (3M), have been studied, varying the concentrations of [Ru(bpy)3] " ", Tl +, T1+, catalyst and temperature. The kinetic data are consistent with an effect involving electron transfer between the electrochemically reversible redox couples [Ru(bpy)3] +/[Ru(bpy)3] and T1 /T1+, the transfer being mediated by Ru02 vH20. ... 

There is a wealth of literature on transport and kinetics in microhetero-geneous catalytic systems [175,176], the influence of particle size [177], and complicated situations in which both catalytic microparticles and electron-transfer mediators are dispersed in a polymer matrix [176-179]. The designs and uses of this type of flow-through sensors have been thoroughly reviewed [180,181]. 

Clusters, as possible catalytic reactors, are perfectly dispersed in solutions. They are thus suitable systems for observing, under quasi-homogeneous conditions by time-resolved techniques, the kinetics of catalyzed electron transfer, which would be inaccessible on a solid catalyst. It was demonstrated that the reaction of radiation-induced free radicals COT and (CH3)2COH catalyzed by metal clusters started by the storage of electrons on clusters as charge pools and that electrons were then transferred pairwise to water-producing molecular hydrogen [22,75]. 

The first explanation offered for the phenomenon of dispersive kinetics is that it is caused by a distribution of rates of primary electron transfer, and that the islowi P lifetimes originate from a minority of reaction centres from the islowi tail of this distribution. The energetic basis for this distribution could be an inhomogeneous distribution of a rate-determining parameter such as X, AG or Vda (or any combination of these) (Figure lOA). The principal alternative explanation is that the multiple lifetimes represent a time-dependent energetic relaxation of the P Ha intermediate due... 

FIGURE 10. Possible origin of dispersive kinetics of primary electron transfer. Forward electron transfer is indicated by the solid arrows, thermal repopulation of the P state (a minor process) by the dotted arrows. (A) Static heterogeneityoelectron transfer takes place from the P state to P Ha states with distribution of free energies The reaction therefore occurs with a distribution of driving forces, and hence a distribution of rates. Most thermal repopulation of the P state occurs from the P Ha" states that are highest in energy. A similar model can be constructed based upon a P —> P a" with two or more values for the... 

Gratzel M. and Frank A. J. (1982), Interfacial electron-transfer reactions in colloidal semiconductor dispersions—kinetic analysis , J. Phys. Chem. 86, 2964-2967. 

It should be noted that the irradiation of electron beam causes elastic and inelastic diffraction in the sample. On the other hand, the energy of primary electrons are dispersed or transferred to sample electrons. Nearly all of the kinetic energy is changed to heat and just a little of it is transferred to the former Cathodoluminescence and secondary electron. These are based on the images of SEM displayed on a cathode ray tube (CRT) and spots on the CRT mimic and the motion of electron beam on the sample. Hence... 

In this paper we report the results of our initial theoretical and experimental investigations into the question of dispersive kinetics for P decay in bacterial RC arising from glass-like structural heterogeneity. The decay of P is due to electron-transfer and it is generally taken that P B"H figures importantly in the formation of P H , where B and H denote the active bacteriochlorophyll and bacteriopheophytin monomers. Discussion continues on the relative importance of the one-step (superexchange) and two-step mechanisms for the production of P BH from In the latter mechanism... 

From the standard quantum mechanical expression for the rate of nonadiabatic electron-transfer, it is apparent that the pure electronic coupling matrix element (V) and adiabatic electronic energy gap (O) are important factors for consideration of dispersive kinetics of the DA —> D A electron-transfer process, where D s donor and A s acceptor. By necessity, we assume that these two variables are uncorrelated. We begin by considering dispersive kinetics from a distribution of Q-values. Next we present some of our experimental data that speak to the question of dispersive kinetics from a distribution of V-values. 

On the basis of a nonadiabatic electron-transfer theory, which exposes the homogeneous width of the nuclear factor from low frequency modes (phonons), and hole burning data we conclude that this nonexponentiality is not due to a distribution of values, f, for the relevant adiabatic electronic energy gap(s) 2. Dispersive kinetics from f in the low temperature limit are judged to be unlikely. Nevertheless, the expression (. 2) for the average electron-transfer rate constant suggests that samples which exhibit sufficiently different Fj-values for the P-band should have measurably different values for in... 

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