Charge Transfer States and the Mechanism of Charge Separation in Bacterial Reaction Centers
The six pigments of the reaction center Rps. viridis consisting of the four bacteriochlorophylls BCMP, BCLP, BCMA, BCLA and the two bacteriopheophytins BPM and BPL are treated quantum mechanically as a hexamer within a π-electron approximation including extensive configuration interactions. The results indicate that the lowest charge transfer (CT) state consists of the oxydized monomer BCMA + and the reduced bacteriopheophytine BPM-which are located on the M-branch. We propose that this CT state might induce an efficient quenching mechanism for excess quanta of light absorbed after initiation of the charge separation. Thus a possible function of the so called inactive M-branch may be a protection mechanism against excitation of P+ which otherwise could damage the special pair.
KeywordsCharge Separation Special Pair Charge Transfer State Bacterial Reaction Center Excitonic Coupling
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