Self-assembled structural transition from vesicle phase to sponge phase and emulsifying properties in mixtures of arginine and fatty acids.

Two fatty acids, octanoic acid (OA) and decanoic acid (DA) were separately mixed with a natural biological molecule, l -arginine (Arg), in aqueous solutions for comparative investigation. Self-assembled structures including micelles, vesicles, sponge structures, were observed by varying the compositions and chain length of fatty acids. The structures of vesicles and sponge phase were determined by freeze fracture-transmission electron microscope (FF-TEM). The transition of self-assembled structures, especially from vesicles to sponge structure, was significantly reflected in the change of rheological properties. The double hydrogen bonding formed between the guanidyl group of Arg and the carboxyl group of fatty acids is considered to be the crucial force, which drives the self-assembly process combining with other non-covalent interaction, electrostatic interaction and hydrophobic interaction. Depending on the nature of the fatty acid, the systems exhibit good emulsion stability. [ABSTRACT FROM AUTHOR]