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A structure-consistent mechanism for dioxygen formation in photosystem II
1Department of Physics, ALBA NOVA, Stockholm University, 106 91 Stockholm, Sweden. ps@physto.se
Chemistry (Weinheim an Der Bergstrasse, Germany)
|August 6, 2008
Summary
This study reveals a new mechanism for O-O bond formation in photosystem II
Area of Science:
- Biochemistry
- Photosynthesis research
- Computational chemistry
Background:
- Photosystem II (PSII) is crucial for oxygenic photosynthesis.
- The oxygen-evolving center (OEC) within PSII catalyzes water oxidation.
- Understanding O-O bond formation in PSII is key to artificial photosynthesis.
Purpose of the Study:
- Investigate the structures of lower S states in PSII.
- Elucidate the mechanism of O-O bond formation at the OEC.
- Propose a new catalytic cycle for water oxidation.
Main Methods:
- Density Functional Theory (DFT) calculations.
- Modeling of the OEC including key amino acids and Arg357.
- Analysis of S state transitions and energy diagrams.
Main Results:
- An optimized S(1) state structure was determined, consistent with EXAFS data.
- A complete catalytic cycle was proposed, explaining S(2) to S(3) relaxation.
- O-O bond formation via an oxygen radical and oxo ligand is energetically favored over reaction with external water.
Conclusions:
- A novel mechanism for O-O bond formation at the PSII OEC is proposed.
- The derived catalytic cycle rationalizes observed structural and electronic transitions.
- Water binding and exchange mechanisms at the OEC were elucidated.
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