Unexpected Dissociation Mechanism of Sodiated N-Acetylglucosamine and N-Acetylgalactosamine

Abstract

The mechanism for the collision-induced dissociation (CID) of two sodiated N-acetylhexosamines (HexNAc), N-acetylglucosamine (GlcNAc), and N-acetylgalactosamine (GalNAc), was studied using quantum-chemistry calculations and resonance excitation in a low-pressure linear ion trap. Experimental results show that the major dissociation channel of the isotope labeled [1-18O, D5]-HexNAc is the dehydration by eliminating HDO, where OD comes from the OD group at C3. Dissociation channels of minor importance include the 0,2A cross-ring dissociation. No difference has been observed between the CID spectra of the α- and β-anomers of the same HexNAc. At variance, the CID spectra of GlcNAc and GalNAc showed some differences, which can be used to distinguish the two structures. It was observed in CID experiments involving disaccharides with a HexNAc at the nonreducing end that a β-HexNAc shows a larger dissociation branching ratio for the glycosidic bond cleavage than the α-anomer. This finding can be exploited for the rapid identification of the anomeric configuration at the glycosidic bond of HexNAc-R′ (R′ = sugar) structures. The experimental observations indicating that the dissociation mechanisms of HexNAcs are significantly different from those of hexoses were explained by quantum-chemistry calculations. Calculations show that ring opening is the major channel for HexNAcs in a ring form. After ring opening, dehydration shows the lowest barrier. In contrast, the glycosidic bond cleavage becomes the major channel for HexNAcs at the nonreducing end of a disaccharide. This reaction has a lower barrier for β-HexNAcs as compared with the barrier of the corresponding α-anomers, consistent with the higher branching ratio for β-HexNAcs observed in experiment.

Unusual free oligosaccharides in human bovine and caprine milk

“…LODES/MS n involves the sequential collision induced dissociation (CID) of oligosaccharide sodium (or lithium) adducts in a mass spectrometer. The sequences of CID are guided by LODES which is derived from carbohydrate dissociation mechanisms 42 – 44 . The mechanisms of oligosaccharide sodium adducts used in this study are summarized as three propensity rules as follows.…”

Identification of Anomericity and Linkage of Arabinose and Ribose through Collision-Induced Dissociation

“…The experimental method used herein was reported in detail in our previous studies; − therefore, only a brief description is provided. Arabinose (≥98%) and ribose (≥99%) were purchased from Sigma-Aldrich (St. Louis, MO), 1,5-α- l -arabinobiose was purchased from Megazyme Inc. (Chicago, IL), and D-[2-D]­ribose (98 atom % D), D-[1,2- 13 C 2 ]­ribose (99 atom % 13 C), and D-[5- 13 C]­ribose (99 atom % 13 C) were purchased from Omicrometer Biochemicals Inc. (South Bend, IN).…”

“…Identifying the arabinose and ribose structures in these polysaccharides is essential for understanding the corresponding biological processes. Although mass spectrometry is more sensitive than other methods (e.g., nuclear magnetic resonance spectroscopy) for identifying carbohydrate structures, differentiating stereoisomers (e.g., arabinose and ribose), anomericity (α- and β-configuration), and the ring form (furanose and pyranose) remains challenging. , We recently developed a novel mass spectrometry method, on the basis of the dissociation mechanisms, for the identification of linkages, anomericity, and stereoisomers of monosaccharides such as glucose, galactose, and mannose, − amino sugars, , and xylose . This method can be used for in situ identification of the monosaccharides produced from oligosaccharides through collision-induced dissociation (CID) inside mass spectrometers.…”

“…Except for amino sugars, all monosaccharide sodium adducts and lithium adducts have been found to possess the same major dissociation channels (i.e., dehydration and cross-ring cleavage) and similar dissociation mechanisms. However, only the pyranose forms of these monosaccharides have been studied; − no monosaccharides in furanose form have been studied. In this work, we examined the arabinose and ribose isomers through chromatography, CID mass spectra, quantum chemistry calculations, and transition state theory.…”

Unusual milk oligosaccharides and the biosynthetic pathways

“…LODES/MS n involves the sequential collision induced dissociation (CID) of oligosaccharide sodium (or lithium) adducts in a mass spectrometer. The sequences of CID are guided by LODES which is derived from carbohydrate dissociation mechanisms [39][40][41] . The mechanisms of oligosaccharide sodium adducts used in this study are summarized as three propensity rules as follows.…”