Binary mixed micelles of triton X-100 and selected bile salts: Thermodynamic stabilization and pKa values of micellar bile acids

Abstract

Bile acid anions are biosurfactants which form small micelles. To enhance the hydrophobic volume of the micelle, bile salts are used as mixed micelles with non-ionic surfactants. Micellar-bound bile acids (sodium-hyodeoxycholate, HD and sodium-cholate, C in binary mixed micelles with non-ionic surfactant Triton X-100) at concentration of 10cmc have higher pKa values than bile acids from the aqueous solution. Different pKa values of micellar and non-micellar bile acids (ΔpKa) are due to the excess Gibbs energy GHAE which is a function of interaction coefficient and mole fraction of Triton X-100 in the binary surfactant mixture. In the mixed micelles ΔpKa values show synergistic interactions between different building units, similarly as interaction coefficient.