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

Abstract

A new method is introduced to determine the kinetic parameters of electron transfer reactions of biologically important compounds, based on the measurements of the half-peak width (ΔE p/2 ) of the square-wave voltammograms. A simple surface (diffusionless) redox reaction, and a simple electrode reaction occurring from dissolved state are considered 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 the electron transfer reaction. The dimensionless kinetic parameter K is defined as K = k s ( fD) − 0.5 for the redox reaction taking place from dissolved state, whereas for the surface redox reaction K is defined as K = k s /f (k s is the standard rate constant of electron transfer, f is the SW frequency, and D is the diffusion coefficient). A set of linear regression equations for the dependences ΔE p/2 vs. ln(K) are derived, which can be used for rapid and precise determination of the charge-transfer kinetic parameters. The estimated values for the standard rate constants of various biologically relevant redox systems using this approach are in very good agreement with the experimental values determined by other square-wave voltammetric methods. The square-wave voltammetric half-peak width method can be used as a simple and reliable alternative to other voltammetric methods developed for the kinetic characterization of electron transfer rates.

Catalytic mechanism in successive two-step protein-film voltammetry—Theoretical study in square-wave voltammetry

“…7) [25]. Alternatively, the electron transfer kinetic parameters can be estimated from the frequency dependence analysis of the half-peak widths of square-wave voltammograms, by using the analytical equations provided in our recent theoretical work [29]. For the determination of the electron transfer coefficients α, one can also use the methodology elaborated in our recent work [28].…”

“…For both, the successive two-step EE reaction and for simple twoelectron one-step surface redox reaction, the half-peak widths decrease with decreasing of the SW frequency. However, the values of the half-peak widths of the SW voltammograms for the successive two-step EE reaction are on average 40 mV broader than that of the one-step two-electron reaction [29,30]. This information can be of help to resolve (qualitatively) the doubts whether a given voltammogram is due to successive two-step EE reaction, or it is the result of a simple one-step reaction.…”

“…The redox transformations of the aforementioned proteins can only be described by theoretical models considering successive two-step electron transfer. In the last few years, we started theoretical considerations of various redox mechanisms relevant to protein-film voltammetry, and we published scores of theoretical and experimental works in the past decade [17,21,22,25,[27][28][29][30][31][32][33][34]. In this paper we consider the surface catalytic mechanism that follows the two-step surface EE (electron-electron) redox reaction, which can be described by the following reaction scheme: The common designation of this complex protein-film redox mechanism in the electrochemical terminology is a surface EEC′, or surface EECat [13,14].…”

Square-wave protein-film voltammetry: new insights in the enzymatic electrode processes coupled with chemical reactions

“…Indeed, electrode mechanisms of uniformly adsorbed redox active biological molecules coupled with follow-up or preceding chemical reactions attract significant attention as they are considered as adequate models for some physiological systems [7,13,16,17]. We have presented recently several theoretical models of surface processes coupled to chemical reactions [18][19][20][21][22][23][24][25][26][27][28], revealing a set of intriguing, unique voltammetric features under conditions of SWV. In the present work, a further attempt is made to throw a light to the specific features of surface electrode processes coupled with a follow-up, preceding or regenerative chemical reaction.…”

Simultaneous determination of catechol and hydroquinone based on poly (diallyldimethylammonium chloride) functionalized graphene-modified glassy carbon electrode

“…According to this equation, the k s for CC were calculated as 3.85 and 3.65 s −1 for HQ. Furthermore, the k s was calculated by the square-wave voltammograms [39], and the results were similar (Supplementary material).…”