ABSTRACT
This chapter summarizes the molecular structure and biophysical behavior of phospholipids. Glycerophospholipids are major components of endogenous lung surfactant and most exogenous lung surfactants. All phospholipids are surface active due to their amphipathic (polar and nonpolar) molecular structure, but individual phospholipids vary significantly in the specifics of their film behavior and surface properties. Some aspects of phospholipid surface behavior can be correlated with the properties of their hydrated bilayers and whether they are in the rigid gel phase or the more fluid liquid crystal phase at the temperature of interest. Another factor relevant for the surface activity of phospholipids is their aggregation in water to form lamellae, liposomes, hex phases, and less regular structures. Phospholipid aggregation affects adsorption and is largely responsible for the complex aqueous phase microstructure of endogenous lung surfactant and many exogenous lung surfactants. Phospholipid aggregation can be further modified by interactions with surfactant apoproteins leading, for example, to tubular myelin formation in endogenous surfactant. Coverage in this chapter provides an overview of phospholipid film, phase, aggregation, and adsorption behavior.
