Influence of silica nanoparticles on phase behavior and structural properties of DPPC-Palmitic acid Langmuir monolayers

The effect of silica nanoparticles on the thermodynamic and structural properties of monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), palmitic acid (PA) and a mixture of them, has been investigated using a combination of Langmuir trough technique and Brewster Angle Microscopy (BAM). This study shows that the presence of nanoparticles in the aqueous sub-phase affects the surface pressure-area (Pi-A) isotherm, leading to a different phase behavior of the monolayer. The observed effects are explained assuming the incorporation of nanoparticles into the monolayer driven by the adsorption of lipid molecules onto the silica which makes the nanoparticles more hydrophobic. This process hinders the ordering and affects the composition of the investigated lipid monolayers significantly modifying also their quasi-equilibrium dilational elasticity. The reported results are useful in the framework of a wider study aimed at elucidating the impact of nanoparticles on the physico-chemical properties of pulmonary surfactant, being DPPC its major component and PA utilized as an important component in the formulation of therapeutic substitutes. (C) 2011 Elsevier B.V. All rights reserved.