Osmotic and structural studies on Bolaamphiphile Vesicles

Unilamellar and multilamellar unsymmetric vesicles were obtained from aqueous dispersions of an anionic bolaform compound, trisodium (2,5,20,23-tetraoxo-21 (22)-sulfonato-1,6,19,24-tetraoxacyclohexatriacontan-3-ylthio)succinate, by sonication and centrifugation. Scanning electron microscopy (SEM) and light-scattering techniques show that a correlation between the method of preparation of the vesicles and their sizes is present. Osmotic studies were performed to investigate the permeability of the vesicles and their structural properties. Natural liposomes behave as ideal osmometers when an osmotic shrinkage is induced by adding NaCl or KCl solutions. This work shows that vesicles obtained from a bolaamphiphilic compound behave as ideal osmometers; enthalpic and entropic factors (obtained by transition state theory) for the osmotic shocks are reported. The temperature dependence of the vesicular dispersion absorbance at 400 nm does not show any phase transition between 10 and 80°C. This is also confirmed by DSC measurements between − 10 and 100°C. An empirical Freundlich-type equation is proposed for the time dependence of the turbidity changes occurring in the osmotic experiments.