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The self-assembly of cationic and anionic amphiphile mixtures into vesicles in aqueous media was studied using two different systems: (i) decanoic acid and trimethyldecylammonium bromide and (ii) hexadecanedioic acid (a simple bola-amphiphile) and trimethyldecylammonium bromide. The resulting vesicles with varying amphiphile ratios were characterized using parameters such as the critical vesicle concentration, pH sensitivity, and encapsulation efficiency. We also produced and observed giant vesicles from these mixtures using the electroformation method and confocal microscopy. The mixed catanionic vesicles were shown to be more stable than those formed by pure fatty acids. Those containing bola-amphiphile even showed the encapsulation of a small hydrophilic solute (8-hydroxypyrene-1,3,6-trisulfonic-acid), suggesting a denser packing of the amphiphiles. Compression and kinetics analysis of monolayers composed of these amphiphiles mixtures at the air/water interface suggests that the stabilization of the structures can be attributed to two main interactions between headgroups, predominantly the formation of hydrogen bonds between protonated and deprotonated acids and the additional electrostatic interactions between ammonium and acid headgroups.
Caschera et al. (Fri,) studied this question.