Sub-picosecond measurements of primary electron transfer in Rhodopseudomonas viridis reaction centers using near-infrared excitation

Rate constants for the primary photoinduced electron transfer reactions within the reaction center protein of the photosynthetic bacterium Rhodopseudomonas viridis have been measured using transient optical absorption spectroscopy following excitation of the primary donor P960 directly with 950 nm laser flashes. The time resolution of the experiments was 0.45 ps. The reduction of BPheo b as indicated by absorption changes at 543 nm exhibits monophasic kinetics with a 1.7 × 10¹¹ s^1̄ rate constant following direct excitation of P960. Spectral changes at 805 and 835 nm due to perturbations of the intermediary BChl b occur synchronously with those at 543 nm. There is no evidence for formation of BChl b^- as a distinct chemical intermediate preceding the reduction of BPheo b.