Related Experiment Video
Updated: Aug 7, 2026
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
Chemically induced dynamic electron polarization generated through the interaction between singlet molecular oxygen
Claudia G Martínez1, Steffen Jockusch, Marco Ruzzi
1Department of Chemistry, Columbia University, New York, New York 10027, USA.
The Journal of Physical Chemistry. A
|July 13, 2006
Summary
Chemically induced dynamic electron polarization (CIDEP) using nitroxide radicals quantifies singlet oxygen lifetime. Deuterium isotope effects confirm singlet oxygen
Area of Science:
- Physical Chemistry
- Chemical Kinetics
- Spectroscopy
Background:
- Singlet oxygen is a reactive oxygen species implicated in various chemical and biological processes.
- Nitroxide radicals, such as TEMPO derivatives, are widely used spin probes.
- Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful tool for studying radical species.
Purpose of the Study:
- To investigate the use of absorptive chemically induced dynamic electron polarization (CIDEP) for detecting singlet oxygen.
- To correlate nitroxide spin polarization decay times with singlet oxygen lifetimes.
- To determine the relative spin polarization efficiencies of different TEMPO derivatives.
Main Methods:
- Generation of absorptive CIDEP via singlet oxygen quenching by TEMPO derivatives.
- Time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy to measure nitroxide spin polarization decay.
- Singlet oxygen phosphorescence spectroscopy to measure singlet oxygen lifetime.
- Deuterium isotope labeling and isotope labeling of nitroxides (15N, 14N) for mechanistic studies.
Main Results:
- A correlation was observed between nitroxide spin polarization decay time and singlet oxygen lifetime.
- A deuterium isotope effect on spin polarization decay time provided evidence for singlet oxygen involvement.
- Relative spin polarization efficiencies of TEMPO derivatives were determined: 4-hydroxy-TEMPO > TEMPO > 4-oxo-TEMPO.
- Quenching rate constants showed an inverse trend: 4-hydroxy-TEMPO < TEMPO < 4-oxo-TEMPO.
Conclusions:
- Absorptive CIDEP is a viable method for probing singlet oxygen.
- The spin polarization decay time of nitroxides serves as a reliable indicator of singlet oxygen lifetime.
- The efficiency of spin polarization by singlet oxygen varies among different TEMPO derivatives.
Related Concept Videos
01:20Radical 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...
01:11Radical 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...
01:03Radical Formation: Overview
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 latter, also known...
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 latter, also known...
00:54Radical Formation: Homolysis
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
01:16Radical 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...
01:02Radical 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...