Synergic metal-ion sequestration by borate–polyhydroxy-aminocarboxylate systems as studied by 11B, 13C and 113Cd nuclear magnetic resonance spectroscopy
Abstract
Borate ester formation with 2-amino-2-deoxy-D-gluconate and 2-amino-2-deoxy-D-galactonate has been studied using 11B and 13C NMR spectroscopy. The esters were found to be mainly formed at the threo-diol positions. The metal-ion sequestering abilities of the borate–ligand systems for various alkaline-earth and transition-metal ions have been investigated by 11B, 13C and 113Cd NMR and titration procedures. Synergic metal-ion sequestration appeared to be dependent on the metal ion, pH and the overall stability constant of the borate esters. The largest effects were measured in the borate–2-amino-2-deoxy-D-gluconate system upon adding CdII or NiII. In this system CdII is complexed by one of the borate diesters via two carboxylate and two amino groups and probably two oxygens of the borate moiety.