A Hydrogen-Bond Stabilized Mechanism of Oxygen Evolution in Photosystem II: A Proposed Computational Experiment

The ability of plants to take in water and release oxygen into the atmosphere is crucial to the survival of life on Earth. During photosynthesis, water is oxidized to O2 (dioxygen) at the Oxygen Evolving Complex (OEC) of Photosystem II. Structurally, the OEC resembles a box with an open lid, consisting of metal atoms (four manganese and one calcium) bridged by oxygen atoms. The mechanism of action of this complex, however, is not well understood. Various mechanisms have been proposed in recent years to explain how the OEC oxidizes water to dioxygen, but all of these mechanisms contain gaps and require further attention. I believe I have come across a previously unconsidered feature of the OEC that is essential for its function. The oxidation of water (that is, the loss of electrons from the water molecule, resulting in its transformation to dioxygen) occurs primarily through H2O\u27s oxygen atom, where most of its electron density is located. The metal atoms of the OEC perform the oxidation. In the complex, each of these metal atoms is flanked by two oxygen atoms.. I noticed that these two oxygen atoms are perfectly positioned to serve as hydrogen-bonding “docking sites” for the two hydrogens in a water molecule while the metal atom interacts with the water molecule\u27s central oxygen atom. It is my belief that this interaction could be necessary to stabilize the water molecule as it is being oxidized. If true, it is likely that this stabilizing interaction is required for efficient water oxidation at the OEC, which has tremendous implications for the development of renewable energy technology – specifically, that including oxo bridges in the structure of synthetic water oxidation catalysts is necessary to design an efficient energy source whose only by-product is molecular oxygen. In this study, principles of physical and inorganic chemistry are applied to currently proposed OEC mechanisms to determine which is most favorable; a computational experiment will then be designed which could probe whether hydrogen bonding at the oxo bridges increases the efficiency of the OEC