Effect of diphenylalanine on model phospholipid membrane organization

The influence of peptides over the thermodynamic and mechanic stability of lipid membranes is studied. To this end, diphenylalanine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine are selected as model systems for peptide and lipid bilayers, respectively. Vesicles at different peptide-lipid ratios were prepared and characterized using different experimental methodologies. Densitometry and differential scanning calorimetry were used to deter-mine the influence of the peptide over the melting transition properties (temperature, volume and enthalpy) for bulk multilamellar vesicles, whereas viscoelastic and nanomechanical properties of supported vesicle layers and supported lipid bilayers were studied using quartz crystal microbalance with dissipation monitoring and atomic force microscopy, respectively. The influence of the sample preparation methodology-solvents for obtaining the lipid films and hydration media-is also characterized. The analysis of the experimental data reveals that diphenylalanine affects the lipid membrane, decreasing lipid molecular cooperativity in a concentration-dependent manner and inducing an overall weakening of membrane organization.