Uncovering Nonconventional and Conventional Hydrogen Bonds in Oligosaccharides through NMR Experiments and Molecular Modeling: Application to Sialyl Lewis-X

We describe the direct NMR detection of a C-H···O nonconventional hydrogen bond (Hbond) and provide experimental and theoretical evidence for conventional Hbonds in the pentasaccharide sialyl Lewis-X (sLe(X)-5) between 5 and 37 °C in water. Extensive NMR structural studies together with molecular dynamics simulations offer strong evidence for significant local dynamics in the Le(X) core and for previously undetected conventional Hbonds in rapid equilibrium that modulate structure. These NMR studies also showed temperature-dependent (1)H and (13)C line broadening. The resulting model emerging from this study is more complex than a simple rigid core description of Le(X)-like molecules and improves our understanding of stabilizing interactions in glycans.