Alkyl chain length asymmetry effects of mixed n-acyl sarcosinate and N-cetylpyridinium chloride surfactants: Spontaneous formation of stable nanovesicles as excipient

Abstract

The effect of hydrocarbon chain length of sodium-n-acyl sarcosinate (SNAS) and N-cetylpyridinium chloride (CPC) surfactants has been studied at various mixing ratios and concentrations. The variation of the chain length of the anionic surfactant produces a significant effect on the stability of mixed surfactant systems. The unilamellar vesicles formed by the mixtures are shown to be thermodynamically stable in different ratios and concentration in aqueous media. These vesicles formed by surfactant mixtures are stable for a long period of time such as several years both for anionic-rich and cationic-rich side in very dilute solutions. The stability of the vesicles was validated by UV absorbance spectra which remain unchanged for a long time. Both cationic and anionic surfactants are soluble in water forming micellar solutions individually, but mixing of two surfactants in different mole ratios and concentration forms stable vesicles. Dynamic light scattering (DLS) as well as transmission electron microscopic (TEM) experiments was performed to investigate the structural properties of the different types of aggregates and the formation of nano-vesicular structures as well. The effect of salt, pH, temperature, and cholesterol on the microviscosity of the domains was evaluated by using steady-state fluorescence depolarization method. Fluorescence microscopic images technique and conductivity measurements have corroborates the formation of hollow spherical structure of the vesicles. The surface chemical properties of the mixed surfactant systems and the stability of vesicles have been studied systematically keeping in view the primary aim of the study.