An investigation of slow charge separation in a Tyrosine M210 to Tryptophan mutant of the Rhodobacter sphaeroides reaction center by femtosecond mid-infrared
نویسندگان
چکیده
Energy and electron transfer in a tyrosine M210 to tryptophan (YM210W) mutant of the Rhodobacter sphaeroides reaction center (RC) were investigated through time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy at room temperature, with the aim to further characterize the primary charge separated states in the RC. This mutant is known to display slow and multi-exponential charge separation, and was used in earlier work to prove the existence of an alternative route for charge separation starting from the accessory bacteriochlorophyll in the active branch, BL. The mutant RCs were excited at 860 nm (direct excitation of the primary donor (P) BChls (PL/PM)), 795 nm (direct excitation of BL), 600 nm (unselective excitation) and 805 nm (direct excitation of both accessory bacteriochlorophyll cofactors BL and BM). Absorption changes associated with carbonyl (C=O) stretch vibrational modes of the cofactors and protein were recorded in the region between 1600 cm and 1775 cm, and both a sequential analysis and simultaneous target analysis of the data was performed. The decay of P in the YM210W mutant was multi-exponential with lifetimes of 25 ps and 111 ps. The lifetime of PBL state was ~ 6 times longer in the YM210W RC than in the R-26 RC (~ 4.3 ps vs. ~0.7 ps), and in the mid-IR difference absorption spectrum of PBL the stretching frequency of the 9-keto C=O group of BL in the ground state was located around 1678 cm, consistent with the presence of a This chapter is based on the manuscript: Natalia P. Pawlowicz, Ivo H. M. van Stokkum, Jacques Breton, Rienk van Grondelle, Michael R. Jones, submitted to PhysicalChemistry ChemicalPhysics.
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