Rate constants monolayer oxidation

The first exponential term in both equations is independent of the applied potential and is designated as k and A(L for the forward and backward processes, respectively. These represent the rate constants for the reaction at equilibrium, e.g. for a monolayer containing equal concentrations of both oxidized and reduced forms. However, the system is at equilibrium at E0/ and the products of the rate constant and the bulk concentration are equal for the forward and backward reactions, i.e. k must equal Therefore, the standard heterogeneous electron transfer rate constant is designated simply as k°. Substitution into Equations (2.19) and (2.20) then yields the Butler-Volmer equations as follows ... 

The formal potentials of adriamycin and quinizarin are almost identical. Therefore, binary monolayers, formed by simultaneous adsorption of both anthraquinones, exhibit only a single voltammetric peak. In these circumstances, traditional elec-troanalytical techniques cannot be used to determine the surface coverages of the individual species. However, as illustrated in Figure 5.29, the large difference in rate constant for the oxidation of the two anthraquinones can be exploited to temporally resolve the charge associated with oxidizing each adsorbate. The only requirement of this approach is that the interfacial kinetics of the individual components should be sufficiently different that two single exponential decays are observed. 

W(s rj) is the rate constant and j(s rj) the (infinitesimal) current density from a given electronic level s, f(s) the Fermi function, p(s) ihs electronic level density. Fox and Fred the population of the oxidized and reduced state, respectively, of the redox (bio)molecule close to the electrode surface, either in a monolayer film, or of mobile reactants, and e the electronic charge, a is the observable electrochemical transfer coefficient... 

Cytochrome c can be strongly adsorbed in its native state on tin oxide electrodes at coverages of several tenths of a monolayer. Measurements of unimolecular electron transfer rate constants for adsorbed cytochrome c can be readily made in the absence of solution cytochrome c using cyclic voltammetry. The kinetic results are consistent with an interfacial model involving electrostatic interaction between the tin oxide and the exposed heme edge of the cytochrome as well as an electrostatically driven adsorbate reorientation capability to account for the anomalous dependence of rate constant on scan rate. Other possible explanations for the... 

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