Interaction of phospholipid membranes with poly(ethylene glycol)s.

1. The water-soluble polymer, poly(ethylene glycol), causes concentration-dependent increases in the temperature of the gel--liquid crystalline phase transitions of aqueous dispersions of dipalmitoyl phosphatidylcholine and of dipalmitoyl phosphatidylethanolamine. 2. For dipalmitoyl phosphatidylcholine it has been further demonstrated that poly(ethylene glycol) increases the transition enthalpy and entropy while decreasing the cooperativity of the transition. 3. These results are discussed in relation to the possible modes of action of poly(ethylene glycol) in promoting cell fusion.