Manathunga Madushanka, Yang Xuchun, Orozco-Gonzalez Yoelvis, Olivucci Massimo
Department of Chemistry, Bowling Green State University , Bowling Green, Ohio 43403, United States.
Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 Université de Strasbourg-CNRS, F-67034 Strasbourg, France.
J Phys Chem Lett. 2017 Oct 19;8(20):5222-5227. doi: 10.1021/acs.jpclett.7b02344. Epub 2017 Oct 11.
Spectral data show that the photoisomerization of retinal protonated Schiff base (rPSB) chromophores occurs on a 100 fs time scale or less in vertebrate rhodopsins, it is several times slower in microbial rhodopsins and it is between one and 2 orders of magnitude slower in solution. These time scale variations have been attributed to specific modifications of the topography of the first excited state potential energy surface of the chromophore. However, it is presently not clear which specific environment effects (e.g., electrostatic, electronic, or steric) are responsible for changing the surface topography. Here, we use QM/MM models and excited state trajectory computations to provide evidence for an increase in electronic mixing between the first and the second excited state of the chromophore when going from vertebrate rhodopsin to the solution environments. Ultimately, we argue that a correlation between the lifetime of the first excited state and electronic mixing between such state and its higher neighbor, may have been exploited to evolve rhodopsins toward faster isomerization and, possibly, light-sensitivity.
光谱数据表明，在脊椎动物视紫红质中，视黄醛质子化席夫碱（rPSB）发色团的光异构化发生在100飞秒或更短的时间尺度上，在微生物视紫红质中则慢几倍，而在溶液中则慢1至2个数量级。这些时间尺度的变化归因于发色团第一激发态势能面地形的特定改变。然而，目前尚不清楚是哪些特定的环境效应（如静电、电子或空间效应）导致了表面地形的变化。在这里，我们使用量子力学/分子力学（QM/MM）模型和激发态轨迹计算，来证明从脊椎动物视紫红质到溶液环境时，发色团第一激发态和第二激发态之间电子混合的增加。最终，我们认为第一激发态的寿命与该状态及其更高能级相邻态之间的电子混合之间的相关性，可能已被用于使视紫红质朝着更快的异构化以及可能的光敏感性方向进化。
