The FeII(citrate) Fenton reaction under physiological conditions

Erzsébet Illés; Shanti G Patra; Vered Marks; Amir Mizrahi; Dan Meyerstein

doi:10.1016/j.jinorgbio.2020.111018

The Fe^II(citrate) Fenton reaction under physiological conditions

J Inorg Biochem. 2020 May:206:111018. doi: 10.1016/j.jinorgbio.2020.111018. Epub 2020 Feb 4.

Authors

Erzsébet Illés¹, Shanti G Patra¹, Vered Marks¹, Amir Mizrahi², Dan Meyerstein³

Affiliations

¹ Department of Chemical Sciences, The Center for Radical Reactions, the Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications, Ariel University, Ariel 40700, Israel.
² Department of Chemistry, Nuclear Research Centre Negev, Beer-Sheva 84190, Israel.
³ Department of Chemical Sciences, The Center for Radical Reactions, the Schlesinger Family Center for Compact Accelerators, Radiation Sources and Applications, Ariel University, Ariel 40700, Israel; Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel. Electronic address: danm@ariel.ac.il.

PMID: 32050088
DOI: 10.1016/j.jinorgbio.2020.111018

Abstract

The Fenton reaction of Fe^II(citrate) in the presence and absence of bicarbonate (HCO₃^-) is studied. It is found that the rate constant of the Fenton reaction (k_obs) increases with increasing [citrate]. k_obs also increase with increasing [HCO₃^-]; this effect is most significant at biological citrate concentrations. Methane and ethane gases are formed from (CH₃)₂SO when the Fenton reaction is carried out in the presence of large [citrate] due to the reaction of the citrate radical, (^-₂OC)CH₂C(OH)(CO₂^-)CH(CO₂^-)/(^-₂OC)CH₂C(O)(CO₂^-)CH₂(CO₂^-) with (CH₃)₂SO. In the absence of citrate (CH₃)₂SO₂ is the main product of the Fenton reaction. However, in the presence of 0.10 mM citrate, no (CH₃)₂SO₂ is formed, some (CH₃)SOOH is formed, along with a low yield of beta-ketoglutaric acid. Formation of (CH₃)SOOH and beta-ketoglutaric acid are due to the citrate radical and Fe^IV(citrate). In the presence of bicarbonate formation of abundant beta-ketoglutaric acid confirms the formation of carbonate radical anion (CO₃^-). Thus, bicarbonate affects the mechanism and kinetics of the reaction dramatically. Hydroxyl radicals (OH) are not formed in the presence of bicarbonate and probably also not in its absence. These results point out that hydroxyl radicals, formed by the Fenton reaction, do not initiate oxidative stress in biological systems.

Keywords: Bicarbonate; Biological oxidative stress; Carbonate anion radical; Fe(II)(citrate); Fe(IV) = O; Fenton reaction.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bicarbonates / chemistry
Citrates / chemistry
Citric Acid / chemistry*
Ferrous Compounds / chemistry*
Hydrogen Peroxide / chemistry
Hydroxyl Radical / chemistry
Iron / chemistry
Ketoglutaric Acids / chemistry
Kinetics
Magnetic Resonance Spectroscopy
Oxidation-Reduction
Oxidative Stress

Substances

Bicarbonates
Citrates
Fenton's reagent
Ferrous Compounds
Ketoglutaric Acids
Citric Acid
Hydroxyl Radical
ferrous citrate
Hydrogen Peroxide
Iron