The influence of the incorporation of cholesterol and water on the particle size, bilayer thickness, melting behavior, and relative sucrose ester composition of reversed vesicles

Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration

We recently found that rough glass surfaces (RGSs) can in situ mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (C_nTABs, n = 12, 14, and 16), a kind of typical cationic STAs. That is, a C_nTAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried C_nTAB aggregates were then rehydrated in a monomer solution of C_nTAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS in situ mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of C_nTABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of C_nTABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.

Phospholipid vesicle stability and temporal variations in acyl chain organization

We report on our investigation of the long-term dimensional stability and acyl chain organization of unilamellar vesicles containing 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC) and DMPC with cholesterol. Vesicles of 100% DMPC, 80% DMPC/20% cholesterol and 70% DMPC/30% cholesterol, formed by extrusion in aqueous buffer solution (pH 8) were shown to remain dimensionally stable for periods in excess of 600 h by dynamic light scattering (DLS) measurements. The rotational diffusion dynamics of perylene confined in the vesicle acyl chain region revealed structural evolution that was dependent on vesicle composition. Re-extrusion of the vesicles caused no changes in the average diameter or size distribution, but did give rise to diminished organization in the lipid acyl chain region for DMPC vesicles. Cholesterol-containing vesicles exhibited somewhat less pronounced change in organization on re-extrusion, suggesting a structurally mediating role for cholesterol.