Changes in Solubilities of α- and β-Cyclodextrins in Water by Complex Formations with Adamantanecarboxylate

Abstract

Solubility (30mg.cm-3) of α-cyclodextrin in water at pH7 and 30°C in the presence of the equimolar amount of adamantane-1-carboxylate [1] is much smaller than that (170mg.cm-3) in the absence of 1. In contrast, solubility of β-cyclodextrin (65mg.cm-3)in the presence of [1] is larger than that (21mg.cm-3) in the absence of 1. The enhancement of solubility of β-cyclodextrin by [1] is ascribed to the conformational change of β-cyclodextrin by the inclusion of bulky [1] into its cavity, which promotes the interactions between the hydroxyl groups of β-cyclodextrin and the solvent water molecules.