Pure and Applied Chemistry

Abstract: The active center of vanadate-dependent peroxidases (VPOs) is represented by vanadate covalently attached to a histidine, with vanadium in a trigonal-bipyramidal environment. Protein phosphatases and kinases are inhibited by the phosphate analog vanadate [V^VO₂(OH)₂^- and V^IVO(OH)₃^-], which can be related to the coordination of vanadium to histidine or a hydroxide function as provided by tyrosinate or serinate. The vanadium centers in these proteins have been modeled by employing chiral ONO ligands. The penta-coordinated chiral complexes [VO(OMe)(L¹)] (H₂L¹ = substituted diethanolamine) are distorted trigonal-bipyramidal with the methoxy group and the amine-N in the axial positions. These structural models of VPO also mimic the sulfide-oxidation activity of the peroxidases. The complexes [VO(H₂O)L³] (H₂L³ = Schiff-base ligands based on salicylaldehyde derivatives (o-vanillin; 2-hydroxy-naphthylaldehyde) and L- or D,L-tyrosine, or D,L-serine are tetragonal-pyramidal; the OH functions of the amino acid moieties are not directly coordinated to vanadium; they are involved, however, in complex hydrogen-bonding networks. The oxo/peroxo anion [VO(O₂)(L²)₂]^3- (H₂L² = 2,5-dipicolinic acid) contains a slightly asymmetrically bonded O₂^2-, featuring structural characteristics of the peroxo/hydroperoxo intermediates of the peroxidases. XD structure results are reported for the following complexes: R,S- and R,R-[VO(OMe)(L¹)], K₃[VO(O₂)(L²)₂].4.5H₂O, the Tyr derivatives L-[VO(H₂O)L³].MeOH and D,L-[VO(H₂O)L³].H₂O, and the Ser derivative D,L-[VO(H₂O)L³].2H₂O.