Binding and stabilization of curcumin by mixed chitosan–surfactant systems: A spectroscopic study

The effect of the biopolymer chitosan, in presence of a cationic surfactant, viz., cetyl trimethyl ammonium bromide (CTAB) and a non-ionic surfactant, viz., polyoxyethylene (20) sorbitan monooleate (TW80) on the solubility and spectroscopic properties of the bioactive compound curcumin has been studied at physiological pH (7.4) condition. Based on the solvent and medium sensitive absorption and fluorescence properties of curcumin, the apparent binding constants of curcumin to chitosan, chitosan–CTAB and chitosan–Tween-80 systems have been estimated. From the fluorescence quenching by potassium iodide and acrylamide of the chitosan entrapped curcumin solutions, it has been found that curcumin is non-uniformly distributed in the colloidal chitosan solution. Curcumin is located mostly inside the hydrophobic interior of chitosan while a small fraction resides in the cationic centres of chitosan. The stability provided to curcumin by chitosan alone and in the presence of CTAB and TW80 has been investigated by spectrophotometric analysis of the kinetics of degradation of curcumin. It has been observed that the reaction rate constants were decreased in various systems in the order: chiotsan-TW80 > chitosan–CTAB > chitosan. The interaction of curcumin with chitosan has been found to be exothermic and driven by hydrophobic interactions, hydrogen bond formation, and electrostatic interactions.