Structural characterization of the primary donor in photosynthetic bacteria by its electronic g-tensor

Semiempirical molecular orbital calculations of the electronic g-tensor have been performed on the primary donor cation radical P865+· of Rb. sphaeroides R-26 reaction centers (RCs). These calculations are based on Stone's theory for free radical doublet states and RHF-INDO wave functions and orbital energies. The result is in qualitative agreement with recent W-band (95 GHz) EPR measurements of the g-tensor in RC single crystals which show a breaking of C2 symmetry in the primary donor electronic structure.