Methionine is one of the amino acids most susceptible to oxidation and therefore a target of reactive oxygen species (ROS) in proteins. The first step has been known for a long time [Archirel2016, Neschchadin2014] and leads to free radicals with 2 centers and 3 electrons characterized in pulse radiolysis and quantum chemistry, but the products formed other than methionine sulfoxide at the end of the process are not well understood. We have thus undertaken a thorough study of their characterization in model molecules containing the thioether function: small peptides in which methionine is linked to various residues and at various positions in the polypeptide chain (N-terminal, C-terminal, mid-chain) ) [Archirel2019, Gregori2017]. Characterization was performed by mass spectrometry coupled with infrared spectroscopy (CLIO). Quantum chemistry calculations allowed us to propose mechanisms and geometries for these products [Bergès2020]. We have thus identified previously unknown products, including double bonds, cycles, etc. [Jiang2022, Jiang2023]. More recently, we turned to the oxidation of DNA bases, both purines and pyrimidines [Ma2018], and showed that HO° radicals led only to hydroxylation [Jiang2023]. Finally, regarding protein oxidation, we use gamma radiolysis to test the stability properties of various proteins (ancestral and resurrected proteins) with respect to heat and ionizing radiation [Halgand2020].

Some examples of free radicals in the Gly Met peptide possessing a 2-center and 3-electron bond. 1 SN bond; 2 SO bond; 3 SS bond in the dipeptide MetMet.