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

Abstract

Redox mechanisms in which the redox transformation is coupled to other chemical reactions are of significant interest since they are regarded as relevant models for many physiological systems. Protein-film voltammetry, based on surface confined electrochemical processes, is a methodology of exceptional importance, which is designed to provide information on enzyme redox chemistry. In this work, we address some theoretical aspects of surface confined electrode mechanisms under conditions of square-wave voltammetry (SWV). Attention is paid to a collection of specific voltammetric features of a surface electrode reaction coupled with a follow-up (EC rev), preceding (C rev E) and regenerative (EC') chemical reaction. While presenting a collection of numerically calculated square-wave voltammograms, several intriguing and simple features enabling kinetic characterization of studied mechanisms in time-independent experiments (i.e., voltammetric experiments at a constant scan rate) are addressed. The aim of the work is to help in designing a suitable experimental setup for studying surface electrode processes, as well as to provide a means for determination of kinetic and/or thermodynamic parameters of both electrode and chemical steps.

Theoretical Aspects of a Surface Electrode Reaction Coupled with Preceding and Regenerative Chemical Steps: Square‐wave Voltammetry of a Surface CEC’ Mechanism

“…the chemical, electrochemical, and regenerative step) take place also in the so‐called “dead‐time” (or non‐current measuring time window) of each potential pulse . As shown in our recent works , the chemical and electrochemical reactions going on in the “dead‐time” of many potential pulses may lead to phenomena that are opposite than those “expected” by EC or CE reactions. Indeed, the specific current measuring manner in SWV also contributes significantly to the phenomena observed at this complex surface electrode mechanism.…”

“…Voltammograms are simulated for small equilibrium constant of preceding chemical reaction ( K eq=0.001) and very small kinetic of preceding chemical step ( ϵ =0.001). Interestingly, the SW voltammograms, simulated under such conditions, resemble to the voltammetric patterns typical of a surface EC mechanism . An increase of K catalytic up to value of 0.25 produces decrease of the backward (reoxidation) SW current component and slight increase of the forward SWV current branch (Figure a–c).…”

“…In the end of this section, it is worth to mention that the phenomenon of “quasireversible maximum” is very useful methodology to get access to the kinetics of electron transfer reaction between working electrode and the redox adsorbates as explained in . In the elaborated surface CEC’ mechanism, the position of “quasireversible maximum” is affected neither by chemical parameters ϵ nor by catalytic parameter K catalytic (see Figure 9).…”

Diffusional Electrochemical Catalytic (EC’) Mechanism Featuring Chemical Reversibility of Regenerative Reaction-Theoretical Analysis in Cyclic Voltammetry

“…[1][2][3] The search to relate energy conversion in living cells with the enzymes redox chemistry has motivated scientists to look for simple and reliable methods to study complex protein molecules with cheap electrochemical techniques. [1][2][3][4][5][6] In parallel, significant work has been focused on the development of theoretical electrochemical methods to study the redox chemistry of enzymes, but also of other physiological compounds. [1,2,[7][8][9][10][11][12][13] Additionally, great efforts have been made in last couple of decades to comprehend the redox chemistry of many drugs, while relevant electrochemical methods were developed to get insight into the chemistry of drug-drug interactions.…”

“…[4,7,9,14] Cyclic voltammetry is recognized as the most valuable voltammetric technique, suitable for studying electrochemical and chemical features of many substances. [1][2][3][4][5][6][7][8][9]11,[14][15][16][17][18] The cyclic voltammetry allows us to get insight into chemical changes that occur during an electrochemical transformation of given "electroactive" substances at working electrode. [7] Due to many efforts focused on the designing of sustainable voltammetric experimental methods for studying redox chemistry of enzymes and drugs, in the past three decades we witness great resurgence in the development of theories of cyclic voltammetry for studying various electrode mechanisms.…”