Abstract: A new PE-PEG derivative with an active carboxylic terminal, DPPE-PEG3000-COOH, was synthesized and purified. Its incorporation into small unilamellar liposomes composed of egg phosphatidylcholine and cholesterol conferred the liposomes prolonged circulation in blood and reduced accumulation in the RES, as the traditional methoxy-PEG derivatives of PE displayed. With the active carboxylic groups on the surface, DPPE-PEG3000-COOH liposomes can be linked with some active molecules, which provide liposomes with special functions.

Key words: Liposomes, Liposomes, Active carboxylic terminal, Active carboxylic terminal, Polyethylene glycol (PEG), Polyethylene glycol (PEG), Long-circulating, Long-circulating