Calculation of the electron affinities of the chromophores involved in photosynthesis

We examine the electron affinities (EA) of the postulated electron acceptor chromophores of the photosynthetic reaction center in R. Viridis. We estimate a difference of EA's between bacteriochlorophyll-b and bacteriopheophytin-b of 0.19 eV, in excellent agreement with the experimental value reported at 0.20 eV, We estimate this difference in situ at 0.42 eV, compared to an experimental estimate of 0.34 eV. These results support those of Thompson and Zerner (J. Am. Chem. Sec. 1991, 113, 8210) that in the absence of specific interactions between BChl-L-side and the environment, electron transfer to BChl-L-side might not be directly involved in the overall electron transfer process.