title: Cationized Carbohydrate Gas-Phase Fragmentation Chemistry.
abstract: We investigate the fragmentation chemistry of cationized carbohydrates using a combination of tandem mass spectrometry, regioselective labeling, and computational methods. Our model system is D-lactose. Barriers to the fundamental glyosidic bond cleavage reactions, neutral loss pathways, and structurally informative cross-ring cleavages are investigated. The most energetically favorable conformations of cationized D-lactose were found to be similar. In agreement with the literature, larger group I cations result in structures with increased cation coordination number which require greater collision energy to dissociate. In contrast with earlier proposals, the Bn-Ymfragmentation pathways of both protonated and sodium-cationized analytes proceed via protonation of the glycosidic oxygen with concerted glycosidic bond cleavage. Additionally, for the sodiated congeners our calculations support sodiated 1,6-anhydrogalactose Bnion structures, unlike the preceding literature. This affects the subsequent propensity of formation and prediction of Bn/Ymbranching ratio. The nature of the anomeric center (α/β) affects the relative energies of these processes, but not the overall ranking. Low-energy cross-ring cleavages are observed for the metal-cationized analytes with a retro-aldol mechanism producing the0,2A2ion from the sodiated forms. Theory and experiment support the importance of consecutive fragmentation processes, particularly for the protonated congeners at higher collision energies. Graphical Abstract ᅟ.
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, MO, 63121, USA. bythellb@umsl.edu.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Bythell
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, MO, 63121, USA.
authors.forename: Maha T
authors.initials: MT
authors.lastname: Abutokaikah
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, MO, 63121, USA.
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Wagoner
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, MO, 63121, USA.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Guan
authors.affiliation: Department of Chemistry and Biochemistry, University of Missouri, St. Louis, MO, 63121, USA.
authors.forename: Jordan M
authors.initials: JM
authors.lastname: Rabus
keywords: Collision-induced dissociation; Density functional theory; Glycans; Ion structure; Labeling; Mass spectrometry; Metals