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

• We studied the complexation of luteolin with five different cyclodextrins.
• Complexation changed the spectral, phase transitional and other properties of luteolin.
• The inclusion complex was formed with ring B of luteolin inserted into the cavity of G-β-CD.

The formation of supramolecular inclusion complexes between luteolin and five cyclodextrins namely β-cyclodextrin (β-CD), methyl-β-cyclodextrin (M-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and glucosyl-β-cyclodextrin (G-β-CD) was investigated. Results from phase-solubility studies showed that luteolin formed 1:1 stoichiometric inclusion complexes with these cyclodextrins with the G-β-CD complex displaying the greatest stability constant. The supramolecular structure of the luteolin/G-β-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-β-CD. The close association between luteolin and G-β-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-β-CD.