Density functional studies of the spin density distribution of the P865 cation radical in the reaction center of Rb sphaeroides.

Density functional calculations are used to calculate the spin density distribution for the P865 dimer cation radical in the Rb sphaeroides reaction center. Comparison between calculated and experimental hyperfine couplings is performed where good agreement is found for the four nitrogen and 121 proton methyl group hyperfine couplings. Overall, the spin density ratio between the two halves is in agreement with experimental determinations, although the calculations suggest that significant differences in this ratio exists for different regions of the bacteriochlorophyll macrocycles. Calculated spin density asymmetry changes brought about by mutational changes in the immediate amino acid environment agree with experimental interpretations.