Enantioselectivity of basic analytes in CZE enantioseparation under reversed‐polarity mode using sulfated β‐cyclodextrins as chiral selectors: An unusual temperature effect

Abstract

Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-CDs (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octopamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (-)-enantiomers of the two catecholamines and dopamine at 40 degrees C are greater than those at 25 degrees C with MI-S-beta-CD, even at a concentration as low as 0.3% w/v. Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This phenomenon results from the inequality of the temperature effect on the mobility of the two enantiomers. In contrast, norephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (-)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 and 25 degrees C is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7% w/v for enantioseparation of isoproterenol, 0.4% w/v for epinephrine, and 0.3% w/v for octopamine. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.

Cyclodextrin‐mediated enantioseparation of phenylalanine amide derivatives and amino alcohols by capillary electrophoresis—Role of complexation constants and complex mobilities

“…. Especially amino alcohols such as norephedrine ( 7 ) have been separated by various CDs including neutral and charged derivatives . Initial screening of the enantioseparation of compounds 1–8 by native α‐, β‐, and γ‐CD was performed using 20 mM sodium phosphate buffer, pH 2.5, because the amines are positively charged at this pH providing analyte mobility toward the cathode.…”

“…Negatively charged selectors often exhibit good enantioselectivity toward protonated basic analytes . For instance, the successful application of sulfated β‐CD derivatives to the enantioseparations of 1 and 7 in acidic BGEs has been reported. Screening was performed in 20 mM sodium phosphate buffer, pH 2.5, at a concentration of 40 mg/mL of the HS CDs.…”

Effect of temperature on the enantioselectivity of basic analytes using CE with sulfated β‐cyclodextrins

“…According to our work, the mobility change of the two enantiomers of analytes between 35 and 208C using various concentrations of S-b-CD were different fromt the previous work, as shown in Table 2 [11]. All of the mobility changes of the two enantiomers between 35 and 208C were increased and furthermore, all of the mobility changes of the first eluted enantiomers (i.e., (+)-) were higher than that of the second eluted enantiomers (i.e., ( -)-) whosoever enantioselectivity increased or decreased with the increase in temperature.…”

Cyclodextrins in capillary electrophoresis enantioseparations – Recent developments and applications

“…A detailed study was performed on the temperature effect on the enantioseparation of epinephrine and related drugs using sulfated b-CD at pH 3.0 under reversed polarity conditions as a function of the CD concentration [40]. An increase of the separation selectivity upon increasing the temperature was observed even at low concentrations of sulfated b-CD in the case of epi- nephrine (Fig.…”

“…[38]. Under the experimental conditions of the study [40] the (+)-enantiomers migrated in front of the ( -)-enantiomers. At higher temperatures, the mobilities of the (+)-enantiomers of epinephrine, isoproterenol, and octopamine increased to a higher extent compared to the corresponding ( -)-enantiomers.…”