Water Oxidation by the Manganese Cluster in Photosynthesis
Published Online: 15 DEC 2011
Copyright © 2011 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Inorganic and Bioinorganic Chemistry
How to Cite
Siegbahn, P. E. M. 2011. Water Oxidation by the Manganese Cluster in Photosynthesis. Encyclopedia of Inorganic and Bioinorganic Chemistry. .
- Published Online: 15 DEC 2011
Almost all quantum chemical studies performed on enzyme mechanisms have relied on high-resolution X-ray structures as starting points. Since no such structure yet exists for photosystem II, a model study of this enzyme is unusually difficult. In this chapter, the approach adopted to obtain the mechanism for OO bond formation in this enzyme is described. Another difficulty, in common with many other enzymatic mechanisms, is that electrons and protons are stepwise removed from the active complex. A method is outlined in which accurate redox potentials and pKa values can be obtained from rather small models. In this approach, the main effects of the enzyme, homogeneous and inhomogeneous, are included. The most important result is that the OO bond is formed between an oxygen radical and an oxo group. In the S2 to S3 transition a reconstruction of the oxygen evolving complex takes place due to insertion of a water molecule. Good agreement with most experimental observations is obtained.
- density functional theory;
- OO bond formation;
- Redox potentials;
- pKa values;
- spin requirement