A multi-headed surfactant as an efficient tool in solubilization of dimyristoylphosphatidycholine (DMPC) vesicles

In this study, the solubilization of DMPC (dimyristoylphosphatidycholine) vesicles by a novel multi-headed surfactant, C18N3, is reported. The headgroup of the surfactant contains two types of amine groups, which are protonated at different pH values. The protonation of the headgroup has significant effect on the solubilization process. The penetration of the surfactant into a DMPC monolayer was measured at different initial surface pressures and at different pH values. A linear relationship was found between the initial surfactant pressure (π) and the increase of the surfactant pressure (Δπ). Furthermore, turbidity titration shows that at low pH, the phase behavior with increasing surfactant concentration in the DMPC solution is similar to conventional ionic surfactants. This can be explained by the three-stage model. TEM images at different C18N3 concentrations confirmed the process of solubilization of DMPC vesicles, and small aggregates were observed at 1 mmol/L C18N3. However, at higher pH, where the headgroup is deprotonated, the surfactant was not able to solubilize the DMPC vesicles. TEM images shows a coexistence of vesicles and a lamellar phase. The surfactant/lipid ratio of the multi-headed surfactant at pH 4 and 7 was compared to conventional nonionic surfactants with the same cross-sectional area of the headgroup, and a much lower ratio was observed for the new surfactant.