Potentiometric Studies of Binary and Ternary Complexes Involving Cadmium(II) and Nitrilo-Tris(Methyl Phosphonic Acid) with Amino Acids, peptides and DNA Constituents

The complexing properties of nitrilo-tris(methylphosphonic acid) (NTP) with cadmium(II) were investigated pH-metrically at 25 °C and at ionic strength of 0.1 mol dm^-3 (NaNO₃). Stoichiometry and stability constants for the complexes formed are reported. Cadmium (II) forms Cd(NTP)^4- and the corresponding hydroxy complexes. The ternary complexes are formed in a stepwise mechanism whereby NTP binds to cadmium(II), followed by coordination of amino acids, peptides or DNA. The concentration distribution of the various complex species has been evaluated.