Zeolitic imidazolate framework-67-modified open-tubular column with cyclodextrin for enantioseparation in capillary electrochromatography.

ABSTRACT

The histidine-modified zeolitic imidazolate framework [His-ZIF-67] was prepared with the histidine, 2-methylimidazole, and Co2+ under ambient temperature. His-ZIF-67 was bonded via a glycidyl methacrylate copolymer to the internal surface of capillary and then functionalized with the NH2 -ß-cyclodextrin (NH2 -ß-CD). The materials were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, N2 adsorption-desorption isotherm, X-ray diffraction, and X-ray photoelectron spectroscopy. In comparison with the NH2 -ß-CD@capillary, the NH2 -ß-CD@His-ZIF-67@capillary-coated column shows significantly enhanced resolution for chiral molecules. The NH2 -ß-CD@His-ZIF-67@capillary column achieved the baseline separation of amlodipine and metoprolol (the resolution of amlodipine 1.70; metoprolol 1.50) and the partial separation of atenolol and propranolol (the resolution of atenolol 1.03; propranolol 0.60). These were attributed to the histidine modification and the features of ZIF-67, including an excellent surface area and the abundant porosity. The pH and proportion of organic modifier in the buffer were crucial for enantioseparation performance and were evaluated in detail. The fabricated NH2 -ß-CD@His-ZIF-67@capillary-coated column showed good stability and repeatability (relative standard deviation <6.3%). The molecular modeling with AutoDock and grand canonical ensemble was carried out to evaluate the interactions between chiral stationary phase and racemic drugs.