Cis-trans isomerizations of β-carotene and lycopene:: A theoretical study
Cis-trans isomerizations of β-carotene and lycopene:: A theoretical study
复制标题
DOI：
10.1021/jp8019705
复制
发表时间：
2008-09-25
影响因子：
3.3
通讯作者：
Hu, Ching-Han
中科院分区：
文献类型：
--
作者：
Guo, Wen-Hsin;Tu, Cheng-Yi;Hu, Ching-Han
通过量子化学计算研究了多烯和两种 C40H56 胡萝卜素、β-胡萝卜素和番茄红素在基单线态 (S-0) 和三线态 (T-1) 状态下的全反式到单顺式异构化。在含有 n 个乙炔单元 (P-n) 的多烯的 So 态下，我们发现中心 C=C 旋转的能垒随着 n 的增加而减小。然而，相反，在 T-1 态，旋转势垒随着 n 的增加而增加。对于 C40H56 胡萝卜素，番茄红素的旋转势垒低于相应的 β-胡萝卜素。这种差异使得室温下番茄红素的旋转速率比 β-胡萝卜素高 1-2 个数量级。对于这两种胡萝卜素，向 13-顺式异构体旋转的障碍最低。相对丰度按以下顺序排列：全反式 > 9-顺式 > 13-顺式 > 15-顺式。尽管番茄红素的5-顺式异构体在顺式异构体中具有最低的能量，但由于非常大的旋转势垒，其从全反式形式的形成受到限制。讨论了这项研究可能的生理意义。
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.