AB-INITIO ELECTRONIC-STRUCTURE CALCULATION OF THE REDOX POTENTIALS OF BACTERIOCHLOROPHYLL AND BACTERIOPHEOPHYTIN IN SOLUTION

We have carried out self-consistent reaction field (SCRF) calculations on the bacteriochlorophyll (BChl) and bacteriopheophytin (BPh) molecules at the Hartree-Fock level using the ab initio electronic structure code PSGVB together with an accurate numerical Poisson-Boltzmann solver. These are by far the largest ab initio SCRF computations carried out to date. We calculate redox potentials of these molecules in DMF solution for several geometries and compare the results with experiments of Fajer and co-workers. While the absolute redox energies are substantially in error, due to neglect of electron correlation, the relative redox energies agree qualitatively with the experimental findings. Treatment of solvation is crucial in predicting the proper ordering of the BChl and BPh redox energies. These results have implications for calculation of redox energies of the chromophores in the photosynthetic reaction center.