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

Abstract

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.

Preparation and release mechanism of lavender oil microcapsules with different combinations of coating materials

“…All determinations were operated in triplicate, and mean values calculated. The release data were estimated with the release kinetics equations:…”

Interactions between Bio-Based Compounds and Cyclodextrins

“…Focusing on EOs, and as previously discussed, they may present undesired features, such as volatility, poor aqueous solubility, and stability. Therefore, host-guest supramolecular complexes are often obtained by using solid-state-based methods [14] such as freeze-drying [76,77], coprecipitation [78], and the saturated approach [27], improving the solubility of the EO and thus allowing the use of NMR techniques for the quantitative and qualitative assessment of the complexation process [74]. For example, the complexation of eugenol with β-CD was obtained by using the saturation method, and the obtained complex, in the solid state, was characterized by either 1 H, 13 C, or 2D NMR techniques, confirming the thread of CD's cavity by the aromatic ring of the eugenol [27].…”

“…Also from group II, surface tension has also been used to follow the effect of CDs on the aggregation and interfacial properties of surfactants in CD-surfactant-containing solutions [74] Phase solubility studies Cabreuva essential oil + HP-β-CD [74] Phase solubility studies β-caryophyllene + HP-β-CD [76] UV-vis Black pepper essential oil + HP-β-CD [76] Phase solubility studies CDs 1 + PPs 2 [77] Phase solubility studies, NMR, TGA, DSC β-CD + estragole [78] NMR β-CD + eugenol [27] NMR β-CD + rosmarinic acid [75] NMR Cyclohexylacetic acid + β-CD Phase solubility studies, NMR, HPLC Polymethoxyflavones + HP-β-CD [93] GC, total organic carbon, phase-solubility studies SBE-β-CD, SBE-γ-CD and HP-β-CD + EOS 6 [94,95] 1 CDs: alpha-cyclodextrin (α-CD), beta-cyclodextrin (β-CD), gamma-cyclodextrin (γ-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), randomly methylated-beta-cyclodextrins (RAMEB), low methylated beta-cyclodextrin (CRYSMEB), and sulfobutylether β-cyclodextrin (SBE-β-CD) 2 PPs: trans-anethole, estragole, eugenol, isoeugenol (phenylpropenes), caffeic acid, p-coumaric acid, and ferulic acid (hydroxycinnamic acids) 3 UAS: ultrasonic attenuation spectroscopy APGs: glucopyranosides (octyl G8, decyl G10, dodecyl G12, tetradecyl G14) and two maltosides (decyl M10, dodecyl M12) 5 EOs: essential oils of cedarwood, clove, eucalyptus, and peppermint 6 EOS: essential oils of Artemisia dracunculus, Citrus reticulata Blanco, Citrus aurantifolia, Melaleuca alternifolia, Melaleuca quinquenervia, and Rosmarinus officinalis cineoliferum Table 2. Compilation of the most relevant techniques used to study the interactions between CDs and bio-based compounds.…”

“…Thermal techniques, such as thermal degradation analysis and differential scanning calorimetry, are classical examples of methods used to assess complexation. Moreover, thermal degradation also allows evaluating the thermal stability of the EO upon complexation [90,78].…”

“…Other spectroscopic techniques, such as FTIR and XRD, which can be included in group II, have also been used, but the information is, in our opinion, rather qualitative [30,72,78,91]. Another interesting approach to learn about the formation of host-guest complexes, in solid state, is to study the release kinetics of the EO.…”