Study of phase behavior of nonionic and cationic lipids mixed monolayer at an Air/Water interface

Abstract

The study about the mixture of ionic and nonionic lipids impacts understanding of biological membranes and the gene therapeutic application as a gene carrier. In this thesis, we studied the two-dimensional properties of the mixture of cationic and neutral lipids by using the surface balance, surface wave spectroscopy, and ellipsometry. We observed the effect of ionic lipids on the phase behavior of nonionic lipids monolayer at an air-water interface. From the enhanced damping of the capillary wave, we can confirm that the surface pressure of the neutral lipid monolayer increases after the phase transition from the gaseous to expanded liquid state, which is not observable in the surface pressure measurement due to experimental errors. Another interesting result is that the small amount of ionic lipids about 10 mol% strongly prevents the phase transition from the gaseous to expanded liquid state of the nonionic lipid. When we consider the two-body interactions, there exist less attractive interaction between neutral and cationic lipid molecules than two neural lipids.