Differentiation of carbohydrate isomers by tunable infrared multiple photon dissociation and Fourier transform ion cyclotron resonance mass spectrometry.

摘要

Carbohydrates and their derivatives play a crucial role in many biological processes including fertilization, cell growth, inflammation and post-translational protein modification. The function of carbohydrates in these systems is closely related to their structure, including monosaccharide sequence, glycosidic linkage and stereochemistry. Unfortunately, the number of anomeric configurations and possible linkages between monosaccharide units makes analysis of carbohydrate structures complex. In order to shed light on these larger oligosaccharides, the fragmentation patterns and infrared multiple photon dissociation (IRMPD) spectra of various mono- and disaccharides were obtained and compared. For this work, various tunable infrared sources including a line-tunable continuous-wave carbon dioxide laser and a free electron laser (FEL) were used in conjunction with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS).;The first three projects used a line-tunable carbon dioxide laser to fragment various mono- and disaccharides in both the positive and negative ion modes. In the first project, anomers of lithium-cation attached O-methyl-gluco- and galactopyranosides were fragmented. The identity and anomeric configuration of each monosaccharide was accurately determined by comparing fragmentation patterns and ratios of certain fragments. A second project explored the fragmentation pattern of lithiated glucose-containing disaccharides having various linkages (1-2, 1-3, 1-4 and 1-6) and anomeric configurations (alpha and beta). Both the linkage and anomeric configuration of the various disaccharides were successfully identified based on their fragmentation patterns at several wavelengths. Next, irradiation of deprotonated and chlorinated glucose-containing disaccharides produced fragmentation patterns in which cleavage of the glycosidic bond resulted in major abundances of m/z 161 and 179 fragment ions. Along with differentiating the anomeric configuration for the chlorinated disaccharides, comparison of the abundances for major fragment ions also resulted in the positive identification of the linkages for both sets of disaccharides.;Lastly, several deprotonated (negatively charged) mono- and disaccharides were fragmented with a FEL. The IRMPD spectra of the monosaccharide anions (m/z 179) from both the deprotonated monosaccharides and those isolated by fragmentation of various disaccharides were taken. A C-O stretching band characteristic of aldehydes was present in all spectra at ∼1720 wavenumbers and gave spectroscopic evidence of the monosaccharide ring opening and therefore loss of anomericity.