Faculty of Physics, St. Petersburg University, St. Petersburg, Russia.
J Phys Chem B. 2011 Dec 15;115(49):14572-81. doi: 10.1021/jp208758r. Epub 2011 Nov 11.
To study the effects of water on conformational dynamics of polyalcohols, Molecular Dynamics simulations of glycerol-water liquid mixtures have been carried out at different concentrations: 42.9 and 60.0 wt % of glycerol, respectively. On the basis of the analysis of backbone conformer distributions, it is found that the surrounding water molecules have a large impact on the populations of the glycerol conformers. While the local structure of water in the liquid mixture is surprisingly close to that in pure liquid water, the behavior of glycerols can be divided into three different categories where roughly 25% of them occur in a structure similar to that in pure liquid of glycerol, ca. 25% of them exist as monomers, solvated by water, and the remaining 50% of glycerols in the mixture form H-bonded strings as remains of the glycerol H-bond network. The typical glycerol H-bond network still exists even at the lower concentration of 40 wt % of glycerol. The microheterogeneity of water-glycerol mixtures is analyzed using time-averaged distributions of the sizes of the water aggregates. At 40 wt % of glycerol, the cluster sizes from 3 to 10 water molecules are observed. The increase of glycerol content causes a depletion of clusters leading to smaller 3-5 molecule clusters domination. Translational diffusion coefficients have been calculated to study the dynamical behavior of both glycerol and water molecules. Rotational-reorientational motion is studied both in overall and in selected substructures on the basis of time correlation functions. Characteristic time scales for different motional modes are deduced on the basis of the calculated correlation times. The general conclusion is that the presence of water increases the overall mobility of glycerol, while glycerol slows the mobility of water.
为了研究水对多元醇构象动力学的影响，我们对甘油-水液体混合物进行了分子动力学模拟，分别在不同浓度下进行：42.9 和 60.0wt%的甘油。基于对主链构象分布的分析，我们发现周围的水分子对甘油构象的分布有很大的影响。尽管液体混合物中水分子的局部结构与纯液态水非常接近，但甘油的行为可以分为三种不同的类别，其中约 25%的甘油存在于类似于纯甘油的结构中，约 25%的甘油以单体形式存在，被水分子溶剂化，而混合物中其余 50%的甘油形成氢键串，作为甘油氢键网络的残留物。即使在甘油浓度为 40wt%的较低浓度下，典型的甘油氢键网络仍然存在。通过水-甘油混合物的时间平均大小分布分析其微不均匀性。在 40wt%的甘油中，观察到 3 到 10 个水分子的簇尺寸。甘油含量的增加导致簇的耗尽，导致较小的 3-5 个分子簇主导。为了研究甘油和水分子的动力学行为，我们计算了它们的平移扩散系数。基于时间相关函数，我们研究了整体和选定子结构中的旋转-定向运动。基于计算的相关时间，推导出了不同运动模式的特征时间尺度。总的结论是，水的存在增加了甘油的整体流动性，而甘油则降低了水的流动性。
