Study of a cationic lipid monolayer adsorbed by anion at the air-water interface

Abstract

We have studied counter-ion effects on two-dimensional phase behavior of cationic lipid, 1,2-Dioleoyl-3-Trimethylammonium-Propane (DOTAP), using the Brewster Angle Microscope (BAM), Ellipsometry and 2-Dimensional Isotherm. When DOTAPs are spreaded on pure water, DOTAPs are unstable because of positive charges on their head group. In the case of Sodium acrylate, it increases the stability and the monolayer has sharp plateau region in the isotherm at surface pressure of about 43 mN/m. At that plateau, circular domains are observed in the BAM image. And we confirm that this is a first-order transition from monolayer to tri-layer. Furthermore we studied how the chain length of anion polymer in the subphase affects tri-layer domain shape in the transition regime.