Search

Comparative enantioseparations were performed with three neutral cyclodextrins (CDs) in capillary electrophoresis (CE). In particular, native beta-CD was compared with single component heptakis(2,3-di-O-acetyl)-beta-CD (HDA-beta-CD) and randomly acetylated beta-CD (Ac-beta-CD) with the emphasis on the enantiomer migration order. The opposite affinity of the enantiomers of several chiral analytes was observed towards native beta-CD and its acetylated derivatives. The enantiomer affinity pattern of some chiral analytes was also opposite towards the two acetylated derivatives of beta-CD. In the case of the chiral drug clenbuterol (CL) an attempt was made to evaluate the possible structural reasons of the affinity reversal using one- and two-dimensional as well as transverse rotating frame nuclear Overhauser effect spectroscopy (ROESY). Significant differences were observed between the structure of the CL complexes with beta-CD and HDA-beta-CD.

Opposite migration order was observed for the enantiomers of the chiral beta2-adrenergic drug clenbuterol (CL) in capillary electrophoresis (CE) when resolved with native beta-cyclodextrin (beta-CD) and heptakis (2,3-diacetyl-6-sulfo)-beta-CD (HDAS-beta-CD). The possible mechanisms of the affinity reversal of the CL enantiomers depending on the structure of the CD were studied using 1H-nuclear magnetic resonance (1H-NMR) spectrometry and one-dimensional rotating frame nuclear Overhauser and exchange spectrometry (1-D ROESY). Significant differences were observed between the structure of the (+/-)-CL complexes with beta-CD and HDAS-beta-CD.

The effect of the amount of the chiral selector, cellulose tris(3,5-dichlorophenylcarbamate) (CDCPC) on the separation characteristics of enantiomers of some charged and neutral analytes was studied in capillary electrochromatography (CEC). For better understanding of the effect of the loading of the chiral selector on the particles and pore size of the packing material, laser-beam particle size analyzer and scanning electron microscopy (SEM) were used. As shown in this study, CDCPC can be used for CEC enantioseparations of a wide range of chiral charged and neutral analytes with high efficiency. The loading of the polysaccharide derivative on the surface of silica materials even in high amounts does not markedly affect the particle size and porous structure of the packing material. The separation characteristics are strongly affected by the loading of CDCPC onto silica gel in both CEC and capillary liquid chromatography (CLC).