A Mass Spectrometric Approach for Probing the Stability of Bioorganic Radicals

Abstract

AbstractGlycyl radicals are important bioorganic radical species involved in enzymatic catalysis. Herein, we demonstrate that the stability of glycyl‐type radicals (X‐.CH‐Y) can be tuned on a molecular level by varying the X and Y substituents and experimentally probed by mass spectrometry. This approach is based on the gas‐phase dissociation of cysteine sulfinyl radical (X‐Cys‐Y) ions through homolysis of a CαCβ bond. This fragmentation produces a glycyl‐type radical upon losing CH2SO, and the degree of this loss is closely tied to the stability of the as‐formed radical. Theoretical calculations indicate that the energy of the CαCβ bond homolysis is predominantly affected by the stability of the glycyl radical product through the captodative effect, rather than that of the parent sulfinyl radical. This finding suggests a novel experimental method to probe the stability of bioorganic radicals, which can potentially broaden our understanding of these important reactive intermediates.