Evaluating the role of acidic, basic, and polar amino acids and dipeptides on a molecular electrocatalyst for H₂ oxidation

Abstract

Outer coordination sphere interactions reduce the overpotential for H2 oxidation catalysts (brown ellipse) compared to those that have –COOH groups but don't have stabilizing interactions (blue ellipse).

Photo‐Driven Hydrogen Evolution by an Artificial Hydrogenase Utilizing the Biotin‐Streptavidin Technology

“…Substitution of the serine residue S112 by either an Asp (Sav S112D, TON = 920 after 6 h, light green trace, Figure ,b ) or a Arg (Sav S112R, TON = 970 after 6 h, turquoise trace, Figure ,b ) lead to an increase in TON compared to Sav WT (green trace, Figure ,b ). We speculate that this might be due to the presence of close lying amino acids capable of acting as a proton relay, potentially facilitating outer‐sphere protonation of the Co‐H species, as suggested in related studies . Thus an increase in the rate of H 2 formation at the ArM, and a concomitant removal of reducing equivalents from the system, would be expected.…”

Hydrogen evolution from water catalyzed by cobalt-mimochrome VI*a, a synthetic mini-protein

“…The efficiency of these enzymes is ascribed to the protein matrix, which provides a defined environment for the active site to tune reduction potential, provide second-sphere interactions, and transfer electrons and protons 4,7,8. Synthetic H 2 -evolution electrocatalysts have been reported with second-sphere interactions or proton shuttling sites proposed to lower overpotentials; most require organic solvents or water-solvent mixtures,9–12 but a few function in water 13–15…”

Unifying Activity, Structure, and Spectroscopy of [NiFe] Hydrogenases: Combining Techniques To Clarify Mechanistic Understanding

“…It has become increasingly apparent that outer sphere effects in the protein are important, and the best hydrogenase-inspired molecular catalysts incorporate proton transfer pathways. [26][27][28] Understanding of residues involved in proton transfer in [NiFe] hydrogenase catalysis is still fairly rudimentary, however. [29][30][31][32] A number of residues in the vicinity of the active site have been identified by site-selective mutagenesis as being critical to catalysis, with specific mutations greatly impairing, or completely suppressing, catalytic activity.…”