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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.
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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...
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Free Radical Threshold Value: A New Universal Body Constant.

Leonhard Zastrow1, Olivier Doucet, Louis Ferrero

  • 1Centre of Experimental and Applied Cutaneous Physiology (CCP), Department of Dermatology, Venereology and Allergology, Charité - Universitätsmedizin Berlin, Berlin, Germany.

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Summary

Researchers discovered a universal free radical threshold value (FRTV) that distinguishes beneficial from harmful free radical effects. This threshold, approximately 3.5 × 10^12 rad/mg ROS/LOS, was confirmed in human skin and porcine liver tissues.

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Area of Science:

  • Biochemistry
  • Free radical biology
  • Oxidative stress research

Background:

  • Reactive oxygen species (ROS) and lipid oxygen species (LOS) form the body's free radical ground state.
  • The balance between ROS and LOS influences physiological and pathological processes.
  • Understanding free radical effects requires defining thresholds for their impact.

Purpose of the Study:

  • To present evidence for a universal free radical threshold value (FRTV).
  • To define the borderline between advantageous and adverse free radical effects.
  • To experimentally verify the FRTV in human skin and porcine liver.

Main Methods:

  • Quantitative Electron Spin Resonance (ESR) x-band spectroscopy.
  • In vitro experiments on ex vivo human skin and fresh porcine liver.
  • Irradiation of tissues with UV + VIS, UVB + UVA, and VIS light.

Main Results:

  • A universal FRTV of approximately 3.5 × 10^12 rad/mg ROS/LOS was calculated and experimentally verified.
  • The FRTV was confirmed in both human skin and porcine liver tissues.
  • A ROS > LOS ratio was found to be beneficial, while LOS > ROS was deleterious, consistent across tissues relative to the FRTV.

Conclusions:

  • The FRTV represents a critical biological constant.
  • This threshold differentiates beneficial from harmful free radical activity.
  • The findings suggest a new universal body constant for free radical management.