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 sp. DSM 2874. After purification by column and thick-layer chromatography they were identified as anionic rhamnolipids. 1H and 13C-NMR studies showed that 2 of these, .beta.(.beta.(2-O-.alpha.-L-rhamnopyranosyloxy)decanoyl)decanoic acid and .beta.(.beta.(2-O-.alpha.-L-rhamnopyranosyl-.alpha.-L-rhamnopyranosyloxy)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 2 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 .apprx. 30 mN/m and the interfacial-tension from 42 to .apprx. 1 mN/m. The critical micelle concentrations were of the order of 5-200 mg/l, depending on the structure of the molecule.