Interactions of synthetic polymers with cell membranes and model membrane systems. Part 6. Disruption of phospholipid packing by branched poly(ethylenimine) derivatives

High-sensitivity differential scanning calorimetry was used to examine the phase transition behavior of mixtures of dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) with linear or branched poly(ethylenimine) derivatives. Unmodified poly(ethylenimines), branched or linear, caused no observable change in the melting of DPPC. Both polymers broadened the DPPG melting endotherm and produced small changes in the melting temperature. Attachment of side chains 6-12 carbon atoms in length produced hydrophobic poly(ethylenimine) derivatives which bound strongly to DPPC with complete disruption of the multilamellar vesicle structure