Mobility of Poly(Ethylene Oxide) Segments on Surface of Lecithin Liposomes

To better understand the dynamics of PEO-lipid-modified phosphatidylcholine liposomes (fusogenic liposomes), the mobility of the PEO segment on the liposomal surface and the fluidity of the bilayer were investigated by measuring the spin-lattice relaxation time (T 1 ) by 13 C-NMR spectroscopy and by fluorescence depolarization. 13 C-NMR studies revealed that the PEO-lipids in this work exhibit similar behavior on liposomal surfaces irrespective of the PEO chain length. Furthermore, with regard to the relationship between morphology and dynamics of the PEO-lipid and phosphatidylcholine mixture, it was found that the mobility of PEO segments are altered by the morphology; liposome < aqueous micelle < monomeric dispersion in organic solution. Fluorescence depolarization studies revealed that liposomal membranes were tighter with the addition of PEO-lipid(12,a31) than with the addition of PEO-lipid(12,a13). In contrast, the reconstitution of PEO-lipid(12,a5) into liposomes increased membrane fluidity.