The role of charge in the surfactant-assisted stabilization of the natural product curcumin

No Thumbnail Available
Authors
Wang, Zifan
Leung, Mandy H. M.
Kee, Tak W.
English, Douglas S.
Issue Date
2010-04-20
Type
Article
Language
eng
Keywords
Research Support, Non-U.S. Gov't , Research Support, U.S. Gov't, Non-P.H.S.
Research Projects
Organizational Units
Journal Issue
Alternative Title
Abstract

Colloidal solutions of surfactants that form micelles or vesicles are useful for solubilizing and stabilizing hydrophobic molecules that are otherwise sparingly soluble in aqueous solutions. In this paper we investigate the use of micelles and vesicles prepared from ionic surfactants for solubilizing and stabilizing curcumin, a medicinal natural product that undergoes alkaline hydrolysis in water. We identify spectroscopic signatures to evaluate curcumin partitioning and deprotonation in surfactant mixtures containing micelles or vesicles. These spectroscopic signatures allow us to monitor the interaction of curcumin with charged surfactants over a wide range of pH values. Titration data are presented to show the pH dependence of curcumin interactions with negatively and positively charged micelles and vesicles. In solutions of cationic micelles or positively charged vesicles, strong interaction between the Cur(-1) phenoxide ion and the positively charged surfactants results in a change in the acidity of the phenolic hydrogen and a lowering of the apparent lowest pK(a) value for curcumin. In the microenvironments formed by anionic micelles or negatively charged bilayers, our data indicates that curcumin partitions as the Cur(0) species, which is stabilized by interactions with the respective surfactant aggregates, and this leads to an increase in the apparent pK(a) values. Our results may explain some of the discrepancies within the literature with respect to reported pK(a) values and the acidity of the enolic versus phenolic protons. Hydrolysis rates, quantum yields, and molar absorption coefficients are reported for curcumin in a variety of solutions.

Description
Click on the DOI link below to access the article (may not be free).
Citation
Langmuir : the ACS journal of surfaces and colloids. 2010 Apr 20; 26(8): 5520-6.
Publisher
American Chemical Society
License
Journal
Volume
Issue
PubMed ID
DOI
ISSN
1520-5827
0743-7463
EISSN