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 meas uring the spin-lattice relaxation time (T-1) by C-13-NMR spectroscopy and b y fluorescence depolarization. C-13-NMR studies revealed that the PEO-lipid s in this work exhibit similar behavior on liposomal surfaces irrespective of the PEO chain length. Furthermore, with regard to the relationship betwe en morphology and dynamics of the PEO-lipid and phosphatidylcholine mixture , it was found that the mobility of PEO segments are altered by the morphol ogy; 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 P EO-lipid(12,a13). In contrast, the reconstitution of PEO-lipid(12,a5) into liposomes increased membrane fluidity.