Binary and ternary complexes of cadmium(II) involving ethylenediamine-N ',N '-diacetic acid and amino acids or peptides

The present work examines the acid-base equilibria of Ethylenediamine-N,N - diacetic acid (EDDA) and the formation equilibria of binary and ternary com plexes of cadmium (II) with EDDA and amino acids or peptides. Cd(II) is fou nd to form a 1:1 complex with EDDA. The ternary complexes are formed in a s tepwise mechanism, whereby the EDDA binds to Cd(II), followed by ligation o f the amino acid or peptide. The amino acid, lysine, forms protonated and d eprotonated ternary complexes. The stability constants of the ternary compl exes have been quantified in relation to the corresponding binary complexes . The concentration distribution of the various complex species has been ev aluated.