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Related Concept Videos

Radical Autoxidation01:20

Radical Autoxidation

The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...

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A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke
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A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke

Published on: January 2, 2012

Non-phenolic radical-trapping antioxidants.

Mario C Foti1, Riccardo Amorati

  • 1Istituto di Chimica Biomolecolare del CNR, via P. Gaifami 18, Catania, Italy. mario.foti@icb.cnr.it

The Journal of Pharmacy and Pharmacology
|November 12, 2009
PubMed
Summary

Non-phenolic antioxidants are vital radical scavengers in biology, employing diverse mechanisms like H-atom donation and addition reactions to protect biomolecules from oxidative damage.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Physiology

Background:

  • Biological systems utilize a combination of small molecules and enzymes for antioxidant defense.
  • Uncontrolled radical production, particularly peroxyl radicals, drives autoxidation, damaging lipids, proteins, and nucleic acids.

Purpose of the Study:

  • To review the mechanisms, rates, and thermodynamics of radical-trapping by biologically relevant non-phenolic antioxidants.
  • To elucidate the diverse roles of non-phenolic compounds in cellular protection.

Main Methods:

  • Literature review of biochemical and kinetic studies on non-phenolic antioxidants.
  • Analysis of reaction mechanisms including H-atom donation, addition reactions, co-oxidation, and catalytic quenching.
  • Evaluation of kinetic data for antioxidant and pro-oxidant effects.

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

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Detection of Nitric Oxide and Superoxide Radical Anion by Electron Paramagnetic Resonance Spectroscopy from Cells using Spin Traps
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Detection of Nitric Oxide and Superoxide Radical Anion by Electron Paramagnetic Resonance Spectroscopy from Cells using Spin Traps

Published on: August 18, 2012

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A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke
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A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke

Published on: January 2, 2012

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

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Detection of Nitric Oxide and Superoxide Radical Anion by Electron Paramagnetic Resonance Spectroscopy from Cells using Spin Traps
13:21

Detection of Nitric Oxide and Superoxide Radical Anion by Electron Paramagnetic Resonance Spectroscopy from Cells using Spin Traps

Published on: August 18, 2012

Main Results:

  • Non-phenolic antioxidants are abundant and crucial radical scavengers.
  • Identified mechanisms include H-atom donation (ascorbic acid, uric acid), addition reactions (carotenoids), co-oxidation (gamma-terpinene), and catalytic quenching (nitroxides, FeCl(3)).
  • Kinetic data are presented to rationalize antioxidant efficacy and potential pro-oxidant activities.

Conclusions:

  • Non-phenolic antioxidants employ varied strategies to neutralize harmful radicals.
  • Understanding these mechanisms is key to comprehending biological redox balance.
  • The pro-oxidant potential of some antioxidants, like ascorbate, is also highlighted.