Physicochemical characterisation of the supramolecular structure of luteolin/cyclodextrin inclusion complex

The formation of supramolecular inclusion complexes between luteolin and five cyclodextrins namely beta-cyclodextrin (beta-CD), methyl-beta-cyclodextrin (M-beta-CD), hydroxyethyl-beta-cyclodextrin (HE-beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and glucosyl-beta-cyclodextrin (G-beta-CD) was investigated. Results from phase-solubility studies showed that luteolin formed 1:1 stoichiometric inclusion complexes with these cyclodextrins with the G-beta-CD complex displaying the greatest stability constant. The supramolecular structure of the luteolin/G-beta-CD complex was investigated by ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). Results showed clearly the formation of a supramolecular complex in which the guest molecule, luteolin, was entrapped inside the cavity of the host, G-beta-CD. The close association between luteolin and G-beta-CD resulted in changes in some of the characteristic spectral, phase transitional and morphological properties of luteolin. Furthermore, molecular docking study showed that the complex was formed with the B ring of luteolin inserted into the cavity of G-beta-CD. (C) 2013 Elsevier Ltd. All rights reserved.