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Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates
Author(s) -
Zelenka Jan,
Cibulka Radek,
Roithová Jana
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201906293
Subject(s) - chemistry , flavin group , photochemistry , microsecond , electrospray ionization , reaction intermediate , photodissociation , mass spectrometry , electron transfer , radical , catalysis , spectroscopy , organic chemistry , physics , chromatography , astronomy , enzyme , quantum mechanics
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.