Photocatalytic regeneration of nicotinamide cofactor biomimetics drives biocatalytic reduction by Old Yellow enzymes

Abstract

A key approach in developing green chemistry involves converting solar energy into chemical energy of biomolecules through photocatalysis. Photocatalysis can facilitate the regeneration of nicotinamide cofactors during redox processes. Nicotinamide cofactor biomimetics (NCBs) are economical substitutes for natural cofactors. Here, photocatalytic regeneration of NADH and reduced NCBs (NCBs_red) using graphitic carbon nitride (g-C₃N₄) was developed. The process involves g-C₃N₄ as the photocatalyst, Cp*Rh(bpy)H₂O²⁺ as the electron mediator, and Triethanolamine as the electron donor, facilitating the reduction of NAD⁺ and various oxidative NCBs (NCBs_ox) under light irradiation. Notably, the highest reduction yield of 48.32 % was achieved with BANA⁺, outperforming the natural cofactor NAD⁺. Electrochemical analysis reveals that the reduction efficiency and capacity of cofactors relies on their redox potentials. Additionally, a coupled photo-enzymatic catalysis system was explored for the reduction of 4-Ketoisophorone by Old Yellow Enzyme XenA. Among all the NCBs_ox and NAD⁺, the highest conversion ratio of over 99 % was obtained with BANA⁺. After recycled for 8 times, g-C₃N₄ maintained over 93.6 % catalytic efficiency. The photocatalytic cofactor regeneration showcases its outstanding performance with NAD⁺ as well as NCBs_ox. This work significantly advances the development of photocatalytic cofactor regeneration for artificial cofactors and its potential application.

Keywords: Cofactor regeneration; Nicotinamide cofactor biomimetics; Old Yellow Enzymes; Photocatalysis; g-C(3)N(4).