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Water Oxidation by the Manganese Cluster in Photosynthesis

  1. Per E. M. Siegbahn

Published Online: 15 SEP 2009

DOI: 10.1002/0470862106.ia620

Encyclopedia of Inorganic Chemistry

Encyclopedia of Inorganic Chemistry

How to Cite

Siegbahn, P. E. M. 2009. Water Oxidation by the Manganese Cluster in Photosynthesis. Encyclopedia of Inorganic Chemistry. .

Author Information

  1. Stockholm University, Stockholm, Sweden

Publication History

  1. Published Online: 15 SEP 2009


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 O[BOND]O 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 O[BOND]O 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.


  • photosynthesis;
  • density functional theory;
  • O[BOND]O bond formation;
  • Redox potentials;
  • pKa values;
  • spin requirement