15N Endor Experiments on the Primary Donor Cation Radical D+ in Bacterial Reaction Center Single Crystals of RB. Shaeroides R-26

The rates of the electron transfer processes in reaction centers (RC’s) of photosynthetic bacteria are controlled both by the spatial and the electronic structure of the involved donor and acceptor molecules. The spatial structure of bacterial RC's has been determined by X-ray diffraction for Rhodopseudomonas (Rp.) viridis 1 and for Rhodobacter (Rb.) sphaeroides.2 The electronic structure of the transient radical species formed in the charge separation process can be elucidated by EPR and ENDOR techniques.3 The information is contained in the electron-nuclear hyperfine couplings (hfc’s) which, after assignment to specific nuclei, yield a detailed picture of the valence electron spin density distribution in the respective molecules.3,4