Diclofenac on boron-doped diamond electrode: from electroanalytical determination to prediction of the electrooxidation mechanism with HPLC-ESI/HRMS and computational simulations

Comparison of the degradation mechanisms of diclofenac in the presence of iron octacarboxyphthalocyanine and myeloperoxidase

The degradation process of diclofenac (DCF) by hematoprotein myeloperoxidase (MPO) and iron octacarboxyphthalocyanine (FePcOC) in the presence of hydrogen peroxide was compared. During the oxidation of diclofenac, in the presence of iron octacarboxyphthalocyanine (FePcOC) and hydroxyl radicals (HO^•) (from H₂O₂), an intermediate product (dimer with an m/z value of 587) with the characteristic yellow colouration and an intense band at λ_max = 451 nm is formed. Iron octacarboxyphthalocyanine oxidises in the presence of hydrogen peroxide, following the first-order reaction kinetics for FePcOC and H₂O₂. The concentration of diclofenac does not affect the initial reaction rate. For comparison, the oxidation of DCF in the presence of myeloperoxidase and hydrogen peroxide also provided yellow-coloured solutions with an absorption maximum at λ_max = 451 nm. However, LC-MS/MS analysis indicates the presence of at least seven main products of the diclofenac oxidation process in the final reaction mixture, including two dimers with the ion mass [M-H]^¯ = 587.01. The mechanism of the diclofenac degradation with hematoprotein myeloperoxidase is more complex than with iron octacarboxyphthalocyanine. Furthermore, the biological activity of diclofenac and DCF dimer (iron octacarboxyphthalocyanine and hydroxyl radicals degradation product) was tested. In this case, the long-term assayed in vitro against E. coli, colorectal HCT116 and melanoma Me45 cancer cells were performed.

Oxidation of diclofenac in the presence of iron(II) octacarboxyphthalocyanine

This paper presents the results of the research on the influence of catalytic activity of iron(II) octacarboxyphthalocyanines (FePcOC) on the transformation of diclofenac (DCF) which is the most popular anti-inflammatory analgesic. Diclofenac poses a serious threat to the natural environment. The paper demonstrates that diclofenac, in the presence a monomeric form of iron octacarboxyphthalocyanine and hydroxyl radicals (HO^•) (from H₂O₂), undergoes a transformation into diclofenac-2,5-iminoquinone (DCF-2,5-IQ), causing distinct changes in the UV-Vis absorption spectrum. In the presence of iron octacarboxyphthalocyanine and H₂O₂, the previously colourless diclofenac solution becomes intense orange. As a result, a new band at approx. 450 nm appears in the absorption spectrum. HPLC analysis has shown that the concentration of diclofenac decreases with time. TD-DFT calculations using the CAM-B3LYP/6-31+G (d, p) method have been conducted to confirm experimental data concerning the formation of a new band at λ_max = 450 nm.

Electrochemical measurements and theoretical studies for understanding the behavior of catechol, resorcinol and hydroquinone on the boron doped diamond surface

Using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)) with a boron-doped diamond (BDD) electrode it was possible to study the behavior of hydroquinone (HQ), catechol (CT) and resorcinol (RS), in aqueous solutions as well as to associate the electrochemical profiles with computational simulations. It led to understanding the factors that influence the direct electrooxidation of HQ, CT and RS on the BDD surface. Theoretical calculations demonstrated that the compounds with lower HOMO energy and high ionization potential (IP) are more stable, showing a higher E_pa, denoting that HOMO energies and IP are related to the difficulty of oxidizing (losing an electron) a specific compound. Analyzing the electro-oxidation reactions of HQ, CT and RS by using computational calculations, it was possible to verify the reversibility behavior, direct oxidation pathway and the possible intermediates formed during electron-transfer. The results clearly demonstrated that the reversibility was attained for HQ and CT, while this behavior is not feasible, thermodynamically speaking, for RS and this was confirmed by DFT calculations. For direct oxidation mechanisms, HQ and CT are quickly oxidized, but RS produces stable intermediates. These experimental and theoretical results also explain the behavior when the compounds were analyzed by electroanalytical techniques, suggesting that the interactions by direct electron-transfer determine the stability of response (sensitivity) as well as the limit of detection. The results are described and discussed in light of the existing literature.

Using electrochemical techniques it was possible to study the behavior of hydroquinone, catechol and resorcinol, at boron doped diamond surface in aqueous solutions as well as to associate the electrochemical profiles with computational simulations.