Evidence for a Very Early Intermediate in Bacterial Photosynthesis. A Photon-Echo and Hole-Burning Study of the Primary Donor Band in Rhodopseudomonas Sphaeroides

Two coherent spectroscopic methods, accumulated photon echo and population bottleneck hole-burning, have been employed in a study of the decay rate of the primary donor (P) of Rhodopseudomonas sphaeroides at 1.5 K. The decay rate is instrument-limited in the photon-echo experiment, implying a population relaxation time <100 fs. The hole-burning study revealed the P absorplion at 900 nm to be largely homogeneousy broadened, from which a decay time of ≈25 fs was inferred. Comparison of these data with a photon-echo study of the bacteriochlorophyll a monomer suggests that this ultrafast process is not due to vibrational relaxation within P*, but to an excited state electronic decay mechanism. It is suggested that the initial event after excitation in P is a very rapid charge separation within the dimer pair, prior to the electron-transfer process, which occurs on a much longer timescale

Role of charge-transfer states in bacterial photosynthesis

Photon echo, photon-echo excitation, and "hole-burning" data recorded in the 800-990 nm region of Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis reaction centers are reported. The primary process in these reaction centers, following excitation, was found to occur in ≈25 fsec; the long-wavelength band of the primary electron donor (P) was largely homogeneously broadened. In accordance with a previous explanation of hole-burning and photon-echo measurements on Rb. sphaeroides, we interpret this as resulting from a dephasing of the excitation in P into a background of strongly coupled charge-transfer states. The previously reported picosecond lifetime of the excited P state is assigned to decay of these strongly mixed states. Further, a coupling between P and an adjacent bacteriochlorophyll was observed. The extent of this coupling and the role of charge-transfer states in the functioning of reaction centers is discussed

Role of charge-transfer states in bacterial photosynthesis

Photon echo, photon-echo excitation, and "hole-burning" data recorded in the 800-990 nm region of Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis reaction centers are reported. The primary process in these reaction centers, following excitation, was found to occur in ≈25 fsec; the long-wavelength band of the primary electron donor (P) was largely homogeneously broadened. In accordance with a previous explanation of hole-burning and photon-echo measurements on Rb. sphaeroides, we interpret this as resulting from a dephasing of the excitation in P into a background of strongly coupled charge-transfer states. The previously reported picosecond lifetime of the excited P state is assigned to decay of these strongly mixed states. Further, a coupling between P and an adjacent bacteriochlorophyll was observed. The extent of this coupling and the role of charge-transfer states in the functioning of reaction centers is discussed.

Evidence for a Very Early Intermediate in Bacterial Photosynthesis. A Photon-Echo and Hole-Burning Study of the Primary Donor Band in Rhodopseudomonas Sphaeroides

Two coherent spectroscopic methods, accumulated photon echo and population bottleneck hole-burning, have been employed in a study of the decay rate of the primary donor (P) of Rhodopseudomonas sphaeroides at 1.5 K. The decay rate is instrument-limited in the photon-echo experiment, implying a population relaxation time <100 fs. The hole-burning study revealed the P absorplion at 900 nm to be largely homogeneousy broadened, from which a decay time of ≈25 fs was inferred. Comparison of these data with a photon-echo study of the bacteriochlorophyll a monomer suggests that this ultrafast process is not due to vibrational relaxation within P*, but to an excited state electronic decay mechanism. It is suggested that the initial event after excitation in P is a very rapid charge separation within the dimer pair, prior to the electron-transfer process, which occurs on a much longer timescale.

Transient IR study of Blue Light Sensing Proteins

In this work we present the identification of redox intermediates of flavin and tryptophan after photoexcitation in glucose oxidase, Y21W AppA mutant and lAppA by the means of TRIR spectroscopy