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A New Rapid and Simple Method to Determine the Kinetics of Electrode Reactions of Biologically Relevant Compounds from the Half-Peak Width of the Square-Wave Voltammograms

This paper describes a novel theoretical methodology for the determination of the kinetic parameters of electron transfer reaction based on the half-peak width ( Ep/2) sensitivity of the square-wave voltammograms. A simple redox reactions taking place from dissolved state and a simple surface (difusionless) redox reaction have been taken as model systems. In the region of quasireversible electron transfer, the half-peak widths of theoretical square-wave voltammograms are linear functions of the logarithm of the dimensionless kinetic parameter ln(K) that characterizes the rate of electron transfer reaction. The dimensionless kinetic parameter K is defined as K = ks(fD)-0.5 for the redox reaction from dissolved state, while for the surface redox reaction K is defined as K = ks/f (ks is the standard rate constant of electron transfer, f is the SW frequency, while D is the diffusion coefficient). We give set of linear theoretical equations of the dependences  Ep/2-ln(K) that can be used for rapid and precise determination of the physical parameters describing the electron transfer reactions by the considered redox systems. The estimated values for the standard rate constants of various redox systems by using this procedure are in very good qualitative and quantitative agreement with the experimental values determined by square-wave voltammetric methods. The square-wave voltammetric half-peak width methodology can be used as a simple and reliable alternative for the other voltammetric methods developed for kinetics characterizations of the electron transfer rates.

charge-transfer kinetics; standard rate constant; square-wave voltammetry; half-peak width; theoretical calculations; protein-film voltammetry

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