Morphology and structures in double-, triple- and quadruple-chain phospholipid monolayers at the air/water interface.

The structure of double-, triple- and quadruple-chain phospholipid monolayers has been studied by Synchrotron x-ray diffraction. The double-chain mixed-linkage species exhibit an oblique structure at all pressures investigated. The triple-chain phospholipids show at lower lateral pressures a rectangular unit cell with a phase transition at higher pressures to a hexagonal packing of vertically arranged chains. The quadruple-chain lipid exhibits only the hexagonal phase structure. The position of the ether linkage and of the branched chain on the glycerol backbone has also a strong influence on the monolayer structures. Fluorescence microscopy shows different domain shapes for the different molecules investigated. The anisotropy of the domain shapes seems to be connected with the anisotropy of the structure. Obviously, the compound with the larger lattice anisotropy (larger chain tilt) exhibits dendritic domains. [ABSTRACT FROM AUTHOR]