Two possible approaches to quantitative analysis of compression diagrams of lipid monolayers

Abstract

Experimental curves of lateral pressure and Volta potential previously measured vs. area of dimyristoylphosphatidylserine (DMPS) monolayer (PA diagram) (Ermakov et al., 2010) are analyzed in the framework of the model introduced by Ruckenstein and Li (1996, 1998) for lipid clusters. The same curves are described by some empirical parameters as an alternative mechanistic approach. Both approaches agree with each other and describe the compression diagrams at low and high pressures (high and low areas). Analytical expressions for the asymptotic approximations in the cluster model are suggested. The product of pressure and area (equal to the energy of monolayer compression) as well as Volta potential shown in lateral pressure scale are proposed for experimental data presentation suitable for the quantitative analysis. It is also proposed to represent this function, as well as Volta potential vs. the lateral pressure. Monolayer compressibility module evaluated for the “expanded liquid” area was used to describe the shape of experimental curves. This parameter approximates well the shape of the compression diagrams and Volta potential changes if the interface potential is assumed to be proportional to the mechanical work of the monolayer compression.