Alarcón Laureano M, Rodríguez Fris J A, Morini Marcela A, Sierra M Belén, Accordino S A, Montes de Oca J M, Pedroni Viviana I, Appignanesi Gustavo A
Departamento de Química and INQUISUR-UNS-CONICET, Universidad Nacional del Sur, Av. Alem 1253, 8000, Bahía Blanca, Argentina.
Subcell Biochem. 2015;71:161-87. doi: 10.1007/978-3-319-19060-0_7.
The comprehension of the structure and behavior of water at interfaces and under nanoconfinement represents an issue of major concern in several central research areas like hydration, reaction dynamics and biology. From one side, water is known to play a dominant role in the structuring, the dynamics and the functionality of biological molecules, governing main processes like protein folding, protein binding and biological function. In turn, the same principles that rule biological organization at the molecular level are also operative for materials science processes that take place within a water environment, being responsible for the self-assembly of molecular structures to create synthetic supramolecular nanometrically-sized materials. Thus, the understanding of the principles of water hydration, including the development of a theory of hydrophobicity at the nanoscale, is imperative both from a fundamental and an applied standpoint. In this work we present some molecular dynamics studies of the structure and dynamics of water at different interfaces or confinement conditions, ranging from simple model hydrophobic interfaces with different geometrical constraints (in order to single out curvature effects), to self-assembled monolayers, proteins and phospholipid membranes. The tendency of the water molecules to sacrifice the lowest hydrogen bond (HB) coordination as possible at extended interfaces is revealed. This fact makes the first hydration layers to be highly oriented, in some situations even resembling the structure of hexagonal ice. A similar trend to maximize the number of HBs is shown to hold in cavity filling, with small subnanometric hydrophobic cavities remaining empty while larger cavities display an alternation of filled and dry states with a significant inner HB network. We also study interfaces with complex chemical and geometrical nature in order to determine how different conditions affect the local hydration properties. Thus, we show some results for protein hydration and, particularly, some preliminary studies on membrane hydration. Finally, calculations of a local hydrophobicity measure of relevance for binding and self-assembly are also presented. We then conclude with a few words of further emphasis on the relevance of this kind of knowledge to biology and to the design of new materials by highlighting the context-dependent and non-additive nature of different non-covalent interactions in an aqueous nanoenvironment, an issue that is usually greatly overlooked.
理解界面处及纳米限域条件下水的结构与行为是若干核心研究领域（如水合作用、反应动力学和生物学）中备受关注的一个问题。一方面，众所周知，水在生物分子的结构形成、动力学及功能方面起着主导作用，掌控着诸如蛋白质折叠、蛋白质结合及生物功能等主要过程。反过来，在分子水平上支配生物组织的相同原理，对于在水环境中发生的材料科学过程也同样适用，这些原理负责分子结构的自组装，以创建合成的纳米级超分子材料。因此，从基础和应用的角度来看，理解水合作用原理，包括发展纳米尺度下的疏水性理论，都是至关重要的。在这项工作中，我们展示了一些关于水在不同界面或限域条件下的结构与动力学的分子动力学研究，范围从具有不同几何约束的简单模型疏水界面（以便区分曲率效应）到自组装单分子层、蛋白质和磷脂膜。揭示了水分子在扩展界面处尽可能牺牲最低氢键（HB）配位的趋势。这一事实使得第一水合层高度取向，在某些情况下甚至类似于六方冰的结构。在空腔填充中也显示出类似的最大化氢键数量的趋势，亚纳米级的小疏水空腔保持为空，而较大的空腔则呈现填充和干燥状态的交替，内部有显著的氢键网络。我们还研究了具有复杂化学和几何性质的界面，以确定不同条件如何影响局部水合性质。因此，我们展示了一些蛋白质水合的结果，特别是一些关于膜水合的初步研究。最后，还给出了与结合和自组装相关的局部疏水性测量的计算结果。然后，我们通过强调在水性纳米环境中不同非共价相互作用的上下文依赖性和非加和性这一通常被大大忽视的问题，进一步强调了这类知识对生物学和新材料设计的相关性，从而得出结论。
