Inclusion complex of Callistemon viminalis essential oil prepared by kneading

Abstract

The essential oil of Callistemon viminalis (EOC) is rich in monoterpenes that present a wide range of biological properties, including antibacterial, antifungal, insecticidal, and antioxidant activities. However, applications of EOC are limited by its volatility and low solubility in water. The formation of inclusion complexes (ICs) with cyclodextrins (CDs) offers a way to improve the characteristics of unstable substances such as EOC. Therefore, the aim of this work was to characterize and analyze the composition of EOC, to complex it with β-CD using a kneading technique, and to perform controlled release assays. The formation of the IC was observed using infrared spectroscopy (IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Molecular dynamics was performed to analyse the interaction of β-CD with the majority compounds present in the EOC. The IR spectra and the results of the DSC and TGA calorimetric analyses showed that the physicochemical characteristics of the IC were different to those of the free EOC. The XRD and SEM analyses revealed structural and morphological changes after IC formation, hence confirming that complexation had occurred. In the case of the free EOC, 86% had been released after 2 days of dialysis, while the IC showed 65% release of the oil after 8 days, indicating that formation of the EOC/β-CD inclusion complex was effective in retarding the release of the EOC.Theoretical data showed that the most stable IC was obtained with α-terpineol, one of the major components of EOC. The results suggested that the activity of the IC should be evaluated in existing EOC applications.