Interaction of l-arginine with dihexadecylphosphate unilamellar liposomes: the effect of the lipid phase organization

Abstract

The interaction of l-arginine with unilamellar liposomes of dihexadecylphosphate sodium salt (DHP-Na) has been investigated using calorimetric, light scattering, fluorescence spectroscopy and zeta-potential techniques. Heating from room temperature, the bilayer exhibits a phase transition from a subgel (L c) to the gel (L β′) phase as well as a pre-transition (L β′–P β′), which is followed by the main lipid phase transition (P β′–L α). Direct studies of the interaction of l-arginine with the DHP-Na bilayers via isothermal titration calorimetry at 27 °C depict significant differences between samples in the L c and the L β′ phases reflecting the effect of molecular organization of the lipids upon the interaction. While l-arginine has only a small impact upon the L c to L β′ phase transition, it affects more significantly the transition temperature as well as the shape of the DSC peaks of the main lipid phase transition. Based on fluorescence and zeta-potential studies, the permeability of l-arginine through the liposomal membrane is higher within the temperature range of the main lipid phase transition. Encapsulated l-arginine obstructs the formation of the subgel phase.