Experimental and Theoretical Studies of Sodium Cation Interactions with D-Arabinose, Xylose, Glucose, and Galactose

The binding of Na+ to arabinose (Ara), xylose (Xyl), glucose (Glc), and galactose (Gal) is examined in detail by Studying the collision-induced dissociation (CID) of the four sodiated monosaccharide complexes with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Analysis of the energy-dependent CID cross-sections provides 0 K sodium cation affinities for experimental complexes after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations for a number of geometric conformations of each Na+(L) complex with a comprehensive analysis of the alpha and beta anomeric forms are determined at the B3LYP/6-311+G(d,p) level with single-point energies calculated at MP2(full), B3LYP, and B3P86 levels using a 6-311+G(2d,2p) basis set. This coordinated examination of both experimental work and quantum chemical calculations allows for determination of the bond energy for both the alpha and beta forms of each monosaccharide studied here. An understanding of the energetic contributions of individual structural characteristics as well as the energetic trends in binding among the monosaccharides is developed. Structural characteristics that affect the energetics of binding involve multidentate sodium cation coordination, ring sterics, and hydrogen bonding schemes. The overall trend in sodium binding affinities for the eight ligands follows beta-Ara < alpha-Ara < beta-Xyl < beta-Glc < alpha-Glc < alpha;-Xyl < alpha-Gal < beta-Gal.