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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: 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...
Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals01:17

Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals

Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
Radical Formation: Elimination00:51

Radical Formation: Elimination

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 with respect to...
Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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 molecule. These three...
Overview of DNA Repair02:25

Overview of DNA Repair

In order to be passed through generations, genomic DNA must be undamaged and error-free. However, every day, DNA in a cell undergoes several thousand to a million damaging events by natural causes and external factors. Ionizing radiation such as UV rays, free radicals produced during cellular respiration, and hydrolytic damage from metabolic reactions can alter the structure of DNA. Damages caused include single-base alteration, base dimerization, chain breaks, and cross-linkage.
Chemically...

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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
14:22

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

Published on: April 15, 2013

Phenyl radical-induced damage to dipeptides.

Sen Li1, Mingkun Fu, Steven C Habicht

  • 1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.

The Journal of Organic Chemistry
|September 24, 2009
PubMed
Summary

Phenyl radicals cause gas-phase damage to dipeptides, with susceptibility varying by peptide site and phenyl radical electrophilicity. This study details the specific attack order and sequence influence on damage patterns.

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Area of Science:

  • Chemical dynamics
  • Mass spectrometry
  • Biomolecular analysis

Background:

  • Dipeptides are fundamental building blocks of proteins.
  • Understanding molecular damage mechanisms is crucial for biochemistry and medicine.
  • Phenyl radicals are reactive species that can interact with biological molecules.

Purpose of the Study:

  • To investigate the gas-phase damage induced by phenyl radicals on dipeptides.
  • To determine the relative susceptibility of different sites within dipeptides to phenyl radical attack.
  • To explore the influence of phenyl radical electrophilicity and amino acid sequence on reaction selectivity.

Main Methods:

  • Utilizing laser-induced acoustic desorption (LIAD) for sample introduction.
  • Employing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) for high-resolution mass analysis.
  • Analyzing product branching ratios from reactions between phenyl radicals and 17 different dipeptides.

Main Results:

  • Established an order of susceptibility for dipeptide sites to phenyl radical attack, with heteroaromatic side chains and sulfur-containing groups being most vulnerable.
  • Observed that the amino acid sequence significantly influences the selectivity of these radical-induced reactions.
  • Correlated increased phenyl radical electrophilicity with enhanced dipeptide damage.

Conclusions:

  • The gas-phase reaction of phenyl radicals with dipeptides is site-selective, depending on the chemical environment within the dipeptide.
  • Amino acid sequence and phenyl radical properties are key determinants of damage patterns.
  • This research provides insights into radical-induced biomolecular degradation pathways.