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

The behaviour of asparagine as ligand (L) towards cadmium(ll), lead(ll) and zinc(ll) has been studied at 25 degrees C with 1.00 mot 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 beta = 3.05 +/- 0.03), CdL(2) (log beta = 5.40 +/- 0.05), CdL(3) (log beta = 6.15 +/- 0.1) and ZnL (log beta = 4.43 +/- 0.03), ZnL(2) (log beta = 7.95 +/- 0.04), ZnL(3) (log beta = 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 beta = 3.60 +/- 0.03), PbL(2) (log beta = 5.29 +/- 0.05), PbHL (log beta = 8.50 +/- 0.1), PbH(2)L(2) (log beta = 18.70 +/- 0.1). The results are discussed and compared with those obtained for other amino acids.