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 as reported by Domin et al. (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 S∴N radical cation. QTAIM analysis and valence bond (VB) treatment allowed for the characterization of the 2c∴3e nature of S∴N and S∴OH bonds. VB analysis estimated the probability of the heterolytic rupture of the •OH adduct that is modified by the presence of water molecules. Graphical abstract Oxidation of amino acid methionine by •OH radicals in the presence of discrete water molecules. Oxidation of amino acid methionine by •OH radicals in the presence of discrete water molecules.

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• 存在离散水分子时甲硫氨酸的 OH 氧化：DFT、QTAIM 和价键分析

氨基酸甲硫氨酸 (Met, CAS 63-68-3) 被 •OH 自由基氧化过程的第一步，导致 Met-OH• 加合物，然后是 Met 自由基阳离子，在过去几年中进行了理论上的研究，考虑到水环境作为一个连续体。在这项工作中，按照我们用于氧化二甲硫醚的相同程序，如 Domin 等人报道的那样。(J Phys Chem B, 121:9321)，从分子动力学计算中获取•OH 自由基与Met 的离散水分子以及相对位置。当正确模拟水时，水分子的存在会强烈改变 Met-OH 加合物和阳离子的相对能量。根据末端官能团和•OH 基团的位置，发现了几种稳定的结构；然而，最稳定的自由基是 N 中心或 S∴N 自由基阳离子。QTAIM 分析和价键 (VB) 处理允许表征 S∴N 和 S∴OH 键的 2c∴3e 性质。VB 分析估计了因水分子的存在而改变的•OH 加合物的异裂破裂的可能性。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸的图形摘要。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸的图形摘要。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸的图形摘要。在离散水分子存在下，通过•OH 自由基氧化氨基酸蛋氨酸。