title: Characterization of complexes between phenethylamine enantiomers and β-cyclodextrin derivatives by capillary electrophoresis-Determination of binding constants and complex mobilities.
abstract: To optimize chiral separation conditions and to improve the knowledge of enantioseparation, it is important to know the binding constants K between analytes and cyclodextrins and the electrophoretic mobilities of the temporarily formed analyte-cyclodextrin-complexes. K values for complexes between eight phenethylamine enantiomers, namely ephedrine, pseudoephedrine, methylephedrine and norephedrine, and four different β-cyclodextrin derivatives were determined by affinity capillary electrophoresis. The binding constants were calculated from the electrophoretic mobility values of the phenethylamine enantiomers at increasing concentrations of cyclodextrins in running buffer. Three different linear plotting methods (x-reciprocal, y-reciprocal, double reciprocal) and nonlinear regression were used for the determination of binding constants with β-cyclodextrin, (2-hydroxypropyl)-β-cyclodextrin, methyl-β-cyclodextrin and 6-O-α-maltosyl-β-cyclodextrin. The cyclodextrin concentration in a 50 mM phosphate buffer pH 3.0 was varied from 0 to 12 mM. To investigate the influence of the binding constant values on the enantioseparation the observed electrophoretic selectivities were compared with the obtained K values and the calculated enantiomer-cyclodextrin-complex mobilities. The different electrophoretic mobilities of the temporarily formed complexes were crucial factors for the migration order and enantioseparation of ephedrine derivatives. To verify the apparent binding constants determined by capillary electrophoresis, a titration process using ephedrine enantiomers and β-cyclodextrin was carried out. Furthermore, the isothermal titration calorimetry measurements gave information about the thermal properties of the complexes.
authors.affiliation: University of Würzburg, Institute for Pharmacy and Food Chemistry, Würzburg, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Wahl
authors.affiliation: University of Würzburg, Institute for Pharmacy and Food Chemistry, Würzburg, Germany.|Department of Physical Chemistry, Faculty of Pharmaceutical Sciences, Hoshi University, Tokyo, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Furuishi
authors.affiliation: Department of Physical Chemistry, Faculty of Pharmaceutical Sciences, Hoshi University, Tokyo, Japan.
authors.forename: Etsuo
authors.initials: E
authors.lastname: Yonemochi
authors.affiliation: University of Würzburg, Institute for Pharmacy and Food Chemistry, Würzburg, Germany.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Meinel
authors.affiliation: University of Würzburg, Institute for Pharmacy and Food Chemistry, Würzburg, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Holzgrabe
mesh_terms: D002151:Calorimetry; D019075:Electrophoresis, Capillary / Q000379:methods*; D024202:Electrophoretic Mobility Shift Assay; D010627:Phenethylamines / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D010627:Phenethylamines; D047392:beta-Cyclodextrins
keywords: Binding constant; Capillary electrophoresis; Cyclodextrin; Enantiomer separation; Ephedrine