University of Lille, Science and Technology, LASIR (UMR CNRS A8516), Bât. C5, Cité Scientifique, 59655 Villeneuve d'Ascq Cedex, France.
Normandie Université, UNICAEN, CERMN (Center d'Etudes et de Recherche sur le Médicament de Normandie)-FR CNRS INC3M, Boulevard Becquerel, 14032 Caen Cedex, France.
J Chem Phys. 2017 Jun 21;146(23):234507. doi: 10.1063/1.4985630.
The information about the structure of dimethyl sulfoxide (DMSO)-water mixtures at relatively low DMSO mole fractions is an important step in order to understand their cryoprotective properties as well as the solvation process of proteins and amino acids. Classical MD simulations, using the potential model combination that best reproduces the free energy of mixing of these compounds, are used to analyze the local structure of DMSO-water mixtures at DMSO mole fractions below 0.2. Significant changes in the local structure of DMSO are observed around the DMSO mole fraction of 0.1. The array of evidence, based on the cluster and the metric and topological parameters of the Voronoi polyhedra distributions, indicates that these changes are associated with the simultaneous increase of the number of DMSO-water and decrease of water-water hydrogen bonds with increasing DMSO concentration. The inversion between the dominance of these two types of H-bonds occurs around X = 0.1, above which the DMSO-DMSO interactions also start playing an important role. In other words, below the DMSO mole fraction of 0.1, DMSO molecules are mainly solvated by water molecules, while above it, their solvation shell consists of a mixture of water and DMSO. The trigonal, tetrahedral, and trigonal bipyramidal distributions of water shift to lower corresponding order parameter values indicating the loosening of these orientations. Adding DMSO does not affect the hydrogen bonding between a reference water molecule and its first neighbor hydrogen bonded water molecules, while it increases the bent hydrogen bond geometry involving the second ones. The close-packed local structure of the third, fourth, and fifth water neighbors also is reinforced. In accordance with previous theoretical and experimental data, the hydrogen bonding between water and the first, the second, and the third DMSO neighbors is stronger than that with its corresponding water neighbors. At a given DMSO mole fraction, the behavior of the intensity of the high orientational order parameter values indicates that water molecules are more ordered in the vicinity of the hydrophilic group while their structure is close-packed near the hydrophobic group of DMSO.
二甲亚砜（DMSO）-水混合物在相对较低的 DMSO 摩尔分数下的结构信息是理解其抗冷冻性质以及蛋白质和氨基酸的溶剂化过程的重要步骤。使用最佳再现这些化合物混合自由能的势能模型组合的经典 MD 模拟来分析 DMSO 摩尔分数低于 0.2 的 DMSO-水混合物的局部结构。在 DMSO 摩尔分数为 0.1 左右观察到 DMSO 局部结构的显著变化。基于团簇和 Voronoi 多面体分布的度量和拓扑参数的证据表明，这些变化与随着 DMSO 浓度的增加，DMSO-水和水-水氢键数量的同时增加和减少有关。这两种氢键类型的主导地位的反转发生在 X = 0.1 左右，超过这个值，DMSO-DMSO 相互作用也开始发挥重要作用。换句话说，在 DMSO 摩尔分数低于 0.1 时，DMSO 分子主要被水分子溶剂化，而在其之上，它们的溶剂化壳由水和 DMSO 的混合物组成。水的三角、四面和三角双锥分布向较低的相应序参数值移动，表明这些取向的松动。添加 DMSO 不会影响参考水分子与其第一个相邻氢键水分子之间的氢键，而会增加涉及第二个水分子的弯曲氢键几何形状。第三个、第四个和第五个水分子的紧密堆积局部结构也得到了加强。与先前的理论和实验数据一致，水与第一、第二和第三 DMSO 相邻原子之间的氢键比与相应水分子之间的氢键更强。在给定的 DMSO 摩尔分数下，高强度取向序参数值的行为表明水分子在亲水基团附近的有序性更高，而在 DMSO 的疏水区附近则紧密堆积。
