Oligosaccharides are a subclass of carbohydrates that contain three to ten monosaccharides linked by glycosidic bonds. Structural diversity allows oligosaccharides to participate in many biological processes. Mass spectrometry techniques are important in the structural analysis of oligosaccharides. Oligosaccharides tend to deprotonate during electrospray ionization (ESI) and are extremely challenging to multiply protonate, making analysis difficult. Derivatization such as permethylation is commonly utilized when studying carbohydrates to increases ion intensity in ESI by increasing sample volatility, stability, and protonation. Metalation eliminates the need for protonation in positive ion mode analysis. Metal adducts allow acquisition of structurally informative fragmentation. The goals of this work are to examine trivalent metals for sequence analysis of various derivatized and underivatized carbohydrates, and determine the optimum trivalent metal for oligosaccharide fragmentation. Five oligosaccharides were studied: maltotetraose, 3α,4β,3α-galactotetraose, maltoheptaose, stachyose, and nystose. They have varying monomer units, structural arrangements, and include non-reducing sugars. Solutions of both derivatized and native oligosaccharides were prepared and mixed with a variety of trivalent nitrate metal salts. The mixtures were subjected to ESI and the resulting multiply-charged metallated carbohydrate ions were isolated and fragmented by collision-induced dissociation (CID) or electron transfer dissociation (ETD). Isotopic labeling of the reducing end of the sugars was used to reduce ambiguity in the spectra obtained. The dominant ion produced via ESI is [M+Met-H]2+. This varies from previous work where divalent metals produced doubly charged ions without proton loss. High signal intensity and extensive pre-cursor ion dissociation was observed without permethylation, and permethylation did not promote the production of triply charged ions. The intensities of the precursor ions with each metal varied based on the oligosaccharide structure. The arrangement of the monosaccharides being stacked or linear affects the oligosaccharides ability to adduct a metal, and varies based on ionic radius of the metals. Extensive precursor ion dissociation was observed for all oligosaccharides with all metals. The extent of fragmentation is greatly dependent on the identity of the cationizing metal with both dissociation methods.

Electron transfer dissociation and collision-induced dissociation mass spectrometry of trivalent metal adducted oligosaccharides

255th National Meeting (2018)

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