Enantioseparation performance of novel benzimido-β-cyclodextrins derivatized by ionic liquids as chiral stationary phases.

Four novel β-cyclodextrin (β-CD) derivatives functionalized by ionic liquids, in which the substituents and cyclodextrin cavity are linked by a CH2-N=C group, were successfully prepared, and the corresponding chiral stationary phases (CSPs) based on silica gel, namely mono-6-deoxy-6-(p-N,N,N-trimethylaminobenzimide)-β-CD nitrate CSP (4a), mono-6-deoxy-6-(p-N,N,N-trimethylaminobenzimide)-β-CD tosylate CSP (4b), mono-6-deoxy-6-(p-N-methylimidazolemethylbenzimide)-β-CD nitrate CSP (4c) and mono-6-deoxy-6-(p-N-methylimidazolemethylbenzimide)-β-CD tosylate CSP (4d), were applied in high-performance liquid chromatography (HPLC). A large number of analytes including chiral 1-phenyl-2-nitroethanol derivatives, aromatic alcohols and ferrocene derivatives were investigated to evaluate the separation performance of the four CSPs, and excellent enantioseparations were obtained for most of the analytes. For 1-phenyl-2-nitroethanol derivatives and aromatic alcohols, the cationic substituent with smaller volume on β-CD derivative was beneficial for the enantioseparation of most compounds. Furthermore, the anion structures on these CSPs play an important role in the separation of solutes. The analytes with smaller molecular volume were more effectively separated on CSP 4b with the tosylate anion by offering hydrogen-bonding and π-π interactions, while the nitrate anions on CSPs 4a and 4c were more favorable for the separation of the compounds with larger volumes due to the weaker steric bulk. The enantiomeric separation results of ferrocene derivatives further showed good separation capability of CSPs 4b and 4c. The cooperation of cationic and anionic substituents on β-CD derivatives is essential for the separation of these chiral compounds.