Hepatakis(2-O-methyl-3,6-di-O-sulfo)-beta-cyclodextrin: A single-isomer, 14-sulfated beta-cyclodextrin for use as a chiral resolving agent in capillary electrophoresis

The first single-isomer, 14-sulfated beta -cyclodextrin, the sodium salt of heptakis(2-O-methyl-3,6-di-O-sulfo)-beta -cyclodextrin (HMdiSu) has been u sed to separate 24 pharmaceutical weak base enantiomers in pH 2.5 backgroun d electrolytes using capillary electrophoresis. For the weakly binding base s, the cationic effective mobilities decreased, approached zero, and then i ncreased again. For the strongly binding bases, the cationic effective mobi lities decreased, became anionic at very low concentrations of HMdiSu, pass ed an anionic mobility maximum, then decreased again as the HMdiSu concentr ation was increased. Viscosity corrections according to Walden's rule did n ot eliminate these unexpected effective mobility extrema. The mobility extr ema were rationalized by extending the charged resolving agent migration mo del (CHARM model) to include ionic strength effects.