期刊
JOURNAL OF PHYSICAL CHEMISTRY B
卷 112, 期 38, 页码 12158-12167出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp8019705
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资金
- National Science Council of Taiwan, Republic of China
The all-trans to mono-cis isomerizations of polyenes and two C40H56 carotenes, beta-carotene and lycopene, at the ground singlet (S-0) and triplet (T-1) states are studied by means of quantum chemistry computations. At the So state of polyenes containing n acetylene units (P-n), we find that the energy barrier of the central C=C rotation decreases with n. In contrast, however, at the T-1 state, the rotational barrier increases with n. For the C40H56 carotenes, the rotational barriers of lycopene are lower than those of their beta-carotene counterparts. This difference renders the rotational rates of lycopene to be 1-2 orders of magnitude higher than those of beta-carotene at room temperature. For both these carotenes, the barrier is lowest for the rotation toward the 13-cis isomer. The relative abundances are in the following order: all-trans > 9-cis > 13-cis > 15-cis. Although the 5-cis isomer of lycopene has the lowest energy among the cis isomers, its formation from the all-trans form is restricted, owing to a very large rotational barrier. The possible physiological implications of this study are discussed.
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