THE MONOLAYER BEHAVIOR AND TRANSFER CHARACTERISTICS OF PHOSPHOLIPIDS AT THE AIR-WATER-INTERFACE

The monolayer behavior of phospholipids at the air/water interface and their transfer characteristics on the solid substrates have been inve stigated with a constant-perimeter type Langmuir trough. From the surf ace pressure-area (II-A) isotherm, evaluated were the cross-sectional area of an oriented molecule, phase transition, and the miscibility of mixed monolayers. The monolayer state depends on the chain length and its mobility, and by adding proper salts, the monolayers were stabili zed. The miscibility of mixed monolayers was also discussed with colla pse pressure and excess area. The monolayers of all lipids were transf erred into only one layer on hydrophobic substrates, and up to two lay ers on hydrophobic substrates;The multilayer formation of dipalmitoylp hosphatidic acid (DPPA) was significantly affected by the subphase pH and the addition of multivalent salts. As a transfer promoter, DPPA or octadecylamine (ODA) was used as a component in a mixture with lipid materials, and their mixed monolayers resulted in good transfer charac teristics. The transferred mass and film thickness of DPPA, determined by using a quartz crystal microbalance (QCM) and by an ellipsometry r espectively, were proportional to the number of transfer. The lattice spacing of DPPA was 20.3 Angstrom per layer by ellipsometry, and 22.78 Angstrom per layer by X-ray diffraction. These indicated that the tra nsferred multilayers had well-defined layered structures of Y-type.