Steady-state catalytic wave-shapes for 2-electron reversible electrocatalysts and enzymes.
Using direct electrochemistry to learn about the mechanism of electrocatalysts and redox enzymes requires that kinetic models be developed. Here we thoroughly discuss the interpretation of electrochemical signals obtained with adsorbed enzymes and molecular catalysts that can reversibly convert their substrate and product. We derive analytical relations between electrochemical observables (overpotentials for catalysis in each direction, positions, and magnitudes of the features of the catalytic wave) and the characteristics of the catalytic cycle (redox properties of the catalytic intermediates, kinetics of intramolecular and interfacial electron transfer, etc.). We discuss whether or not the position of the wave is determined by the redox potential of a redox relay when intramolecular electron transfer is slow. We demonstrate that there is no simple relation between the reduction potential of the active site and the catalytic bias of the enzyme, defined as the ratio of the oxidative and reductive limiting currents; this explains the recent experimental observation that the catalytic bias of NiFe hydrogenase depends on steps of the catalytic cycle that occur far from the active site [Abou Hamdan et al., J. Am. Chem. Soc. 2012, 134, 8368]. On the experimental side, we examine which models can best describe original data obtained with various NiFe and FeFe hydrogenases, and we illustrate how the presence of an intramolecular electron transfer chain affects the voltammetry by comparing the data obtained with the FeFe hydrogenases from Chlamydomonas reinhardtii and Clostridium acetobutylicum, only one of which has a chain of redox relays. The considerations herein will help the interpretation of electrochemical data previously obtained with various other bidirectional oxidoreductases, and, possibly, synthetic inorganic catalysts.
CNRS, Aix-Marseille Univ, BIP UMR 7281, IMM FR 3479, 31 chemin J. Aiguier, 13402 Marseille Cedex 20, France.
Vincent
V
Fourmond
Carole
C
Baffert
Kateryna
K
Sybirna
Thomas
T
Lautier
Abbas
A
Abou Hamdan
Sébastien
S
Dementin
Philippe
P
Soucaille
Isabelle
I
Meynial-Salles
Hervé
H
Bottin
Christophe
C
Léger
D055162:Biocatalysis; D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D046969:Clostridium acetobutylicum / Q000201:enzymology; D055664:Electrochemical Techniques; D004583:Electrons; D006864:Hydrogenase / Q000737:chemistry / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction
D007506:Iron-Sulfur Proteins; C118830:iron hydrogenase; C043296:nickel-iron hydrogenase; D006864:Hydrogenase