Mohorič Tomaž, Hribar-Lee Barbara, Vlachy Vojko
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia.
J Chem Phys. 2014 May 14;140(18):184510. doi: 10.1063/1.4875280.
Molecular dynamics simulations with separate thermostats for rotational and translational motion were used to study the effect of these degrees of freedom on the structure of water around model solutes. To describe water molecules we used the SPC/E model. The simplest solute studied here, the hydrophobe, was represented as a Lennard-Jones particle. Since direct interaction between the hydrophobe and water molecules has no angular dependence the influence of the increase of the rotational temperature on the solvation of a hydrophobe is only indirect. In the next step the central solute was assumed to be charged with either a positive or a negative charge to mimic an ion in water. Hence, depending on the charge of the ion, the neighboring water molecules assumed different angular distributions. The principal conclusions of this work are: (i) an increase of the translational temperature always decreases the height of the first peak in the solute-water radial distribution function; (ii) an increase of the rotational temperature yields an increase in the first peak in the solute-water radial distribution function for hydrophobes and cations; (iii) in contrast to this, the solvation peak decreases around ions with sufficiently large negative charge; and (iv) an increase of the rotational temperature affects cations in an opposite way to anions. For this reason complex molecules with a small net charge may not be very sensitive to variation of the rotational temperature.
利用针对旋转和平移运动分别设置恒温器的分子动力学模拟，研究这些自由度对模型溶质周围水结构的影响。为描述水分子，我们使用了SPC/E模型。这里研究的最简单溶质——疏水物，被表示为一个 Lennard-Jones 粒子。由于疏水物与水分子之间的直接相互作用没有角度依赖性，旋转温度升高对疏水物溶剂化的影响只是间接的。下一步，假设中心溶质带有正电荷或负电荷，以模拟水中的离子。因此，根据离子的电荷，相邻水分子呈现不同的角度分布。这项工作的主要结论是：(i) 平移温度升高总是会降低溶质 - 水径向分布函数中第一个峰的高度；(ii) 旋转温度升高会使疏水物和阳离子的溶质 - 水径向分布函数中的第一个峰增加；(iii) 与此相反，对于带有足够大负电荷的离子，溶剂化峰减小；(iv) 旋转温度升高对阳离子和阴离子的影响相反。因此，净电荷小的复杂分子可能对旋转温度的变化不太敏感。
