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

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.