On the Curcumin and β-Cyclodextrin Interaction in Aqueous Media. Spectrophotometric and Electrochemical Study

It is shown from UV/Vis spectrophotometry measurements, that up to two inclusion complexes between curcumin and beta-cyclodextrin, namely H(3)Cur(beta-CD) and H(2)Cur(beta-CD)(2), can be formed in aqueous solution at pH-3.6, where the fully protonated and neutral species of curcumin, H(3)Cur, predominate depending on the beta-CD concentration. The thermodynamic formation constants of these supramolecular complexes were determined and the molar absorptivity coefficients of H(3)Cur, H(3)Cur(beta-CD) and H(3)Cur(beta-CD)(2), species were assessed. In the absence of beta-CD curcumin degradation increases linearly with time at a rate of 3.25%min(-1). However, in its presence, the rate drastically diminishes to 0.11 % min(-1). These results were corroborated from independent electrochemical measurements using a bare carbon paste electrode. At 0.01 M beta-CD the first voltammogram cycle displayed single anodic and cathodic peaks while the second cycle is formed by two anodic peaks and one cathodic, all of them being due to single-electron adsorption-controlled processes. The current of these peaks can be used to quantify curcumin concentration in real samples.