Encapsulation and isomerization of curcumin with cyclodextrins characterized by electronic and vibrational spectroscopy

FT-Raman and UV–visible adsorption spectroscopy are applied for the first time in the structural study of the antioxidant, antitumoral polyphenol curcumin and its complexation with β- and γ-cyclodextrin. Additionally, high performance liquid chromatography linked to UV spectroscopy was employed to monitor the encapsulation yield of curcumin. These techniques indicate that the effectiveness of the encapsulation is higher in the case of γ-cyclodextrin (γ-CD) likely due to the better fit of the polyphenol size with the dimensions of the γ-CD cavity. Raman spectra provided specific structural information from the ligand which indicates that the encapsulation takes place at the level of the aromatic rings, through H-bonds, and that a tautomerization from the planar keto enol form to the non-planar diketo form of curcumin also occurs. These changes may lead to an increase of the chemical stability, the bioavailability and the biological activity of curcumin.