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Primary Charge Separation Routes in the BChl:BPhe Heterodimer Reaction Centers of Rhodobacter sphaeroides†
journal contribution
posted on 1999-05-19, 00:00 authored by Marion E. van Brederode, Ivo H. M. van Stokkum, Evaldas Katilius, Frank van Mourik, Michael R. Jones, Rienk van GrondelleEnergy transfer and the primary charge separation process are studied as a function of excitation
wavelength in membrane-bound reaction centers of Rhodobacter sphaeroides in which the excitonically
coupled bacteriochlorophyll homodimer is converted to a bacteriochlorophyll-bacteriopheophytin heterodimer, denoted D [Bylina, E. J., and Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7226]. In
the HM202L heterodimer reaction center, excitation of D using 880 nm excitation light results in a 43 ps
decay of the excited heterodimer, D*. The decay of D* results for about 30% in the formation of the
charge separated state D+QA- and for about 70% in a decay directly to the ground state. Upon excitation
of the monomeric bacteriochlorophylls using 798 nm excitation light, approximately 60% of the excitation
energy is transferred downhill to D, forming D*. Clear evidence is obtained that the other 40% of the
excitations results in the formation of D+QA- via the pathway BA* → BA+HA- → D+HA- → D+QA-. In
the membrane-bound “reversed” heterodimer reaction center HL173L, the simplest interpretation of the
transient absorption spectra following B excitation is that charge separation occurs solely via the slow
D*-driven route. However, since a bleach at 812 nm is associated with the spectrum of D* in the HL173L
reaction center, it cannot be excluded that a state including BB is involved in the charge separation process
in this complex.
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excitation wavelengthB excitationbacteriochlorophyll homodimerpathway B880 nm excitation light resultscharge separation processHL 173L reaction center812 nmstate D43 ps decayB B798 nm excitation lightexcitation energycharge separationexcitations resultsRhodobacter sphaeroidesground statemonomeric bacteriochlorophyllsU.S.Aabsorption spectraPrimary Charge Separation RoutesHM 202L heterodimer reaction center
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