Comparative enantioseparations with native β-cyclodextrin and heptakis-(2-O-methyl- 3,6-di-O-sulfo)-β-cyclodextrin in capillary electrophoresis

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Abstract
Twenty‐three cationic chiral analytes were resolved in capillary electrophoresis using native β‐cyclodextrin and single isomer heptakis‐(2‐O‐methyl‐3,6‐di‐O‐sulfo)‐β‐cyclodextrin as chiral selectors. For 12 of 16 chiral analytes resolved with both chiral selectors the enantiomer migration order was opposite. In selected cases the structure of cyclodextrin‐analyte complexes in aqueous solution was investigated using one‐dimensional transverse rotating frame nuclear Overhauser and exchange spectroscopy. It was found that in contrast to mainly inclusion‐type complexes between chiral analytes and β‐cyclodextrin, external complexes are formed between the chiral analytes and structurally crowded, highly charged heptakis‐(2‐O‐methyl‐3,6‐di‐O‐sulfo)‐β‐cyclodextrin.