Effect of grafted PEG-2000 on the size and permeability of vesicles.

The permeability of PEG-derivatized vesicles produced by the extrusion technique (VETs) to encapsulated D-glucose has been studied. Vesicles were prepared from mixtures of dipalmitoylphosphatidylcholine (DPPC), phosphatidylinositol (PI) and dipalmitoylphosphatidylethanolamine with covalently attached poly(ethylene glycol) of molecular weight 2000 (DPPE-PEG2000). The occurrence of an irreversible temperature-induced size transition of the PEG-derivatized VETs was detected close to the temperature of the main phase transition of the predominant phospholipid component by photon correlation spectroscopy. The permeability of the vesicles towards radioactive D-glucose was studied by a method similar to the one proposed by Johnson and Bangham at 25, 37 and 50 degrees C for VETs with DPPE-PEG content from 0 to 9 mol%. A complex effect of the PEG-coverage was found with a maximum leakage in the range of the transition of the polymer from the mushroom to the brush conformation.