BA and BB Absorbance Perturbations Induced by Coherent Nuclear Motions in Reaction Centers from Rhodobacter sphaeroides upon 30-fs Excitation of the Primary Donor

Subpicosecond oscillations in the B (accessory bacteriochlorophylls) band were found in native and B B -modified reaction centers from Rhodobacter sphaeroides R26 and of the mutant YM210W at 293 K using 30 fs excitation pulses at 865 nm. The (30 ± 3) and (12 ± 2) cm -1 modes were found to be enhanced with respect to the broad structure around 150 cm -1 in all reaction centers (RC). The maximal amplitude of both modes is observed in native and B B -modified RCs, while their minimal amplitude is registered in the YM210W mutant, in which the rate of ET is significantly decreased. In the presence of Q A 2- new modes at 50 and 95 cm -1 are observed, concomitant with a decrease of the 30 cm -1 mode. These results are discussed in terms of the influence of protein motions, induced by the excitation of P, on the Q Y transition of B A at 800 nm and their relation to the primary electron transfer.