Spontaneous formation of vesicles and dispersed cubic and hexagonal particles in amino acid-based catanionic surfactant systems
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Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride ( ALA) and NR-lauroyl-arginine-methyl ester hydrochloride ( LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate ( HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate ( SOS) and sodium cetyl sulfate ( SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy ( cryo-TEM), dynamic light scattering ( DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure ( cubosomes) and internal hexagonal structure ( hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. ( Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications.