title: Spectral exhibition of electron-vibrational relaxation in P* state of Rhodobacter sphaeroides reaction centers.
abstract: Electron-vibrational relaxation in the excited state of the primary electron donor, bacteriochlorophyll dimer P, in the reaction centers (RCs) of purple photosynthetic bacteria Rhodobacter sphaeroides is modeled. A multimode model of three states (i.e., the ground state Pg, initially excited P1*, and relaxed excited P2*) is used to calculate the incoherent dynamics of the difference (ΔA) spectra on a femtosecond timescale for the YM210 W mutant RCs. The relaxation processes are described by the step-ladder model. The model shows that the electron-vibrational relaxation in the excited state of P is visualized by the transient red shift of the stimulated emission from P*. The dynamics of this shift is observed as a change in the ΔA spectrum shape in its red-most part, within a few hundreds of femtoseconds after excitation. As a result, an initial rise in the red-side ΔA kinetics is delayed with respect to the blue-side kinetics. The time constant of the P1* → P2* electronic relaxation (54 fs) and the Pg, P1*, and P2* vibrational relaxations (120 fs), used in the model, provided the best fit of the experimental time-resolved ΔA spectra and kinetics at 90 and 293 K. The possible nature of the P1* → P2* electronic relaxation is discussed.
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russia, yakov@genebee.msu.su.
authors.forename: Andrei G
authors.initials: AG
authors.lastname: Yakovlev
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Shuvalov
mesh_terms: D001429:Bacteriochlorophylls / Q000378:metabolism*; D004579:Electron Transport; D007700:Kinetics; D008962:Models, Theoretical; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000502:physiology*; D013057:Spectrum Analysis
chemical_list: D001429:Bacteriochlorophylls; D045322:Photosynthetic Reaction Center Complex Proteins