Phospholipid monolayers between fluid and solid states.
Monolayers of the phospholipid dimyristoyl phosphatidic acid on the surface of water have been studied by a combination of the new techniques of synchrotron x-ray diffraction and fluorescence microscopy with classical surface pressure data. The pressure vs. area isotherm changes slope at the surface pressures pi c and pi s. The optical technique demonstrates that between pi c and pi s the fluid phase coexists with a denser "gel" phase. Electron diffraction data have shown that the gel phase has bond orientational order over tens of micrometers. However, the x-ray data demonstrate that positional correlations extend only over tens of angstroms. Thus, the gel phase is not crystalline. Above pi s a solid phase is formed with a positional correlation range that is eight times longer for the chemically purest films.
D020404:Glycerophospholipids; D008081:Liposomes; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008968:Molecular Conformation; D010712:Phosphatidic Acids; D013816:Thermodynamics; D014961:X-Ray Diffraction
D020404:Glycerophospholipids; D008081:Liposomes; D010712:Phosphatidic Acids; C025602:dimyristoylphosphatidic acid