Hydrogenases interconvert H2 and protons at high rates and with high energy efficiencies, providing inspiration for the development of molecular catalysts. To understand how the protein scaffold can influence a catalytically active site we have been designing artificial enzymes with using a well understood H2 oxidation complex, [Ni(PR2NR'2)2]2+, as a core. By attaching amino acids or dipeptides, the resulting complexes (CyAA) can catalyze fully reversible H2 production/oxidation, a feature reminiscent of the hydrogenase enzymes, and require both outer coordination sphere interactions and the introduction of a proton transfer pathway. Arginine and phenylalanine result in the fastest reversible catalysts, but require different conditions to achieve reversibility. Acidic, protic solutions are a consistent feature to achieve reversibility, conditions relevant for fuel cells, however, both temperature and solvent can control reversibility. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site, and the subtle cooperative interactions that contribute to reversibility will be discussed within the context of additional studies of natural and non-natural amino acids which do not operate reversibly. Larger dipeptide complexes will also be discussed, as we move to a more complex outer coordination sphere. Importantly, this work shows that outer coordination sphere interactions can play an equally important role for artificial enzymes as the protein scaffold does for redox active enzymes.

Artifical enzymes: Attaching a protein-like scaffold on molecular catalysis is essential for high efficiency

254th National Meeting (2017)

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