Carbonate-radical-anions, and not hydroxyl radicals, are the products of the Fenton reaction in neutral solutions containing bicarbonate - ICS84 The 84th Annual Meeting of the Israel Chemical Society

Erzsébet Illés ^1,2 Amir Mizrahi ³ Vered Marks ¹ Dan Meyerstein ^1,4

¹Department of Chemical Sciences, Ariel University, Ariel, Israel
²Center for Energy Research, Radiation Chemistry Department, Institute for Energy Security and Environmental Safety, Hungarian Academy of Sciences, Budapest, Hungary
³Department of Chemistry, Nuclear Research Center Negev, Beer-Sheva, Israel
⁴Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel

The Fenton reaction, Fe(H₂O)₆²⁺ + H₂O₂ → Oxidizing product, is of major importance in biology as the major source of oxidative stress, and in advanced oxidation processes. It is commonly assumed that OH· is the product of the Fenton reaction. The results presented herein point out that OH· is indeed the oxidizing product in acidic solutions for [Fe(H₂O)₆²⁺] > [H₂O₂]; Fe^IV_aq is the active oxidizing product in neutral solutions; in slightly acidic solutions for [H₂O₂] > [Fe(H₂O)₆²⁺] a mixture of OH· and Fe^IV_aq is formed. Another open question was what is the product of the Fenton reaction in the presence of HCO₃^-in the solution. A recent DFT calculation suggests that Fe^IV(CO₃)_aq decomposes into Fe^III_aq + CO₃·^-.^[¹^] This might suggest that in biological systems, in which HCO₃^- is always present e.g. in the human body the bicarbonate concentration is approximately 40 mM,^[²^] CO₃·^-might be formed mainly via the Fenton reaction and not only via the reaction of peroxo-nitrite with CO₂ ^[²^] and thus be of major importance in oxidative stress.

Therefore one of the goals of this work was to prove that CO₃·^-, and not OH·, is the active oxidizing product in neutral solutions containing HCO₃^- even at low concentrations, i.e. under physiological conditions. The implications of our understanding of the origins of oxidative stress and of catalytic oxidations in advanced oxidation processes were studied.

The products of the Fenton reaction in different conditions were analyzed/determined by ¹H NMR and GC with FID and TCD detectors. The UV-Vis kinetic spectrophotometric measurements were performed using conventional spectrophotometer and a stopped flow instrument.

[1] H. Kornweitz, A. Burg, D. Meyerstein, J. Phys. Chem. A 119 (2015) 4200-4206.

[2] D.B. Medinas, G. Cerchiaro, D.F. Trindade, O. Augusto, IUBNB Life 59 (2007) 255-262.