Charge separation in photosynthetic reaction centers

Structural influences on the direction of electron transfer (ET) in the charge separation process of Rps. viridis and Rb. sphaeroides are studied using quantum chemical models to calculate the electronic factor. Our results support the sequential mechanism for the primary charge separation. Using crystallographic coordinates refined in 1994 [1,2] (Fig. 1), we find a larger coupling between the special pair D and the accessory bacteriochlorophyll (BChl) BA of the A branch than between D and Bg of the inactive B branch. The coupling between BA and bacteriopheophytin Phi(A) is accomplished by two methyl groups, directly connected to the conjugated pi system of the chromophore. A full account of this work was recently published [3].