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Cucurbit[7]uril complexes aggregate into well-defined trimers in dimethyl sulfoxide in the presence of a selection of cations, as long as the host cavity is filled with a guest that leaves one carbonylated portal available for cation binding. 

Peptidoglycans are diverse co- and post-translational modifications of key importance in myriad biological processes. Mass spectrometry is employed to infer their biomolecular sequences and stereochemisties, but little is known about the critical gas-phase dissociation processes involved. Here, using tandem mass spectrometry (MS/MS and MS n ), isotopic labelling and high-level simulations, we identify and characterize a facile isomerization reaction that produces furanose N-acetylated ions. This reaction occurs for both O- and N-linked peptidoglycans irrespective of glycosidic linkage stereochemistry (α/β). Dissociation of the glycosidic and other bonds thus occur from the furanose isomer critically altering the reaction feasibility and product ion structures. 

We present cryogenic infrared spectra of sodiated β-cyclodextrin [β-CD + Na] + , a common cyclic oligosaccharide, and its main dissociation products upon collision-induced dissociation (CID). We characterize the parent ions using high-resolution ion mobility spectrometry and cryogenic infrared action spectroscopy, while the fragments are characterized by their mass and cryogenic infrared spectra. We observe sodium-cationized fragments that differ in mass by 162 u, corresponding to B n /Z m ions. For the m / z 347 product ion, electronic structure calculations are consistent with formation of the lowest energy 2-ketone B 2 ion structure. For the m / z 509 product ion, both the calculated 2-ketone B 3 and the Z 3 structures show similarities with the experimental spectrum. The theoretical structure most consistent with the spectrum of the m / z 671 ions is a slightly higher energy 2-ketone B 4 structure. Overall, the data suggest a consistent formation mechanism for all the observed fragments.