Mimini Vebi, Ianni Federica, Marini Francesca, Hettegger Hubert, Sardella Roccaldo, Lindner Wolfgang
University of Vienna, Department of Analytical Chemistry, Währingerstrasse 38, 1090, Vienna, Austria; University of Natural Resources and Life Sciences Vienna (BOKU), Department of Chemistry, Institute for Chemistry of Renewable Resources, Konrad-Lorenz-Straße 24, A-3430, Tulln, Austria.
University of Perugia, Department of Pharmaceutical Sciences, Via Fabretti 48, 06123, Perugia, Italy.
Anal Chim Acta. 2019 Oct 31;1078:212-220. doi: 10.1016/j.aca.2019.06.006. Epub 2019 Jun 5.
In the present paper, we demonstrated that Cinchona alkaloid cyclohexyl sulfonic acid-based zwitterionic chiral selectors (SOs) and the respective chiral stationary phases (CSPs) can be successfully employed for the enantioseparation of underivatized thus zwitterionic amino acids (the selectands, SAs) even in the absence of ionic additives in the eluent, generally used as displacer counter-ions in ion exchange chromatography. Therefore, we provided evidence that cooperative "intramolecular and intermolecular counter-ion effects" of the zwitterionic SO moiety and the zwitterionic SAs can be sufficient to modulate alone the retention characteristics without a loss of stereoselectivity. Four fully constrained β-amino acids were used as target compounds for this study. The analyses were carried out with either neat methanol, acetonitrile, water or their binary hydro-organic mixtures. A U-shaped retention profile was observed both with methanol- and acetonitrile-based eluents. Except a few cases, enantioselectivity experienced a remarkable amelioration at the "balanced region" of a buffer free hydroorganic mobile phase composition. At "the bottom" of the U-shaped curve, high α- and resolution values could be reached with most of the screened mobile phases. An electrostatically driven "attraction-repulsion model" was postulated to explain the very favourable characteristic of the two studied zwitterion-type CSPs for the retention and enantiomer separation of zwitterionic analytes.
在本论文中，我们证明了基于金鸡纳生物碱环己基磺酸的两性离子手性选择剂（SOs）和相应的手性固定相（CSPs）能够成功用于未衍生化的两性离子氨基酸（被选择物，SAs）的对映体分离，即使洗脱液中不存在通常在离子交换色谱中用作置换抗衡离子的离子添加剂。因此，我们提供了证据，表明两性离子SO部分和两性离子SAs的协同“分子内和分子间抗衡离子效应”足以单独调节保留特性而不损失立体选择性。四种完全受限的β-氨基酸用作本研究的目标化合物。分析使用纯甲醇、乙腈、水或它们的二元水-有机混合物进行。在基于甲醇和乙腈的洗脱液中均观察到U形保留曲线。除少数情况外，在无缓冲剂的水-有机流动相组成的“平衡区域”，对映体选择性有显著改善。在U形曲线的“底部”，大多数筛选的流动相都能达到高α值和分离度值。提出了一个静电驱动的“吸引-排斥模型”来解释所研究的两种两性离子型CSPs对两性离子分析物的保留和对映体分离的非常有利的特性。
