POTENTIOMETRIC STUDIES OF BINARY AND TERNARY COMPLEXES OF ZN(II) WITHTRIETHYLENETETRAMINE AS PRIMARY LIGAND AND SELECTED AMINO-ACIDS AND DNA UNITS AS SECONDARY LIGANDS

The acid-base equilibria of triethylenetetramine (Trien) and the forma tion equilibria of binary and ternary complexes of Zn(II) with Trien a s primary ligand and some selected amino acids and DNA units as second ary ligands have been investigated. The results showed the formation o f a 1:1 Zn(Trien)(2+) complex. At higher pH, the Zn(Trien)(2+) complex is hydrolysed to give Zn(Trien) (OH)(+) and Zn(Trien)(OH)(2) complexe s. The fraction of the mono-hydroxo species attains a maximum of 81.3% at pH 10. The stability constants K(Zn(Trien)A)(Zn(Trien)) for the te rnary complexes were determined. Histidine coordinates in a histamine- like way. Lysine and ornithine ligate by the two amino groups. Serine and methionine are bound in a glycine-like mode. However, penicillamin e, cysteine and glutathione ligate partly like mercaptoethylamine and partly like mercaptopropionic acid. In the case of DNA complexes, inos ine is bound through the N-1 atom. However, uracil, uridine, thymine a nd thymidine ligate through the N-1 atom. The relative stabilities of ternary complexes are compared with those of the corresponding binary complexes in term of Delta log K values. The concentration distributio n diagrams of the complexes are evaluated.