Swiss Federal Institute of Aquatic Science and Technology, Eawag, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Environ Sci Technol. 2020 Dec 1;54(23):15057-15065. doi: 10.1021/acs.est.0c05230. Epub 2020 Nov 17.
Aromatic amines are relevant aquatic organic contaminants whose photochemical transformation is affected by dissolved organic matter (DOM). The goal of this study is to elucidate the underlying mechanism of the inhibitory effect of DOM on such reactions. The selected model aromatic amine, 4-(dimethylamino)benzonitrile (DMABN), was subjected to laser flash photolysis in the presence and absence of various model photosensitizers. The produced radical cation (DMABN) was observed to react with several phenols and different types of DOM on a time scale of ∼100 μs. The determined second-order rate constants for the quenching of DMABN by phenols were in the range of (1.4-26) × 10 M s and increased with increasing electron donor character of the aromatic ring substituent. For DOM, quenching rate constants increased with the phenolic content of the DOM. These results indicate the reduction of DMABN to re-form its parent compound as the basic reaction governing the inhibitory effect. In addition, the photosensitized oxidation of the sulfonamide antibiotic sulfadiazine (SDZ) was studied. The observed radical intermediate of SDZ was quenched by 4-methoxyphenol less effectively than DMABN, which was attributed to the lower reduction potential of the SDZ-derived radical compared to DMABN.
芳香胺是相关的水生有机污染物，其光化学转化受溶解有机物（DOM）的影响。本研究的目的是阐明 DOM 对这些反应抑制作用的潜在机制。选择的模型芳香胺，4-（二甲氨基）苯甲腈（DMABN），在存在和不存在各种模型光敏剂的情况下进行激光闪光光解。产生的自由基阳离子（DMABN）在约 100 μs 的时间尺度内与几种酚类和不同类型的 DOM 反应。由酚类猝灭 DMABN 的确定二级速率常数在（1.4-26）×10 M s 的范围内，并随芳环取代基的供电子特性的增加而增加。对于 DOM，猝灭速率常数随 DOM 中酚类含量的增加而增加。这些结果表明，将 DMABN 还原为其母体化合物是控制抑制作用的基本反应。此外，还研究了磺酰胺抗生素磺胺嘧啶（SDZ）的光敏氧化。SDZ 的观察到的自由基中间体比 DMABN 更有效地被 4-甲氧基苯酚猝灭，这归因于与 DMABN 相比，SDZ 衍生的自由基的还原电位较低。
