Photosynthetic diode: electron transport rectification by wetting the quinone cofactor.

We report 11 μs of molecular dynamics simulations of the electron-transfer reaction between primary and secondary quinone cofactors in the bacterial reaction center. The main question addressed here is the mechanistic reason for unidirectional electron transfer between chemically identical cofactors. We find that electron is trapped at the secondary quinone by wetting of the protein pocket following electron transfer on the time-scale shorter than the backward transition. This mechanism provides effective rectification of the electron transport, making the reaction center a molecular diode operating by cyclic charge-induced electrowetting.