title: Dynamics of energy transfer and trapping in the light-harvesting antenna of Rhodopseudomonas viridis.
abstract: By low intensity picosecond absorption spectroscopy it is shown that the exciton lifetime in the light-harvesting antenna of Rhodopseudomonas (Rps.) viridis membranes with photochemically active reaction centers at room temperature is 60 +/- 10 ps. This lifetime reflects the overall trapping rate of the excitation energy by the reaction center. With photochemically inactive reaction centers, in the presence of P+, the exciton lifetime increases to 150 +/- 15 ps. Prereducing the secondary electron acceptor QA does not prevent primary charge separation, but slows it down from 60 to 90 +/- 10 ps. Picosecond kinetics measured at 77 K with inactive reaction centers indicates that the light-harvesting antenna is spectrally homogeneous. Picosecond absorption anisotropy measurements show that energy transfer between identical Bchlb molecules occurs on the subpicosecond time scale. Using these experimental results as input to a random-walk model, results in strict requirements for the antenna-RC coupling. The model analysis prescribes fast trapping (approximately 1 ps) and an approximately 0.5 escape probability from the reaction center, which requires a more tightly coupled RC and antenna, as compared with the Bchla-containing bacteria Rhodospirillum (R.) rubrum and Rhodobacter (Rb.) sphaeroides.
authors.affiliation: Department of Physical Chemistry, University of Umeå, Sweden.
authors.forename: F G
authors.initials: FG
authors.lastname: Zhang
authors.forename: T
authors.initials: T
authors.lastname: Gillbro
authors.forename: R
authors.initials: R
authors.lastname: van Grondelle
authors.forename: V
authors.initials: V
authors.lastname: Sundström
mesh_terms: D004735:Energy Transfer; D007700:Kinetics; D008027:Light; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D012241:Rhodopseudomonas / Q000378:metabolism*; D013997:Time Factors
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins