Gas-phase fragmentation studies of a series of biotin derivatives and of a core oligosaccharide by tandem mass spectrometry

Sioud, Salim (2010) Gas-phase fragmentation studies of a series of biotin derivatives and of a core oligosaccharide by tandem mass spectrometry. Masters thesis, Memorial University of Newfoundland.

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Abstract

The gas-phase fragmentation of a series of commercially available biotinyl reagents have been evaluated by electrospay ionization mass spectrometry (ESI-MS) and collision induced dissociation tandem mass spectrometry (CID-MS/MS) analyses using a QqTOF-MS/MS hybrid instrument. In general it has been observed that the CID-MS/MS fragmentation routes of the five precursor protonated molecules obtained from the biotin linkers I-5 afforded a series of product ions formed essentially by similar routes. The genesis and structural identities of all the product ions obtained from the biotin linkers I-5 have been assigned. All of the exact mass assignments of the protonated molecules and the product ions were verified by conducting separate CID-MS/MS analysis of the deuterium labeled precursor ions. -- The ESI-QqTOF-MS structural eluciadation of the core oligosaccharide of Aeromonas hydrophila (chemotype II) lipopolysaccharide has been investigated and it was demonstrated that it contained a 4-O-linked posphorylated group Kdo residue which was glycosylated by the remaining outer core oligosaccharide through its O-5 position. After, releasing the core oligosaccharide from the native LPS with acid, the phosphorylated Kdo residue eliminated phosphoric acid to produce a core oligosaccharide containing a mixture of diastereomeric 4,8- and 4,7-anhydro-α-keto acids and an open olefinic Kdo residue. The characteristic glycone sequence was elucidated by CID-MS/MS of the protonated molecule of the native core oligosaccharide. In addition, the analysis of the Hakamori permethylated core oligosaccharide was carried out by ESI-QqTOF-MS and MALDI-TOF-MS analyses. The presence of more than nine isobaric isomers of this core was noticed. The collision-induced dissociation analysis (CID-MS/MS) of the various protonated permethylated core oligosaccharide molecules showed a similar and diagnostic fragmentation pattern. -- To confirm these obtained results, the permethylation of the core oligosaccharide SJ-48R has been performed with a different methylation method (Ciucanu & Kerek method). It was realized that the extra minor satellite signals obtained in the ESI-QqTOF-MS and MALDI-TOF-MS analyses were DMSO stable covalent addition products, which have occurred by a Michael addition on the 4,8-Kdo exocyclic double bond and on the C-3-C-4 double bond of the olefinic open-chain Kdo residue. To our knowledge, this is the first time that DMSO adducts have been observed in the gas phase, and they have never before been reported.

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