Host-guest complexes of estragole with β-cyclodextrin: an experimental and theoretical investigation

Estragole (ES) has multiple biological activities and is widely used in food preservation. However, the applications of ES are limited because of its low water solubility and high volatility nature. In this paper, the β-cyclodextrin (β-CD) inclusion complex of ES was prepared by a co-precipitation method with the aim of enhancing its thermal stability and realize its controlled release. Solubility experiments were performed to evaluate the effect of β-CD on ES aqueous solubility. Release experiments of ES from its inclusion complexes were carried out at different temperatures with a relative humidity (RH) and Avrami's equation was used to analyse the release data. The antimicrobial activity of the free and included ES was also examined. The results indicated that the host–guest interactions played a crucial role in enhancing the properties of ES. The inclusion complex was investigated using physico-chemical techniques such as Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA and DSC), 1H and 2D nuclear magnetic resonance (NMR). The inclusion processes between β-CD and ES were simulated using the semi-empirical PM3 and ONIOM [B3LYP/6-31g(d):PM3] methods. Copyright © 2016 John Wiley & Sons, Ltd.