title: Orientation of B798 BChl a Q y transition dipoles in Chloroflexus aurantiacus chlorosomes: polarized transient absorption spectroscopy studies.
abstract: Isotropic and anisotropic pump-probe spectra of Cfx. aurantiacus chlorosomes were measured on the fs-through ps-time scales for the B798 BChl a Q y band upon direct excitation of the B798 band at T = 293 K and T = 90 K. Upon direct excitation of the B798 band, the anisotropy parameter value r(λ) was constant within the whole BChl a Q y band at any delay time at both temperatures. The value of the anisotropy parameter r decayed from r = 0.4 at both temperatures (at 200 fs delay time after excitation) to the steady-state values r = 0.1 at T = 293 K and to r = 0.09 at T = 90 K (at 30 ÷ 100 ps delay time after excitation). The results were considered within the framework of the model of uniaxial orientation distribution of BChl-a transition dipoles within a single Cfx. aurantiacus chlorosome. This implies that the B798 BChl a Q y transition dipoles, randomly distributed around the normal to the baseplate plane, form the angle θ with the plane. For this model, the theoretical dependence of the steady-state anisotropy parameter r on the angle θ was derived. According to the theoretical dependence r(θ), the angle θ corresponding to the experimental steady-state value r = 0.1 at T = 293 K was found to equal 55°. As the temperature drops to 90 K, the angle θ decreases to 54°.
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russian Federation.
authors.forename: Andrei
authors.initials: A
authors.lastname: Yakovlev
authors.forename: Vladimir
authors.initials: V
authors.lastname: Novoderezhkin
authors.forename: Alexandra
authors.initials: A
authors.lastname: Taisova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shuvalov
authors.forename: Zoya
authors.initials: Z
authors.lastname: Fetisova
mesh_terms: D016880:Anisotropy; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D041861:Chloroflexus / Q000378:metabolism*; D005454:Fluorescence Polarization; D015388:Organelles / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D001426:Bacterial Proteins; C026083:bacteriochlorophyll A proteins, Bacteria