Metal complexes of N-hydroxy-imino-di-α-propionic acid and related ligands

Abstract

N-hydroxy-imino-di-α-propionic acid, the ligand present in the natural oxovanadium(IV) complex ‘amavadin’ which occurs in the toadstool Amanita muscaria, has been synthesised, as well as two related ligands—N-hydroxy-iminodiacetic acid and imino-di-α-propionic acid—useful for comparison purposes. The formation of complexes of these ligands with VO 2+, Ni 2+ has been studied and their stability constants have been determined. The two N-hydroxy-substituted ligands, of low basicity, form ML 2 complexes with VO 2+, unlike the more basic derivatives of iminodiacetic acid. Since substitution of ligands bonded to the apical site trans to the oxo ligand is very fast and the formation of ML 2 complexes of VO 2+ exposes that apical site to the reaction media, this may be the reason why oxovanadium(IV) and the unusual derivative of iminodiacetic acid present in ‘amavadin’ were selected for the biological role that this complex plays in the toadstool.