title: Excitation relaxation in the chemically modified photosynthetic reaction center from Rhodobacter sphaeroides 601.
abstract: The ultrafast excitation relaxation in the sodium borohydride-treated reaction center of Rhodobacter sphaeroides 601 was investigated with selective excitation. From the femtosecond pump-probe measurement at 790 nm, the excitation relaxation demonstrates a biexponential decay with time constants of about 200 fs and 1.4 ps. By comparison with the result from sodium ascorbate-pretreated modified RS601, it could be concluded that the dynamical trace at 790 nm mainly originates from the contribution of accessory bacteriochlorophyll in the active side, and the electrochromic shift arising from the induced positive charge on the special pair primarily affects the absorption band in the red region of the accessory bacteriochlorophyll in RS601. With direct excitation of the special pair, the charge separation and subsequent electron transfer were observed in borohydride-modified RS601. The 2.8 ps component was ascribed to the charge separation and electron transfer from P* to H(A). From the dynamical traces at 790, 800 and 818 nm, the ultrafast energy relaxation from the excited accessory bacteriochlorophyll in the active side is consistent with a two-step energy transfer mechanism. This dynamical observation in modified RS601 is of significance in understanding the physical mechanism of excitation relaxation and energy transfer in the photosynthetic primary process.
authors.affiliation: Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433, PR China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Guo
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liu
authors.forename: Ye
authors.initials: Y
authors.lastname: Liu
authors.forename: Yonglong
authors.initials: Y
authors.lastname: Zou
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Chunhe
authors.initials: C
authors.lastname: Xu
authors.forename: Shixiong
authors.initials: S
authors.lastname: Qian
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D001894:Borohydrides / Q000494:pharmacology*; D002478:Cells, Cultured; D004735:Energy Transfer / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D007834:Lasers; D010775:Photic Stimulation / Q000379:methods; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D012242:Rhodobacter sphaeroides / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*
chemical_list: D001894:Borohydrides; D045322:Photosynthetic Reaction Center Complex Proteins; C025364:sodium borohydride