MICROCALORIMETRIC TITRATION OF ALPHA-CYCLODEXTRIN WITH SOME STRAIGHT-CHAIN ALPHA,OMEGA-DICARBOXYLATES IN AQUEOUS-SOLUTION AT DIFFERENT TEMPERATURES

The complex formation of alpha-cyclodextrin and straight-chain aliphat ic alpha,omega-dicarboxylates, -O2C(CH2)nCO2-(n = 6, 7, 8), in aqueous solution has been studied by titration microcalorimetry at 288.15, 29 8.15 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 enthalp y-entropy compensation effects, which result in weak temperature depen dences of the Gibbs energies. The heat capacities of binding are large and negative. This confirms the view that the binding of non-polar mo ieties to cyclodextrins is to a large extent a result of hydrophobic d ehydration. Experimental conditions causing deviations from the 1 : 1 model, are also discussed.