Browsing by Author "Tsuda, Motoyuki"

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Sub-5-fs real-time spectroscopy of transition states in bacteriorhodopsin during retinal isomerization
(2007-03-01)
Kobayashi, Takayoshi
;
Yabushita, Atsushi
;
Saito, Takashi
;
Ohtani, Hiroyuki
;
Tsuda, Motoyuki
By using a sub-5-fs visible laser pulse, we have made the first observation of the vibrational spectra of the transition state during trans-cis isomerization in the retinal chromophore of bacteriorhodopsin (bR(S68)). No instant isomerization of the retinal occurs in spite of electron promotion from the bonding pi-orbital to the anti-bonding pi*-orbital. The difference between the in-plane and out-of-plane vibrational frequencies (about 1150-1250 and 900-1000 cm(-1), respectively) is reduced during the first time period. The vibrational spectra after this period became very broad and weak and are ascribed to a "silent state." The silent state lasts for 700-900 fs until the chromophore isomerizes to the cis-C-13=C-14 conformation. The frequency of the C = C stretching mode was modulated by the torsion mode of the C-13=C-14 double bond with a period of 200 fs. The modulation was clearly observed for four to five periods. Using the empirical equation for the relation between bond length and stretching frequency, we determined the transitional C=C bond length with about 0.01 angstrom accuracy during the torsion motion around the double bond with 1-fs time resolution.
Time-Resolved Spectroscopy of Ultrafast Photoisomerization of Octopus Rhodopsin under Photoexcitation
(2012-02-16)
Yabushita, Atsushi
;
Kobayashi, Takayoshi
;
Tsuda, Motoyuki
;
電子物理學系
;
Department of Electrophysics
A primary process in vision is the cis-trans photoisomerization of a chromophore of rhodopsin, called retinal. In the present work, we have performed ultrafast time-resolved spectroscopy of octopus rhodopsin. using a sub-5-fs pulse laser. In comparison with our previous study on bacteriorhodopsin, we found that octopus rhodopsin follows similar dynamics after photoexcitation but with different time constants. Spectrogram analysis showed that a C=N stretching mode appeared directly after photoexcitation. After reaching the conical intersection region at 80 fs, the overlapping hydrogen out-of-plane and in-plane C=C-H modes emerged as distinct peaks at similar to 200 fs, finishing a rapid relaxation along the coordinate related with these modes. The intensities of these peaks and a C=C stretching mode were found to be modulated at a period of similar to 500 fs, reflecting torsional motion around the C=C double bond before thermalization with the distribution of structural variations in the all-trans structure in configuration space.