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

Abstract

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.