Asparagine as a ligand for cadmium(II), lead(II) and zinc(II)

Abstract

The behaviour of asparagine as ligand (L) towards cadmium(II), lead(II) and zinc(II) has been studied at 25°C with 1.00 mol L−1 NaCl as a constant ionic medium. Experimental data obtained by measuring the electromotive force of galvanic cells involving glass and amalgam electrode of cadmium, lead or zinc, respectively, are explained in terms of complex formation. The presence of CdL (log β = 3.05 ± 0.03), CdL2 (log β = 5.40 ± 0.05), CdL3 (log β = 6.15 ± 0.1) and ZnL (log β = 4.43 ± 0.03), ZnL2, (log β = 7.95 ± 0.04), ZnL3 (log β = 9.35 ± 0.07) is assumed, respectively. In the case of lead(II), it is necessary to assume also the existence of complexes formed by assumption of protons: PbL (log β = 3.60 ± 0.03), PbL2 (log β = 5.29 ± 0.05), PbHL (log β = 8.50 ± 0.1), PbH2L2 (log β = 18.70 ±0.1). The results are discussed and compared with those obtained for other amino acids.