Cationic cyclodextrins chemically-bonded chiral stationary phases for high-performance liquid chromatography

Abstract

Two covalently bonded cationic β-CD chiral stationary phases (CSPs) prepared by graft polymerization of 6A-(3-vinylimidazolium)-6-deoxyperphenylcarbamate-β-cyclodextrin chloride or 6A-(N,N-allylmethylammonium)-6-deoxyperphenylcarbamoyl-β-cyclodextrin chloride onto silica gel were successfully applied in high-performance liquid chromatography (HPLC). Their enantioseparation capability was examined with 12 racemic pharmaceuticals and 6 carboxylic acids. The results indicated that imidazolium-containing β-CD CSP afforded more favorable enantioseparations than that containing ammonium moiety under normal-phase HPLC. The cationic moiety on β-CD CSPs could form strong hydrogen bonding with analytes in normal-phase liquid chromatography (NPLC) to enhance the analytes’ retention and enantioseparations. In reversed-phase liquid chromatography (RPLC), the analytes exhibited their maximum retention when the pH of mobile phase was close to their pKa value. Inclusion complexation with CD cavity and columbic/ionic interactions with cationic substituent on the CD rim would afford accentuated retention and enantioseparations of the analytes.