Glycans are biomolecules in which one or more monosaccharide units are covalently O-linked to each other at large variety of different combinations. Their role in a wide range of biological processes, such as intracellular transport, cell recognition, cell-cell interactions, immune functions, therapeutics, protein regulations and interactions are well acknowledged in several reviews and scientific investigations over two decades. The detailed characterization of glylcan structure still remains one of the most challenging tasks to bio-analysts due to the micro-heterogeneity and diversity of these molecules. This dissertation presents the first results of glycan photofragmentaton by 157 nm light in a linear ion trap.;Cross-ring fragments corresponding to high-energy fragmentation pathways were observed in abundance for all studied structures and they provide better sequence coverage than low- and high energy CID experiments. Furthermore, the ion-trap facilitates MSn experiments on the diagnostic glycosidic fragments and cross-ring product ions generated through photofragmentation, thus allowing unambiguous assignment of all of the isomeric structures associated with the model glycoprotein utilized in our study. We also extended the application of 157 nm photofragmen-tation to Leukotriene C4 isomers (5, 6) and (14, 15) for the first time and successfully differentiated their structures. Photofragmentation is found to be suitable for the structural identification and isomeric differentiation of cysteinyl leukotrienes and is more informative than low- or high energy CID methods. Photofragmentation is demonstrated to be a powerful technique for the structural characterization of glycans and lipids.
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