Complexation equilibria of oxy-acid–2-amino-2-deoxy-d-gluconic acid–metal(II) ion ternary systems in aqueous solution as studied by potentiometry. Binding characteristics of borate and germanate

The complexation equilibria for the boric acid–d-glucosaminic acid and d-glucosaminic acid–metal(II) ion binary systems, the boric acid–d-glucosaminic acid–metal(II) ion ternary system, and the corresponding binary and ternary systems with germanic acid instead of boric acid involving nickel(II), zinc(II), cadmium(II) and lead(II) as the metal(II) ion have been investigated in aqueous solution at 25°C and I=0.1 mol dm−3 (NaClO4) by potentiometric measurements (d-glucosaminic acid is 2-amino-2-deoxy-d-gluconic acid). The complexes have been characterized in aqueous solution by 13C NMR spectra and the pKa values. The 1:2 ester of borate and d-glucosaminate shows a selectivity for metal(II) ions different from the free d-glucosaminate ligand. It has been demonstrated that the coordination site of the 1:2 ester can distinguish the difference in metal ion size. Such selectivity for metal(II) ions in the boric acid system is discussed by comparison with the germanic acid system.