Dipartimento di Fisica, Università degli Studi di Perugia, Via Pascoli, I-06123 Perugia, Italy.
J Phys Chem B. 2012 Jun 28;116(25):7499-508. doi: 10.1021/jp301988f. Epub 2012 Jun 18.
Extended depolarized light scattering (EDLS) measurements have been recently employed to investigate the dynamics of water solvating biological molecules, giving evidence of the presence of two different dynamical regimes among water molecules. An interpretation of EDLS has been proposed that provides an independent estimate of the retardation factor of slowdown with respect to fast water molecules and of the number of solvent molecules affected by this slowing down. Nevertheless this measure is an inherently complex one, due to the collective nature of the physical property probed. In the present work a molecular dynamics (MD) approach has been used to more deeply understand experimental results. Time correlation functions of the collective polarizability anisotropy have been calculated for the prototype disaccharide trehalose in aqueous solutions as a function of concentration. The unique capability of MD to disentangle the contributions to the dynamics arising from solute, solvent, and cross terms between the two allowed us to check the reliability of an interpretation that assumes a spectral separation of water and sugar dynamics, as well as to highlight the very presence of two distinct relaxation processes in water. The two processes have been attributed to the dynamics of bulk and hydration water, respectively. A retardation factor of ~5 and concentration dependent hydration numbers have been observed, in good agreement with experimental results [Paolantoni, M.; et al. J. Phys. Chem. B 2009, 113, 7874-7878].
扩展去极化光散射 (EDLS) 测量最近被用于研究水溶剂生物分子的动力学，为水分子中存在两种不同的动力学状态提供了证据。已经提出了对 EDLS 的一种解释，该解释提供了对慢化相对于快速水分子的滞后因子以及受这种慢化影响的溶剂分子数量的独立估计。然而，由于所探测物理性质的集体性质，这种测量本身就是复杂的。在本工作中，使用分子动力学 (MD) 方法更深入地理解实验结果。作为浓度的函数，计算了原型二糖海藻糖在水溶液中集体极化率各向异性的时间相关函数。MD 的独特能力可以将溶质、溶剂和两者之间的交叉项对动力学的贡献分开，这使我们能够检查假设水和糖动力学的光谱分离的解释的可靠性，并突出在水中存在两个不同的弛豫过程。这两个过程分别归因于体相和水合水的动力学。观察到~5 的滞后因子和浓度相关的水合数，与实验结果非常吻合 [Paolantoni, M.; 等人。J. Phys. Chem. B 2009, 113, 7874-7878]。
