Kara Bren

Mini-enzymes for Hydrogen Production and Small Molecule Activation

In nature, energy storage and small-molecule activation reactions are catalyzed by enzymes that facilitate multi-electron, multi-proton reactions. Inspired by nature’s catalysts, we are employing simple metallopeptides and metalloporphyrin-peptide assemblies as catalysts of energy-relevant reactions. In this talk, the catalytic activity of these engineered mini-enzymes toward the reduction of aqueous protons and nitrite will be described.  The first of these catalysts is acetylated cobalt-substituted microperoxidase-11 (CoMP11-Ac). CoMP11-Ac is an electrocatalyst for hydrogen production from water at neutral pH with high faradaic efficiency and low sensitivity to oxygen. Investigation of mechanism reveals that the choice of buffer influences the mechanism of the electrocatalytic reaction. A related catalyst is cobalt mimochrome VI*a (CoMC6*a), a small synthetic protein consisting of a cobalt deuteroporphyrin and two covalently attached peptides. The structure of CoMC6*a can be altered by changing solution conditions, and we show that enhancing folding decreases the overpotential for hydrogen production. Finally, we report results on cobalt complexes of peptides with the sequence XXH, models of the amino-terminal copper- and nickel-binding (ATCUN) motif. The cobalt complex of GGH (CoGGH) catalyzes proton reduction electrocatalytically and in the presence of a photosensitizer. Furthermore, CoGGH shows remarkable activity toward nitrite reduction, yielding ammonium as a major product. Optimization of conditions for catalytic activity and ongoing studies of mechanism will be discussed.