METAL COMPLEXES OF BIOLOGICALLY OCCURRING AMINOPHOSPHONIC ACIDS

Abstract

The interaction of 1-aminoethylphosphonic acid, 2-aminoethylphosphonic acid and 2-amino-3-phosphomopropionic acid with Cu(II), Ni(II), Zn(II), Co(II), Mn(II), Mg(II) and Ca(II) has been investigated potentiometrically. Stability constants for the protonated and normal 1:1 and 1:2 metal-ligand complexes are reported at 25.0° and μ = 0.2(KNO₃). The transition and alkaline earth metal ions show preferential binding to different sites on the ligands, the former interacting with carboxylate, phosphonate, and amine groups, while the latter show predominant interaction with the phosphonate moiety. The present study shows that compounds containing C–P bonds form more stable metal complexes than the corresponding compounds containing C–O–P bonds. This is partly due to the higher basicity of the phosphonate ligands and partly due to more favourable chelate ring formation. Structures are suggested for the various complexes.