Do molecules as small as neopentane induce a hydrophobic response similar to that of large hydrophobic surfaces?
Do molecules as small as neopentane induce a hydrophobic response similar to that of large hydrophobic surfaces?
复制标题
DOI：
10.1021/jp030652k
复制
发表时间：
2003-10-23
影响因子：
3.3
通讯作者：
Berne, BJ
中科院分区：
文献类型：
--
作者：
Huang, X;Margulis, CJ;Berne, BJ
这是两篇论文中的第一篇，旨在从原子的角度理解不同长度尺度下的疏水性以及不同尺寸的疏水溶质的局部密度和角度分布等特性如何变化。在随后的出版物中，我们将描述纳米尺寸的片状分子的疏水水合和疏水相互作用。分子动力学被用来计算三种不同分子（氩、甲烷和新戊烷）周围的水的径向和取向分布函数。此外，还计算了两个新戊烷分子间的平均力势。对这些体系的完整OPLS/AA（1）力场的结果与溶质-溶剂WCA截断OPLS/AA（1）力场进行了比较。这项工作解决了一个问题的大小的新戊烷的分子是否足够大，以诱导类似的大疏水分子或石蜡壁的疏水反应。我们对这个问题的回答是肯定的。与氩和甲烷相反，新戊烷分子附近的第一壳层中的水分子的取向分布与石蜡壁附近的取向分布非常相似。此外，潜在的平均力，两个新戊烷分子之间，与WCA截断OPLS/AA的潜力，显示出一个dewetting-like过渡很像两个宏观疏水物体之间发现的。我们的结论是，新戊烷定义了一个长度尺度的观察大规模的疏水性。较小的分子适合水包合物，而较大的分子迫使水重组，使得存在指向疏水表面的悬挂OH键。大规模的疏水性出现在溶质分子小如新戊烷直径（d约5.2埃）。
This is the first of two papers aimed at understanding, from an atomistic perspective, hydrophobicity at different length scales and how properties such as local densities and angular profiles change for hydrophobic solutes of different sizes. In a subsequent publication we will describe the hydrophobic hydration and hydrophobic interaction of platelike molecules of nanoscale size. Molecular dynamics is used to compute radial and orientational distribution functions of water around three different molecules: argon, methane, and neopentane. In addition, the potential of mean force between two neopentane molecules is computed. The results for the full OPLS/AA(1) force field are compared with the solute-solvent WCA truncated OPLS/AA(1) force field for these systems. This work addresses the question of whether a molecule of the size of neopentane is large enough to induce a hydrophobic response similar to that of large hydrophobic molecules or paraffin walls. We answer this question in the affirmative. The orientational distribution of water molecules in the first shell neighboring the neopentane molecule is very similar to that near a paraffin wall, in contrast to argon and methane. In addition, the potential of mean force, between two neopentane molecules, with the WCA truncated OPLS/AA potential, displays a dewetting-like transition much like that found between two macroscopic hydrophobic objects. We conclude that neopentane defines a length scale for the observation of large-scale hydrophobicity. Smaller molecules fit into a water clathrate, whereas larger molecules force the water to reorganize such that there are dangling OH bonds pointing toward the hydrophobic surface. Large-scale hydrophobicity arises in solute molecules as small as neopentane with diameter (d approximate to 5.2 Angstrom).