Complex formation between α-cyclodextrin and amines in water and DMF solvents

Complexation between α-cyclodextrin (α-CD) and aliphatic amines in water and DMF solvents was studied by calorimetry. Amines form complexes with α-CD in both solvents but the nature of the complexes is quite different. In DMF the amines donate a hydrogen from the amine N-H group to the cyclodextrin forming a normal hydrogen bonded complex. In DMF solutions with large amine concentrations, complexes other than 1:1 are observed. In contrast, in aqueous environment the amines form inclusion complexes in which the amine alkyl group penetrates the α-CD cavity and is stabilized by van der Waals interactions. The equilibrium constants for the complexes formed in water solvent increase with increasing alkyl chain length due to an entropy effect.