Complexation of aliphatic alcohols by α- and β-cyclodextrins and their partial methylated derivatives in aqueous solution

The complexation of aliphatic alcohols by alpha- and beta-cyclodextrins and their partially methylated derivatives has been studied by means of calorimetric titrations in aqueous solution. The methyl substituents have no pronounced influence upon the complex formation. alpha-Cyclodextrin and the partially methylated derivative form with only few exceptions more stable than beta-cyclodextrin. With increasing chain length of the alcohols the values of the stability constants and reaction enthalpies increase in case of the complex formation with alpha-cyclodextrin and partially methylated alpha-cyclodextrin. In contrast the complex formation becomes disfavoured by the reaction entropy with an increasing number of methylene groups. The values of the reaction enthalpies with the beta-cyclodextrins are close to zero. Thus the complexation is only favoured by entropic contributions.