Study of Flavonoid/Hydroxypropyl-β-Cyclodextrin Inclusion Complexes by UV-Vis, FT-IR, DSC, and X-Ray Diffraction Analysis

The objective of this study was to investigate characterization of inclusion complexes of flavonoids with hydroxypropyl-β-cyclodextrin (HP-β-CD). The inclusion complexes of flavonoids with HP-β-CD was prepared by the freeze-drying method and its characterization was investigated by different analytical techniques including ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry, and X-ray diffractometry. The catechin/HP-β-CD complex exhibited the highest encapsulation efficiency (83.37%), followed by epicatechin/HP-β-CD (81.51%), morin hydrate/HP-β-CD (81.38%), and quercetin/HP-β-CD (81.16%). The inclusion complexes of HP-β-CD showed a decrease in the absorption of flavonoids with a small shift (≈2 nm) of the λ_max, while similar to the characteristic absorption peak of flavonoids. However, the FT-IR spectra of the flavonoid/HP-β-CD inclusion complexes did not display any features that were like the pure flavonoids, although the spectra were very similar to that of HP-β-CD. The melting point of flavonoids disappeared, and the thermal properties of HP-β-CD were altered following formation of the inclusion complex between flavonoids and HP-β-CD, resulting in a shift in the melting peak.