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Abstract

Glycans have essential structural and functional roles in living organisms and at the same time represent the most complex class of biomolecules, which makes their analysis critical yet extremely challenging. Fucose is a deoxy monosaccharide that is linked to every fourth non-reducing end in mammalian glycans. In mass spectrometry, fucose migration is a reoccurring issue that can lead to false sequence assignments. The reaction involves an intramolecular transfer of a fucose mono- saccharide to adjacent or remote sites. In preceding research, fucose migration was observed in glycan fragments produced by collision-induced dissociation in tandem mass spectrometry and was strictly associated with the fragmentation process. Comparable to the investigation of peptide scrambling in the early 2000’s, multidimensional approaches are needed to shed light on the reaction. In this work, cold-ion infrared spectroscopy and ion mobility-mass spectrometry are employed to investigate the gas-phase structures of fucosylated glycans of biological relevance. The results show that fucose migration reactions can occur in intact glycan ions independent of fragmentation. Two intact trisaccharides as well as a fragmented tetrasaccharide rearrange to the same chemical structure. A mobile proton located at the amide functional group is likely to catalyze the reaction in these molecules. The results obtained from an in-source activation experiment as well as from utilizing a cooled ion trap suggest an interconversion to one of the trisaccharides. The observation indicates a possible low-energy barrier for this migration reaction and generalizes fucose migration to an issue that may universally occur in mass spectrometry experiments.