2005 Fiscal Year Final Research Report Summary
Studies on unique light-harvesting systems in photosynthesis and their applications
| Project/Area Number |
16550114
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Functional materials chemistry
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
AKIMOTO Seiji Hokkaido Univ., Grad.School of Eng., Res.Associate, 大学院・工学研究科, 助手 (40250477)
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| Project Period (FY) |
2004 – 2005
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| Keywords | photosynthesis / energy transfer / electron transfer / fluorescence / up-conversion / femtosecond / time-resolved spectroscopy / molecular assembly |
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| Research Abstract |
Ultrafast excitation relaxation dynamics and energy transfer processes in the light-harvesting complex II(LHC II) of Arabidopsis thaliana and those in chloroplasts of the siphonaxanthin(Siph)-containing green alga Codium fragile, were examined at physiological temperature using femtosecond time-resolved fluorescence spectroscopy. In the A.thaliana LHC II, energy transfer from lutein to Chl α proceeded with a rate constant of k_<ET>=1.8-1.9×10^<13>s^<-1> and a yield of approximately φ_<ET>=0.70, whereas that from neoxanthin to Chl α had a rate constant of k_<ET>=6.5×10^<11>s^<-1> and a yield at the most of φ_<ET>=0.09. Fluorescence anisotropy decay of lutein in LHC II showed a value larger than 0.4 at the initial state and decayed to approximately 0.1 in 0.3 ps, indicating that two lutein molecules interact with each other in LHC II. On the other hand, Siph in the C.fragile chloroplasts exhibited a new absorption band at approximately 530 nm. Based on fluorescence anisotropy decay and an anisotropy value of r(t)=0.30, the origin of this band was determined as a new excited state (S_X) located between the S_2 and S_1 states. The S_2 (or S_x) fluorescence lifetime of Siph was observed as being identical both in a benzene solution and in the chloroplasts, indicating that an efficient Siph-to-chlorophyll (Chl) α energy transfer is achieved only via the S_1 state of Siph. This was confirmed by fluorescence anisotropy decay measurements ; the Siph S_1 fluorescence lost its polarization with a time constant 400 fs, which corresponded to the energy transfer time from the S_1 state of Siph to the Chl α.
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