Molecular microcapsules and inclusion interactions of eugenol with β-cyclodextrin and its derivatives

Abstract

The molecular microcapsules and inclusion interactions of eugenol (EG) with β-cyclodextrin (β-CD) and three derivatives, heptakis-2,6-di-β-CD (DM-β-CD), mono [2-O-(2-hydroxyethyl)]-β-CD (HE-β-CD), and mono [2-O-(2-hydroxypropyl)]-β-CD (HP-β-CD) have been investigated by fluorescence and infrared spectroscopy. The interaction capacities of β-CDs with EG were as the following order: HP-β-CD > DM-β-CD > HE-β-CD > β-CD. Effects of pH value, concentrations of CDs, and temperature on the inclusion interactions were studied to obtain further knowledge on the mechanism of inclusion process. The formation constants were derived by the modified Hildebrand–Benesi equation. The results show that EG with CDs formed 1:1 host–guest complexes. The thermodynamic parameters of inclusion process, ΔG, ΔH and ΔS were determined. Based on the thermodynamic results, the inclusion process was deduced to be an exothermic and enthalphy-driven process. Furthermore, the IR spectra study has been made to confirm the inclusion and to provide information on the geometry of EG inside the cavity of β-CD.