Water soluble complexes of curcumin with cyclodextrins: Characterization by FT-Raman spectroscopy

Many recent reports on curcumin, a polyphenol from Curcuma longa, provide mounting evidence on the pharmacological activity of this natural product. However, the pharmaceutical use of this molecule is hampered due to its poor solubility in the aqueous media. Inclusion complex formation with cyclodextrins has been reported as a means to enhance its aqueous solubility. Most of these studies provide infrared (IR) spectroscopic data as an evidence to support inclusion complex formation. However, characterization of the solid inclusion complexes using IR spectroscopy is hindered due to interfering vibrations of cyclodextrin. In this study, fully water soluble complexes of curcumin with three hydroxypropyl derivatives of cyclodextrins were isolated and characterized. Decrease in the intensity of aromatic ring vibrations and shift in peak position from 1626 cm−1 observed in Raman spectrum provided fresh insights into the type of interactions occurring in the water soluble complex. A new structure for the inclusion complex has been proposed. From the results it was demonstrated that Raman spectroscopy would provide clearer and better evidence of inclusion complex formation.