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Artificial co-enzyme based on carbamoyl-modified viologen derivative cation radical for formate dehydrogenase in the catalytic CO2 reduction to formate

Formate dehydrogenase (CbFDH) from Candida boidinii is a useful biocatalyst for CO2 reduction to formate in the photoredox system, and consists of a visible-light sensitizer and an electron mediator. The electron mediator, single-electron reduced 4,4′-bipyridinium salts (4,4′-BPs) represented by methylviologen act as the co-enzyme for CbFDH in the CO2 reduction to formate. Considering that the single-electron reduced 4,4′- or 2,2′-BPs activate the CbFDH-mediated CO2 reduction to formate, the architecture of the effective co-enzyme based on the chemical modification of BP is useful for the development of the catalytic reduction of CO2 to formate with CbFDH. NAD+ has a carbamoyl group or nicotinamide moiety, which can form hydrogen bonds with some amino residues in CbFDH. Thus, we predicted that the affinity of 4,4′-BP for CbFDH could be improved by introducing a carbamoyl group or nicotinamide moiety into 4,4′-BP. In this work, the interaction between the single-electron reduced 1-carbamoylmethyl-1′-methyl-4,4′-bipyridinium salt, 1,1′-dicarbamoylmethyl-4,4′-bipyridinium salt and 1-nicotinamidethyl-1′-methyl-4,4′-bipyridinium salt and CbFDH in the CO2 reduction to formate is elucidated by enzymatic kinetic analysis, the docking simulation and density functional theory calculation.