Determination of enantiomerization barrier of thioridazine by dynamic capillary electrophoresis using sulfated cyclodextrins as chiral selectors.

The enantiomerization of thioridazine (THD) using sulfated beta-CDs (S-beta-CDs) as chiral selectors in a citrate buffer at pH 3.0 was investigated by dynamic CE. The enantiomers of THD were well separated with dual CD systems consisting of S-beta-CD and a neutral CD. The electropherograms featuring a plateau formation, which indicated the occurrence of the enantiomerization of THD were obtained. The unified equation implemented in the software program DCXplorer was employed to evaluate elution profiles and to determine rate constants of the enantiomerization of THD. Activation parameters were evaluated from temperature-dependent measurements between 15 and 25 degrees C with an increment of 2 degrees C. The enantiomerization barriers of THD in two different electrophoretic systems were determined. Comparative studies on enantioseparation of THD using S-beta-CDs with different degree of substitution and positions of sulfate substituent, such as randomly sulfate-substituted beta-CD, 18-sulfate-substituted beta-CD and heptakis(2,3-dihydroxy-6-O-sulfo)-beta-CD reveal that the interactions between chiral selectors and THD plays an important role in the enantioseparation and enantiomerization of THD.