Comparative study on the interactions of cationic gemini and single-chain surfactant micelles with curcumin

The interactions of curcumin with cationic micelles of gemini surfactant trimethylene-1,3-bis-(dodecyldimethyl ammonium bromide) (C12C3C12Br2) and single-chain surfactant dodecyltrimethylammonium bromide (DTAB) were investigated. At pH 13, the trianionic curcumin (Cur(3-)) had rapid degradation to about 21.5% with an observed rate constant (k(obs)) of 0.0402 h(-1) in water, whereas DTAB micelle and C12C3C12Br2 micelle can suppress Cur(3-) degradation to 9.6% with k(obs) = 0.0174 h(-1) and to 5.0% with k(obs) = 0.00782 h(-1), respectively. Cur(3-) also showed higher intensities of characteristic peaks with the position changes in absorption and fluorescence spectra as well as increased anisotropy (r) in two surfactant micelles than in water. These results were ascribed to the solubilization of Cur(3-) in the palisade layer of DTAB and C12C3C15Br2 micelles through the attractive electrostatic interactions between negatively charged groups of Cur(3-) and quaternary ammonium headgroups of surfactants, which was also supported by the values of lowest pK(a) (pK(a1)) and corresponding thermodynamic parameters of curcumin in water, DTAB and C12C3C12Br2 micelles. The stronger electrostatic attractions between Cur(3-) and the micelle of C12C3C12Br2 brought about more increased stability of Cur(3-) and more remarkable changes in absorption and fluorescence spectra of Cur(3-) in C12C3C12Br2 micelle than in DTAB micelle. (C) 2012 Elsevier B.V. All rights reserved.