Comment on Interpretation of Mechanochemical Properties of Lipid Bilayer Vesicles from the Equation of State or Pressure−Area Measurement of the Monolayer at the Air−Water or Oil−Water Interface

Abstract

There are quite a few types of equation of state and abundant π−a curves of various lipid monolayers at the air−water or the oil−water interface in the literature. However, it has been a problem to interpret mechanochemical properties of bilayer vesicles from the π−a information of the monolayer. In fact, even the bilayer surface pressure has not yet been well characterized although the monolayer surface pressure has already been traditionally defined as the lowering in the surface tension from the clean interfacial tension due to the presence of the monolayer. The monolayer−bilayer correspondence problem, therefore, could not be well defined and completely solved despite its importance in practice to apply the monolayer π−a data to elucidate bilayer vesicle properties. In the present analysis, we thus first define the bilayer leaflet pressure as the intrinsic pressure of the lipid layer−water substrate system. This intrinsic surface pressure should be the same function of the lipid density and the temper...