The effect of divalent ions on L-α-phosphatidylcholine from egg yolk monolayers at the air/water interface.

The Langmuir monolayers of L-α-phosphatidylcholine from egg yolk were studied by Wilhelmy method. The surface pressure versus molecular area isotherm of lipid on pure water and different subphase (with a presence of divalent ions: Sr2+ , Cd2+ , Ba2+ , Pb2+ ) was obtained. The limiting area of the isotherms depends on the presence of subphase ions. The addition of divalent ions to the subphase stabilized the monolayers and increased the limiting areas of the monolayer. During the compression in monolayer complexes of 1:1 and 2:1 stoichiometry between L-α-phosphatidylcholine from egg yolk and divalent ions are formed. We used the equilibrium theory to describe the behavior of monolayer components at the air/water interface. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants and area occupied by one molecule of LMe2+ or L2 Me2+ complexes, and complex formation energy (Gibbs free energy) values. These mathematically derived and experimentally confirmed values are of great importance for the interpretation of phenomena occurring in lipid monolayers and bilayers.