Radicals in ‘biologically relevant’ concentrations behave differently: Uncovering new radical reactions following the reaction of hydroxyl radicals with DMSO

Lerner, Ana Beatriz Coutinho; Kornweitz, Haya; Zilbermann, Israel; Yardeni, Guy; Saphier, Magal; Bar‐Ziv, Ronen; Meyerstein, Dan

doi:10.1016/j.freeradbiomed.2020.11.012

Cited by 11 publications

(8 citation statements)

References 42 publications

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“…In order to identify the nature of ROS formed in the Cu-catalyzed Fenton reaction, the following ROS probes were used: L-histidine (a scavenger of singlet oxygen) DMSO (a scavenger of hydroxyl radicals) and the SOD enzyme (a superoxide radical anion scavenger) [ 51 ].…”

Section: Resultsmentioning

confidence: 99%

“…In order to characterize the nature of radical species (ROS) formed in the course of Cu-flavonoid catalyzed Fenton reactions, the following radical scavengers were used: L-histidine (20 mM) as a scavenger for singlet oxygen ( 1 O 2 ), DMSO (6 µL) as a scavenger for hydroxyl radicals ( • OH), and the superoxide dismutase (SOD) enzyme (15U) as a scavenger of superoxide radical anions (O 2 •− ) [ 51 ].…”

Section: Methodsmentioning

confidence: 99%

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Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Šimunková

Barbieriková

Jomová

et al. 2021

IJMS

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Kaempferol is a flavonoid that occurs in tea and in many vegetables and fruits, including broccoli, cabbage, beans, grapes, apples, and strawberries. The efficacy of Kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways. Indeed, this matter has already been the focus of a number of published studies and reviews. The aim of the present study was to elucidate the antioxidant vs. prooxidant properties of flavonoids in the presence of the redox-active metal, copper (II) ion, by means of the Fenton reaction. The specific motivation of this work is that, since an increased level of Cu(II) ions is known to be associated with many disease states such as neurological conditions (Alzheimer’s disease) and cancer, any interaction between these ions and flavonoids might affect the outcome of therapeutic uses of the latter. The structure of the Cu-kaempferol complex in DMSO was investigated by means of low temperature EPR spectroscopy, which confirmed the existence of at least two distinct coordination environments around the copper (II) ion. UV vis-spectra of kaempferol and its Cu(II) complex in DMSO revealed an interaction between the 5-OH (A ring) group and the 4-CO (C ring) group of kaempferol with Cu(II) ions. An ABTS assay confirmed that kaempferol acted as an effective radical scavenger, and that this effect was further enhanced in the form of the Cu(II)-kaempferol complex. Quantitative EPR spin trapping experiments, using DMPO as the spin trap, confirmed suppression of the formation of a mixture of hydroxyl, superoxide, and methyl radicals, in a Fenton reaction system, upon coordination of kaempferol to the redox-active Cu(II) ions, by 80% with respect to the free Cu(II) ions. A viscometric study revealed a better DNA-intercalating ability of the Cu-kaempferol complex than for free kaempferol, essential for conferring anticancer activity of these substances. The results of the viscometric measurements were compared with those from a DNA damage study of Cu-kaempferol complexes in a Fenton reaction system, using gel electrophoresis. At low concentrations of kaempferol (Cu–kaempferol ratios of 1:1 and 1:2), a very weak protective effect on DNA was noted, whereas when kaempferol was present in excess, a significant DNA-protective effect was found. This can be explained if the weakly intercalated kaempferol molecules present at the surface of DNA provide protection against attack by ROS that originate from the Fenton reaction involving intercalated Cu(II)-kaempferol complexes. Following the application of ROS scavengers, L-histidine, DMSO, and SOD, gel electrophoresis confirmed the formation of singlet oxygen, hydroxyl radicals, and superoxide radical anions, respectively. We propose that the prooxidant properties of Cu-kaempferol complexes may provide anticancer activity of these substances. When present in excess, kaempferol displays antioxidant properties under Cu-Fenton conditions. This suggests that kaempferol might prove a suitable candidate for the prevention or treatment of oxidative stress related medical conditions that involve a disturbed metabolism of redox metals such as copper, for example, Menkes disease, and neurological disorders, including Alzheimer’s disease. For the potential use of kaempferol in clinical practice, it will be necessary to optimize the dose size and critical age of the patient so that this flavonoid may be beneficial as a preventive drug against cancer and neurological disorders.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Šimunková

Barbieriková

Jomová

et al. 2021

IJMS

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“…Ethane and methane are formed when the oxidizing species is a single-electron oxidizing agent, primary oxidizing radicals, such as SO 4 •– . 63 The relative yields of ethane and methane depend on the steady-state concentrations of methyl radicals. The results at pH 2.4 for the PMS system clearly show that ethane is almost the only product.…”

Section: Resultsmentioning

confidence: 99%

“…•− . 63 The relative yields of ethane and methane depend on the steady-state concentrations of methyl radicals. The results at pH 2.4 for the PMS system clearly show that ethane is almost the only product.…”

Section: Methodsmentioning

confidence: 99%

Reaction of Fe_aq^II with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of Fe_aq^IV and Carbonate Radical Anions

Vijay

Marks

Mizrahi³

et al. 2023

Environ. Sci. Technol.

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Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO5 –, PMS) or peroxydisulfate (S2O8 2–, PDS) with Fe(H2O)6 2+ (Feaq II). This paper presents results on the kinetics and mechanisms of reactions between Feaq II and PMS or PDS in the absence and presence of bicarbonate (HCO3 –) at different pH. In the absence of HCO3 –, Feaq IV, rather than the commonly assumed SO4 •–, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO2) and phenyl methyl sulfone (PMSO2), respectively, confirming the generation of Feaq IV by the Feaq II-PMS/PDS systems without HCO3 –. Significantly, in the presence of environmentally relevant concentrations of HCO3 –, a carbonate radical anion (CO3 •–) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of Feaq IV and CO3 •– in the Feaq II-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

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“…The bispidine-iron-oxido complexes are highly reactive and with various substrates produce CH 3 radicalsin published work, we have independently trapped, spectroscopically and by kinetic and product analysis characterized FeO species and CH 3 radicals (a more comprehensive summary of the published mechanistic work is given in the Supporting Information). ,,,, Depending on the molecules available in solution, the methyl radicals react to CH 4 , CH 3 OH, and other C 1 and C 2 products. ,, In other studies, it has been shown that CH 4 and C 2 H 6 are produced when irradiating dimethyl sulfoxide (DMSO, (CH 3 ) 2 SO) (by radiolysis or photochemically) in the presence of H 2 O 2 ; CH 3 OH and CH 2 O are formed when bicarbonate is present. , Moreover, recent studies indicate that carbonate radical ions may be of importance in aqueous Fe 2+ /O 2 systems (note, however, that the reactions studied in our experiments generally are at low pH, where the concentration of carbonate is neglectable)…”

Section: Introductionmentioning

confidence: 99%

Natural Abiotic Iron-Oxido-Mediated Formation of C₁ and C₂ Compounds from Environmentally Important Methyl-Substituted Substrates

Hädeler,

Velmurugan,

Lauer

et al. 2023

J. Am. Chem. Soc.

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Organic and inorganic volatile compounds containing one carbon atom (C 1 ), such as carbon dioxide, methane, methanol, formaldehyde, carbon monoxide, and chloromethane, are ubiquitous in the environment, are key components in global carbon cycling, play an important role in atmospheric physics and chemistry, e.g., as greenhouse gases, destroy stratospheric and tropospheric ozone, and control the atmospheric oxidation capacity. Up to now, most C 1 compounds in the environment were associated with complex metabolic and enzymatic pathways in organisms or to combustion processes of organic matter. We now present compelling evidence that many C 1 and C 2 compounds have a common origin in methyl groups of methyl-substituted substrates that are cleaved by the iron oxide-mediated formation of methyl radicals. This scenario is derived from experiments with a mechanistically well-studied bispidine-iron-oxido complex as oxidant and dimethyl sulfoxide as the environmentally relevant model substrate and is supported by computational modeling based on density functional theory and ab initio quantum-chemical studies. The exhaustive experimental model studies, also involving extensive isotope labeling, are complemented with the substitution of the bispidine model system by environmentally relevant iron oxides and, finally, a collection of soils with varying iron and organic matter contents. The combination of all data suggests that the iron oxidemediated formation of methyl radicals from methyl-substituted substrates is a common abiotic source for widespread C 1 and C 2 compounds in the environment.

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Radicals in ‘biologically relevant’ concentrations behave differently: Uncovering new radical reactions following the reaction of hydroxyl radicals with DMSO

Cited by 11 publications

References 42 publications

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Reaction of Fe_aq^II with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of Fe_aq^IV and Carbonate Radical Anions

Natural Abiotic Iron-Oxido-Mediated Formation of C₁ and C₂ Compounds from Environmentally Important Methyl-Substituted Substrates

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Radicals in ‘biologically relevant’ concentrations behave differently: Uncovering new radical reactions following the reaction of hydroxyl radicals with DMSO

Cited by 11 publications

References 42 publications

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions

Natural Abiotic Iron-Oxido-Mediated Formation of C1 and C2 Compounds from Environmentally Important Methyl-Substituted Substrates

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Product

Resources

About

Reaction of Fe_aq^II with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of Fe_aq^IV and Carbonate Radical Anions

Natural Abiotic Iron-Oxido-Mediated Formation of C₁ and C₂ Compounds from Environmentally Important Methyl-Substituted Substrates