Surface-up click access to allylimidazolium bridged cyclodextrin dimer phase for efficient enantioseparation

In this work, a novel allylimidazolium-bridged bis(beta-cyclodextrin) chiral stationary phase was fabricated via a surface-up thiol-ene click chemistry reaction between 7-SH-beta-cyclodextrin and 1-allylimidazole-beta-cyclodextrin bonded on a silica surface. The structure of the allylimidazolium-bridged bis(beta-cyclodextrin) chiral stationary phase was characterized by Fourier transform infrared spectra, C-13 nuclear magnetic resonance, thermogravimetric analysis, and elemental analysis. Its chiral chromatographic performances were systematically evaluated by separating 35 racemic analytes including isoxazolines, dansyl-amino acids, and flavanones under reversed-phase high-performance liquid chromatography. Compared with the corresponding bottom and top layer of the beta-cyclodextrin stationary phase, the allylimidazolium-bridged bis(beta-cyclodextrin) chiral stationary phase afforded significantly accentuated chiral recognition ability due to its abundant hydrogen bond sites, electrostatic interactions, and synergistic inclusion. Furthermore, the allylimidazolium-bridged bis(beta-cyclodextrin) chiral stationary phase showed better enantioseparation ability compared to other reported bridged cyclodextrin stationary phases. In particular, Ar-Phs and dansyl-amino acid could be completely separated by allylimidazolium-bridged bis(beta-mono-6(A)-deoxy-6-allylimidazolium-beta-cyclodextrin chiral stationary phase) chiral stationary phase with high resolutions of 1.14-7.20 and 3.16-5.82, respectively. Molecular docking reveals that good enantioseparation ability arises from the different interaction modes and the synergistic effect of allylimidazolium-bridged bis(beta-cyclodextrin) chiral stationary phase.