title: Higher order inclusion complexes and secondary interactions studied by global analysis of calorimetric titrations.
abstract: This paper investigates the use of isothermal titration calorimetry (ITC) as a tool for studying molecular systems in which weaker secondary interactions are present in addition to a dominant primary interaction. Such systems are challenging since the signal pertaining to the stronger primary interaction tends to overshadow the signal from the secondary interaction. The methodology presented here enables a complete and precise thermodynamic characterization of both the primary and the weaker secondary interaction, exemplified by the binding of β-cyclodextrin to the primary and secondary binding sites of the bile salt glycodeoxycholate. Global regression analysis of calorimetric experiments at various concentrations and temperatures provide a precise determination of ΔH, ΔG°, and ΔC(p) for both binding sites in glycodeoxycholate (K1 = 5.67 ± 0.05 × 10(3) M(-1), K2 = 0.31 ± 0.02 × 10(3) M(-1)). The results are validated by a (13)C NMR titration and negative controls with a bile salt with no secondary binding site (glycocholate) (K = 2.96 ± 0.01 × 10(3) M(-1)). The method proved useful for detailed analysis of ITC data and may strengthen its use as a tool for studying molecular systems by advanced binding models.
authors.affiliation: NSM, Research Unit for Functional Biomaterials, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Schönbeck
authors.forename: René
authors.initials: R
authors.lastname: Holm
authors.forename: Peter
authors.initials: P
authors.lastname: Westh
mesh_terms: D001665:Binding Sites; D002151:Calorimetry; D006002:Glycodeoxycholic Acid / Q000737:chemistry*; D012044:Regression Analysis; D013696:Temperature; D013816:Thermodynamics; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D047392:beta-Cyclodextrins; D006002:Glycodeoxycholic Acid; C031215:betadex