Influence of coordination number and ligand size on the dissociation mechanisms of transition metal monosaccharide complexes

Several features of metal-carbohydrate complexes, in the form of deprotonat ed metal/N-glycoside ions, were varied in order to determine which types of complexes would best enable mass spectrometric differentiation of the ster eochemical features of the coordinated monosaccharides. Metal complexes wer e generated by using transition metals such as nickel, copper, and zinc. Ad ditionally, the size and coordination number of ligands in the complex, as well as the number of these ligands coordinated to the metal, were varied. By using a quadrupole ion trap mass spectrometer, multistage mass spectrome tric experiments were performed on the electrospray-generated metal N-glyco side complexes. Several tricoordinate Ni N-glycoside systems were capable o f differentiating the stereochemistry about the C-2 center in the monosacch aride ring, whereas the tricoordinate Cu/en system allowed for the differen tiation of both the C-2 and C-4 stereocenters. No stereochemical differenti ation was possible from four- or five-coordinate species with the exception of the four-coordinate Zn/dien complexes. Chang es in the metal center or size of the N-glycoside ligand generated the greatest changes in the produc t ion spectra of the tricoordinate complexes. Such alterations in four- or five-coordinate complexes often did not result in greatly differing product ion spectra. Whereas the product ion spectra of most metal/N-glycoside com plexes could be easily categorized according to structural features of the precursor ion, exceptional species such as the four coordinate [Zn(dien/mon osaccharide)-H](+) precursor ion, also capable of differentiating the stere ochemical features about C-2 and C-4, can give unexpected stereochemical in formation. (C) 1999 Elsevier Science B.V.