Study of the interaction between polyphenol, quercetin and three micelles with different electric charges in acidic and aqueous media

The interactions between the polyphenol quercetin, Q, with three surfactant aggregates with different electric charges named micelles, were studied in aqueous solutions with pH values 4.7 and 7.0, to determine the following parameters: critical micellar concentration (CMC), micelle size and binding constant of the complex (Q-Micelle) proposing interaction sites for the formation of the complex. The surfactants used were: hexadecyltrimethyl ammonium bromide (cationic surfactant), CTAB, sodium dodecyl sulfate (anionic surfactant), SDS, and triton X-100 (non-ionic surfactant), TX100, used as Q fluorescence promoters to determine the CMC. The CMC values of the above surfactants at pH 4.7 were: 0.80 & PLUSMN; 0.10, 1.39 & PLUSMN; 0.07 and 0.59 & PLUSMN; 0.05 mM respectively, being lower than those reported in the water. With dynamic light scattering measurements, the hydrodynamic diameters of each micelle were calculated resulting in values of: 2.4 & PLUSMN; 0.5, 5.0 & PLUSMN; 1.1 and 8.4 & PLUSMN; 4.3 nm at pH 4.7 and: 2.1 & PLUSMN; 0.4, 4.9 & PLUSMN; 1.1 and 11.5 & PLUSMN; 4.1 nm at pH 7.0 respectively. In addition, the binding constants of the complex (Q-Micelle) with 1:1 stoichiometry were calculated from emission fluorescence data giving Log K values: 2.94 & PLUSMN; 0.02, 2.54 & PLUSMN; 0.02, and 3.63 & PLUSMN; 0.05 M-1 respectively. Finally, from the experimental data by UV-Vis spectrophotometry, the change in the behavior of the Q spectrum upon the addition of each of the surfactants to the system was analyzed, showing a decrease in absorbance when SDS and TX100 were added in an acidic medium, as a consequence of the photo-instability of the drug, suggesting that Q interacts with the outside of these micelles and is not fully incorporated inside them.