Alvira Elena
Departamento de Física, Universidad de La Laguna, San Cristóbal de La Laguna, Spain.
Front Chem. 2020 Sep 8;8:823. doi: 10.3389/fchem.2020.00823. eCollection 2020.
The complexes formed by β-cyclodextrin and some amino acids (alanine, valine, leucine, and isoleucine) in vacuo are studied by molecular mechanics and dynamics simulations. These methods have been improved with respect to our previous studies with amino acids, regarding the determination of molecular structures or initial enantiomer dispositions in the molecular dynamics trajectories. The greatest contribution to the interaction energy is from the van der Waals term, although the discrimination between enantiomers is due mainly to the electrostatic contribution. The lowest energy structures of the complexes obtained from molecular mechanics are inclusion complexes in which the carboxylic end of amino acids is pointing toward the narrow (D-) or wide rim (L-) of β-cyclodextrin. The position probability density provided by molecular dynamics also confirms inclusion complex formation, because the guests spend most time inside the cavity of β-cyclodextrin along its axis, with the carboxylic end pointing toward the narrow rim. The L-amino acids are the first eluted enantiomers in all cases and chiral discrimination increases with the size of guests, except leucine, which has the lowest capacity to discriminate. During the simulation, Ala and Val remain in weakly enantioselective regions, while Leu and Ile stay in zones with great chiral selectivity.
通过分子力学和动力学模拟研究了β-环糊精与某些氨基酸（丙氨酸、缬氨酸、亮氨酸和异亮氨酸）在真空中形成的配合物。在分子动力学轨迹中分子结构的确定或初始对映体配置方面，相对于我们之前对氨基酸的研究，这些方法已经得到了改进。对相互作用能的最大贡献来自范德华项，尽管对映体之间的区分主要归因于静电作用。从分子力学获得的配合物的最低能量结构是包合物，其中氨基酸的羧基端指向β-环糊精的窄（D-）或宽边缘（L-）。分子动力学提供的位置概率密度也证实了包合物的形成，因为客体沿着β-环糊精的轴在其腔内花费的时间最多，羧基端指向窄边缘。在所有情况下，L-氨基酸都是首先洗脱的对映体，并且手性区分随着客体尺寸的增加而增加，但亮氨酸除外，其区分能力最低。在模拟过程中，丙氨酸和缬氨酸留在弱对映选择性区域，而亮氨酸和异亮氨酸留在具有高对映选择性区域。
