Spontaneous Vesicle Based Excipient Formation in Mixtures of Sodium N‑(<i>n</i>‑Alkanoyl)‑L‑alaninate and N‑Cetylpyridinium Chloride: Effect of Hydrocarbon Chain Length

The hydrocarbon chain length effects of sodium N-alkanoyl-L-alaninate and N-cetylpyridinium chloride surfactants have been studied at various mixing ratios and concentrations. Both cationic and anionic surfactants form micellar solution in water, whereas by mixing the two surfactants in different compositions and concentrations, stable unilamellar vesicles are formed spontaneously. The variation of the chain length of the anionic surfactant produces a large effect on the stability of mixed surfactant systems. The vesicles formed by the mixtures are found to be thermodynamically stable in different composition and concentration in aqueous media. These vesicles formed by surfactant mixtures are stable for more than one month both for anionic- and cationic-rich side in very dilute solutions. The stability of the vesicle was examined by measuring the turbidity, which remains unchanged for a long time. Dynamic light scattering as well as transmission electron microscopic experiments were performed to investigate the structural properties of the different types of aggregates as well as the formation of vesicular structures. The effect of salt, pH, temperature, and cholesterol on the microviscosity of the domains was evaluated by using steady-state fluorescence depolarization method. Confocal fluorescence microscopic images technique and conductivity measurements have confirmed hollow sphere structure of the vesicles. In the presence of 10 mol % cholesterol and varying solution pH, the mixed surfactant vesicles exhibited leakage of the encapsulated calcein dye, which showed potential application in pH-triggered drug release. The surface chemical properties of the mixed surfactant system, stability, and potential applications of vesicle have been studied systematically