Zhong Yang, Warren G Lee, Patel Sandeep
Department of Chemistry and Biochemistry, 238 Brown Laboratory, University of Delaware, Newark, Delaware 19716, USA.
J Comput Chem. 2008 May;29(7):1142-52. doi: 10.1002/jcc.20877.
We study bulk structural and thermodynamic properties of methanol-water solutions via molecular dynamics simulations using novel interaction potentials based on the charge equilibration (fluctuating charge) formalism to explicitly account for molecular polarization at the atomic level. The study uses the TIP4P-FQ potential for water-water interactions, and the CHARMM-based (Chemistry at HARvard Molecular Mechanics) fluctuating charge potential for methanol-methanol and methanol-water interactions. In terms of bulk solution properties, we discuss liquid densities, enthalpies of mixing, dielectric constants, self-diffusion constants, as well as structural properties related to local hydrogen bonding structure as manifested in radial distribution functions and cluster analysis. We further explore the electronic response of water and methanol in the differing local environments established by the interaction of each species predominantly with molecules of the other species. The current force field for the alcohol-water interaction performs reasonably well for most properties, with the greatest deviation from experiment observed for the excess mixing enthalpies, which are predicted to be too favorable. This is qualitatively consistent with the overestimation of the methanol-water gas-phase interaction energy for the lowest-energy conformer (methanol as proton donor). Hydration free energies for methanol in TIP4P-FQ water are predicted to be -5.6 +/- 0.2 kcal/mol, in respectable agreement with the experimental value of -5.1 kcal/mol. With respect to solution microstructure, the present cluster analysis suggests that the microscale environment for concentrations where select thermodynamic quantities reach extremal values is described by a bipercolating network structure.
我们通过分子动力学模拟研究甲醇 - 水溶液的整体结构和热力学性质，使用基于电荷平衡（波动电荷）形式的新型相互作用势，以在原子水平明确考虑分子极化。该研究使用TIP4P - FQ势描述水 - 水相互作用，以及基于CHARMM（哈佛分子力学中的化学）的波动电荷势描述甲醇 - 甲醇和甲醇 - 水相互作用。在整体溶液性质方面，我们讨论了液体密度、混合焓、介电常数、自扩散常数，以及与局部氢键结构相关的结构性质，这些性质在径向分布函数和聚类分析中有所体现。我们进一步探索了水和甲醇在由每种物质主要与另一种物质的分子相互作用所建立的不同局部环境中的电子响应。目前用于醇 - 水相互作用的力场对大多数性质表现良好，与实验值偏差最大的是过量混合焓，预测值过于有利。这在定性上与对最低能量构象（甲醇作为质子供体）的甲醇 - 水气相互作用能的高估一致。TIP4P - FQ水中甲醇的水合自由能预测为 -5.6 +/- 0.2 kcal/mol，与 -5.1 kcal/mol的实验值相当吻合。关于溶液微观结构，目前的聚类分析表明，在某些热力学量达到极值的浓度下，微观尺度环境由双渗流网络结构描述。
