Fragmentation reactions in the mass spectrometry analysis of neutral oligosaccharides

A method is described to obtain multicollision dissociation threshold (MCDT ) values. These values provide relative reaction thresholds for dissociatio n in the three major gas-phase fragmentation reactions of oligosaccharides complexed to alkali metal ions. The quasimolecular ions are produced using matrix-assisted laser desorption/ionization Fourier transform mass spectrom etry. The MCDTs for alkali metal ion dissociation and glycosidic bond and c ross-ring cleavages were resolved from the kinetic energy dependence of col lision-induced dissociation (CID) products. The relative strengths of alkal i metal ion binding to N,N'-diacetylchitobiose (chitobiose) and N,N',N "-tr iacetylchitotriose (chitotriose) were probed using sustained off-resonance irradiation (SORI) CID. Experiments to evaluate MCDT values and the method for obtaining them were performed by studying alkali metal ion coordinated crown ethers. Molecular dynamic simulations were also performed to provide insight into the alkali metal ion binding of chitin-based oligosaccharides. The relative dissociation thresholds of glycosidic bond cleavages and cros s-ring cleavages were determined for various alkali metal ion coordinated o ligosaccharides. The activation barriers of glycosidic bond cleavages were found to depend on the size of the alkali metal ion. Cross-ring cleavages w ere found to be independent of the alkali metal ion but dependent on linkag e type. The results suggest that glycosidic bond cleavages are charge-induc ed while cross-ring cleavages are charge-remote processes.