Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates. (23rd August 2019)

• Record Type: Journal Article
• Authors: Zelenka, Jan; Cibulka, Radek; Roithová, Jana
• Is Part Of: Angewandte Chemie. Volume 131:Number 43(2019)
• Page Start: 15558
• Page End: 15566
• Publication Date: 2019-08-23
• Subjects: Flavin -- Ionenspektroskopie -- Massenspektrometrie -- Peroxy-Intermediate -- Photooxidation; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201906293
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Flavin‐based catalysts are photoactive in the visible range which makes them useful in biology and chemistry. Herein, we present electrospray‐ionization mass‐spectrometry detection of short‐lived intermediates in photooxidation of toluene catalysed by flavinium ions (Fl + ). Previous studies have shown that photoexcited flavins react with aromates by proton‐coupled electron transfer (PCET) on the microsecond time scale. For Fl +, PCET leads to FlH .+ with the H‐atom bound to the N5 position. We show that the reaction continues by coupling between FlH .+ and hydroperoxy or benzylperoxy radicals at the C4a position of FlH .+ . These results demonstrate that the N5‐blocking effect reported for alkylated flavins is also active after PCET in these photocatalytic reactions. Structures of all intermediates were fully characterised by isotopic labelling and by photodissociation spectroscopy. These tools provide a new way to study reaction intermediates in the sub‐second time range. Abstract : Ein Wechsel des aktiven Zentrums erfolgte nach N5‐Wasserstoffblockierung durch einen protonengekoppelten Elektronentransfer. Kurzlebige Peroxy‐Flavinium‐Intermediate wurden mittels Massenspektrometrie und Ionenspektroskopie charakterisiert. Obwohl der Effekt der N5‐Wasserstoffblockierung vor mehr als 40 Jahren vorhergesagt wurde, ist dies der erste direkte Nachweis.