Water Splitting
Photosynthetic water splitting (or oxygen evolution) is one of the most important reactions on the planet, since it is the source of nearly all the atmosphere's oxygen. Moreover, artificial photosynthetic water-splitting may contribute to the effective use of sunlight as an alternative energy-source.
The mechanism of water oxidation is still not fully elucidated, but we know many details about this process. The oxidation of water to molecular oxygen requires extraction of four electrons and four protons from two molecules of water. The experimental evidence that oxygen is released through cyclic reaction of oxygen evolving complex (OEC) within one PSII was provided by Pierre Joliot et al. They have shown that, if dark-adapted photosynthetic material (higher plants, algae, and cyanobacteria) is exposed to a series of single turnover flashes, oxygen evolution is detected with typical period-four damped oscillation with maxima on the third and the seventh flash and with minima on the first and the fifth flash (for review see ). Based on this experiment, Bessel Kok and co-workers introduced a cycle of five flash-induced transitions of the so-called S-states, describing the four redox states of OEC: When four oxidizing equivalents have been stored (at the S4-state), OEC returns to its basic and in the dark stable S0-state. Finally, the intermediate S-states were proposed by Jablonsky and Lazar as a regulatory mechanism and link between S-states and tyrosine Z.
Read more about this topic: Photosystem II
Famous quotes containing the words water and/or splitting:
“This sand seemed to us the connecting link between land and water. It was a kind of water on which you could walk, and you could see the ripple-marks on its surface, produced by the winds, precisely like those at the bottom of a brook or lake. We had read that Mussulmans are permitted by the Koran to perform their ablutions in sand when they cannot get water, a necessary indulgence in Arabia, and we now understand the propriety of this provision.”
—Henry David Thoreau (1817–1862)
“I had an old axe which nobody claimed, with which by spells in winter days, on the sunny side of the house, I played about the stumps which I had got out of my bean-field. As my driver prophesied when I was plowing, they warmed me twice,—once while I was splitting them, and again when they were on the fire, so that no fuel could give out more heat. As for the axe,... if it was dull, it was at least hung true.”
—Henry David Thoreau (1817–1862)