Mimicking vanadium haloperoxidases: vanadium(iii)–carboxylic acid complexes and their application in H2O2 detection

Abstract

Vanadium(III) complexes [V(2,6-pdc)₂(H₂O)₂]·2H₂O (1) and V(2,6-pdc)(htba)(H₂O)₂ (2), (2,6-pdc = 2,6-pyridinedicarboxylic acid, htba = 2-acetoxy-4-trifluoromethylbenzoic acid) have been synthesized by the reaction of V₂(SO₄)₃ with 2,6-pdc (for 1) or 2,6-pdc and htba (for 2) under hydrothermal conditions at 120 °C for 36 hours. Because the vanadium(III) was easily oxidized into higher oxidation states, we included the reducing agent vitamin C to protect the vanadium(III) center. The complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, and single-crystal X-ray diffraction. Structural analysis revealed that the central metal V atoms in the complexes 1 and 2 were seven-coordinate, forming pentagonal bipyramid geometries. The complexes catalyzed the bromination of the organic substrate phenol red in the presence of H₂O₂, bromide and buffer. Compared with vanadium complexes having other oxidation states, the vanadium(III) complexes had better catalytic activity (the maximum reaction rate constant was 2.424 × 10²k(mol L⁻¹)⁻² s⁻¹). The mimicking vanadium haloperoxidases also overcame some serious disadvantages of natural enzymes. Therefore, the reaction system described herein can be considered as an effective model for hydrogen peroxide determination.