Artificial Photosynthesis for Production of ATP, NAD(P)H, and Hydrogen Peroxide

The initial product of photosynthesis is NADPH (dihydronicotinamide adenine dinucleotide phosphate), which is produced from the oxidized form (NADP⁺) by reduction with two electrons and one proton released from Photosystem I (PSI) via ferredoxin. The proton gradient generated across the thylakoid membrane produces a proton-motive force, which is utilized to synthesize ATP by the use of ATP synthase. NADPH is used as a hydride source in the Calvin–Benson cycle to produce sugars by photosynthesis. In addition to NADP⁺, PSI can reduce O₂ by two electrons with two protons to produce hydrogen peroxide (H₂O₂), which can be used as a fuel in H₂O₂ fuel cells. This Minireview focuses on artificial photosynthetic systems to produce the products of natural photosynthesis, such as ATP, NAD(P)H and H₂O₂ from NAD⁺ and O₂ with water using solar energy, respectively. ATP was produced by use of an artificial photosynthetic membrane, composed of a photosynthetic reaction center mimic that pumps protons into the interior of the liposome, where F-type ATP synthase was incorporated. Solar-driven catalytic water splitting produces hydrogen, which can reduce NAD⁺ to NADH with an iridium complex catalyst in a slightly alkaline solution at room temperature. H₂O₂ has been produced by the combination of four-electron oxidation of H₂O with four protons to evolve O₂ and two-electron/two-proton reduction of O₂ under sun-light irradiation. H₂O₂ can also be produced by direct reaction of H₂ and O₂ by the combination of an iridium complex catalyst and flavin coenzyme.