Time-dependent oxidation during nano-assisted laser desorption ionization mass spectrometry: a useful tool for structure determination or a source of possible confusion?

This work reports on a new and extremely simple approach for determination of a double bond position by a laser desorption ionization mass spectrometry. It is solely based on the catalytic properties of nanostructured surfaces used in nanoassisted laser desorption ionization experiments. These surfaces can induce oxidation of analytes, which results in a mass shift that can be detected by mass spectrometry. If a site of unsaturation is oxidized and cleaved, the m/z difference is diagnostic of the position of a double bond. By demonstrating that the oxidation depends on the analyte surface dwell time, it was proven that it is caused by the surface activity and not by the laser desorption ionization process itself. Control matrix-assisted laser desorption/ionization (MALDI) experiment showed only a limited partial oxidation and no time dependency of the process. The ability to determine a position of a double bond was demonstrated on polyunsaturated phospholipids and cyclosporine A. In some other cases, however, the unexpected oxidation could cause confusion, as demonstrated for a glycosphingolipid from a porcine brain extract.

Characterization of pseudacyclins A-E, a suite of cyclic peptides produced by Pseudallescheria boydii.

Pseudallescheria boydii sensu lato is an emerging fungal pathogen causing fatal infections in both immunocompromised and immunocompetent hosts. In this work, two P. boydii isolates (human and animal origin) have been identified as being producers of cyclic peptides. Five putative nonribosomal peptides with a unique structure, which have been named pseudacyclins, were characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. The most abundant representative of the pseudacyclins was quantified also on fungal spores. The presence of these peptides on inhaled fungal spores creates the possibility for exploitation of pseudacyclins as early indicators of fungal infections caused by Pseudallescheria species.