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Radical Reactivity: Overview01:11

Radical Reactivity: Overview

2.1K
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
2.1K
Radical Autoxidation01:20

Radical Autoxidation

2.1K
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...
2.1K
Radical Formation: Overview01:03

Radical Formation: Overview

2.1K
A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
2.1K
Radical Formation: Addition00:47

Radical Formation: Addition

1.7K
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an...
1.7K
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

1.8K
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...
1.8K
Radical Formation: Elimination00:51

Radical Formation: Elimination

1.7K
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions...
1.7K

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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A Rigorously Simple Quantitative Model for Free Radical Behavior in Aerobic Biological Systems.

Leonhard Zastrow1, Jürgen Lademann2, Martina C Meinke1

  • 1Department of Dermatology, Venereology and Allergology, Center of Experimental and Applied Cutaneous Physiology, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.

Skin Pharmacology and Physiology
|November 17, 2024
PubMed
Summary

Life depends on enzymatic free radical chemistry, with reactive oxygen species (ROS) and lipid oxygen species (LOS) forming key components. A Multilevel Antioxidant Regulation, Repair and Protection System (MARRPS) maintains balance, with the Free Radical Threshold Value (FRTV) critical for health.

Keywords:
Evolutionary principleFree radical ground stateFree radical threshold valueFree radicalsLipid oxygen speciesReactive oxygen speciesUniversal quantitative free radical action model

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Area of Science:

  • Biochemistry and cellular metabolism
  • Free radical chemistry in biological systems
  • Oxidative stress and antioxidant defense mechanisms

Background:

  • Human life relies on oxygen respiration and enzymatic, free radical-dependent water chemistry at physiological pH and temperature.
  • Cellular metabolic processes involve reactive oxygen species (ROS) and lipid oxygen species (LOS) with varying half-lives.
  • Free radicals are fundamental components of biological processes.

Purpose of the Study:

  • To elucidate the fundamental chemical processes underlying aerobic life.
  • To define the regulatory mechanisms and thresholds governing free radical levels in biological systems.
  • To establish a universal constant for life processes based on free radical dynamics.

Main Methods:

  • Analysis of mitochondrial oxygen conversion into ROS and LOS.
  • Investigation of endogenous and exogenous radical generation triggers.
  • Characterization of the Multilevel Antioxidant Regulation, Repair and Protection System (MARRPS).
  • Definition and quantification of the Free Radical Ground State (FRGS), Free Radical Threshold Value (FRTV), and Free Radical Pathological Conditions (FRPC).

Main Results:

  • Mitochondria are the primary source of ROS and LOS.
  • External factors like radiation also contribute to radical formation, producing similar mixtures.
  • MARRPS maintains steady states of radical mixtures.
  • The Free Radical Threshold Value (FRTV) is approximately 3.58 × 10^12 radicals/mg.
  • Exceeding FRTV with LOS > ROS triggers uncontrolled radical chain reactions.

Conclusions:

  • The Free Radical Threshold Value (FRTV) is a universal body constant essential for all regular life processes.
  • The described model of free radical regulation applies universally to all aerobic life.
  • Failure of MARRPS leads to pathological conditions and diseases.