Fragmentation of oligosaccharides

Because the soft ionization methods used for oligosaccharides produce few fragments, collision-induced dissociation (CID) or post-source decay (PSD) must be used for structural study. These two techniques have been applied to deprotonated, protonated or alkaliated 

MeHex 0-Me Hex O-MeHex O-MeHex O-MeHex O-MeHex O-MeHex-O-Me 

Collision-induced dissociation ESI/MS/MS trace of doubly charged sodium adduct of methylated maltoheptulose (m/z = 760.7). Reproduced (modified) from Reinhold V.N., Reinhold B.B. and Costello C.E., Anal. Chem., 67, 1772, 1995, with permission. 

In general, MS/MS allows one to determine the sequence and the branching pattern of oligosaccharides. The isomer position of each of their glycosidic bonds also can be 

However, this spectrum is different from the peracetylated one because it displays more secondary fragments. This process, due to the presence of HexNac, leads from the B2 ion to the preferential loss of the substituent at the 3 position of the HexNac residue, in this case a tetramethylated hexose, to produce the H2 fragment at m/z 402. From this last ion, the loss of the substituent at the 4 position, here a trimethylated deoxyhexose, yields the E 2 fragment at m/z 196. This spectrum, as with that of the peracetylated compound, allows 

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Figure 4.4 Nomenclature for mass spectral fragmentation of oligosaccharides.

Mercaptolysis of glycosidically linked sugars, that is, treatment of the sugar with ethanethiol and a mineral acid, is an established procedure for fragmentation of oligosaccharides and polysaccharides, and generally... 

The use of the fragmentation of oligosaccharides by using post-source decay (PSD) MALDI-TOF MS was shown by Van Alebeek et al. (31). This technique was reported to permit the determination of the positions of methyl esters or other substituents in the sequencing of methyl-esterified oligogalacturonides (31). Nevertheless, also by using PSD MALDI-TOF MS no fragmentation of O-acetylated XOS was obtained. 

A symposium report deals with the use of n.m.r. spectroscopy for piecing together fragments of oligosaccharides, inter alia, isolated from liverworts (HeE2ticae).5... 

Devakumar, a. TIiompson, M. S. Reilly, J. P. Fragmentation of oligosaccharide ions with 157 nm vacuum ultraviolet light. Rapid Common. Mass Spectrom. 2005, 19, 2313-2320. 

Amino-sugars and Related Compounds. Part IV. Isolation and Properties of Oligosaccharides Obtained by Controlled Fragmentation of Chitin, S. A. Barker, A. B. Foster, M. Stacey, and J. M. Webber, J. Chem. Soc., (1958) 2218 - 2227. 

Typical spectra obtained are shown in Fig. 1.2. Moreover, substantial radiolytically-mediated elevations in the concentration of serum formate, arising from the oxidation of carbohydrates present by OH radical, were also detectable. In addition to the above modifications, 7-radiolysis of inflammatory knee-joint synovial fluid generated an oligosaccharide species of low molecular mass derived from the radiolytic fragmentation of hyaluronate as outlined in the previous section dealing with oxidative damage to carbohydrates. The... 

Recall from Chapter 23.2.4 that humic substances are isolated from seawater by adsorption on a hydrophobic resin followed by elution using solvents of varying pH. The desorbed compounds are fractionated into two classes, humic acids fulvic acids based on their solubility behavior. A model structure for a humic acid is illustrated in Figure 23.10a in which fragments of biomolecules, such as sugars, oligosaccharides. 

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