The analytical potential of the complexation of three isomeric monosaccharides (D-glucose, D-galactose, D-fructose)and two methyl glycosides ( O-methyl-α-D-glucose and O-methyl-β-D-glucose)by three metal ions, Ag+, Cu+ and Pb2+, has been investigated by fast-atom bombardment (FAB)ionization and tandem mass spectrometry. Our results have shown that the unimolecular reactivity of Ag+ complexes allows the characterization of the C(4)stereochemistry of the pyranose ring, whereas a distinction between D-glucose and D-fructose is not achieved. On the other hand, each of the three [Cu + monosaccharide]+ complexes exhibits specific dissociation patterns. We have also observed that Pb2+ ions induce the richest reactivity and are of particular interest for the identification of the three isomers. Finally, this study has demonstrated that the stereochemistry of the anomeric center of O-methyl-D-glucose is easily determined by reaction with Ag+ or Pb2+ ions. Several mechanisms are proposed to account for the main fragmentations of cationized glucose.

Tandem mass spectrometry was used in the analysis of Cu + -D-glucose complexes. The MIKE spectrum of these complexes generated by FAB shows that the loss of a water molecule is the most important spontaneous fragmentation, followed by a second dehydration or the loss of H 2 , whereas the metal ion Cu + is never eliminated. A theoretical survey of the potential energy surface, based on the use of density functional theory approaches, shows that the attachment of Cu + to the different basic centers of glucose induces nonnegligible bond activation phenomena within the sugar moiety. As a consequence, the cleavage of the C-O linkages of the six-membered ring leads to open complexes which are systematically much more stable than those in which the cyclic structure of the sugar is preserved. These significant stability differences reflect the preference of Cu + to yield bisligated complexes in which the metal forms almost linear arrangements with two oxygen atoms of the neutral through the participation of sd hybrids. The Cu + cation has a catalytic effect on these ring-opening mechanisms. Several pathways for the successive loss of two molecules of water can be envisaged with the origin in the cyclic and the open glucose-Cu + complexes. In general, the most stable product ions are those formed by a spontaneous fragmentation of the most stable open structures.

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