A Family of Single-Isomer Chiral Resolving Agents for Capillary Electrophoresis. 3. Heptakis(2,3-dimethyl-6-sulfato)-β-cyclodextrin

Abstract

The third member of a new family of single-isomer charged cyclodextrins, the sodium salt of heptakis(2,3-dimethyl-6-sulfato)-β-cycldextrin, has been synthesized, characterized, and used for the capillary electrophoretic separation of the enantiomers of neutral, acidic, basic, and zwitterionic analytes. Though heptakis(2,3-dimethyl-6-sulfato)-β-cyclodextrin complexes much less strongly with any of the analytes tested here than the previously synthesized heptakis(2,3-diacetyl-6-sulfato)-β-cyclodextrin and heptakis-6-sulfato-β-cyclodextrin, it offers excellent enantioselectivities, complementary to those of the other two single-isomer, differently functionalized charged cyclodextrins. Confirming the predictions of the charged resolving agent migration model, heptakis(2,3-dimethyl-6-sulfato)-β-cyclodextrin allowed for the reversal of the migration order of the enantiomers of neutral analytes as the cyclodextrin concentration was increased. Just as with the previous two single-isomer charged resolving agents, separation selectivity for the acidic, basic, and zwitterionic analytes could increase, decrease, or pass a maximum as the cyclodextrin concentration was increased, depending on the respective binding strength of the enantiomers and the ionic mobilities of both the complexed and noncomplexed forms of the enantiomers.