Evidence of O–O Bond Formation in the Final Metastable S<sub>3</sub> State of Nature’s Water Oxidizing Complex Implying a Novel Mechanism of Water Oxidation

2019-01-18T18:49:51Z (GMT) by Thomas A Corry Patrick J O’Malley
A novel mechanism for the final stages of Nature’s photosynthetic water oxidation to molecular oxygen is proposed. This is based on a comparison of experimental and broken symmetry density functional theory (BS-DFT) calculated geometries and magnetic resonance properties of water oxidizing complex models in the final metastable oxidation state, S<sub>3</sub>. We show that peroxo models of the S<sub>3</sub> state are in vastly superior agreement with the current experimental structural determinations compared with oxo–hydroxo models. Comparison of experimental and BS-DFT calculated <sup>55</sup>Mn hyperfine couplings for the electron paramagnetic resonance (EPR) visible form shows better agreement for the oxo–hydroxo model. An equilibrium between oxo–hydroxo and peroxo models is proposed for the S<sub>3</sub> state and the major implications for the final steps in the water oxidation mechanism are analyzed and discussed.