Self-Assembly of Bilayer Vesicles Made of Saturated Long Chain Fatty Acids.

Saturated long chain fatty acids (sLCFA, e.g., C14:0, C16:0, and C18:0) are potentially the greenest and cheapest surfactants naturally available. However, because aqueous sodium soaps of sLCFA are known to crystallize, the self-assembly of stable bilayer vesicles has not been reported yet. Here, by using such soaps in combination with guanidine hydrochloride (GuHCl), which has been shown recently to prevent crystallization, we were capable of producing stable bilayer vesicles made of sLCFA. The phase diagrams were established for a variety of systems showing that vesicles can form in a broad range of composition and pH. Both solid state NMR and small-angle neutron scattering allowed demonstrating that in such vesicles sLCFA are arranged in a bilayer structure which exhibits similar dynamic and structural properties as those of phospholipid membranes. We expect these vesicles to be of interest as model systems of protocells and minimal cells but also for various applications since fatty acids are potentially substitutes to phospholipids, synthetic surfactants, and polymers.

Self-assembly and foaming properties of fatty acid-lysine aqueous dispersions.

We report on dispersions of fatty acid-lysine salts in aqueous solutions which are further used to produce foams. The alkyl chain length is varied from dodecyl to stearic. In aqueous solutions, the lysine salt of the dodecyl chain yields an isotropic solution, probably micelles, whereas for longer alkyl chains, vesicles formed but crystallized upon resting at room temperature or when kept at 4 degrees C. Solid-state NMR showed that in vesicles fatty acids are embedded in a lamellar arrangement passing from a gel to a fluid state upon heating; the transition temperature at which it occurs was determined by DSC. Those results are confirmed by small-angle neutron scattering which also give additional information on the bilayer structure. Incredibly stable foams are obtained using the palmitic acid/Lys salt whereas for other alkyl chain length, poor or no foam is formed. We conclude that the foamability is related to the phase behavior in aqueous solution.