Photochemistry of visual pigment chromophore models by ab initio molecular dynamics
Photochemistry of visual pigment chromophore models by ab initio molecular dynamics
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DOI：
10.1021/jp0683216
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发表时间：
2007-04-12
影响因子：
3.3
通讯作者：
Buss, Volker
中科院分区：
文献类型：
--
作者：
Weingart, Oliver;Schapiro, Igor;Buss, Volker
用从头算激发态分子动力学方法研究了甲基取代和生色团扭曲对不同四双键视网膜模型生色团的光反应的影响。通过零点能量采样产生随机分布的起始几何构型；弗兰克-康登激发后，反应在S-1表面上进行。为了确定光产物及其构型，讨论并应用了一种简化的方法--扭角跟随法。我们发现发色团的扭曲对光反应的结果有显著的影响：从视紫红质包埋的11顺式视网膜发色团获得的二面角，模型发色团的反应速度比松弛的发色团提高了3倍。此外，反应以完全立体选择性的方式进行，只涉及顺式双键，最低量子产率为72%。对于快速和选择性的光化学，键扭转比甲基取代更有效，这与视紫红质类似物的光物理测量结果一致。我们的结论是，除了蛋白质口袋引起的几何扭曲外，没有必要假设蛋白质和发色团之间的其他特定相互作用来影响视紫红质中的选择性和超快光反应。
Ab initio excited-state molecular dynamics calculations have been performed to study the effect of methyl substitution and chromophore distortion on the photoreaction of different four-double-bond retinal model chromophores. Randomly distributed starting geometries were generated by zero-point energy sampling; after Franck-Condon excitation the reaction was followed on the S-1 surface. For determining the photoproduct and its configuration, a simplified approachtorsion angle followingis discussed and applied. We find that chromophore distortion significantly affects the outcome of the photoreaction: with dihedral angles taken from the rhodopsin-embedded 11-cis-retinal chromophore, the reaction rate of the model chromophore is increased by a factor of 3 compared to that of the relaxed chromophore. Also, the reaction proceeds in a completely stereoselective manner involving only the cis double bond and with a minimum quantum yield of 72%. Bond torsion is more effective than methyl substitution for fast and selective photochemistry, which is in agreement with photophysical measurements on rhodopsin analogues. We conclude that apart from the geometric distortions caused by the protein pocket it is not necessary to postulate other specific interactions between the protein and the chromophore to effect the selective and ultrafast photoreaction in rhodopsin.