关键词: 过氧亚硝酸, 自由基, 酪氨酸, 密度泛函理论

Abstract: The mechanisms of the reaction of peroxynitrous acid and tyrosine were studied using the density functional theory (DFT) at B3LYP/6-311G(d,p) level. The geometries of all the molecules were optimized; the harmonic vibration frequencies and the energies were calculated as well. The calculation results showed that stepwise mechanism rather than concerted mechanism was preferred for the reaction of peroxynitrous acid and tyrosine. The stepwise pathway started with homolysis of the HO—ONO bond to discrete·OH and·NO2 radicals, which then reacted with tyrosine via two different pathways: (i) the H atom of tyrosine hydroxyl was abstracted by·OH to produce IM3, which then combined with·NO2 forming the intermediate (IM1). Subsequently, the IM1 underwent further transformation leading to the product of 3-nitrotyrosine. (ii) the·OHwas added to the phenol ring of tyrosine to produce the IM2, which then combined with·NO2 forming the intermediate (IM21). The IM21 also underwent further transformation leading to the product of 3-hydroxytyrosine. The activation energies of the rate-determining steps of these two pathways were 82.86 and 48.05 kJ·mol-1, respectively. This conclusion was in good agreement with the corresponding experimental data. Additionally, effects of aqueous solvation of water on this reaction were also investigated and the results indicated that the reaction preferably took place in water.

Key words: Peroxynitrous acid, Radical, Tyrosine, Density functional theory