Ranking of gas-phase acidities and chloride affinities of monosaccharides and linkage specificity in collision-induced decompositions of negative ion electrospray-generated chloride adducts of oligosaccharides.
Negative ion electrospray-tandem mass spectrometry has been employed to study chloride adducts of saccharide molecules. Decompositions of [M + Cl]- obtained under identical low-energy collision conditions allow the approximate ranking of chloride affinities and gas-phase acidities of a series of isomeric monosaccharides. The ketohexoses are found to be more acidic than the aldohexoses. Chloride adduct decompositions are examined for a glucopyranosyl fructose and a glucopyranosyl glucose series. For each disaccharide series, the linkage position is shown to markedly influence the favored pathways of [M + Cl]- decompositions, initiated either by loss of neutral HCl to form [M - H]- and possibly leading to further (consecutive) decompositions, or by loss of M to form Cl-. Upon formation of [M - H]-, both cross-ring cleavages and glycosidic bond decompositions were observed in varying degrees for the two series of disaccharides. Remarkably, for three non-reducing polysaccharides that each contain a terminal sucrose group at the "downstream" end, chlorine-containing product ions arising from cleavage of the Glcalpha-2Fru linkage have been observed. Apart from Cl-, chlorine-containing product ions are not observed for any of the other disaccharides investigated, and they appear to be specifically diagnostic of a terminal Glcalpha-2Fru linkage. Their appearance is rationalized based upon a substantially reduced tendency for HCl loss from these non-reducing polysaccharides.
Zhu
J
J
Department of Chemistry, University of New Orleans, Louisiana 70148, USA.
Cole
R B
RB
D000465:Algorithms; D002240:Carbohydrate Sequence; D002712:Chlorides / Q000737:chemistry*; D004187:Disaccharides / Q000737:chemistry; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry*; D011887:Raffinose / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013395:Sucrose / Q000737:chemistry; D013816:Thermodynamics
D002712:Chlorides; D004187:Disaccharides; D009844:Oligosaccharides; D013395:Sucrose; D011887:Raffinose