Novel methoxypropylimmidazolium β-cyclodextrin for improved enantioseparation of amino acids

A new single-isomer cationic cyclodextrin, mono-6A-[3-(3-methoxypropyl)imidazol-1-ium]-6A-β-cyclodextrin chloride, has been synthesized and successfully used for the chiral separation of dansyl amino acids in capillary electrophoresis. With methoxy functionality, the new cationic cyclodextrin exhibits significantly improved enantioselectivities. Excellent enantioseparations for amino acids are obtained in chiral selector concentration range between 2.5 mM to 15 mM at pH 6.0. Chiral resolution as high as 7.3 was achieved for Dns-Aca with 5 mM chiral selector. Comparison study and theoretical calculation with Wren’s model attribute the enhanced enantioseparation to the stronger inclusion complexation between amino acids and cyclodextrin. The binding constants for dansyl amino acids and the cationic cyclodextrins are calculated to be 173–253 M−1, while the optimum cyclodextrin concentrations were estimated to be 4.1–7.6 mM.