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

Abstract

Twelve basic analytes, including ephedrine and its structurally related compounds, were used to study the influence of capillary temperature on enantioselectivity in CE enantioseparations under reversed polarity mode using sulfated beta-CD (S-beta-CD) as chiral selectors. All of the effective mobility changes of (+)-enantiomers between 35 and 20 degrees C were higher than those of (-)-enantiomers whosoever enantioselectivity increased or decreased with an increase in temperature. However, the unusual temperature effect that enantioselectivity was increased with an increase of temperature was observed for the compounds with hydroxyl substitution on phenyl ring and had relationship with the molecular structures. With performing NMR studies on the selected selector-analyte complexes, the results led to a deeper understanding of the chiral discrimination process. Inspection of the complexation-induced chemical shifts (CICS) of the enantiomers showed that the phenyl ring sits deeply and slantways in the cavity of S-beta-CD and alkyl chain pointed out of the wider rim of S-beta-CD with ion-ion and hydrogen bond interactions between analytes and S-beta-CD.

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.…”

Application of cyclodextrins in chiral capillary electrophoresis

“…Sulfated ␤-CD Amlodipine [241], Betti bases [300], borreverine [259], bupivacaine [178], 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone [283], cetirizine [91,301], citalopram [97], hydroxyflavanones [324], fluoxetine [302], helquats [293,303], 4,5-disubstituted imidazoles [304], lorazepam [108,162], 3-hydroxymexiletine [305], modafinil [134,306], nicotine and its related compounds [307], nicotine butyric acid [90], ofloxacin and ornidazole [132], 3,4-dihydroxyphenylalanine [238,[308][309][310], phenylalanine [308], isoprenaline [92], rotigotine and related chiral impurities [252], thioridazine [311], tolterodine and methoxytolterodine [89], tryptophan [312], tyrosine [238,308], benzoxazolinonic aminoalcohols [294], 13 new amphetamine-like designer drugs [313], 12 basic analytes [314], 19 cathinone derivatives [315], impurity of clopidogrel [316], four antimalarial drugs [280], four basic drugs [295], five basic drugs [296], six basic drugs…”

“…Examples of commercially available randomly substituted CDs are neutral methylated CDs and 2‐hydroxypropylated CDs , and negatively charged carboxymethylated CDs and sulfated CDs . The only commercially available positively charged randomly substituted CD is quaternary ammonium β‐CD that has been used for the separation of negatively charged analytes .…”

Chiral selectors in CE: Recent developments and applications

“…It was separated online with phosphorescence detection mode, and the optimum separation conditions were applied for its quantification in a pharmaceutical formulation and in a spiked urine sample. Additionally, S‐β‐CD was also used for the separation of other chiral drugs, such as cetirizine , amisulpride , clopidogel , modafinil , ephedrine and structurally related compounds .…”