title: Low-intensity pump-probe measurements on the B800 band of Rhodospirillum molischianum.
abstract: We have measured low-intensity, polarized one-color pump-probe traces in the B800 band of the light-harvesting complex LH2 of Rhodospirillum molischianum at 77 K. The excitation/detection wavelength was tuned through the B800 band. A single-wavelength and a global target analysis of the data were performed with a model that accounts for excitation energy transfer among the B800 molecules and from B800 to B850. By including the anisotropy of the signals into the fitting procedure, both transfer processes could be separated. It was estimated in the global target analysis that the intra-B800 energy transfer, i.e., the hopping of the excitation from one B800 to another B800 molecule, takes approximately 0.5 ps at 77 K. This transfer time increases with the excitation/detection wavelength from 0.3 ps on the blue side of the B800 band to approximately 0.8 ps on the red side. The residual B800 anisotropy shows a wavelength dependence as expected for energy transfer within an inhomogeneously broadened cluster of weakly coupled pigments. In the global target analysis, the transfer time from B800 to B850 was determined to be approximately 1.7 ps at 77 K. In the single-wavelength analysis, a speeding-up of the B800 --> B850 energy transfer rate toward the blue edge of the B800 band was found. This nicely correlates with the proposed position of the suggested high-exciton component of the B850 band acting as an additional decay channel for B800 excitations.
authors.affiliation: Department of Biophysics and Physics of Complex Systems, Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. markus@nat.vu.nl
authors.forename: Markus
authors.initials: M
authors.lastname: Wendling
authors.forename: Frank van
authors.initials: Fv
authors.lastname: Mourik
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Jante M
authors.initials: JM
authors.lastname: Salverda
authors.forename: Hartmut
authors.initials: H
authors.lastname: Michel
authors.forename: Rienk van
authors.initials: Rv
authors.lastname: Grondelle
mesh_terms: D016880:Anisotropy; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D004735:Energy Transfer; D007834:Lasers; D008027:Light; D008954:Models, Biological; D010775:Photic Stimulation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D011521:Protochlorophyllide / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D012246:Rhodospirillum / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D012680:Sensitivity and Specificity
chemical_list: D001426:Bacterial Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; C001348:holochrome protein, Rhodospirillum rubrum; D011521:Protochlorophyllide