Density Functional Theory Investigations of Change-Transfer Cofactors in Photosynthesis

Energy demands continue to grow as we deplete our fossil fuel resources and damage the global environment. The world is in need of affordable and efficient renewable energy, so we turn to nature to provide a blueprint. Photosynthesis performs highly efficient solar energy conversion and our goal is to better understand and replicate its design principles. Quinones play an important role in charge-transfer during photosynthesis. The two quinones in photosystem II (PSII), the primary and secondary plastoquinone, Q$_{\mathrm{A}}$ and Q$_{\mathrm{B}}$, have identical chemical structures but perform different functions, namely, Q$_{\mathrm{A}}$ participates in electron transfer reactions while Q$_{\mathrm{B}}$ conducts proton-coupled electron transfer reactions. In this study, we used density functional theory (DFT) to investigate the electronic structure, solvent effects, energy levels and magnetic properties of the primary quinone of PSII and related quinone models. We validated our DFT calculations by comparing the calculated and experimental magnetic parameters.