Formation and decompositions of chloride adduct ions,

The ability to promote chloride-attachment ions of the form [M + Cl]- in negative ion electrospray ionization mass spectrometry (ESI-MS) has been developed using chlorinated solvents such as chloroform and carbon tetrachloride. This approach expands the current capabilities of negative ion ESI-MS by enabling detection of analytes that lack acidic sites and thus exhibit weak [M - H]- signals. In contrast to the remote-site collision-induced dissociation (CID) often observed in positive ion ESI-MS/MS for alkali metal cation adducts, the decomposition of chloride adducts usually proceeds via competitive dissociations to form Cl-, which is not structurally informative, or [M - H]-. The latter can provide structural information via consecutive decompositions. For compounds having higher gas-phase acidities than HCl, a low CID collision energy can promote the formation of [M - H]-, whereas for the majority of compounds with lower gas phase acidities than HCl, higher collision energies generally improve the relative yield of [M- H] . Because chloride attachment occurs primarily at electrophilic hydrogens, the daughter ion ratio, Cl-/[M - H]-, depends primarily upon the difference in gas phase acidity between the analyte molecule and HCl. At higher collision energies, entropic factors take on increased importance in determining the product ratio. The difference between the deltaS(0) terms for formation of Cl and formation of [M - H]- has been estimated for a series of substituted phenols and a series of acetic acid analogs. Finally, a novel neutral loss of CH3Cl from glycerophosphocholine and from ganglioside GM3 methyl ester is reported.

Fingerprinting of large oligosaccharides linked to ceramide by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: highly heterogeneous polyglycosylceramides of human erythrocytes with receptor activity for Helicobacter pylori

Highly microheterogeneous polyglycosylceramides (PGCs) of human erythrocytes with an average composition of about 25 monosaccharides linked to ceramide were analyzed by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). The human gastric pathogen Helicobacter pylori was earlier shown to bind this glycosphingolipid mixture by thin-layer chromatogram binding assay. The receptor activity was present along the whole nonresolved chromatographic interval. Mass spectra of intact PGCs were compared with corresponding spectra of oligosaccharides enzymatically released from the ceramides. Two subfractions of PGCs containing less than one and more than one sialic acid residue per molecule were used. MALDI-MS spectra were recorded in both linear and reflectron mode with the accuracies of </=0.08% and </=0.02%, respectively, which allowed determination of the constituent parts of the detected ions in form of ceramide and number of hexoses, N-acetylhexosamines, fucoses and sialic acids. Molecular species were found based on ceramide with mainly sphingosine and fatty acids 24:0 and 24:1 (with less amounts of 22:0), and with a total number of monosaccharides ranging from 11 (neutral, m/z = 2605 for [M+Na](+)) to 41 (one sialic acid, m/z = 8057 for [M-H](-)). The saccharide composition obtained supported a successively extended and branched N -acetyllactosamine core with substitutions of fucoses (0 up to 8) and sialic acid (0 to 1). The reliable molecular analysis of large oligosaccharides linked to ceramide using this approach will be of great help for the further structure analysis in order to define the epitope for the sialic acid-dependent binding by the bacterium.

Structural analysis of O-linked oligosaccharide-alditols by electrospray-tandem mass spectrometry after mild periodate oxidation and derivatization with 2-aminopyridine

O-linked oligosaccharide-alditols were analyzed by a combination of high-performance liquid chromatography (HPLC) and electrospray-tandem mass spectrometry (ESI-MS/MS). First, oligosaccharide-alditols were treated with sodium meta-periodate under conditions where core N-acetylgalactosaminitol is specifically degraded. The resulting fragments were labeled with 2-aminopyridine and purified on a reversed-phase column. Pyridylamino oligosaccharides yielded protonated molecular ions in positive-ion ES-MS and gave Y-series sequence ions, arising from glycosidic cleavages, by ESI-tandem mass spectrometry. Information on sugar sequence and branching of oligosaccharides linked at C6 and C3 to the N-acetylgalactosaminitol can be obtained. A systematic study of various oligosaccharide-alditols demonstrated that this approach constitutes a powerful tool for the structural characterization of O-glycans available only in limited quantities.

Structural elucidation of underivatized gangliosides by electrospray-ionization tandem mass spectrometry (ESIMS/MS)

The structural characterization of intact polysialogangliosides by electrospray-ionization mass spectrometry (ESIMS) and tandem mass spectrometry (MS/MS) is described. The negative-ion ESI mass spectra of gangliosides, such as a tetrasialoganglioside GQ1b, showed molecularly related ions with high sensitivity and accuracy. Collision-induced dissociation (CID) MS/MS provided adequate information to characterize the number and positions of sialic acids. ESIMS and CIDMS/MS techniques were applied successfully also in the positive-ion mode for characterization of intact gangliosides. Two isomeric disialogangliosides, GD1a and GD1b, are distinguishable from one another by CIDMS/MS in both negative- and positive-ion modes. The technique is readily applicable to structural analyses such as determining the positional isomers of glycoconjugates.