The influence of temperature and pH on the structure of liposomes formed from DMPC

The EPR and NMR spectroscopy was used to determine the structure and physicochemical properties of liposomes prepared from dl-α-phosphatidylcholine dimyristoyl (1,2-ditetradecanoyl-rac-glycerol-3-phosphocholine) (DMPC) by the modified reverse-phase evaporation (mREV). EPR study was carried out in the temperature range from 284 to 310 K, i.e. below and above the phase transition temperature Tc of DMPC. On the basis of EPR spectra of spin marker 2-(carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl (5-DOXYL) incorporated into liposome, the parameters S (empirical order parameter), 2Amax (line widths) and τ (rotational correlation time) were determined. Temperature and pH dependent structural changes of liposome were also described. 31P NMR study of the liposome in the temperature range from 340 to 350 K allowed to suggest that the single-bilayered liposome were obtained.