Hyaluronate tetrasaccharide–Cu(II) interaction: a NMR study

The coordination of Cu(II) to a hyaluronate tetrasaccharide (HA(t)) was investigated in aqueous solution by C-13 and H-1 relaxation measurements at two magnetic fields, 9 and 14 T The HA(t) interaction with the metal ion was monitored following the nuclear paramagnetic relaxation enhancements R-1p and R-2p produced by the copper addition. The data analysis shows that the paramagnetic effect is differently experienced by the nuclei in different monosaccharide residues. A molecular model for the complex HA(t)-Cu(II) was built taking into account the experimental data. The model shows the presence of two binding sites, both involving the carboxylate groups of the two glucuronic acid units. The first site, that best simulates the HA binding site, is located on the ligand core, while the second one is located on the terminal glucuronic acid residue. Both binding sites involve, in addition to the carboxylate groups, the O4 oxygens of the glucuronic acid residues.