Preparation and Characterization of Cationic Vesicles from a New Type of Ion Pair Amphiphile Carbethopendecinium-Dodecylsulfate

The aim of this work was to prepare and characterize a yet undescribed type of catanionic vesicle based on a new ion pair amphiphile, which were formed from carbethopendecinium bromide (also called Septonex) and sodium dodecylsulfate. The vesicles were prepared by mixing an amphiphilic pair together with dioctadecyldimethylammonium chloride and cholesterol at a concentration of 0, 5, 10, 15, 20, 30, 40, and 60 mol %. Final size, polydispersity and stability was studied by dynamic and electrophoretic light scattering. Fluorescence anisotropy, generalized polarization and high-resolution ultrasound spectroscopy were used to determine membrane order and hydration their outer part. The vesicles appeared to be stable in the short term independently of the cholesterol content. From a long-term (28 days) perspective, it was possible to detect a threshold of 15 mol % above which the vesicles were stable. The same cholesterol content threshold also applied to stability at elevated temperatures. Fluorescence measurements showed that the phase transition temperature was located at significantly lower temperatures compared to a similar system composed of hexadecyl-trimethylammonium-dodecyl sulfate. Using differential scanning calorimetry, it was found that this temperature was slightly affected by the cholesterol content and was around 15 °C. The results from ultrasonic spectroscopy together with generalized polarization and anisotropy showed a threshold of 20 mol % cholesterol content, above which the properties of the vesicular membrane, such as its stiffness and hydration, began to change significantly.