MALDI-TOF mass spectrometry of naturally occurring mixtures of monorhamnolipids and dirhamnolipids

MALDI-TOFMS approaches have been developed for high-throughput screening of naturally occurring mixtures of rhamnolipids from Pseudomonas spp. Monorhamnolipids and dirhamnolipids are readily distinguished by characteristic molecular adduct ions, [M+Na]+ and [M−H+Na2]+, with variously acylated rhamnolipids differing by 28 mu. Following proton-deuterium exchange, deuterated [M+Na−41H+42H]+ and [M+Na−61H+62H]+ ions are observed for the monorhamnolipids and dirhamnolipids, respectively, which allows rapid identification of these molecules. The described approach has been validated by compositional analysis using GC/MS, fractionation by RPHPLC, and analysis by 1D and 2D NMR spectroscopy. MALDI-TOFMS analysis allows the rapid screening of variously acylated rhamnolipids, and has potential for selective identification of new surfactants from microbial strains.

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