The effects of coordination number and ligand size on the gas phase dissociation and stereochemical differentiation of cobalt-coordinated monosaccharides

Previously we have shown that stereoisomeric hexosamines and N-acetylhexosamines can be uniquely identified by mass spectrometry when they are derivatized with [Co(DAP)(2)Cl-2]Cl and subjected to ES-MSn studies. Here, we explore why the diastereomers dissociate differently by investigating the role of the auxiliary ligand. Complexes which have two, three, and four auxiliary nitrogens coordinated to the Co, center are investigated. By comparing these complexes, we demonstrate that the ligand affects the dissociations by contributing to both the sterics and the electronics about the metal center. Finally, we use this information to gain new insight about a key dissociation mechanism, loss of formaldehyde, which occurs stereoselectively for the [Co(DAP)(GalNAc-2H)](+) complex. (C) 2001 Elsevier Science B.V.