Modification of fatty acid vesicle using an imidazolium-based surface active ionic liquid: a detailed study on its modified properties using spectroscopy and microscopy techniques $$^{\S }$$ §

Abstract

Fatty acid vesicles have attracted views as model protocell membranes in understanding the emergence of life, but their properties can be further modified in the presence of some external molecules. In this work, we have investigated the spontaneous formation of large unilamellar vesicles (LUVs) of oleic acid in aqueous medium in presence of a popular imidazolium-based cationic surface active ionic liquid (SAIL) $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ and studied the micelle–vesicle transition of aqueous $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ solution in presence of different molar fractions (f) of oleic acid. This newly formed oleic $$\hbox {acid}/[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ vesicles exhibit some modified properties compared to the pure fatty acid vesicles. Unlike pure fatty acid vesicles, these vesicles are stable in the pH range of 2 to 11.2. We have observed the fusion process of these oleic acid/SAIL vesicles to form giant unilamellar vesicles (GUVs) in presence of low concentration of NaCl solution. To investigate the dynamics of different oleic $$\hbox {acid}/[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ self-assemblies, we have used fluorescence correlation spectroscopy (FCS). The translational diffusion behavior of three different dyes, Rhodamine 6G, DCM and Pyrromethene 597, which are non-covalently bound to the different regions of the oleic acid/SAIL self-assemblies, have been determined using FCS during the micelle–vesicle transition and upon varying the pH of the vesicular solution. Oleic acid vesicles prepared in presence of a surface active ionic liquid $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ have been characterized. Modified properties of these vesicles like stability towards a greater pH range as compared to pure oleic acid vesicles and fusion of vesicles in presence of low concentration of NaCl solution have been studied.