Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization
Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization
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DOI：
10.1073/pnas.97.17.9379
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发表时间：
2000-08-15
影响因子：
11.1
通讯作者：
Olivucci, M
中科院分区：
文献类型：
--
作者：
González-Luque, R;Garavelli, M;Olivucci, M
在本文中，我们使用从头算多组态二级微扰理论来建立视黄醛发色团的本征光异构化路径模型。这是通过在孤立条件下，沿着严格确定的视紫红质发色团模型4 - 顺 - γ - 甲基 - 2,4,6,8 - 壬四烯亚胺阳离子和细菌视紫红质发色团模型全反式 - 2,4,6 - 庚三烯亚胺阳离子的光异构化坐标，计算基态（S - 0）以及前两个单重激发态（S - 1、S - 2）的能量来实现的。计算得到的S - 2和S - 1能谱在S - 1反应路径上没有显示出任何避免交叉的特征，并且保持着大于20千卡/摩尔的能隙。此外，对电荷分布的分析表明，沿着该路径S - 2和S - 1的电子结构没有质的变化。因此，S - 1态保持着一种普遍的离子（空穴 - 对）特性，而S - 2态保持着一种共价（点 - 点）特性。这些结果，连同对S - 1反应坐标的分析，支持一种光异构化的两态、双模模型，这对先前提出的模型进行了重大修订。
In this paper we use ab initio multiconfigurational second-older perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing the ground state (S-0) and the first two singlet excited-state (S-1, S-2) energies along the rigorously determined photoisomerization coordinate of the rhodopsin chromophore model 4-cis-gamma-methylnona-2,4,6.8-tetraeniminium cation and the bacteriorhodopsin chromophore model all-trans-hepta-2,4,6-trieniminium cation in isolated conditions. The computed S-2 and S-1 energy profiles do not show any avoided crossing feature along the S-1 reaction path and maintain an energy gap >20 kcal mol(-1). In addition, the analysis of the charge distribution shows that there is no qualitative change in the S-2 and S-1 electronic structure along the path. Thus, the S-1 state maintains a prevalent ionic (hole-pair) character whereas the S-2 state maintains a covalent (dot-dot) character. These results, together with the analysis of the S-1 reaction coordinate, support a two-state, two-mode model of the photoisomerization that constitutes a substantial revision of the previously proposed models.