Electron transfer dissociation and collision-induced dissociation mass spectrometry of metallated oligosaccharides

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Investigations of metallated glycans through tandem mass spectrometry (MS/MS) can further the field of glycomics, the sequencing of the human glycome. The field is hindered by the lack of an analytical technique that can determine all the stereo-diverse features of carbohydrates. In this dissertation, electron transfer dissociation (ETD) and collision-induced dissociation (CID) are utilized with metal-adducted oligosaccharides to explore the potential of these techniques to sequence glycans. The resulting mass spectra provide significant insight and information about the structure of oligosaccharides and how to distinguish between these complicated isomeric species. Using univalent, divalent, and trivalent transition metal adducts is valuable to glycan analysis. The ETD process requires multiply charged ions, which do not form via protonation for neutral glycans, and CID of protonated glycans produces uninformative glycosidic bond cleavage. The univalent and trivalent metals investigated did not produce ions sufficient for ETD studies, but CID of the trivalent metal adducts showed significant fragmentation. Dissociation of [M + Met]²⁺ from the divalent metals formed various fragment ions with ETD producing more cross-ring and internal cleavages, which are necessary for structural analysis. The two dissociation techniques are complementary. For both ETD and CID of all glycans studied, [M + Co]²⁺ provided the most uniform structurally informative dissociation. Permethylation is a common derivatization technique used in the study of glycans. Permethylation reduces the hydrophilicity of oligosaccharides by replacing all hydrogen atoms on oxygen and nitrogen atoms with methyl groups. Permethylation increases ion intensity in electrospray ionization (ESI) and prevents rearrangements of certain monosaccharides. In this study, permethylation reduced the fragmentation by both ETD and CID for the metallated glycans. The spectra for non-derivatized metallated oligosaccharides was more structurally informative, especially with ETD. For some exact mass ions, permethylation reduced the ambiguity in the spectra. The trivalent lanthanide metal series was investigated as metal adducts. ESI on mixtures of trivalent metals and tetrasaccharides produced [M + Met-H]²⁺, [M + Met + NO3]²⁺, and [M + Met-2H]⁺. For the larger heptasaccharide, both [M + Met-H]²⁺ and [M + Met]³⁺ formed. Dissociation of these ions by both ETD and CID yields extensive sequence information. All trivalent lanthanide cations are suitable for sequencing glycans, and the fragmentation did not vary by metal identity.

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Analytical chemistry