Stabilization and linkage analysis of metal-ligated sialic acid containingoligosaccharides

The dissociation of metal-ligated sialyllactose and sialyl-N-acetyllactosam ine was investigated. Metal-ligand derivatization of the carbohydrate sampl es with the diethylenetriamine ligand and one of four transition metals [Co (II), Ni(II), Cu(II), Zn(II)] suppressed sialic acid loss in the collision- induced dissociation process. Suppression of sialic acid loss allows sialic acid linkage information to be gained through tandem mass spectrometry. Si alic acid stabilization is postulated to occur due to the doubly charged me tal ion which allows for deprotonation of the sialic acid moiety. Furthermo re, a connection between the metal center and the amount of sialic acid los s was found. These results were rationalized using the Irving-Williams seri es and a competition between different sites of deprotonation. Analysis of the product ion spectra showed a clear differentiation of sialic acid linka ge. Linkage determination is proposed to be effective due to the available conformations allowed by the different linkages. A more flexible linkage wi ll allow more coordination of the sialic acid residue with the metal center , whereas a less flexible linkage will make this interaction unlikely. (J A m Soc Mass Spectrom 2001, 12, 528-536) (C) 2001 American Society for Mass S pectrometry.