Photochemical production of NADH using cobaloxime catalysts and visible-light energy

In this study, a visible-light-driven photocatalytic system for the generation of dihydronicotinamide adenine dinucleotide (NADH) from aqueous protons was examined using cobaloxime as a catalyst, eosin as a photosensitizer, and triethanolamine as a sacrificial electron donor. Irradiation of a reaction solution containing cobaloxime, eosin, and triethanolamine (TEOA) converted NAD ⁺ to NADH with a yield of 36% in a phosphate buffer. The reaction rates for the production of NADH were dependent on the concentrations of the catalyst, NAD ⁺, and TEOA. Introduction of an electron-donating or -withdrawing substituent in the para position of the pyridine changed the rate constant and affected the conversion efficiency. The rates obtained by the different substituents were linearly correlated with the Hammett coefficients of the introduced substituents. Last, reduction of CO ₂ was carried out in the presence of formate dehydrogenase using NADH photochemically generated using the cobaloxime/eosin/TEOA system.