Li Tanping, Kumar Revati
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
J Chem Phys. 2015 Nov 7;143(17):174501. doi: 10.1063/1.4934661.
We explore the connection between the solvation dynamics of a chromophore upon photon excitation and equilibrium fluctuations of the solvent. Using molecular dynamics simulations, fluorescence Stokes shift for the tryptophan in Staphylococcus nuclease was examined using both nonequilibrium calculations and linear response theory. When the perturbed and unperturbed surfaces exhibit different solvent equilibrium fluctuations, the linear response approach on the former surface shows agreement with the nonequilibrium process. This agreement is excellent when the perturbed surface exhibits Gaussian statistics and qualitative in the case of an isomerization induced non-Gaussian statistics. However, the linear response theory on the unperturbed surface breaks down even in the presence of Gaussian fluctuations. Experiments also provide evidence of the connection between the excited state solvent fluctuations and the total fluorescence shift. These observations indicate that the equilibrium statistics on the excited state surface characterize the relaxation dynamics of the fluorescence Stokes shift. Our studies specifically analyze the Gaussian fluctuations of the solvent in the complex protein environment and further confirm the role of solvent fluctuations on the excited state surface. The results are consistent with previous investigations, found in the literature, of solutes dissolved in liquids.
我们探究了发色团在光子激发后的溶剂化动力学与溶剂平衡涨落之间的联系。利用分子动力学模拟，通过非平衡计算和线性响应理论研究了金黄色葡萄球菌核酸酶中色氨酸的荧光斯托克斯位移。当受扰表面和未受扰表面表现出不同的溶剂平衡涨落时，在前者表面上的线性响应方法与非平衡过程相符。当受扰表面呈现高斯统计时，这种相符性非常好；而在异构化诱导的非高斯统计情况下则是定性相符。然而，即使存在高斯涨落，未受扰表面上的线性响应理论也会失效。实验也为激发态溶剂涨落与总荧光位移之间的联系提供了证据。这些观察结果表明，激发态表面上的平衡统计表征了荧光斯托克斯位移的弛豫动力学。我们的研究专门分析了复杂蛋白质环境中溶剂的高斯涨落，并进一步证实了激发态表面上溶剂涨落的作用。结果与文献中先前对溶解在液体中的溶质的研究一致。
