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| 79.2 - Winter 2005 | ||||||||||||
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Breaking Down the Water Molecule
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By Vadim Tsipenyuk
The oxygen-evolving complex (OEC) is the active site of water oxidation in plants. Understanding the mechanism of the OEC may help scientists create alternate sources of energy. (Credit: Victor S Batista)
The reaction of gaseous hydrogen and oxygen releases water and massive amounts of energy. Though a car powered entirely by the reaction of water and light seems far-fetched, the research of Gary W. Brudvig, professor and chair of chemistry, and Victor Batista, associate professor of chemistry, may one day make this a reality.
Aerobic life on earth is made possible by plants that split water molecules through photosynthesis, thereby releasing oxygen into the atmosphere. The key enzyme involved in this process is the photosystem II (PS II) complex, whose central element is the oxygen-evolving complex (OEC). It is here that a series of oxidation-reduction reactions involving manganese ions take place, driving the process of water-splitting.
In the paper they recently submitted to The Royal Society of Chemistry Journal of Photochemical & Photobiological Sciences, Brudvig and Batista present some novel ideas about the mechanism of water-splitting. One such proposal is that the arginine 357 residue in the OEC acts as a catalytic base in the reaction—an unusual role for arginine residues. Using computational chemistry and quantum mechanics, Batista helped develop a model of the OEC, which he then incorporated, using molecular mechanics, into a model of the entire PS II complex that closely fits experimental data.
According to James P. McEvoy, a postdoctoral associate in the Brudvig lab, the current focus of PS II research is “to understand how nature accomplishes this very important reaction, [because], having understood this reaction, we are in a better position to mimic it artificially.” In fact, Brudvig and his colleagues have already had some success in mimicking the OEC with inorganic materials. These inorganic mimics are the key to the eventual creation of alternate sources of fuel (see “Alternative Energy Sources” on p. 20 of this issue). By catalyzing the reaction of water-splitting on an industrial scale, an inorganic mimic of the entire PS II complex could generate the hydrogen and oxygen gas needed for powering everything from automobiles to turbines, with water as the only byproduct.
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