An Unconventional Zwitterionic Bolaamphiphile Containing PEG as Spacer Chain: Surface Tension and Self-Assembly Behavior

Monolayer lipid membrane formation based on self-assembly of bolaamphiphiles containing hydrophobic spacer are well-established in the literature, but monolayer vesicle formation by so-called hydrophilic poly(ethylene glycol) (PEG) spacer has not been reported to date. Here, a novel L-cysteine-derived bolaamphiphile with PEG as spacer has been developed and characterized. The interfacial properties and the solution behavior of the amphiphile were investigated in pH 7.0 at 25 degrees C. The self-assembly properties of the bolaamphiphile in aqueous buffer were investigated by using different techniques, such as surface tonsiometry, fluorescence spectroscopy, UV-Vis, spectroscopy, isothermal titration calorimetty, dynamic light scattering, transmission electron microscopy and atomic force microscopy Surprisingly, despite having so-called polar spacer in between two polar head groups, it exhibits fon-nation of microstructures in aqueous buffer as well as in water at 25 degrees C. The molecule undergoes self organization leading, to the formation of monolayer vesicles with hydrodynamic diameters between 100 and 250 nm in a wide range of concentration. The thermodynamic parameters clearly suggest that the aggregate formation is mainly driven by the hydrophobic effect. The monolayer vesicles were found to form at a very low concentration (>= 0.63 mM) and within a wide pH range (2-10). The vesicles exhibit-excellent shelf life at physiological temperature.