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

Protein-film voltammetry is established as an effective tool that provides insight to the redox features of various lipophilic proteins by using a simple methodology. Although the protein-film experimental set up is relatively simple, the redox mechanisms of many proteins are quite complicated, and very often they cannot be resolved without having support from adequate mathematical models. In this work we continue our contribution to modeling relevant redox mechanisms in protein-film voltammetry. We present results from the theoretical simulations of catalytic mechanism at the two-step successive surface redox reaction under conditions of square-wave voltammetry. This mechanism is assigned as a surface EEC', and it can be presented by the following simplified scheme: A(ads)+ne- ⇄ B(ads)+ne- ⇄ C(ads)+Substrate → k(cat)B(ads). Our attention is focused on several phenomena of this complex protein-film mechanism, while we give set of qualitative criteria to distinguish this mechanism from similar ones studied under voltammetric conditions. Moreover, we also provide hints to use methodologies for the determination of thermodynamic and kinetic parameters relevant to the protein-film EEC' mechanism. The considered protein-film EEC' mechanism is applicable to all lipophilic redox proteins that undergo electrochemical transformations in more than one successive electron steps. Such examples exist by proteins containing quinone moiety and some polyvalent ions of transition metals as redox active sites.