Complex formation between transition metals and DL-aspartic acid-β-hydroxamic acid (N-hydroxyasparagine)

Abstract

Formation constants and assumptions concerning the bonding mode are reported for the complexes present in aqueous solution in the cobalt(II)–, nickel(II)–, copper(II)–, zinc(II)–, and iron(III)–DL-aspartic acid-β-hydroxamic acid (N-hydroxyasparagine, hasn) systems. The amino nitrogen, the hydroxamate nitrogen, and the carboxylate oxygen are the main co-ordinating donor atoms in the cobalt(II)– and nickel(II)–hasn complexes. The hydroxamate oxygens may also take part in co-ordination in the zinc(II)–hasn system. Very stable 1:1 and 1:2 binary complexes are formed in the iron(III)–hasn system, with tridentate co-ordination (hydroxamate and carboxylate oxygens) of the ligand. Mixed hydroxo complexes are proposed at pH > 5. A polymeric species, with composition [Cu₄A₄H_–2]^2–, is the most stable complex in the copper(II)–hasn system.