Influence of cations of the first group of the Periodic Table of Elements on the thermodynamic stabilization of cholic and deoxycholic acid anion micelles

Abstract

From the dependence of the specific conductivity on the total concentration of surfactants approximation can be made that micelles of cholic acid (SC) anions and deoxycholic acid (SDC) anions in the vicinity of the critical micelle concentration (cmc) do not bind counterions (β = 0). Thermodynamic stabilization of SC and SDC micelles is greatest if the aqueous solution contains CsCl, although Cs+ has the smallest surface charge density. This indicates that the mechanism that exerts the effect of the cations of the first group of the Periodic Table of Elements (PTE) on the micellization of SC and SDC depends on the ionic radii of cations, i.e. the mechanism is different for cations with a large ionic radius and for cations with a small ionic radius. If the micelles do not bind counter ions, then the cations exhibit their activity on water molecules located in the hydrophobic shell above the hydrophobic surface of the monomer. From β = 0 it follows that the excess Gibbs energy of micellization in the presence of cations of the first group of the PTE in the aqueous solution does not contain Debye-Hückel's Gibbs excess energy. Equation analogous to the Dér's equation can be obtained for the critical micellar concentration ratio ln(cmc/cmc′). The paper demonstrated that Der's equation applied to the micelles of bile salts describes the excess Gibbs energy of micellization.