Napoleon Raeanne L, Moore Preston B
Department of Chemistry & Biochemistry, University of the Sciences in Philadelphia, Philadelphia, Pennsylvania 19104, USA.
J Phys Chem B. 2006 Mar 2;110(8):3666-73. doi: 10.1021/jp054933z.
Structurally isomeric octanol interfacial systems, water/vapor, 3-octanol/vapor, n-octanol/vapor, 3-octanol/water, and n-octanol/water are investigated at 298 K using molecular dynamics simulation techniques. The present study is intended to investigate strongly associated liquid/liquid interfaces and probe the atomistic structure of these interfaces. The octanol and water molecules were initially placed randomly into a box and were equilibrated using constant pressure techniques to minimize bias within the initial conditions as well as to fully sample the structural conformations of the interface. An interface formed via phase separation during equilibration and resulted in a slab geometry with a molecularly sharp interface. However, some water molecules remained within the octanol phase with a mole fraction of 0.12 after equilibration. The resulting "wet" octanol interfaces were analyzed using density profiles and orientational order parameters. Our results support the hypothesis of an ordered interface only 1 or 2 molecular layers deep before bulk properties are reached for both the 3-octanol and water systems. However, in contrast to most other interfacial systems studied by molecular dynamics simulations, the n-octanol interface extends for several molecular layers. The octanol hydroxyl groups form a hydrogen-bonding network with water which orders the surface molecules toward a preferred direction and produces a hydrophilic/hydrophobic layering. The ordered n-octanol produces an oscillating low-high density of oxygen atoms out of phase with a high-low density of carbon atoms, consistent with an oscillating dielectric. In contrast, the isomeric 3-octanol has only a single carbon-rich layer directly proximal to the interface, which is a result of the different molecular topology. Both 3-octanol and n-octanol roughen the water interface with respect to the water/vapor interface. The "wet" octanol phases, in the octanol/water systems reach bulk properties in a shorter distance than the "dry" octanol/vapor interfaces.
采用分子动力学模拟技术，在298 K下研究了结构异构的辛醇界面体系，包括水/气相、3-辛醇/气相、正辛醇/气相、3-辛醇/水和正辛醇/水体系。本研究旨在研究强关联的液/液界面，并探究这些界面的原子结构。辛醇和水分子最初随机置于一个盒子中，并使用恒压技术进行平衡，以最小化初始条件下的偏差，并充分采样界面的结构构象。在平衡过程中通过相分离形成了一个界面，得到了具有分子清晰界面的平板几何形状。然而，平衡后仍有一些水分子留在辛醇相中，摩尔分数为0.12。使用密度分布和取向序参数对所得的“湿”辛醇界面进行了分析。我们的结果支持这样的假设，即对于3-辛醇和水体系，在达到本体性质之前，有序界面仅为1或2个分子层深。然而，与大多数通过分子动力学模拟研究的其他界面体系不同，正辛醇界面延伸了几个分子层。辛醇羟基与水形成氢键网络，使表面分子向一个优选方向排列，并产生亲水/疏水层。有序的正辛醇产生了氧原子的低-高密度振荡，与碳原子的高-低密度振荡异相，这与振荡电介质一致。相比之下，异构的3-辛醇在紧邻界面处只有一个富碳层，这是不同分子拓扑结构的结果。相对于水/气相界面，3-辛醇和正辛醇都会使水界面变得粗糙。在辛醇/水体系中，“湿”辛醇相在比“干”辛醇/气相界面更短的距离内达到本体性质。
