Comparison of Bilayer and Monolayer Properties of Phospholipid Systems Containing Dipalmitoylphosphatidylglycerol and Dipalmitoylphosphatidylinositol

Bilayer and monolayer phase behavior at the air−water interface of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylinositol (DPPI), and their binary mixtures with dipalmitoylphosphatidylcholine (DPPC), in the context of their possible roles in lung surfactant function, have been systematically compared. Surface properties, as a function of temperature and composition, were evaluated and analyzed by measuring equilibrium surface pressure−area isotherms (π−A), equilibrium monolayer collapse pressure (πc), and minimum area per molecule at the monolayer collapse pressure (Ac) and by direct observation using fluorescence microscopy. Bilayer properties were evaluated by measuring the main bilayer phase transition temperature (Tm) and the bilayer equilibrium spreading pressure (πe) as a function of temperature and composition. Through thermodynamic analysis, it was found that DPPC/DPPG mix ideally in both the monolayer and bilayer states, whereas DPPC/DPPI (further supported with DPPC/Soy PI) are ...