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

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) using graphitic carbon nitride (g-CN) was developed. The process involves g-CN as the photocatalyst, Cp*Rh(bpy)HO as the electron mediator, and Triethanolamine as the electron donor, facilitating the reduction of NAD and various oxidative NCBs (NCBs) 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 and NAD, the highest conversion ratio of over 99 % was obtained with BANA. After recycled for 8 times, g-CN maintained over 93.6 % catalytic efficiency. The photocatalytic cofactor regeneration showcases its outstanding performance with NAD as well as NCBs. This work significantly advances the development of photocatalytic cofactor regeneration for artificial cofactors and its potential application.