1H NMR Elucidation of Observed Stable Sugar-NaCl-water Complexes in Aqueous Solution

The solvation of sugars in aqueous media matters in the understanding of biological systems and carbohydrate transformations. The presence of NaCl is known to perturb hydrogen bonding of sugar hydrates, however, direct evidence to elucidate mechanism at atom level is very rare even though the “NaCl Effect” was well known in biomass transformations for chemicals/biofuels. Here we report experimental evidences of a clear staircase-like correlation between induced 1H NMR changes of D-glucose/fructose with concentration of NaCl aqueous solution at room temperature; and two stable bonding status was observed in the system. An investigation on NaCl-saccharide interaction combining the calculated molar ratio of NaCl to each monosaccharide showed that chloride anions likely play a key role in both the stabilization of the two stable bonding status via formation of sugar-hydrogen (H2O)-chloride bond and induction of 1H NMR shifts. Via a further half-quantitative study, three structures of stable sugar-NaCl-water complexes were mapped for the first time in tackling the NaCl-monosaccharide interaction at atomic level in an aqueous solution. Based on the maximum of induced 1H NMR shifts, an ideal NaCl usage based on maximum of 1H NMR shift was proposed.