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 berate and germanate

The complexation equilibria for the boric acid-D-glucosaminic acid and D-gl ucosaminic acid-metal(II) ion binary systems, the boric acid-D-glucosaminic acid-metal(II) ion ternary system, and the corresponding binary and ternar y systems with germanic acid instead of boric acid involving nickel(II), zi nc(II), cadmium(II) and lead(II) as the metal(II) ion have been investigate d in aqueous solution at 25 degrees C and I = 0.1 mol dm (3) (NaClO4) by po tentiometric measurements (D-glucosaminic acid is 2-amino-2-deoxy-D-gluconi c acid). The complexes have been characterized in aqueous solution by C-13 NMR spectra and the pK(a) values. The 1:2 ester of berate and D-glucosamina te shows a selectivity for metal(II) ions different from the free D-glucosa minate 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 wit h the germanic acid system. (C) 2000 Elsevier Science S.A. All rights reser ved.