INTERACTIONS OF LIPOSOMES AND HYDROPHOBICALLY-MODIFIED POLY-(N-ISOPROPYLACRYLAMIDES) - AN ATTEMPT TO MODEL THE CYTOSKELETON

The interactions of small unilamellar vesicles (SUV) and water-soluble copolymers were studied by fluorescence spectroscopy, differential sc anning calorimetry (DSC) and quasi-elastic light scattering (QELS). Th e anchoring onto liposomal bilayer membranes of copolymers of N-isopro pylacrylamide, N-(2-(1-naphthyl)ethyl)-N-n-octadecylacrylamide and or N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide (0.5 mol% of the octade cylacrylamide comonomer) was monitored by non-radiative energy transfe r between excited naphthalene and pyrene. The anchoring process occurr ed on zwitterionic lecithin liposomes and on negatively charged phosph atidic acid liposomes, whether the bilayer was in the crystalline or t he liquid-crystalline phase. Insertion of the copolymer octadecyl grou ps within crystalline bilayers was attributed to the presence of packi ng defects. Aqueous solutions of poly-(N-isopropylacrylamide) and of i ts hydrophobically-modified copolymers exhibit a lower critical soluti on temperature (LCST). The coil to globule collapse of the polymer cha ins which is known to occur as the aqueous solution is heated through the LCST, also took place when the copolymers were anchored onto vesic ular bilayers. The copolymers remained anchored during this collapse a nd the liposomes were not destroyed. The process was thermo-reversible . Detailed aspects of the reversibility of the phenomenon depended on the relative values of the phase transition temperatures of the liposo mes and of the polymer LCST.