9216 J. Am. Chem. SOC. 1993,115, 9216-9225 Isolation by High-pressure Liquid Chromatography of the Cis-Trans Isomers of P-Apo-8’-carotenal. Determination of Their &-State Configurations by NMR Spectroscopy and Prediction of Their zyxwv SI- and TI-State Configurations by Transient Raman Spectroscopy Hideki Hashimoto,+** Yousuke Miki,? Michitaka Kuki,? Toshio Shimamura,f Hiroaki Utsumi,l and Yasushi Koyama’lt Contribution from the Faculty zyxwvuts of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan, Matsushita Technoresearch Inc., Yagumo-Nakamachi, Moriguchi, Osaka 570, Japan, and NMR Application Laboratory, JEOL Ltd., Nakagami, Akishima, Tokyo 196, Japan Received May 14, 1993” Abstract: High-pressure liquid chromatography to isolate cis-trans isomers of fl-apo-S’-carotenal was developed, and the configurations of nine isomers, i.e. all-trans, 7-cis, g-cis, 13-cis, 1 5-cis, 13’-cis, 9,13-cis, 9,13’-cis, and 13,13’-cis isomers, were determined by N M R spectroscopy. The C,H- and H,H-COSY, C,H-COLOC, and H,H-ROESY spectra were recorded to assign the olefin proton signals; each cis-trans configuration was identified by the use of the chemical shifts of the olefinic protons and also by NOE correlation peaks among olefinic and methyl protons. Resonance Raman spectroscopy was applied to the above set of isomers except for 9,13’-cis: (1) The Raman spectra of the isomers, in the zyxwvutsrqp SO state, were recorded to identify the key Raman lines of each cis-trans configuration. (2) The Raman spectra of S1 species generated from the isomers were recorded by a two-color or one-color method using picosecond pulses. The C=C stretching Raman line with an abnormally high frequency showed that the zyxw S1 state probed by Raman spectroscopy is actually the 21A,- state, which is vibronically coupled with the SO, ‘A,- state through this a,-type, C=C stretching mode. The zyxwvutsr SI Raman spectra were different from one another, a fact which suggests that each S1 species takes a different configuration and that no isomerization takes place in the SI, 21A,- state. (3) The Raman spectra of T1 species which were generated through intersystem crossing or triplet sensitization were recorded by a picosecond or nanosecond pump-and-probe method. The set of T1 Raman spectra agreed with one another, and analyses by HPLC of triplet-sensitized isomerization showed efficient isomerization from each cis isomer to the all-trans isomer. Both results indicate that extremely efficient isomerization takes place from each cis to all-trans in the T1 state. Parizer- Parr-Pople calculations of the bond order predicted this efficient TI-state isomerization. Introduction Carotenoids in photosynthetic systems have dual functions of light harvesting and photoprotection,’ and a natural selection of the carotenoid configurations has been found in purple photo- synthetic bacteria in relation to the above functions: the all- trans configuration is selected by the light-harvesting complex (LHC) for the light-harvesting function, while the 15-cis configuration is selected by the reaction center (RC) for the photoprotective f u n c t i ~ n . ~ ? ~ As an attempt to reveal the reason for this natural selection, the ground-state and the excited-state properties have been compared among various cis-trans isomers of @-carotene, a prototype symmetric carotenoid: First, a set of cis-trans isomers was isolated by HPLC and their configurations were determined by N M R spectroscopy.M Second, a set of cis-trans isomers t Kwansei Gakuin University. t Present address: Department of Applied Physics, Faculty of Engineering, f Matsushita Technoresearch Inc. A JEOL Ltd. zyxwvutsrqpon * Address correspondence to this author at: Faculty of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan. Fax: 81-798-51- 0914. Phone: 81-798-53-6111 ext 5247. a Abstract published in Aduance ACS Abstracts, September 1, 1993. (1) Cogdell, R. J.; Frank, H. A. Biochim. Biophys. Acta 1987,895,63-79. (2) Koyama, Y. J. Photochem. Photobiol. B Biol. 1991, 9, 265-280. (3) Koyama, Y.; Mukai, Y. Adu. Spectrosc. 1993, 21, 49-137. (4) Tsukida, K.; Saiki, K.; Sugiura, M. J. Nutr. Sci. Vitaminol. 1981,27, (5) Tsukida, K.; Saiki, K.; Takii, T.; Koyama, Y. J. Chromatogr. 1982, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan. 551-561. 245, 359-364. 0002-7863/93/1515-9216$04.00/0 (all-trans, 7-cis, g-cis, 13-cis, and 15-cis) in the SO state was examined by NMR7and resonance Raman*spectroscopy. Third, TI species which were generated from the set of isomers were examined by time-resolved Raman9and time-resolved absorption10 spectroscopy. Fourth, S1 species generated from the isomers were examined by transient Raman and time-resolved absorption ~pectroscopy.~~-~~ Fifth, direct and triplet-sensitized photo- isomerizations as well as thermal isomerizations were analyzed by HPLC.14 Sixth, in order to explain the So-state and TI-state isomerization, the carbon+arbon bond orders of a model polyene in the SO and TI states were calculated by the Parizer-Parr- Pople (PPP) method including single- and double-excitation configurational interactions (SD-C1).14 The results can be summarized as follows: (a) In the SO state, an increase in conjugation, Le. lengthening (shortening) of the C=C (C-C) bond, takes place from both ends toward the center (6) Koyama, Y.; Hosomi, M.; Miyata, A.; Hashimoto, H.; Reames, S. A.; Nagayama, K.; Kato-Jippo, T.; Shimamura, T. J. Chromatogr. 1988, 439, AI zyxwvutsrqp 1-47? . - . . (7) Koyama, Y.; Hosomi, M.; Hashimoto, H.; Shimamura, T. J. Mol. (8) Koyama, Y.; Takatsuka, I.; Nakata, M.; Tasumi, M. J. Raman (9) Hashimoto, H.; Koyama, Y. J. Phys. Chem. 1988.92, 2101-2108. (10) Hashimoto, H.; Koyama, Y.; Ichimura, K.; Kobayashi, T. Chem. (1 1) Hashimoto, H.; Koyama, Y. Chem. Phys. Lett. 1989,154,321-325. (12) Hashimoto, H.; Koyama, Y. Chem. Phys. Lett. 1989,163,251-256. (13) Hashimoto, H.; Koyama, Y.; Hirata, Y.; Mataga, N. J. Phys. Chem. (14) Kuki, M.; Koyama, Y.; Nagae, H. J. Phys. Chem. 1991,95,7171- Strucr. 1989, 193, 185-201. Spectrosc. 1988, 19, 3 7 4 9 . Phys. Lett. 1989, 162, 517-522. 1991, 95, 3072-3076. 7 180. 0 1993 American Chemical Society