IOM-CNR c/o Dipartimento di Fisica e Geologia, Università di Perugia, Via Pascoli, I-06123 Perugia, Italy.
Soft Matter. 2016 Jul 7;12(25):5501-14. doi: 10.1039/c5sm03119b. Epub 2016 Jun 9.
When a solute is dissolved in water, their mutual interactions determine the molecular properties of the solute on one hand, and the structure and dynamics of the surrounding water particles (the so-called hydration water) on the other. The very existence of soft matter and its peculiar properties are largely due to the wide variety of possible water-solute interactions. In this context, water is not an inert medium but rather an active component, and hydration water plays a crucial role in determining the structure, stability, dynamics, and function of matter. This review focuses on the collective dynamics of hydration water in terms of retardation with respect to the bulk, and of the number of molecules whose dynamics is perturbed. Since water environments are in a dynamic equilibrium, with molecules continuously exchanging from around the solute towards the bulk and vice versa, we examine the ability of different techniques to measure the water dynamics on the basis of the explored time scales and exchange rates. Special emphasis is given to the collective dynamics probed by extended depolarized light scattering and we discuss whether and to what extent the results obtained in aqueous solutions of small molecules can be extrapolated to the case of large biomacromolecules. In fact, recent experiments performed on solutions of increasing complexity clearly indicate that a reductionist approach is not adequate to describe their collective dynamics. We conclude this review by presenting current ideas that are being developed to describe the dynamics of water interacting with macromolecules.
当溶质溶解在水中时，它们的相互作用一方面决定了溶质的分子性质，另一方面决定了周围水分子（即所谓的水合水）的结构和动力学。软物质的存在及其特殊性质在很大程度上归因于可能的水-溶质相互作用的广泛多样性。在这种情况下，水不是惰性介质，而是一种活性成分，水合水在决定物质的结构、稳定性、动力学和功能方面起着关键作用。本综述重点讨论了水合水的集体动力学，包括相对于本体的滞后性和动力学受到干扰的分子数量。由于水环境处于动态平衡中，分子不断从溶质周围向本体和本体向溶质方向交换，我们根据所研究的时间尺度和交换率来检查不同技术测量水动力学的能力。特别强调了通过扩展去偏振光散射探测的集体动力学，并讨论了在小分子的水溶液中获得的结果是否以及在何种程度上可以外推到大分子生物的情况。事实上，最近在越来越复杂的溶液上进行的实验清楚地表明，简化论方法不足以描述它们的集体动力学。我们通过介绍当前正在开发的用于描述与大分子相互作用的水动力学的思想来结束本综述。
