A role for manganese in oxygen evolution in photosynthesis

Abstract

The prospects are shrinking rapidly for a future for society based on liquid hydrocarbons as a major source of energy. Among the wide array of alternative sources that are currently undergoing scrutiny, much attention is attracted to the photolysis of water to produce hydrogen and oxygen gases. Water, the starting material, does not suffer from lack of abundance, and there is every likelihood that the environmental consequences of water splitting will be negligible. Solar radiation is the obvious candiate for the ultimate energy source, but of course water cannot be photolyzed directly by the relatively low-energy wave-lengths, greater than 300 nm, that penetrate the earth's atmosphere. Nevertheless, the photolysis of water to produce O{sub 2} and reduced substances, with reduction potentials equivalent to that of H{sub 2}, is accomplished efficiently using sunlight by higher plant photosynthesis. There are even organisms that, under special conditions, will evolve H{sub 2} gas photosynthetically, but not efficiently when coupled with O{sub 2} production. To produce a molecule of O{sub 2} from water requires the removal of four electrons from two H{sub 2}O molecules.