| Co-Investigator(Kenkyū-buntansha) |
WATANABE Yasutaka Kwansei-Gakuin Univ., Fac. Sci., Prof., 理学部, 教授 (50079662)
YAMAZAKI Iwao Hokkaido Univ., Fac. Engineering, Prof., 工学部, 教授 (80002111)
KOYAMA Yasushi Kwansei-Gakuin Univ., Fac. Sci., Prof., 理学部, 教授 (90079666)
KATOH Tetzuya Kyoto Univ., Fac. Sci., Lecturer, 理学部, 講師 (30025308)
KAKITANI Toshiaki Nagoya Univ., Fac. Sci., Assoc. Prof., 理学部, 助教授 (90027350)
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| Research Abstract |
Function of carotenoids in photosynthesis was investigated, mainly on the function as efficient antenna pigments in light harvesting for photosynthesis. The main point is elucidation of mechanism of energy transfer through singlet excited states. For that purpose, isolation methods for intact carotenoid-chlorophyll protein complexes which retain complete energy transfer was developed. The analysis was mainly carried out theoretically and experimentally on pigment-protein complexes as well as isolated carotenoid molecules.
1. Cartenold-chlorophyll protein which holds full capacity of energy transfer was isolated from the brown alga for the first time. 2. Energy transfer was observed only when the absorption maximum of carotenoid is red-shifted and this is attributed to the polarizability of surrounding molecules of carotenoids. 3. The 2Ag state was detected by the timeresolved reseonance Raman scattering, which is postulated to be responsible for the energy transfer from carotenoids. Thi
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s state in the pigment-protein complex, however, could not be detected due to its very short lifetime in the complexes. 4. Fluorescence from isolated carotenoids was clearly observed and relationship to the energy transfer function was elucidated. When a keto group is present at the end of conjugated double bond of carotenoids, which induce asymmetry in carotenoid excited state, fluorescence from the S1 state was observed. Its lifetime is longer than those of carotenoids which have symmetrical structure in their excited state. These two factors can be attributed to a high transfer efficiency. In the isolated pigment-protein complex, fluorescence from carotenoid was not observed, probably due to its short lifeitme in vivo. The transfer time, estimated from the rise of chlorophyll fluorescence was shorter than 2 ps. 5. Theoretical analysis was carried out on the transfer processes. The excitation transfer matrix element was calculated considering multiconfiguration wave functions. For the energy transfer between S1 state of carotenoid and of chlorophyll, the main mechanism changed depending on the-symmetry of carotenoids. In symmetric carotenoids, the quadrupole-dipole interaction is the predominant, on the other hand, in asymmetric carotenoids, dipoledipole interaction can be a main tranfser mechasnism. This is the first theoretical analysis which clearly predict that the dipole interaction is posssible mechanism in the energy transfer in phototosynthetic pigment systems. Less
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