Development of a dye molecule-biocatalyst hybrid system with visible-light induced carbon-carbon bond formation from...

Recently, CO₂ utilization technology, including artificial photosynthesis, has received much attention. In this field, CO₂ is used as a feedstock for fuels, polymers and in other chemical processes. Of note are malic enzymes (MEs) which catalyze the reaction of malic acid to pyruvic acid and CO₂ with the co-enzyme NADP⁺, and catalyze the reverse reaction of pyruvic acid and CO₂ to malic acid with the co-enzyme NADPH. Thus, MEs are also an attractive biocatalyst for carbon-carbon bond formation from CO₂. Studies of the visible light-induced malic acid production from pyruvic acid and CO₂ using an electron donor, a photosensitizer, an electron mediator, ferredoxin-NADP⁺ reductase, NADP⁺, and ME have been reported. However, modification of these systems is required, as they are very complicated. In this study, the visible light-induced carbon-carbon bond formation from pyruvic acid and CO₂ with ME using the photoreduction of 1,1'-diphenyl-4,4'-bipyridinium salt derivatives as a novel electron mediator with water-soluble tetraphenylporphyrin tetrasulfonate (H₂TPPS) in the presence of triethanolamine (TEOA) as an electron donor was developed. When a sample solution containing TEOA, H₂TPPS, 1,1'-diphenyl-4,4'-bipyridinium salt derivative, pyruvic acid, and ME in CO₂-saturated bis-tris buffer was irradiated, the major product was oxaloacetic acid. Thus, a visible light-induced photoredox system for carbon-carbon bond formation from CO₂ with ME using 1,1'-diphenyl-4,4'-bipyridinium salt derivative as an electron mediator was developed.