Microcalorimetric titration of α-cyclodextrin with some straight-chain α,ω-dicarboxylates in aqueous solution at different temperatures

Abstract

The complex formation of α-cyclodextrin and straight-chain aliphatic α,ω-dicarboxylates, ^–O₂C(CH₂)_nCO₂^–(n= 6, 7, 8), in aqueous solution has been studied by titration microcalorimetry at 288.15, 298.15 and 308.15 K. Apparent Gibbs energies, enthalpies, entropies and heat capacities for the 1 : 1 complex formations were derived from the calorimetric data. The thermodynamics of binding show typical enthalpy–entropy compensation effects, which result in weak temperature dependences of the Gibbs energies. The heat capacities of binding are large and negative. This confirms the view that the binding of non-polar moieties to cyclodextrins is to a large extent a result of hydrophobic dehydration. Experimental conditions causing deviations from the 1 : 1 model, are also discussed.