Chemical and Physical Characterization of Four Interfacial-Active Rhamnolipids from Pseudomonas spec. DSM 2874 Grown on n-Alkanes

Abstract

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, β(β(2-O-α-ʟ-rhamnopyranosyloxy)decanoyl)decanoic acid and β(β(2-O-α-ʟ- rhamnopyranosyl-α-ʟ-rhamnopyranosyloxy)decanoyloxy)decanoic acid, were identical with com­pounds described previously, while the other more hydrophilic compounds, β(2-O-α-ʟ-rhamno- pyranosyloxy)decanoic acid and β(2-O-β-ʟ-rhamnopyranosyl-a-ʟ-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 mɴ/m and the interfacial-tension from 42 to about 1 mɴ/m. The critical micelle concentrations were of the order of 5 to 200 mg/l depending on the structure of the molecule.