Photochemical and enzymatic methanol synthesis from HCO3− by dehydrogenases using water-soluble zinc porphyrin in aqueous media

We studied the photochemical and enzymatic synthesis of methanol from HCO3− using formate dehydrogenase (FDH) isolated from Candida boidinii, aldehyde dehydrogenase (AldDH) and alcohol dehydrogenase (ADH) isolated from yeast, and the photoreduction of methyl viologen (MV2+) by the visible-light sensitization using zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of triethanolamine (TEOA). When a sample solution containing ZnTPPS, MV2+, FDH, AldDH, ADH, TEOA, and NaHCO3 in potassium phosphate buffer solution (pH 8) was irradiated, the amount of methanol produced increased with the irradiation time. After irradiation for 3 h, 4.5 μmol dm−3 of methanol was produced from 100 μmol dm−3 NaHCO3. The conversion ratio of HCO3− to methanol was approximately 4.5%. This result indicates that a system for the photochemical synthesis of methanol from HCO3− can be developed by using three dehydrogenases (FDH, AldDH, and ADH) and for the photoreduction of MV2+ through the photosensitization of ZnTPPS in aqueous media.