The Effect of a Cationic Gemini Surfactant, Ethonium, on the Physicochemical Properties of Quercetin in Solutions and on the Surface of Highly Dispersed Silica

Abstract

The formation of supramolecular complexes with ethonium, a cationic gemini surfactant having a broad-spectrum antimicrobial activity, is shown to significantly alter the physicochemical properties (spectral, protolytic, and adsorption properties and solubility) of a natural f lavonol, quercetin. The constant of binding between quercetin and ethonium is calculated. Apparent dissociation constants pK_a1^a of quercetin in solutions of this cationic surfactant are for the first time determined within a broad concentration range. A shift in the pH dependence of quercetin adsorption by 0.5 units to the alkaline region upon the transition from a premicellar ethonium solution to a micellar one correlates with an increase in pK_a1^a under these conditions. The value of quercetin adsorption from aqueous ethonium solutions depends on the concentration of the cationic surfactant, pH of a solution, and the pK_a1^a value of the f lavonol bound into the supramolecular complex.