Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses

Abstract

The ammonia desorption chemical ionization (NH,-DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non-reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [ M + NH, -421 + ion is not formed direct from [ M + NH,] + by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH,+. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH,CO to afford neutral species which complex with NH,'. The structures of the ions resulting from H transfer have been inferred by comparison of their mass-analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [ M + NH,] + ions of compounds of established structure. A ring fragmentation reaction of 1,2 and 3 is reported. + NH, ' +CH3C0 / O A c / ++ NH, ' + H J NH, ' t CH3C0 Figure 1. A partial fragmentation scheme for peracetylated maltotetraose.

Gas phase reactivity of isomeric arylglycosides towards amines. A chemical ionization mass spectrometry and tandem mass spectrometry study

“…Most of these are based on mass spectrometry (MS) and MS/MS approaches [4 -9]. Gas-phase stable complexes obtained by chemical ionization (CI) [10] with different reagents have been used for the structural characterization and differentiation of oligosaccharides and glycosides [11][12][13][14][15][16][17][18][19].…”