Self-Organization Properties and Microstructures of Sodium N-(11-Acrylamidoundecanoyl)-l-valinate and -l-threoninate in Water

Abstract

Abstract A new class of N-acylamino acid surfactants, sodium N-(11-acrylamidoundecanoyl)-l-valinate (SAUV) and -l-threoninate (SAUT), were synthesized and characterized in aqueous solutions. The self-assembly properties were studied by surface tension, fluorescence probe, light scattering, and microscopic techniques. The interfacial properties of the amphiphiles have been investigated at the air/water interface. The critical aggregation concentration (cac) and free energy change of aggregation for both amphiphiles were determined. The results of fluorescence probe and surface tension studies have indicated that initially flat bilayer structures are formed, which upon a further increase of surfactant concentration transform into closed vesicles. The pH and temperature dependence of the bilayer aggregates have been studied. The role of intermolecular hydrogen bonding between amide groups upon aggregation towards microstructure formation in solution has been elucidated. The micropolarity of the hydrophobic domains of the bilayer self-assemblies was estimated by fluorescence probe methods. Dynamic light scattering measurements were performed to determine the mean size of the aggregates. The circular dichroism spectra of SAUV and SAUT suggested the formation of chiral aggregates in dilute solution. The transmission electron micrographs revealed the presence of closed vesicles and twisted ribbons in the aqueous solutions of the amphiphiles. Optical microscopic images also showed the existence of twisted ribbons and rope-like helical structures in the case of SAUV.