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

- In the mixed micelles of HD, C and Triton X-100 ΔpKa characterizes the stabilization of the system.
- Mixed micelles of HD and Triton X-100 are more stable than the system consisting of C and Triton X-100.
- ΔpKa values are the hidden excess Gibbs energy values GHAE=f(βij,α).

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 10 cmc 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.

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