Hydroxyethylammonium monosubstituted cyclodextrin as chiral selector for capillary electrophoresis

• The synthesis of a cationic single-isomer cyclodextrin (CD) as chiral selector.
• The strong chiral recognition of new CD by NMR study.
• The good enantioselectivity (chiral resolution over 5) for acidic and ampholytic racemates.
• Enantioseparation ability comparison for four cationic CDs.

A novel cationic cyclodextrin, mono-6A-(2-hydroxyethyl-1-ammonium)-6A-β-cyclodextrin chloride (HEtAMCD) has been successfully synthesized and applied as chiral selector in capillary electrophoresis. The NMR study revealed this chiral selector has three recognition sites: β-CD, ammonium cation and hydroxy group in the sidearm to contribute three corresponding driving forces including inclusion complexation, electrostatic interaction and hydrogen bonding. The effect of buffer pH and HEtAMCD concentration (2.5–10 mM) on enantioselectivity, chiral resolution as well as effective mobility of analytes was investigated. This elegantly designed CD exhibits outstanding enantioselectivities toward the studied hydroxyl acids and ampholytic racemates in CE with the aid of extra hydrogen bonding. Under optimum pH 6.0, chiral resolutions over 5 can be readily obtained for hydroxy acids with CD concentration below 5 mM. The comparison study between HEtAMCD and our earlier reported ammonium CDs indicates the hydroxyethylammonium group of HEtAMCD significantly increased the enantioselective capability.

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