A comparison of the self-assembly behaviour of sodium N-lauroyl sarcosinate and sodium N-lauroyl glycinate surfactants in aqueous and aqueo-organic media.

Self-assembly of surfactants is influenced by various intermolecular interactions and molecular structure, which dictate packing of molecules in the aggregate and its microstructure. Hydrogen-bonding between amide groups plays a key role in the self-assembly process of N-acyl amino acid surfactants (NAAS). The self-assembly properties of two NAAS, sodium N-lauroyl sarcosinate (SLS) and sodium N-lauroyl glycinate (SLG) that differ only in the head-group structure were compared in aqueous and aqueo-organic media by using a number of methods, including surface tension fluorescence, dynamic light scattering, calorimetry, and microscopy. It was observed that aggregate formation is more favoured in SLG. Studies revealed that while SLS formed small spherical micelles, SLG produced unilamellar vesicles in pH 7 buffer above critical micelle concentration at 25 °C. The stability of SLG vesicles with respect to pH and temperature was also investigated. Furthermore, both SLG and SLS were found to gelify aquo-organic mixtures of varying composition upon heat-cool treatment. Their gelation behaviour was compared by measuring minimum gelation concentration, molecular packing, and morphology and mechanical stability of the thermoreversible gels. The difference in self-assembly behaviour in water as well as in aqueo-organic mixtures was attributed to the steric repulsion and hydrogen-bonding interaction at the head-group of the molecules.

Spontaneous vesicle formation by γ-aminobutyric acid derived steroidal surfactant: Curcumin loading, cytotoxicity and cellular uptake studies.

Cholesterol (Chol) is a ubiquitous steroidal component of cell membrane and is known to modulate the packing of phospholipids within the bilayer. Thus, Chol has been frequently used in the formulation and study of artificial "model membranes" like vesicles and liposomes. In this work, we have developed a novel anionic surfactant by conjugating two biomolecules, cholesterol and γ-aminobutyric acid via a urethane linkage. We have studied its physicochemical behavior in aqueous buffer. The surfactant has been shown to spontaneously form small unilamellar vesicles above a very low critical concentration in aqueous neutral buffer at room temperature. The vesicle phase was characterized by use of fluorescence probe, transmission electron microscopy and dynamic light scattering (DLS) techniques. The vesicle bilayer was found to be much less polar as well as more viscous compared to the bulk water. The vesicle stability with respect to change of temperature, pH, and ageing time was investigated by fluorescence probe and DLS techniques. The loading efficiency of the vesicles for the hydrophobic drug, curcumin, was determined and its release under physiological condition was studied. The in vitro cellular uptake of curcumin-loaded vesicles to human breast cancer cell line (MDA-MB-231) also was investigated. The MTT assay showed that the surfactant was non-cytotoxic up to a relatively high concentration.

Spontaneously formed robust steroidal vesicles: physicochemical characterization and interaction with HSA.

Self-assembled multimolecular aggregates, such as vesicles, have earned tremendous attention for their applications as model membranes and drug delivery systems. Over the past decades, enormous efforts have been dedicated to the development of stable and biocompatible vesicles that form spontaneously in aqueous solution. With the aim of preparing highly stable vesicles, we herein report the physicochemical characterization of a novel cholesterol-based chiral surfactant with l-alanine headgroup. Different techniques, such as surface tensiometry, fluorescence spectroscopy, dynamic light scattering, UV-vis spectroscopy, transmission electron microscopy, and confocal fluorescence microscopy were employed to investigate the self-assembly properties of the aforementioned single-tailed steroidal surfactant in aqueous solution. The surfactant molecule is weakly surface-active, but self-assembles to form unilamellar vesicles facilitated by the strong hydrophobic association of the cholesterol moieties, above a very low critical aggregation concentration. The vesicles are fairly stable with respect to aging, temperature, and pH of the aqueous medium. Additionally, the vesicles were found to fuse together, leading to large unilamellar vesicles. The intervesicular fusion pertaining to high stability of the vesicles could be ascribed to large hydrophobic interactions among steroidal skeletons. Furthermore, the interaction of the vesicles with human serum albumin is also investigated.