Generation, Spectroscopic Characterization by EPR, and Decay of a Pyranine-Derived Radical

✍ Scribed by Carolina Aliaga; Andrea Arenas; Alexis Aspée; Camilo López-Alarcón; Eduardo A. Lissi

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: German
• Weight: 336 KB
• Volume: 90
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200790208

✦ Synopsis

Abstract

The pyraninoxyl radical is readily formed from the MnO~2~‐promoted oxidation of pyranine. The free radical can be formed in high concentrations (mM), and presents a characteristic EPR spectrum that indicates a high spin‐density delocalization. It is relatively stable under nitrogen (half‐life ca. 50 min) but readily decays in presence of O~2~. In spite of its high stability, the radical readily reacts with antioxidants (phenols and ascorbic acid) with a partial recovery of the parent pyranine. High concentrations of the pyraninoxyl radical (ca. 9 μM) are present when pyranine is exposed to a free radical source (10 mM 2,2′‐azobis[2‐amidinopropane], 37°). The fact that these radicals readily react with antioxidants (ascorbic acid and caffeic acid) supports the proposal that protection by antioxidants of peroxyl radical‐promoted pyranine bleaching is mainly due to the occurrence of a repair mechanism.