The Complex formation of cadmium(II) and mercury(II) with aliphatic dipeptides

Abstract

Stability constants for complexes between cadmium(II) and mercury(II) and a series of dipeptides consisting of glycine, alanine, leucine and proline have been determined by the pH-titration method. Influences of the side chains on the stability of the complexes are discussed. Cadmium(II) forms 1:1 complexes of the type CdLH + (LH 2 = H 3 N + CHRCONHCHR′COO −, as well as 1:2 complexes of the type CdL 2H 2. Mercury(II) also forms 1:1 complexes of the type HgLH +; there is, however, only a small tendency for the formation of HgL 2H 2. Possible structures are postulated according to the results of PMR studies on glycylglycine in water in the presence of CdCl 2. The PMR spectra suggest that complex species of the type CdLH 2+ 2 may exist; difficult to detect by the pH-titration method. The complex formation of cadmium(II) is compared with that of mercury(II).