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Femtosecond stimulated Raman spectroscopy of the dark S1 excited state of carotenoid in photosynthetic light harvesting complex

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Yoshizawa M., Nakamura R., Yoshimatsu O., Abe K., Sakai S., Nakagawa K., Fujii R., Nango M., Hashimoto H.

2012

vol. 59

issue 1

49-52

Vibrational dynamics of the excited state in the light-harvesting complex (LH1) have been investigated by femtosecond stimulated Raman spectroscopy (FSRS). The native and reconstituted LH1 complexes have same dynamics. The ν1 (C=C stretching) vibrational mode of spirilloxanthin in LH1 shows ultrafast high-frequency shift in the S1 excited state with a time constant of 0.3 ps. It is assigned to the vibrational relaxation of the S1 state following the internal conversion from the photoexcited S2 state.

Polarization angle dependence of stark absorption spectra of spirilloxanthin bound to the reconstituted LH1 complexes using LH1-subunits isolated from the purple photosynthetic bacterium Rhodospirillum rubrum

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Horibe T., Nakagawa K., Kusumoto T., Fujii R., Cogdell R. J., Nango M., Hashimoto H.

2012

vol. 59

issue 1

97-100

Reconstituted LH1 complexes were prepared using the LH1 subunit-type complexes, isolated from the purple photosynthetic bacterium Rhodospirillum (Rs.) rubrum, and purified all-trans spirilloxanthin. Stark absorption spectra of spirilloxanthin bound to both the native and reconstituted LH1 complexes were compared in different polarization angles (χ) against the external electric field. From the polarization angle dependence of the Stark absorption spectra, two angles were determined in reference to the direction of transition dipole moment (m) of spirilloxanthin: one is the change in polarizability upon photoexcitation (Δα), θΔα and the other is the change in static dipole moment upon photoexcitation (Δμ), θΔμ. Despite the symmetric molecular structure of all-trans spirilloxanthin, its Stark absorption spectra show pronounced values of Δμ. This large Δμ values essentially caused by the effect of induced dipole moment through Δα both in the cases for native and reconstituted LH1 complexes. However, slightly different values of θΔα and θΔμ observed for the native LH1 complex suggest that spirilloxanthin is asymmetrically distorted when bound to the native LH1 complex and gives rise to intrinsic Δμ value.

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2 Acta Biochimica Polonica

2 2012

2 Fujii R.

2 Hashimoto H.

2 Nakagawa K.

2 Nango M.

1 Abe K.

1 Cogdell R. J.

1 Horibe T.

1 Kusumoto T.

1 Nakamura R.

1 Sakai S.

1 Yoshimatsu O.

1 Yoshizawa M.

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Femtosecond stimulated Raman spectroscopy of the dark S1 excited state of carotenoid in photosynthetic light harvesting complex

Polarization angle dependence of stark absorption spectra of spirilloxanthin bound to the reconstituted LH1 complexes using LH1-subunits isolated from the purple photosynthetic bacterium Rhodospirillum rubrum