Nicotinamide adenine dinucleotide as a photocatalyst

Abstract

Nicotinamide adenine dinucleotide (NAD⁺) is a key redox compound in all living cells responsible for energy transduction, genomic integrity, life-span extension, and neuromodulation. Here, we report a new function of NAD⁺ as a molecular photocatalyst in addition to the biological roles. Our spectroscopic and electrochemical analyses reveal light absorption and electronic properties of two p-conjugated systems of NAD⁺. Furthermore, NAD⁺ exhibits a robust photostability under UV-Vis-NIR irradiation. We demonstrate photocatalytic redox reactions driven by NAD⁺, such as O₂ reduction, H₂O oxidation, and the formation of metallic nanoparticles. Beyond the traditional role of NAD⁺ as a cofactor in redox biocatalysis, NAD⁺ executes direct photoactivation of oxidoreductases through the reduction of enzyme prosthetic groups. Consequently, the synergetic integration of biocatalysis and photocatalysis using NAD⁺ enables solar-to-chemical conversion with the highest-ever-recorded turnover frequency and total turnover number of 1263.4 hour⁻¹ and 1692.3, respectively, for light-driven biocatalytic trans-hydrogenation.