Voltammetric Simulations of Multiple Electron Transfer/proton Transfer Coupled Reactions: Flavin Adenine Dinucleotide As a Model System

Cyclic voltammograms were simulated using DigiSim software for reaction mechanisms involving multiple electron transfer steps coupled to proton transfer. Specifically, the overall reaction mechanism of the form O+2e(-)+2H(+) right harpoon over left harpoon RH(2) was used to simulate experimental reduction potentials as a function of pH. The pH-dependent reduction potentials reported in the literature for flavodoxin and free flavin adenine dinucleotide were simulated based on selected reduction potentials and acid dissociation constants. Relationships between reduction potentials and acid dissociation constants are presented to model n=1 and n=2 reaction mechanisms and one- and two-proton-coupled redox reactions. Experimental parameters used in the simulations were selected such that the electron and proton transfer reactions were not rate limiting, and therefore these simulated reactions involve thermodynamic coupling rather than concerted kinetic processes.