Vesicles Formed in Aqueous Mixtures of Cholesterol and Imidazolium Surface Active Ionic Liquid: A Comparison with Common Cationic Surfactant by Water Dynamics

The formation of stable unilamellar vesicles which hold great potential for biological as well as biomedical applications has been reported in the aqueous mixed solution of a surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium chloride ([C₁₆mim]­Cl) and cholesterol. To make a comparison we have also shown the formation of such stable vesicles using a common cationic surfactant, benzyl­dimethyl­hexa­decyl­ammo­nium chloride (BHDC) which has a similar alkyl chain length but different headgroup region to that of [C₁₆mim]­Cl. It has been revealed from dynamic light scattering (DLS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and other optical spectroscopic techniques that the micelles of [C₁₆mim]Cl and BHDC in aqueous solutions transform into stable unilamellar vesicles upon increasing concentration of cholesterol. We find that, as the concentration of cholesterol increases, the solvation and rotational relaxation time of C153 in [C₁₆mim]­Cl/cholesterol solution as well as in BHDC/cholesterol solution gradually increases indicating a significant decrease in the hydration behavior around the self-assemblies upon micelle–vesicle transition. However, the extent of increase in solvation and rotational relaxation time is more prominent in the case of [C₁₆mim]­Cl/cholesterol solutions than in the BHDC/cholesterol system. This indicates that [C₁₆mim]­Cl/cholesterol vesicular membranes are comparatively less hydrated and more rigid than the BHDC/cholesterol vesicular bilayer.