Effect of polyvinyl pyrrolidone on the thermal phase transition of 1,2 dipalmitoyl-sn-glycero-3-phosphocholine bilayer

The purpose of this study was to investigate the interaction of polyvinyl p yrrolidone (PVP) with phospholipid bilayers in an effort to add a new dimen sion to our understanding of polymer interaction with lipids. For the prepa ration of lipid-polymer dispersions, measured amounts of DPPC (1,2 dipalmit oyl-sn-glycero-3-phosphocholine) and PVP were mixed in chloroform. After co mplete elimination of organic solvent, the dry mixtures were hydrated at 50 -55 degrees C. Interactions between DPPC and PVP were assessed by different ial scanning calorimetry (DSC) and photon correlation spectroscopy (PS). Se paration of liposomes and micelles was performed by centrifugation. Liquid scintillation counting and a UV spectrophotometer were used for their analy sis. PVP added as dry powder or added as aqueous solution to dry lipid or p reformed liposomes failed to interact. Only PVP previously dissolved in chl oroform interacted with DPPC. The DPPC main phase transition moved to lower temperatures with increasing PVP concentrations. This reduction of the pha se transition temperature was accompanied by an increase of the DPPC phase transition enthalpy. Analysis of solubilization indicated that the amount o f PVP present in the bilayer is dependent on the PVP bulk concentration. Th e data suggest interaction of PVP previously dissolved in chloroform with t he acyl chains of the phospholipid deep into the bilayer. (C) 1999 Academic Press.