Investigation of curcumin-cyclodextrin inclusion complexation in aqueous solutions containing various alcoholic co-solvents and alginates using an UV-VIS titration method: Studies of curcumin and curcuminoides, XXXV

The effect of pharmaceutical excipients like alcoholic co-solvents and water-soluble polymers on the inclusion complexation of curcumin in hydroxypropyl-β-cyclodextrin and hydroxypropyl-γ-cyclodextrin was investigated with a UV-VIS titration method. The association constants and the stoichiometries of the inclusion complexes in buffered media containing various amounts dl of alcoholic co-solvents and alginates were determined. The results showed a 1 : 1 stoichiometry between curcumin and both the cyclodextrins investigated in buffered media containing 10% (v/v) alcoholic co-solvents, although some 1 : 2 (host : guest) complexation was suspected between curcumin and hydroxypropyl-β-cyclodextrin. The presence of 0.1% (w/v) sodium alginate or propylene glycol alginate did apparently not change the stoichiometry of the complexes formed. Curcumin was found to have a more than 30-fold higher association constant with hydroxypropyl-γ-cyclodextrin compared to hydroxypropyl-β-cyclodextrin in buffer containing 0.5% ethanol. Large variation in the association constants between curcumin and the cyclodextrins as a result of different co-solvents in the aqueous complexing media were found. A decrease in the association constant was seen as the chain lenght of the added co-solvent increased. Further, a decrease in the association constants was observed by addition of alginates in the case of hydroxypropyl-γ-cyclodextrin at 0.5 or 5% (v/v) ethanol. The trend was opposite in the case of hydroxypropyl-β-cyclodextrin, where a 30-90% increase in the association constant was observed in the presence of alginates. The results in the current study showed the large variations in the complexation between curcumin and hydroxypropyl-β-cyclodextrin and hydroxypropyl- γ-cyclodextrin, resepctively, as a result of various alcoholic co-solvents and alginates in the complexing media. The results also illustrated the importance of optimizing the solvent systems when utilizing cyclodextrins as drug carriers.