Spectroscopic properties and the nature of reduction products of bacteriochlorophyll in solution and in the photosynthetic reaction center of Rhodobacter Sphaeroides

Using methods of density functional theory, we calculate the structure and simulate the electronic absorption spectra of the anion-radical of bacteriochlorophyll and its form protonated at the keto carbonyl group in a solution and in the photosynthetic reaction center of Rhodobacter Sphaeroides. We show that, in both cases, the best agreement between the calculated and experimental data is achieved under the assumption that the anion-radical form of bacteriochlorophyll is formed. An experimentally observed large difference between the spectral properties of the reduced form of bacteriochlorophyll in vitro and in vivo is related to peculiarities of the environment of bacteriochlorophyll in the native system and with the fact that, in this case, the initial nuclear configuration of B A has no time to completely relax in accordance with a new electronic configuration during the lifetime of the state P + B − . Taking into account the data obtained in this work, we believe that the recently proposed model of coupling of the primary charge separation in the photosynthetic reaction center of Rhodobacter Sphaeroides with the double proton transfer seems to be unlikely.