Michiya Higuchi

Kyoto University, Kioto, Kyōto, Japan

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Publications (4)5.57 Total impact

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    ABSTRACT: Solvent effects on relaxation dynamics of a keto-carotenoid, siphonaxanthin, were investigated by means of the femtosecond time-resolved fluorescence spectroscopy. After excitation to the S2 state of siphonaxanthin, the S2-->1(n, pi*) internal conversion occurred with a time constant of 30-35 fs, followed by the 1(n, pi*)-->S1 internal conversion in 180-200 fs. Solvent dependence of the internal conversions was small, however intensities of the S1 fluorescence with its lifetime of longer than 10 ps were enhanced in methanol. These were explained by displacement of the potential surfaces and interaction through the hydrogen-bond between the C=O group of siphonaxanthin and solvents.
    Photochemical and Photobiological Sciences 10/2008; 7(10):1206-9. DOI:10.1039/b802658k · 2.27 Impact Factor
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    ABSTRACT: Excitation energy transfer processes in photosystem (PS) I complexes, isolated from the cyanobacterium Gloeobacter violaceus PCC 7421, were studied by steady-state and time-resolved fluorescence spectroscopy. The absence of the longwavelength PS I components was demonstrated by low-temperature absorption spectroscopy, and no corresponding fluorescence components were detected at −196 °C. Time-resolved fluorescence spectra and subsequent analysis of the fluorescence lifetimes of PS I complexes clearly showed that at 22 °C, thermal equilibrium was established among antenna components within 10 ps after excitation. In contrast, at −196 °C, energy flow to the trap was clearly resolved by global analysis on the basis of a single value decomposition method. It was difficult to discern reasons for the absence of the long-wavelength PS I components based on the primary structures of the major subunits of complexes in comparison with other cyanobacteria. The biological relevance of PS I fluorescence at physiological temperature is discussed based on the energy distribution among antenna components including P700, and on a comparative study with Synechocystis sp. PCC 6803.
    Photosynthesis. Energy from the Sun, 12/2007: pages 299-302;
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    ABSTRACT: Siphonaxanthin (Siph) shows a characteristic in vivo absorption band around 535 nm in the pigment-protein complexes in a green alga Codium fragile. To reveal optical properties of the keto-carotenoid, we examined the relaxation dynamics of Siph in solutions by femtosecond time-resolved fluorescence spectroscopy. The fluorescence kinetics after excitation to the S2 state were analyzed by multi-exponential functions with three components, independent of observed wavelengths and are: the 30–35 fs and the 180–200 fs components and a minor one longer than 10 ps. The 30–35 fs component well corresponded to the mirror image of the absorption spectrum in n-hexane; therefore, we assigned this component to the S2 fluorescence. The 180–200 fs component was much smaller than the 30–35 fs component in its amplitude, and its fluorescence anisotropy was higher than that of the S1 fluorescence after the S2 excitation, suggesting that its origin was not from the S2 state nor the S1 state. The possible assignment of the 180–200 fs component is discussed.
    12/2007: pages 319-322;
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    ABSTRACT: Ultrafast excitation relaxation dynamics and energy-transfer processes in the light-harvesting complex II (LHC II) of Arabidopsis thaliana were examined at physiological temperature using femtosecond time-resolved fluorescence spectroscopy. Energy transfer from lutein to Chl a proceeded with a rate constant of k(ET) = 1.8-1.9 x 10(13) s(-1) and a yield of approximately Phi(ET) = 0.70, whereas that from neoxanthin to Chl a had a rate constant of k(ET) = 6.5 x 10(11) s(-1) and a yield at the most of Phi(ET) = 0.09. Fluorescence anisotropic 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. In solution, anisotropy of lutein remained constant (0.38) independent of time, and thus a new excited state inferred between the S(2) (1B(u)) state and the S(1) (2A(g)) state was not applicable for lutein in solution. Energy migration processes among Chl a or Chl b molecules were clearly resolved by kinetic analysis. On the basis of these results, relaxation processes and energy-transfer kinetics in LHC II of A. thaliana are discussed.
    The Journal of Physical Chemistry B 07/2005; 109(25):12612-9. DOI:10.1021/jp050595q · 3.30 Impact Factor