Effect of Hydrocarbon Chain and Amide Linkage on the Interfacial and Self-Assembly Properties of Nicotinic Acid Amphiphiles

Three nicotinic acid amphiphiles, sodium 6-octylnicotinate (SONA), sodium 6-decylnicotinate (SDNA), and sodium 6-decylnicotinic glycinate (SDNAG), have been synthesized, and the effect of hydrocarbon chain length as well as amide linkage on the self-assembly properties in aqueous solutions have been investigated using a number of techniques, including tensiometry, fluorometry, FT-IR spectroscopy, H-1 NMR spectroscopy, UV-vis spectroscopy, dynamic light scattering, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Tensiometry measurements reveal the presence of two critical aggregation concentrations (CACs) for simple aliphatic chain amphiphiles, whereas a single CAC was obtained when glycine was introduced in the headgroup. Gel permeation chromatography studies indicate the presence of closed bilayer aggregates for all of the amphiphiles in aqueous solutions. XRD spectra indicate the presence of a non-interdigited bilayer structure. The presence of bilayer vesicles was confirmed by TEM measurements. Permeability of the bilayer membranes of the vesicles were investigated using the model water-soluble dye methylene blue. The vesicles obtained with nicotinic acid amphiphiles could be used as versatile carriers suitable for both hydrophobic and hydrophilic molecules.