Departamento de Física, Universidad de La Laguna, 38202 La Laguna, Tenerife, Spain.
Molecules. 2019 Mar 14;24(6):1021. doi: 10.3390/molecules24061021.
Molecular mechanics and dynamics simulations were carried out to study the capacity of isoleucine enantiomers to form inclusion complexes with β⁻cyclodextrin, and to be discriminated by this chiral compound, in vacuo and with different solvents. Solvents were characterized not only by the value of dielectric constant ε in the Coulombic interaction energy, but also by the neutral and zwitterion configurations of isoleucine. Whereas the discrimination between the enantiomers for ε ≤ 2 is due to the electrostatic contribution, these differences are mainly due to the Lennard-Jones potential for ε > 2. The most enantioselective regions are located near the cavity walls, independently of the solvent. D-Ile is more stable than L-Ile in broader regions in vacuo, but L-Ile presents more stable locations with water. Isoleucine can form inclusion complexes with β⁻cyclodextrin in vacuo and with different solvents. Two probable configurations are deduced from the molecular dynamics simulation, in which the guest is always inside the cavity and with the carboxylic end of the amino acid oriented towards either rim of β⁻CD. In the simulation, the enantiomers preferentially occupy regions with greater chiral discrimination. The first eluted enantiomer in vacuo and with different solvents is L-Ile, independently of the solvent polarity.
采用分子力学和动力学模拟的方法，研究了异亮氨酸对映体与β-环糊精形成包合物的能力，并研究了β-环糊精对其的手性识别能力，模拟分别在真空中和不同溶剂中进行。溶剂的特征不仅在于库仑相互作用能的介电常数ε值，还在于异亮氨酸的中性和两性离子构型。对于ε≤2 的情况，对映体的区分归因于静电贡献，而对于ε>2 的情况，这些差异主要归因于 Lennard-Jones 势。最具对映选择性的区域位于空腔壁附近，与溶剂无关。在真空中，D-异亮氨酸比 L-异亮氨酸更稳定，但在水中，L-异亮氨酸的稳定位置更多。异亮氨酸可以在真空中和不同溶剂中形成β-环糊精包合物。从分子动力学模拟中推导出两种可能的构象，其中客体始终位于空腔内，并且氨基酸的羧酸端朝向β-CD 的任一边缘。在模拟中，对映体优先占据手性识别能力较强的区域。在真空中和不同溶剂中首先洗脱的对映体都是 L-异亮氨酸，与溶剂的极性无关。
