Jesus A J Lopes, Tomé Luciana I N, Eusébio M Ermelinda S, Rosado Mario T S, Redinha J S
Department of Chemistry, University of Coimbra, 3004-535, Coimbra, Portugal.
J Phys Chem A. 2007 May 3;111(17):3432-7. doi: 10.1021/jp070243e. Epub 2007 Apr 7.
This work presents a theoretical study on the hydration of cyclohexylamine and isomers of cyclohexyldiamine. All possible conformers were fully optimized in solution using the conductor-like polarizable continuum model (CPCM) and density functional theory. Values of the Gibbs energy of solvation, its respective contributions (electrostatic, nonelectrostatic and conformational change), and the relative Gibbs energy of the conformers in aqueous solution and gas phase are reported. From these values and the Boltzmann populations of the conformers in both phases, the weighted mean values of DeltaG(solv) for the compounds are calculated. Three structural features were found to be important for the hydration of these compounds: the distance between the two NH2 groups (proximity disfavors hydration), their position relative to the ring (equatorial is preferred over axial), and the orientation of the nitrogen lone-pairs (gauche is more favorable to hydration than trans). In the particular case of vicinal cyclohexyldiamines, in addition to these two factors, the relative orientation of one group to the other should also be taken into account.
这项工作对环己胺和环己二胺异构体的水合作用进行了理论研究。使用类导体极化连续介质模型（CPCM）和密度泛函理论在溶液中对所有可能的构象异构体进行了完全优化。报告了溶剂化吉布斯自由能的值、其各自的贡献（静电、非静电和构象变化）以及水溶液和气相中构象异构体的相对吉布斯自由能。根据这些值以及两相中构象异构体的玻尔兹曼分布，计算了化合物的ΔG(solv)加权平均值。发现三个结构特征对这些化合物的水合作用很重要：两个NH2基团之间的距离（距离近不利于水合）、它们相对于环的位置（赤道位置优于轴向位置）以及氮孤对的取向（gauche构象比trans构象更有利于水合）。在邻位环己二胺的特殊情况下，除了这两个因素外，还应考虑一个基团相对于另一个基团的相对取向。
