Visible-light-induced enzymatic reactions using an NADH regeneration system of water-soluble zinc porphyrin and homogeneous colloidal rhodium nanoparticles

Abstract

The photo and biocatalyst hybrid system is one of the most ideal artificial photosynthetic systems using solar energy to synthesize various chemicals and fuels. This study was devoted to achieving visible-light-driven molecular conversion with various enzymes using the NADH regeneration system consisting of an electron donor such as triethanol amine (TEOA), zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) as a photosensitizer and colloidal polyvinylpyrrolidone-dispersed rhodium nanoparticles (Rh-PVP) as a catalyst. The irradiation wavelength dependence of NADH regeneration with the system of TEOA, ZnTPPS, Rh-PVP and NAD⁺ was studied and the quantum efficiency for NADH regeneration at monochromatic 420 nm due to the Soret band of ZnTPPS was estimated to be ca. 0.0012%. This NADH regeneration system was also applied to various enzyme-catalyzed redox reactions. By using this NADH regeneration system in the presence of lactate or D-3-hydroxybutyrate dehydrogenases, various enantioselective molecular conversions by visible-light energy were accomplished. By using this NADH regeneration and malate dehydrogenase (decarboxylating), photo and biocatalytic CO₂ fixation to organic molecules based on carbon–carbon bond formation between pyruvate and CO₂ has been successfully achieved. The results not only show an example of colloidal metal nanoparticles used as a catalyst for selective NADH regeneration in general artificial photosynthesis but also the selective production of chemicals/solar fuels directly from CO₂ with visible-light energy.