Synthesis of new dinuclear and mononuclear peroxovanadium(V) complexes containing biogenic co-ligands: a comparative study of some of their properties

Abstract

Dinuclear peroxo complexes of vanadium, [V 2O 2(O 2) 3(asn) 3] · H 2O ( 1) and [V 2O 2(O 2) 3(gln) 3] · H 2O ( 2) have been synthesized from the reaction of V 2O 5 with H 2O 2 and the respective amino acid ligand at pH ca. 2. Similar reactions conducted at pH ca. 5 afforded the monomeric complexes, Na[VO(O 2) 2(asn)] · H 2O ( 3) and Na[VO(O 2) 2(gln)] · H 2O ( 4). The compounds were characterized by elemental analysis and spectral studies. In complexes 1 and 2, the two V(V) centres are bridged by a peroxo group and an amino acid ligand occurring as a zwitterion. The monomeric complexes 3 and 4 contain peroxo groups bonded in a side-on fashion and an amino acid co-ligand binding the V(V) centre through O (carboxylate) atoms. The complexes 1 and 2 rapidly degraded in solution with release of O 2 and formation of diperoxovanadate and decavanadate as shown by 51V NMR spectra whereas complexes 3 and 4 remained stable in solution for over 24 h. Extent and rate of oxygen released from the two types of complexes under the effect of catalase action further evidenced the differences in their V:O 2 2− content and mode of peroxide binding in these species. The μ-peroxovanadate complexes 1 and 2 instantaneously oxidized bromide to a bromination competent intermediate in phosphate buffer at physiological pH, and also efficiently mediated bromination of organic substrates in aqueous-organic media. Complexes 3 and 4 were inactive for bromination under analogous conditions. These findings make the dinuclear complexes 1 and 2 possible candidates of mimic in the action of vanadium in bromoperoxidase.