化学
SN2反应
亲核细胞
溶剂化
键裂
动力学
计算化学
密度泛函理论
水溶液
超氧化物
反应速率常数
光化学
溶剂
立体化学
有机化学
催化作用
酶
物理
量子力学
作者
Lu Bai,Ying Jiang,Dao-Cheng Xia,Zongsu Wei,Richard Spinney,Dionysios D. Dionysiou,Daisuke Minakata,Ruiyang Xiao,Hong-Bin Xie,Liyuan Chai
标识
DOI:10.1021/acs.est.1c06356
摘要
Perfluorocarboxylic acids (PFCAs) exhibit strong persistence in sunlit surface waters and in radical-based treatment processes, where superoxide radical (O2•-) is an important and abundant reactive oxygen species. Given that the role of O2•- during the transformation of PFCAs remains largely unknown, we investigated the kinetics and mechanisms of O2•--mediated PFCAs attenuation through complementary experimental and theoretical approaches. The aqueous-phase rate constants between O2•- and C3-C8 PFCAs were measured using a newly designed in situ spectroscopic system. Mechanistically, bimolecular nucleophilic substitution (SN2) is most likely to be thermodynamically feasible, as indicated by density functional theory calculations at the CBS-QB3 level of theory. This pathway was then investigated by ab initio molecular dynamics simulation with free-energy samplings. As O2•- approaches PFCA, the C-F bond at the alpha carbon is spontaneously stretched, leading to the bond cleavage. The solvation mechanism for O2•--mediated PFCA degradation was also elucidated. Our results indicated that although the less polar solvent enhanced the nucleophilicity of O2•-, it also decreased the desolvation process of PFCAs, resulting in reduced kinetics. With these quantitative and mechanistic results, we achieved a defined picture of the O2•--initiated abatement of PFCAs in natural and engineered waters.
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