Biomolecule structure characterization in the gas phase using mass spectrometry

Carbohydrate/cation interactions were examined in the gas phase using mass spectrometry and the results were compared with computer generated models of the complexes. Monosaccharide/alkali cation complexes of five carbohydrates, D-fructose, D-glucose, D-galactose, D-mannose, and a deuterated analog of D-glucose, 6,6-D-glucose-d(2), were studied. Among the technuques used in this effort were electrospray ionization (ESI), desorption/ionization on silicon (DIOS), matrix-assisted laser desorption/ionization (MALDI) and fast atom/ion bombardment (FAB) mass spectrometry. A series of ESI, DIOS, MALDI and FAB-MS experiments were used to obtain relative cation binding preferences of each monosaccharide. Heterodimers of 6,6-D-glucose-d(2) formed with each of the monosaccharides show that Na+ binding for D-fructose, D-mannose and D-galactose is similar, while D-glucose was 25% weaker. Modeling studies and energy minimization calculations on the alpha and beta forms of the monosaccharide alkali cation complexes are consistent with the experimental data and indicate that D-fructose, D-galactose, and D-mannose undergo tridentate and tetradentate binding with Na+ and Li+ while D-glucose would only form a bidentate complex.