Using non-covalent complexes to direct the fragmentation of glycosidic bonds in the gas phase.

An investigation of the gas phase chemistry of proton bound oligosaccharide (S)-ligand (L) non-covalent complexes, [S + H + L](+) has been carried out using electrospray ionization (ESI) and tandem mass spectrometry in a quadrupole ion trap. When subjected to collision-induced dissociation (CID), these [S + H + L](+) complexes undergo a range of reactions that can be broadly classified into three main types: (1) Simple dissociation into the individual monomers; (2) cleavage of the oligosaccharide to form B-type sequence ions; (3) cleavage of the ligand species. The second type of reaction is particularly interesting as it can produce a "ladder series" of [B(x) + L](+) ions via ligand induced oligosaccharide bond cleavage. This novel gas phase reaction greatly simplifies the sequencing of oligosaccharides. Both the oligosaccharide and ligand were found to influence the type of reaction pathway observed, with the "ladder series" of [B(x) + L](+) ions being favored for permethylated oligosaccharides and for bifunctional ligands. Cytosine is a particularly good ligand at facilitating the formation of [B(x) + L](+) ions. Analogies with condensed phase chemistry of sugars is made and a potential mechanism for ligand induced oligosaccharide bond cleavage is proposed.