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

The positively charged quaternary ammonium cyclodextrin, QA‐β‐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‐β‐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‐β‐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. © 2005 Wiley‐Liss, Inc. Chirality 17:570–576, 2005.