Classification of the solubility behaviour of β‐cyclodextrin in aqueous–CO‐solvent mixtures

Abstract

Abstract The solubility behaviour of β‐cyclodextrin in aqueous mixtures was studied by determining the interactions between the co‐solvent and water. Three clear classes of co‐solvent are evident. In the first, including ethanol, tetrahydrofuran and acetone, there is formation of clathrate hydrates by the co‐solvent. In these systems the solubilization is a maximum at the mole fraction corresponding to the minimum in the partial excess molar volume. The second class, including such solvents as dimethyl sulphoxide and pyridine, forms strong molecular complexes with water, and here a valley and a plateau region occur in the solubility values. In the third class, including formamide and urea, a steady increase in the solubility is observed. For these highly polar solvents no maxima are observed in intrinsic solvent properties such as the partial excess molar volume.