A Comparative Monolayer Film Behavior Study of Monoglucosyl Diacylglycerols Containing Linear, Methyl Iso-, and ω-Cyclohexyl Fatty Acids

This is the authors' abstract. We don't add key points for this paper.

A comparative monomolecular film study of a series of 1,2-di- O -(α- d -glucopyranosyl)- sn -glycerols in which the acyl chains were 16:0, 18:0, 19:iso, and 15:ω-cyclohexyl, was carried out at the air/water interface. Area/temperature isobars were obtained in the 20° through 60 °C range with the lipids going from fully condensed to fully expanded. It was found that the area/molecule shift between the expanded and condensed states decreased in the order 16:0 and 18:0 > 19:iso > 15-ω-cyclohexyl, with the expanded state of the ω-cyclohexyl glycolipid being the most condensed. Reduction of the area/molecule shift arose through an expansion of the condensed state and a condensation of the expanded state. Isotherms of the straight-chain glycolipids showed only a small expansion on changing the pH from 5.6 to 2.0, but the ω-cyclohexyl glycolipid showed no effect. All the glycolipids studied showed thermal stability up to the 60 °C range, in contrast with previously obtained results on similar phosphatidylcholines, which were unstable above 40 °C. These results help explain the greater than 70% abundance of ω-cyclohexyl glycolipids in several strains of Bacillus acidocaldarius, whose natural environment is in hot springs with a pH as low as 3 and a temperature of up to 65 °C. It is postulated that the ability to overcome the acidity arises through the insensitivity of the polar headgroup and the highly impermeable bilayer, whereas a glycolipid headgroup appears essential for survival at high temperatures.