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Hydroxyl radical generation by a light-dependent Fenton reaction
J Van der Zee1, B B Krootjes, C F Chignell
1Department of Medical Biochemistry, Sylvius Laboratoria, Leiden, The Netherlands.
Free Radical Biology & Medicine
|February 1, 1993
Summary
Illuminating iron (Fe3+) with specific light wavelengths in the presence of iron chelators reduces Fe3+ to Fe2+. This process, dependent on light and chelators, also generates hydroxyl radicals when hydrogen peroxide is present.
Area of Science:
- Photochemistry
- Inorganic Chemistry
- Analytical Chemistry
Background:
- Iron (Fe3+) is crucial in biological systems but its redox state influences its reactivity.
- Iron chelators are used to control iron availability and reactivity.
- Understanding light-induced iron redox changes is important for various applications.
Purpose of the Study:
- To investigate the photoreduction of Fe3+ by common iron chelators.
- To explore the generation of reactive oxygen species during this process.
- To elucidate the mechanism of light-induced electron transfer from chelators to iron.
Main Methods:
- UV-Vis spectroscopy to monitor Fe2+ formation using bathophenanthroline disulfonic acid.
- Exposure of Fe3+-chelator complexes to specific light wavelengths (250-450 nm).
- Electron spin resonance (ESR) spectroscopy to detect hydroxyl radicals using DMPO spin trapping.
Main Results:
- Fe3+ was reduced to Fe2+ in the presence of EDTA, EGTA, DTPA, or citrate upon illumination.
- Fe2+ formation correlated with the absorption spectra of the iron-chelator complexes.
- Hydroxyl radicals were generated in the presence of H2O2, with their formation inhibited by scavengers like catalase and mannitol.
Conclusions:
- Light absorption by iron-chelator complexes induces electron transfer from the chelator to Fe3+, causing photoreduction.
- Chelator molecules are susceptible to degradation by oxygen during illumination.
- The photoreaction can generate hydroxyl radicals, indicating potential oxidative stress mechanisms.