生物分子发色团中电子激发的量子动力学：蛋白质环境和溶剂的作用
Quantum dynamics of electronic excitations in biomolecular chromophores: role of the protein environment and solvent
摘要：
我们考虑连续介质模型作为极小模型来理解周围的球状蛋白质和溶剂对生物生色团中电子激发的量子动力学的影响。我们推导出频率依赖的光谱密度的表达式，它描述了在生色团的电子能级耦合到它的环境。谱密度的大小和频率依赖性决定了量子动力学是相干的还是非相干的，从而决定了人们是否可以观察到量子干涉效应，如拉比振荡。我们发现的贡献的光谱密度的发色团环境的每个组件：散装溶剂，蛋白质和水结合到蛋白质。每个组分对生色团量子动力学的相对重要性由动力学的时间尺度决定。我们的研究结果提供了一个自然的解释和模型中观察到的不同的时间尺度的光谱密度提取的溶剂化动力学探测超快激光光谱技术，如动态斯托克斯位移和三脉冲光子回波光谱。我们的结果用于定义在什么条件下激发发色团的动力学由周围蛋白质主导以及何时由溶剂中的介电波动主导。我们表明，即使当发色团被屏蔽从溶剂中的蛋白质超快溶剂化可以占主导地位的溶剂。我们认为，最近看到的超快溶剂化在一些生物生色团不一定要分配到超快蛋白质动力学。从我们的连续模型和实验中提取的光谱密度估计表明，大多数电子激发的量子动力学是不相干的。
英文摘要：
We consider continuum dielectric models as minimal models to understand the effect of a surrounding globular protein and solvent on the quantum dynamics of electronic excitations in a biological chromophore. We derive expressions for the frequency dependent spectral density which describes the coupling of the electronic levels in the chromophore to its environment. The magnitude and frequency dependence of the spectral density determines whether or not the quantum dynamics is coherent or incoherent, and thus whether on not one can observe quantum interference effects such as Rabi oscillations. We find the contributions to the spectral density from each component of the chromophore environment: the bulk solvent, protein, and water bound to the protein. The relative importance of each component to the quantum dynamics of the chromophore is determined by the dynamics' time scale. Our results provide a natural explanation and model for the different time scales observed in the spectral density extracted from the solvation dynamics probed by ultra-fast laser spectroscopy techniques such as the dynamic Stokes shift and three pulse photon echo spectroscopy. Our results are used to define under what conditions the dynamics of the excited chromophore is dominated by the surrounding protein and when it is dominated by dielectric fluctuations in the solvent. We show that even when the chromophore is shielded from the solvent by the protein ultra-fast solvation can be dominated by the solvent. We suggest that the ultra-fast solvation recently seen in some biological chromophores should not necessarily be assigned to ultra-fast protein dynamics. Spectral densities estimated from our continuum models and extracted from experiment suggest that most quantum dynamics of electronic excitations is incoherent.
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