title: Investigation of the pH-dependent complex formation between beta-cyclodextrin and dipeptide enantiomers by capillary electrophoresis and calorimetry.
abstract: The effect of pH on complex formation between beta-CD and the enantiomers of the dipeptides Ala-Phe, Ala-Tyr and Asp-PheOMe was investigated at 298.15 K by CE and calorimetry. Beta-CD displayed a higher enantioselectivity toward the protonated peptides compared to their zwitterionic forms. While stronger binding of the DD-enantiomers than the LL-stereoisomers were found by calorimetry regardless of the ionization state of the peptides, essentially equal complexation constants of the enantiomers were determined by CE for the zwitterionic species of the peptides. The reversal of the enantiomer migration order observed in CE was attributed primarily to a stereoselective complexation-induced pK(a) shift. In calorimetry, complexation of the protonated DD-enantiomers by beta-CD was accompanied by higher enthalpy and entropy changes resulting in more stable complexes compared to the LL-peptides. The enthalpy and entropy of complexation was affected by pH and peptide structure.
authors.affiliation: Department of Pharmaceutical Chemistry, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: Irina V
authors.initials: IV
authors.lastname: Terekhova
authors.forename: Manuela
authors.initials: M
authors.lastname: Hammitzsch-Wiedemann
authors.forename: Yuan
authors.initials: Y
authors.lastname: Shi
authors.forename: Bunleu
authors.initials: B
authors.lastname: Sungthong
authors.forename: Gerhard K E
authors.initials: GK
authors.lastname: Scriba
mesh_terms: D002151:Calorimetry; D004151:Dipeptides / Q000032:analysis*; D019075:Electrophoresis, Capillary; D006863:Hydrogen-Ion Concentration; D013237:Stereoisomerism; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000032:analysis*
chemical_list: D004151:Dipeptides; D047392:beta-Cyclodextrins; C031215:betadex