Structural characterization of inclusion complex of arbutin and hydroxypropyl-β-cyclodextrin

Purpose: To improve the solubility and stability of arbutin and to expand its application by preparing its inclusion complex with hydroxypropyl-beta- cyclodextrin (HP-beta-CD). Methods: An inclusion complex made of arbutin and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was prepared by freeze-drying method. Various analytical techniques, including ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), x-ray diffractometry (XRD) and thermo-gravimetric/differential scanning calorimetry (TG/DSC), were used to characterize the inclusion complex. Results: UV spectra indicated that no new unsaturated bond was formed in the inclusion complex. Infrared analysis showed that the smaller peaks in the proximity of 1450 - 1600 cm(-1) were characteristic of the aromatic nucleus, indicating that the phenyl ring of arbutin was involved in the formation of the inclusion complex. Scanning electron micrographs of the inclusion complex showed that the original morphology of both components disappeared, and some tiny aggregates of amorphous areas of irregular size were present, revealing that the arbutin was dispersed in HP-beta-CD. The powder XRD pattern of the inclusion complex was more similar to that of amorphous HP-beta-CD and did not exhibit the characteristic peaks of arbutin which suggest that arbutin in HP-beta-CD matrix was molecularly dispersed, and existed in an amorphous state. The TG curve of the inclusion complex was a one-step process, partly proving the formation of the complex. Complex formation with HP-beta-CD remarkably improved the physical and chemical stabilities of arbutin. Conclusion: Inclusion complex of arbutin with HP-beta-CD improves the heat stability of arbutin remarkably. This has a potential for expanding the application of arbutin to pharmaceuticals and food.