Complexation and molecular microcapsules of Litsea cubeba essential oil with β-cyclodextrin and its derivatives

The inclusion interactions of beta-cyclodextrin (beta-CD), heptakis (2,6-di-methyl)-beta-CD (DM-beta-CD), mono[2-O-(2-hydroxyethyl)]-beta-CD (HE-beta-CD), and mono[2-O-(2-hydroxy-propyl)]-beta-CD (HP-beta-CD) with Litsea cubeba essential oil (LCEO) were investigated by ultraviolet spectrophotometry, and the various factors affecting the inclusion process were examined in detail. At the same time, the formation constants at different temperatures and the thermodynamic parameters (Delta H, Delta S and Delta G) were calculated. The results suggest that the stoichiometry of the LCEO-CDs inclusion complexes was 1:1 (molar ratio), the formation constants of CDs with LCEO decreased with the increasing of temperature, and the order that the capability associated with LCEO was HP-beta-CD > HE-beta-CD > DM-beta-CD > beta-CD. The thermodynamic measurements showed that the inclusive process was an exothermic and enthalpy-driven process accompanied with a negative entropic contribution, and Van der Waals force plays an important role in the process. In addition, the molecular microcapsule of LCEO in beta-CD was prepared by suspension method. The content of LCEO in the microcapsules was 0.12 g/g and their stabilities were obviously improved because of Van der Waals forces and the steric hindrance. Furthermore, the formation of the inclusion complex was characterized by FTIR.