Chemical and physical characterization of four interfacial-active rhamnolipids from Pseudomonas spec. DSM 2874 grown on n-alkanes.

Four extracellular glycolipids produced under growth-limiting conditions were isolated from the culture broth of Pseudomonas spec. DSM 2874. After purification by column and thick-layer chromatography they were identified as anionic rhamnolipids. 1H and 13C-NMR studies showed that two of these, beta(beta(2-O-alpha-L-rhamnopyranosyloxy)decanoyl)decanoic acid and beta(beta(2-O-alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosylox y)decanoyloxy) decanoic acid, were identical with compounds described previously, while the other more hydrophilic compounds, beta(2-O-alpha-L-rhamnopyranosyloxy)decanoic acid and beta(2-O-alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyloxy) decanoic acid, were new compounds. Surface and interfacial activity of the organic crude extract and of the purified components were determined in different aqueous solutions. The pH-dependence of surface and interfacial properties of the two previously described rhamnolipids (4, 20, 23) were examined in Teorell-Stenhagen-buffer (supplemented with 10% NaCl) at pH 3.0 and pH 9.0. All rhamnolipids reduced the surface-tension from 72 to about 30 mN/m and the interfacial-tension from 42 to about 1 mN/m. The critical micelle concentrations were of the order of 5 to 200 mg/l depending on the structure of the molecule.