KCS

The sunlight used by plants to make biological fuels through photosynthesis is harvested by light-collecting antennas. These chromophores transfer excitation energy to reaction centers where it is converted to electrochemical potebtial energy via photoinduced electron transfer. An organometallic rhodium complex has been frequently employed as an efficient catalyst for hydride transfer during chemical and electrochemical formation of NADH to selectively reduce NAD⁺. Several electrochemical NADH regeneration systems have been reported using Rh catalysts to study electron transfer phenomena. Here, we present a novel, simple system that employs only Pt nanoparticles (PtNPs) for the efficient photochemical generation of NADH. This system first demonstrated that PtNPs can be used in the visible light-driven photogeneration of NADH without an additional chromophore in the presence of a sacrificial electron donor, and can directly perform the catalysis of the NAD⁺ reduction in the absence of another homogeneous heavy-metal catalyst in aqueous media. A visible light-driven photocatalytic system for the generation of NADH from aqueous protons was examined using molecular cobaloxime catalyst. Introduction of an electron-donating or electron-withdrawing substituent in the para position of the pyridine changed the rate constant and affected the conversion efficiency. In addition, the reduction of CO₂ was carried out in the presence of formate dehydrogenase using the NADH photochemically generated using cobaloxime. Bulk electrolysis of NAD⁺ carried out with a Rh catalyst in the absence and presence of platinum nanoparticles (PtNPs) generates enzymatically active 1,4-NADH. Functionalized ITO electrodes are used to regenerate NADH using a rhodium catalyst electrochemically in a buffer solution. Amino- and mercapto-functionalized electrodes featured higher activity and stability for electrocatalytic generation of NADH than a bare ITO electrode.