Biomolecule structure characterization in the gas phase using mass spectrometry

Abstract

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‐d2, 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‐d2 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.