We describe the direct NMR detection of a C-H center dot center dot center dot 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 degrees 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 H-1 and C-13 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.