Date of Award
Master of Science
"Low temperature absorption and nonphotochemical hole-burning (NPHB) spectroscopies were applied to the FMO antenna protein from the green sulfur bacterium Prosthecochloris (P.) aestuarii and LH2 complex of purple bacterium Rhdopseudomonas (Rps.) acidophila in order to understand the energy transfer dynamics. Hole-burning into the lowest energy absorption band at 825 nm of the FMO complex generated low energy satellite holes at 18, 24, 36, 48, 72, 120 and 165 cm−1, which led two interpretations. The possibility that some of these holes are due to correlated downward energy transfer from the two higher energy states was rejected. The results of theoretical simulations revealed that these holes are due to intermolecular phonons and low energy intramolecular vibrations of the bacteriochlorophyll (BChl) a molecule and that the 36 cm−1 and higher energy modes are most likely due to the intramolecular BChl a modes. The simulations also determined the Huang-Rhys factor (S) for the modes. They ranged between 0.05 and 0.25. The lifetimes of the highest and intermediate energy Q[Subscript y]-states, among the three states that contribute to the 825 nm band, due to downward energy transfer were found to be 26 and 99 ps, respectively, at liquid helium temperatures. The additional decay channel on the high energy side of the B800 absorption band in the LH2 was analyzed by comparing NPHB results for intact LH2 and B800-deficient LH2 complexes. The zero-phonon hole (ZPH) action spectrum of the lowest exciton level (A symmetry) and the temperature dependence of the B850 absorption band indicated that deletion of B800 molecules does not affect on the excitonic structure of the B850 ring. Those results and the fact that ZPH widths associated with the B800 band (of B800-deficient LH2) were found to be independent of [Lambda subscript B] within the band led to the tentative conclusion that the decay channel is due to mixed B800-B850 levels and the levels probably contribute significantly to the high energy side of the B800 band. These mixed states may decay by two pathways, downward relaxation to B800 levels that are mainly ""B800"" in character and to levels that are mainly ""B850"" in character."
Matsuzaki, Satoshi, "Nonphotochemical hole-burning studies of energy transfer dynamics in antenna complexes of photosynthetic bacteria" (2002). Retrospective Theses and Dissertations. 19554.