Influence of the Interfacial Peptide Organization on the Catalysis of Hydrogen Evolution
The hydrogen evolution reaction is catalyzed by peptides and proteins adsorbed on electrode materials with high overpotentials for this reaction, Such as mercury. The catalytic response characteristics are known to be very sensitive to the composition and structure of the investigated biomolecule, opening the way to the implementation of a label-free, reagentless electroanalytical method in protein analysis. Herein, it is shown using the model peptide Cys-Ala-Ala-AlaAla-Ala that the interfacial organization significantly influences the catalytic behavior. This peptide forms at the electrode two distinct films, depending on the concentration and accumulation time. The low-coverage film, composed of flat-lying molecules (area per molecule of similar to 250-290 angstrom(2)), yields a well-defined catalytic peak at potentials around -1.75 V. The high-coverage film, made of upright-oriented peptides (area per molecule of similar to 43 angstrom(2)), is catalytically more active and the peak is observed at potentials less negative by similar to 0.4 V. The higher activity, evidenced by constant-current chronopotentiometry and cyclic voltammetry, is attributed to an increase in the acid dissociation constant of the amino acid residues as a result of the low permittivity of the interfacial region, as inferred from impedance measurements. An analogy is made to the known differences in acidic-basic behaviors of solvent-exposed and hydrophobic domains of proteins.