Departamento de Química Física, Facultad de Química, Universidad de Vigo, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain.
Phys Chem Chem Phys. 2013 Nov 7;15(41):18204-16. doi: 10.1039/c3cp51668g.
The microsolvation study of a group of amines with a variable number of water molecules was performed by conducting a theoretical analysis of the properties of the clusters formed by the amines with up to seven molecules of water. We describe the microsolvation of several amines focusing on the dissociation of a water molecule that transfers a proton to the amine and forms a hydroxide ion. Ab initio calculations were performed on these clusters employing the DFT/B3LYP and MP2 methods with the 6-311++G(2d,p) basis set. Several stationary points for each cluster were thus located and characterized as minima from frequency calculations. Intermolecular BSSE corrected interaction energies were obtained. The protonation mechanism of the amines was examined in terms of some parameters that include the lengths of the bonds involved in the process of proton transfer and the frequencies associated with certain O-H and N-H stretching modes. On the basis of the calculations, all studied amines present similar behavior but trimethylamine, whose limitations to be integrated in the water hydrogen bond network cause the instability of some of their complexes. The cyclic configurations are the most stable structures up to five water molecules due to the presence of cooperative effects associated with the hydrogen bonds of water molecules. However, when the number of water molecules increases the spatial forms become the most stable configurations. The dissociated forms were not found to have the most stable configuration in any of the studied systems but energetic differences between the dissociated and non-dissociated forms decrease with the number of water molecules.
我们通过对含多达七个水分子的胺类形成的团簇的性质进行理论分析，对一组胺类的微溶剂化进行了研究。我们描述了几种胺的微溶剂化，重点研究了转移质子到胺上并形成氢氧根离子的水分子的离解。我们使用 DFT/B3LYP 和 MP2 方法，结合 6-311++G(2d,p)基组，对这些团簇进行了从头算计算。因此，对每个团簇的几个稳定点进行了定位和特征化，从频率计算中确定为最小值。获得了校正了分子间 BSSE 的相互作用能。我们从包括参与质子转移过程的键长和与某些 O-H 和 N-H 伸缩模式相关的频率等几个参数来检查胺的质子化机制。基于计算，所有研究的胺类都表现出相似的行为，但三甲胺由于其限制与水分子的氢键网络集成，导致其一些配合物不稳定。在五个水分子的范围内，环状构型是最稳定的结构，因为与水分子氢键相关的协同效应的存在。然而，当水分子数量增加时，空间形式成为最稳定的构型。在任何研究体系中，离解形式都没有找到最稳定的构型，但离解形式和不解离形式之间的能量差异随水分子数量的增加而减小。
