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Updated: Feb 12, 2026

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
Published on: April 15, 2013
The photoreactive free radical in eumelanin
Albertus B Mostert1, Shermiyah B Rienecker2,3, Christopher Noble2
1Department of Chemistry, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK.
Abstract:
Melanin is the primary photoprotecting pigment in humans as well as being implicated in the development of deadly melanoma. The material also conducts electricity and has thus become a bioelectronic model for proton-to-electron transduction. Central to these phenomena are its spin properties-notably two linked species derived from carbon-centered and semiquinone radicals. Using a novel in situ photoinduced electron paramagnetic resonance technique with simultaneous electrical measurements, we have elucidated for the first time the distinct photoreactivity of the two different radical species. We find that the production of the semiquinone is light- and water-driven, explaining the electrical properties and revealing biologically relevant photoreactivity.
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