Complexo de inclusão entre óleo essencial de Callistemon viminalis e β-ciclodextrina: preparação, caracterização, atividade antibacteriana, antifúngica e testes de toxicidade

Abstract

Essential oils (EOs) are composed of naturally occurring bioactive compounds from the secondary metabolism of some plants. EO of Callistemon viminalis (EOC) is rich in chemical components with diverse biological properties (antibacterial, antifungal, insecticide, antitumor, among others). The use of EOs has grown greatly in recent years, but their use in high concentrations can be harmful to human health. The formation of inclusion complexes (ICs) of EOs with cyclodextrins (CDs) are being increasingly studied in order to reduce some undesirable characteristics such as high volatility and low solubility of EOs. Therefore, the objective of this study was to prepare the IC between EOC and -CD by the methods of kneading (KN) and co-precipitation (CO-P). Characterization of IC formation by spectroscopic techniques, calorimetric, scanning electron microscopy (SEM), X-ray diffraction (XRD) and molecular modeling (MM) were performed. To observe the changes in the EOC properties as (solubility, volatility, antibacterial activity, antifungal and phospholipase toxicity, hemolytic and lettuce seeds) after the formation of ICs. The water solubility of the EOC was increased 8-fold. The release rate of EOC in the ICs was improved with an average of 72% release after eight days, versus 83% release of pure EOC in two days. The spectroscopic and calorimetric results demonstrated that the EOC/β-CD IC has different physicochemical characteristics from the free EOC. The structural and morphological changes observed by SEM and XRD also confirmed the formation of IC by reducing the degree of crystallinity. The antibacterial and antifungal activity of EOC was improved after complexation, with a reduction of inhibitory minimum concentration (IMC) from 250 to 125 μg mL -1 for S. aureus in ICs prepared by KN and CO-P respectively. For L. monocytogens the reduction in IMC was from 250 to 62.5 μg mL -1 in IC prepared by KN. For the fungus A. flavus the IMC of 125 μg mL -1 reduced to 62.5 μg mL -1 for the IC prepared by KN and for the A. ochraceus fungus the IMC of 62.5 μg mL -1 was reduced to 15, 62 μg mL -1 in ICs prepared by KN and CO-P. The toxicity of EOC in ICs was reduced in the test with lettuce seeds, presenting germination percentage (% GR) for KN of 91.3% and of 75.3% for CO-P. CIs inhibited the action of both phospholipases A2 from Bothrops atrox venom, more pronounced on IC prepared by KN. The major components found in the EOC were 1,8-cineole (67.70%), α-pinene (15.01%) and α-terpineol (7.72%). Molecular modeling (MM) revealed that these components formed energetically favorable ICs, but the up-to-aa (axial-anti, anti) position terpineol and the more stable IC with a ΔE = -69.42 kJ mol -1 when compared to the other complexed components alone. The formation of IC between EOC/β-CD is a good alternative to improve the solubility and volatility that this EO presents, maintaining its biological properties. It reduces its toxicity and prolongs its action, thus increasing its use, in a way that is safer for man and the environment.