Evaluation of chiral discrimination of highly negatively charged enantiomers by quaternary ammonium beta-cyclodextrin using 1H NMR

The positively charged quaternary ammonium cyclodextrin, QA-beta-CD, was previously used as a chiral selector to achieve baseline resolution of two of the dianionic enantiomers of disodium 3-(p-isothiocyanatophenoxy)-3-(p-isothiocyanatophenyl)propane-1,2-disulfate by capillary electrophoresis. The basis of the chiral discrimination between QA-beta-CD and the enantiomers was investigated by (1)H NMR spectroscopy. COSY and NOESY spectra were used to infer the role that molecular interactions and the stereocenters have upon association of QA-beta-CD with the enantiomers. A parallel two-step complexation model is used to rationalize the NMR and the chiral discrimination observed during separation of the enantiomers.