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Theoretical Study on OH-initiated Degradation Mechanism and Kinetic property of Sulfamethoxazole

Ning Wang, Chenxi Zhang, Yuning Leng, Chen Gong, Xiaomin Sun


Sulfamethoxazole (SMX) is a typical antibiotic which may bring potential risk to human and aquatic ecosystems. In this paper, the OH-initiated degradation mechanisms of sulfamethoxazole are studied at the MPWB1K/6-311+G(3df,2p)// MPWB1K/6-31+G(d,p) level. The thermodynamic parameters and reaction pathways are analyzed in detail. The addition, abstraction and bond-broken reactions are the three main reaction mechanisms, and bond-broken reactions may lead to the direct degradation of SMX. The rate constants are calculated using the transition state theory and canonical variational transition with small-curvature tunneling correction at the temperature range of 200-500 K. The Arrhenius equations of rate constants are fitted. The rate constants of addition and abstraction reactions at 298.15 K are 3.03×10-23 cm3molecule-1s-1 and 6.86×10-24 cm3molecule-1s-1, respectively. The rate constants of bond-broken reactions are much lower than those of the addition and abstraction reactions, but their significance can not be ignored.

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