Picosecond absorption spectroscopy was used to monitor laser-induced oxidation-reductions of reaction center (RC) bacteriochlorophyll (P) and bacteriopheophytin (I) in Rhodopseudomonas sphaeroides RC preparations on exposure to different chemicals. The DrO isotope substitution of H20 or partial substitution of water by organic solvents (ethylene glycol, glycerol, propylene glycol, dimethyl sulfoxide) causes the appearance of a fast, nanosecond component of P+ reduction, the result of an increased probability of recombination of the primary ion-radical products P+II + PI. The effect is accompanied by a noticeable slowing down of electron transfer from photoreduced bacteriopheophytin to the primary quinone acceptor QA. The effect of the organic solvents, kncwn as cryoprotectors, is correlated with their degree of hydrophobicity, i.e. the ability to penetrate the RC protein and interact with bound water and protein hydrogen bonds. The conclusion drawn from the data is that the dielectric relaxation processes through which the intermediate energy levels of the carriers in the PIQA system are lowered to levels necessary for the stabilization of the photochemically separated charges proceed with the involvement of protons of the nearest water-protein surrounding of the RC pigments and electron transport cofactors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.