The first steps of the oxidation process of amino acid methionine (Met, CAS 63-68-3) by  OH radicals, leading to Met-OH • adduct and then to Met radical cation, were investigated theoretically over the last few years considering the aqueous environment as a continuum. In this work, following the same procedure that we used for the oxidation of dimethyl sulfide (Domin et al. (2017) J Phys Chem B, 121:9321), discrete water molecules as well as relative positions of the OH radical to Met were taken from Molecular Dynamics calculations. The presence of water molecules strongly modifies the relative energies of Met-OH adducts and cations when water is properly modeled. Depending on the terminal functional groups and on the position of the • OH radical several stable structures were found, however the most stable radical is the N-centered or the SN radical cation. QTAIM analysis and Valence Bond (VB) treatment allowed for the characterization of the 2c3e nature of SN and SOH bonds. VB analysis estimated the probability of the heterolytic rupture of the OH adduct that is modified by the presence of water molecules.