Physicochemical Characterization of Tetraether Lipids from Thermoplasma acidophilum II. Film Balance Studies on the Monomolecular Organization of the Main Glycophospholipid in Monofilms

The bipolar main tetraether lipid (MPL) o f Thermoplasma acidophilum has been shown to form typical liquid expanded films at the air-water interface. The limiting molecular area at the collaps pressure is approximately Ac = 7 3 A 2 per molecule. Monopolar diphytanyl diether lipids were found to occupy the same area at high surface pressure as MPL. Thus, it was concluded that in the monofilm only one o f the two polar headgroups o f the MPL m olecules is hydrated, i.e. that the single MPL molecules arc oriented upright. The packing properties o f MPL in the monofilm are determined by the properties o f the branched alkyl chains only; the polar head groups do not contribute to the space requirement in the film. The collaps pressure o f the MPL film is approximately 39 mN m -1 at 8 °C. At a surface pressure o f jt = 30 mN m _1 and 20 °C the film is stable for many hours.