Characterization of the physicochemical properties of phospholipid vesicles prepared in CO2/water systems at high pressure

Abstract

Phospholipid vesicles were prepared by the nonsolvent method using high-pressure CO2/water systems. The membrane properties of vesicles prepared at different pressures and temperatures were mainly characterized based on analysis of the membrane fluidity and membrane polarity, using the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene and 6-dodecanoyl-N,N-dimethyl-2-naphthylamine, respectively. The CO2(liquid)/water(liquid) and the CO2(supercritical)/water(liquid) two-phase (heterogeneous) systems resulted in the formation of vesicles with high yield (ca. 85%–88%). The membrane fluidity and polarity of the vesicles were similar to those of liposomes prepared by the conventional method. It is suggested that high-pressure CO2 can be used to form an appropriate hydrophobic–hydrophilic interface where phospholipid molecules as a self-assembled membrane.

Systematic Characterization of DMPC/DHPC Self-Assemblies and Their Phase Behaviors in Aqueous Solution

“…By combining the information obtained from each fluorescent probe (DPH and Laurdan), the phase state and phase separation behavior of the membrane can be systematically discussed [22][23][24]28]. The phase state (ordered phase or disordered phase) of the membrane can be investigated based on the positioning of the obtained data in the Cartesian diagram, where the quadrants are set using the transition of the membrane properties (polarity (y-axis) and membrane fluidity (x-axis)) [24].…”

“…The phase state (ordered phase or disordered phase) of the membrane can be investigated based on the positioning of the obtained data in the Cartesian diagram, where the quadrants are set using the transition of the membrane properties (polarity (y-axis) and membrane fluidity (x-axis)) [24]. By plotting the data obtained from each self-assembly system, the interfacial membrane properties of various kinds of self-assemblies can be directly compared [23,28]. The details are summarized in our previous work (see the supporting materials of Bui et al [22]).…”

“…Interfacial membrane properties such as membrane fluidity and membrane polarity, which are evaluated using fluorescent probes, are also important factors to characterize self-assemblies [21][22][23]. In lipid bilayer vesicles, the interfacial properties can be used to determine the phase states [22,24]; the solid-ordered phase (gel phase) and liquid-disordered phase (liquid-crystalline phase) show quite different membrane fluidity and polarity.…”