Photosystem II (PSII) is a large protein-cofactor complex, over 700 kDa in its dimeric form, widely known for its side reaction, which results in the oxidation of water to produce the oxygen in the air that we breathe1. The minutiae of its structure and function are notoriously elusive to crystallographers and spectroscopic chemists alike, due to its size and congested optical spectra. And yet, understanding the unparalleled oxidizing power of the chlorophyll P680 cation could change the future of agriculture and power generation in a world gasping for clean, renewable energies. In particular, the two charge pathways in the PSII reaction centre (RC) are not equally active and the preference for one (the D1 branch) over the other is thought to be controlled by the surrounding protein environment. The aim of this research project was to produce a working model of the PSII RC capable of describing charge transfer behaviour. Using Time Dependent Density Functional Theory to probe the excited states of the models, preferential charge transfer down the ‘active’ D1 pathway was successfully predicted. Comparison to mutant models, His-198-Ala and His-197-Ala, confirmed the reliability of the model. Also, for the first time, 22 whole amino acid residues have been included in the quantum mechanical model so that their effects on the RC cofactors can be observed.

Mapping charge transfer pathways in wild-type and mutant photosystem II using time dependent density functional theory

251st National Meeting (2016)

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