Abstract
Lipids are biomolecules with a broad variety of chemical structures, which renders them essential not only for various biological functions but also interestingly for biotechnological applications. Rhamnolipids are microbial glycolipids with surface-active properties and are widely used biosurfactants. They are composed of one or two l-rhamnoses and up to three hydroxy fatty acids. Their biosynthetic precursors are 3-hydroxy(alkanoyloxy)alkanoic acids (HAAs). The latter are also present in cell supernatants as complex mixtures and are extensively studied for their potential to replace synthetically derived surfactants. The carbon chain lengths of HAAs determine their physical properties, such as their abilities to foam and emulsify, and their critical micelle concentration. Despite growing biotechnological interest, methods for structural elucidation are limited and often rely on hydrolysis and analysis of free hydroxy fatty acids losing the connectivity information. Therefore, a high-performance liquid chromatography-mass spectrometry method was developed for comprehensive structural characterization of intact HAAs. Information is provided on chain length and number of double bonds in each hydroxy fatty acid and their linkage by tandem mass spectrometry (MS/MS). Post-column photochemical derivatization by online Paternὸ–Büchi reaction and MS/MS fragmentation experiments generated diagnostic fragments allowing structural characterization down to the double bond position level. Furthermore, the presented experiments demonstrate a powerful approach for structure elucidation of complex lipids by tailored fragmentation.
Highlights
Introduction3-(3-Hydroxyalkanoyloxy)alkanoic acids (HAAs) are known as the hydrophobic building blocks of the surface-active rhamnolipids (RLs), which are glycolipids with a hydrophilic part composed of one to two glycosidic-linked rhamnose moieties
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.3 iAMB – Institute of Applied Microbiology, ABBt – Aachen Biology and Biotechnology, RWTH Aachen University, 52074 Aachen, Germany3-(3-Hydroxyalkanoyloxy)alkanoic acids (HAAs) are known as the hydrophobic building blocks of the surface-active rhamnolipids (RLs), which are glycolipids with a hydrophilic part composed of one to two glycosidic-linked rhamnose moieties
These examinations were carried out based on a cell supernatant derived from E. coli, as no commercial authentic standard of hydroxy(alkanoyloxy)alkanoic acids (HAAs) is available
Summary
3-(3-Hydroxyalkanoyloxy)alkanoic acids (HAAs) are known as the hydrophobic building blocks of the surface-active rhamnolipids (RLs), which are glycolipids with a hydrophilic part composed of one to two glycosidic-linked rhamnose moieties. Both the free HAAs and the glycolipids are promising alternatives to the petroleum-derived surfactants, with the latter being reported to suffer from a low biodegradation and high aquatic toxicity [1,2,3]. With respect to variations in the chain length and the additional presence of double bonds as well as the combinatorial variety of the two β-hydroxy fatty acid chains, they present the predominate factor for the congeners’ diversity. In order to vary the corresponding congeners’ properties, novel studies focus on the production of new structures divergent from the naturally synthesized, intending RLs as well the mere HAA moiety as biosurfactants [28, 29]
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