On the dimerization of chlorophyll in photosystem II.

In photosystem II, absorbed light energy is transferred to a reaction centre consisting of chlorophyll units. Release of an electron from the reaction centre is the starting point for the charge separation and electron transport chain in PSII. Crystal structures of the reaction centre have identified two chlorophyll monomers forming a dimer with a partial structural overlap, thus being stabilized by van der Waals interactions. However, the magnitude of this interaction is not accurately known. In this work, the structure of the chlorophyll dimer has been optimized for the first time using dispersion-corrected density functional theory (B3LYP-DCP) revealing the magnitude of dimerization to be approximately -17 kcal mol(-1). The dispersion interaction is shown to be of great significance for the chlorophyll dimer stabilization. In addition, the redox potential of the chlorophyll dimer is calculated to be 1283 mV in good agreement with recent experimental data.