Inhibitory effects of cyclodextrins by inclusion on the catalytic activity of glycyrrhizinate for the hydrolysis of a nonionic ester surfactant

Abstract

α-,β- and γ-Cyclodextrins (CyDs) and related derivatives have been investigated for their inhibitory effects on the catalytic activity of dipotassium glycyrrhizinate (GK2) in the hydrolysis of polyoxyethylene(60) hydrogenated castor oil, a non-ionic ester surfactant (HCO-60). The activity of GK2 was found to be completely inhibited in the presence of an equimolar amount of γ-CyD owing to the formation of a 1:1 host–guest complex. β-CyD behaved similarly. However, neither inhibition nor complexation was observed in the case of α-CyD. Circular dichroic spectroscopy, using the absorption at 340 nm due to the enone chromophore of GK2, was found to be a useful means to study the details of inclusion of GK2 by CyDs.