Collision-Induced\nDissociations of Linear Hexose and\nDisaccharides with Linear Hexose at the Reducing End

Characterization of carbohydrate structures using mass\nspectrometry\nis a challenging task. Understanding the dissociation mechanisms of\ncarbohydrates in the gas phase is crucial for characterizing these\nstructures through tandem mass spectrometry. In this study, we investigated\nthe collision-induced dissociation (CID) of glucose, galactose, and\nmannose in their linear forms, as well as the linear forms of hexose\nat the reducing end of 1–6 linked disaccharides, using quantum\nchemistry calculations and tandem mass spectrometry. Our results suggest\nthat the dehydration reaction in linear structures is unlikely to\noccur due to the significantly high reaction barrier compared to those\nof CO migration and C–C bond cleavage. We demonstrate\nthat the different intensities of the cross-ring fragments observed\nin the CID spectra can be explained by the different transition state\nenergies of CO migration and C2–C3, C3–C4, and\nC4–C5 bond cleavages, and the branching ratios of the cross-ring\nfragments are significantly different between glucose and galactose.\nThe application of the cross-ring fragments to oligosaccharides reveals\nthat the stereoisomers of glucose and galactose in oligosaccharides\ncan be differentiated based on the relative intensities of the cross-ring\nfragments produced by the C2–C3 bond cleavage and C3–C4\nbond cleavage, a differentiation that cannot be achieved by conventional\ntandem mass spectrometry.