Synthetic glycolipids monolayer and related Langmuir-Blodgett films: Importance of the amphipathic balance

Synthetic glycolipids were chosen on account of their ability to form a monolayer at the air/water interface, The first (G(1)) is a 1,3-dialkyl glycerol constituted by two identical C-11 hydrocarbon chains and a hydrophilic N-acetyl glucosamine in position 2. The saccharidic moiety was separated from the glycerol backbone by an ethylene glycol spacer, The second molecule (G(2)) has the same structure but without the spacer, The G(1) isotherm is smooth and continuous. The G(2) isotherm is characterized by an atypical discontinuity. The study of the compression mode, the temperature variations, and compression-decompression cycle experiments allowed the characterization of this discontinuity. It corresponds to a supersaturation in the monolayer; it is related to a low relaxation speed and it occurs just before the transition phase. On CaF2 surfaces, the G(1) and G(2) monolayers were transferred but they were not firmly retained, Hydrophilic surfaces constituted by the carboxylic head groups of behenic acid LB films allowed the retention of the glycolipid layers, On such surfaces, only two G(1) layers could be transferred, whereas G(2) Langmuir-Blodgett films were built up with an XY stacking, These results are discussed with respect to the amphipathic balance within the glycolipid molecules. (C) 1997 Academic Press.