Excited-state properties and physiological functions of biological polyenes: the triplet-excited region of retinoids and carotenoids

Y. Koyama; Yumiko Mukai; Michitaka Kuki

doi:10.1117/12.146119

17 June 1993 Excited-state properties and physiological functions of biological polyenes: the triplet-excited region of retinoids and carotenoids

Y. Koyama, Yumiko Mukai, Michitaka Kuki

Author Affiliations +

Proceedings Volume 1921, Laser Spectroscopy of Biomolecules; (1993) https://doi.org/10.1117/12.146119
Event: Laser Spectroscopy of Biomolecules: 4th International Conference on Laser Applications in Life Sciences, 1992, Jyvaskyla, Finland

Abstract

Both experimental and theoretical results which indicate the presence of the triplet-excited region in retinoids and carotenoids are reviewed. The triplet- excited region is defined as a region where changes in the bond order take place, upon triplet excitation, toward its inversion, i.e., a double bond becomes more signal bond-like and a single bond becomes more double bond-like. (1) It has a span of approximately six conjugated double bonds, (2) it is localized in the central part of a conjugated chain, and (3) it triggers `cis' to `trans' isomerization in the T₁ state. The experimental and theoretical results include: (1) the T₁ Raman spectra of all-trans-retinal and its homologues; (2) the T₁-state isomerization of isomeric retinal; (3) the T₁-state isomerization of isomeric (beta) -carotene; (4) the PPP-SD-CI calculations of the bond orders of the carbon-carbon bonds in a set of model polyenes; and (5) the normal-coordinate analysis of the T₁ Raman lines of undeuterated and deuterated all-trans-retinal. Finally, (6) the biological implication of 'the triplet-excited region' is discussed in relation to the photo-protective function of a 15-cis carotenoid bound to the bacterial photoreaction center.

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Y. Koyama, Yumiko Mukai, and Michitaka Kuki "Excited-state properties and physiological functions of biological polyenes: the triplet-excited region of retinoids and carotenoids", Proc. SPIE 1921, Laser Spectroscopy of Biomolecules, (17 June 1993); https://doi.org/10.1117/12.146119

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