Influence of metal ion and coordination geometry on the gas phase dissociation and stereochemical differentiation of N-glycosides

A series of metal cationized N-glycoside complexes is studied by tandem mas s spectrometry. The complexes are of the form [M(dien)(hex)(n) - H](+), [M( dien)(hex)(n)Cl](+), or [M(dien)(hex)(2)](2+), where M = Co2+, Cu2+, Ni2+, or Zn2+ and n = 1 or 2. The presence of a metal as the charge carrier promo tes more extensive cleavage of the carbon backbone of the saccharide moiety compared to the protonated analogues, thus providing greater structural in formation. Results obtained for the four coordinate singly charged deproton ated complexes differentiate [M(dien)(Glc) - H](+) versus [M(dien)(Gal) - H ](+) for a given metal. Such differentiation is not possible for the corres ponding five coordinate complexes, indicating that the coordination number of the metal plays an important role. Tandem mass spectra for both of these four and five coordinate complexes indicate that the geometry around the m etal dictates the observed dissociation patterns. Furthermore, the metals Z n and Cu promote unique modes of dissociation not observed for the Ni and C o complexes. Finally, the chlorinated and doubly charged complexes give ris e to very few dissociation pathways by MS/MS. It is proposed that this lack of product ions is due to the absence of lone pair electrons on the metal alkoxide that drive the dissociation. (C) 2000 Elsevier Science B.V.