Analysis of Glycosyl Bond Cleavage and Related Isotope Effects in Collision-Induced Dissociation Quadrupole-Time-of-Flight Mass Spectrometry of Isomeric Trehaloses

Abstract

The configuration isomers alpha,alpha-, alpha,beta-, and beta,beta-trehalose are distinguishable by a relative ion abundance analysis using collision-induced dissociation MS/MS measurements in electrospray ionization quadrupole-time-of-flight mass spectrometry. The relative abundance of the Y-type fragment ion of alpha,alpha-trehalose is the highest and that of beta,beta-trehalose is the lowest, indicating that alpha-glycosyl bonds cleave more easily than beta-glycosyl bonds. The relative ion abundance depends on both the alpha- and beta-glycosyl linkage type and the number of alpha-glycosyl bonds. The reaction path of glycosyl bond cleavage is calculated computationally using the molecular orbital method in the form of Hartree-Fock theory in conjunction with the 6-31G(d) basis set. The results are consistent with the experimental data. Isotope effects on the fragmentation of the glycosyl bonds are detected in the experiments of the H2O/D2O solvent systems. Furthermore, the isotope effect regarding beta,beta-trehalose is larger than those of alpha,alpha- and alpha,beta-trehalose, indicating that the isotope effect on the beta-glycosyl bond cleavage is larger than that on the alpha-glycosyl bond cleavage. The thermal energy increase in trehalose-d8 molecules over the corresponding trehalose molecules is calculated from the vibrational modes.

Blackbody Infrared Radiative Dissociation of Protonated Oligosaccharides

“…Cleavage of the glycosidic bonds of the B ions can also lead to smaller B ions, vide infra. Sequential water loss has been observed in CID experiments performed on protonated (or ammonium adducts) ions of some monosaccharides [7] and oligosaccharides [8]. For example, CID of the ammonium adducts of xylopentaose leads to B ions that have lost up to five water molecules [8].…”

“…However, it is more difficult to rationalize a tight TS for B ion formation. Assuming the rate limiting step for B ion formation involves cleavage of the glycosidic linkage following protonation of the oxygen atom [7], a loose TS (with a positive ΔS ‡ ) is expected. The small A-factors established from the BIRD measurements would seem to suggest that this view of B ion formation is incorrect or, at the very least, that the rate limiting step does not involve simple bond fission.…”

“…For singly charged, protonated and alkali-metal cationized oligosaccharides, cleavage of a glycosidic bond at the non-reducing side yields an oxacarbenium ion (referred to as a B-type ion) and a smaller neutral oligosaccharide [5]. Glycosidic bond cleavage may also be accompanied by proton transfer resulting in the formation of a smaller charged oligosaccharide (referred to as a Y-type ion) and a neutral epoxide [3,[5][6][7]. There is experimental evidence that it is an exchangeable hydrogen (e.g.…”

“…There is experimental evidence that it is an exchangeable hydrogen (e.g. from a neighboring hydroxyl group) that is transferred to produce Y ions [7]. The fragmentation mechanisms for protonated oligosaccharides are believed to be charge induced, whereby protonation of the glycosidic oxygen results in delocalization of the ring oxygen electrons and a concomitant weakening of the glycosidic bond [8].…”

“…Despite the widespread application of tandem MS to characterize the structures of oligosaccharides, there have been relatively few studies of the dissociation mechanisms [7][8][9][10][11][12][13][14][15][16][17][18][19]. Perhaps the most detailed investigation into oligosaccharide fragmentation mechanisms is the recent study by Suzuki et al [9].…”