Publication in Journal of Inorganic Biochemistry

Copper(II) tetrapyrazole-based complex as a new peroxidase-mimetic compound

Authors: Marek Šebela, Giorgio Zoppellaro, Zdeněk Trávníček

Full-text: https://doi.org/10.1016/j.jinorgbio.2025.112911

A copper(II) tetrapyrazole-based complex of the composition of [Cu(tpyr)(H₂O)(ONO₂)]NO₃ (1), where tpyr represents a tetradentate N-donor ligand formed by the condensation of 1H-pyrazole-5-carbaldehyde in NaOH/ MeOH medium, has been prepared and characterized by elemental analysis, infrared spectroscopy, ultraviolet- visible spectroscopy, mass spectrometry, electron paramagnetic resonance and single-crystal X-ray diffraction. Spectrophotometric measurements demonstrated a remarkable peroxidase activity of the complex, which utilized hydrogen peroxide for the oxidation of phenolic compounds such as guaiacol or 3,5-dichloro-2-hydroxybenzene sulfonic acid.  The optimum conditions for this  reaction  were  found  at  pH  8  in  ammonium  bicarbonate  buffer, although  the  activity  was  low  but  still  detectable  at  pH  5–6  in  ammonium  acetate.  As a peroxidase mimic, the complex exhibited enzyme-like Michaelis-Menten kinetics, showing a hyperbolic dependence of the reaction rate on hydrogen peroxide concentration. The determined K_m and k_cat values were 651 μmol⋅l-1  and 6.7 × 10-4  s-1, respectively, compared  to 41  μmol⋅l-1  and 73 s-1  for  horseradish peroxidase.  EPR spectroscopy  of  the  reaction mixture revealed no change in the copper (II) oxidation state during catalysis, suggesting that the oxidation of guaiacol may occur simultaneously with the reduction of hydrogen peroxide to water at the copper centre.