Carotenoid-Mediated Long-Range Energy Transfer in the Light Harvesting–Reaction Center Complex from Photosynthetic Bacterium Roseiflexus castenholzii

Energy Transfer and Exciton Relaxation in B880-B800-RC Complex through Two-Dimensional Electronic Spectroscopy

“…The LH1 of Rf l. castenholzii contains two rings, the periplasm-side B880 consisting of 30 strong coupled BChl a molecules plus a gap and the cytoplasm-side B800 consisting of 15 weakly coupled BChl a molecules plus a gap (Figure 1). 18 The B800 → B880 EET, with a ∼2 ps time constant obtained by pump−probe measurements, 21,22 is about 1−3 times slower than the B800 → B850 EET in LH2, 0.5−1 ps. 12,23 The energy trapping of B880 by the open and closed RC have time constants of ∼60 and ∼200 ps.…”

Light-Quality-Adapted Carotenoid Photoprotection in the Photosystem of Roseiflexus castenholzii

“…This phenomenon seems counterintuitive, as it was not seen for nir -LH-RC or other types of bacterial antennae, including LH1 and LH2 complexes. − The Q y -state energy of B800 BChl a is less than the sum of 3 Car* and 3 BChl* energy, E B800 S < E B00 T + E Car T ; therefore, the photogeneration of 3 Car* via singlet heterofission (SHF), 1 B800* + Car → 3 BChl* + 3 Car*, seems energetically unfavorable. In the case of nir -LH-RC, recent femtosecond time-resolved spectroscopic studies have shown that the B800-Car SHF reaction takes place upon selective B800 Q y excitation; however, the triplet pair ( 3 BChl*··· 3 Car*) thus generated does not result in net 3 Car* production, and instead, it involves the promotion of the B800-to-B880 SEET process. In this work, the abnormally high 3 Car* yield upon B800 Q y excitation observed for bg -LH-RC can be attributed to the specific interaction between the C9 atom (π-conjugation system) of B800 and the keto O atom of its nearest neighbor keto-γ-carotene (cf.…”