Evaluation of synergistic enantioseparation systems with chiral spirocyclic ionic liquids as additives by capillary electrophoresis

In recent years, chiral ionic liquids (CILs) have attracted more and more attention in the field of enantioseparation. In this study, two novel spirocyclic chiral ionic liquids, 1-butyl-3-methylimidazolium(T-4)-bis[(2S)-2-(hydroxy-kappa O)-3-methylbutanoato-kappa O]borate (BMIm(+)BLHvB(-)) and 1-butyl-3-methylimidazolium (T-4)-bis[(alpha S)-alpha-(hydroxy-kappa O)-4-methylbenzeneacetato-kappa O]borate (BMIm(+)BSMB(-)), were applied for the first time in capillary electrophoresis (CE) to establish synergistic systems for enantiomeric separation. Significantly improved separations of five tested analytes were observed in the CILs synergistic systems based on three beta-cyclodextrin derivatives (CD), compared with conventional single CD separation systems. Several principal parameters such as CILs concentration, cyclodextrin concentration, buffer pH, and applied voltage were systematically investigated with BMIm(+)BLHvB(-)/hydroxypropyl-beta-CD selected as a model system to optimize the enantioseparation. Molecular modeling was applied to further demonstrate the chiral recognition mechanism of the CILs/hydroxypropyl-beta-CD synergistic system, which showed a good agreement with the experimental results.