UNS: Oligomers Derived from Emerging Nitroaromatic Pollutants in Anaerobic Environments: Mechanisms, Fate and Toxicity

[1510698]【领域】许多用作炸药、杀虫剂和药品的有机化合物都使用氮代替芳香族化合物。这些化合物在农业和射击场使用后或从工业和家庭排放物中进入水生环境。众所周知，这些化合物在有氧存在的水中可形成聚合物。目前的范式是，这些化合物的聚合只发生在氧气溶解于水的条件下。然而，初步证据表明，偶联反应也可能在缺氧情况下发生，这可能对它们在地下水和其他低氧浓度水域中的毒性产生重要影响。本课题的主要目的是为微生物还原硝基芳香族污染物产生的反应中间体之间的厌氧偶联反应提供机理基础。在厌氧环境中，硝基芳香族化合物将通过亚硝基和羟胺中间体进行还原（生物）转化为芳香胺。该研究将探讨是否某些分类群的厌氧微生物的硝基还原酶基因变得丰富，作为硝基芳香族化合物的生物还原的结果。接下来，该项目将测试三种假设的耦合机制。前两种反应涉及芳香羟胺或胺对亚硝基苯中间体的亲核攻击，分别形成偶氮键（Ar-N+(O-)=N-Ar）或偶氮键（Ar-N=N-Ar）。第三种假说是由金属氧化芳胺形成的自由基的耦合。偶联反应的程度取决于硝基芳烃的结构。仅与一个硝基偶联的化合物可能仅限于二聚体；然而，具有多个硝基的结构可以继续偶联形成大的聚合物。随着硝基芳烃污染物的持续供应，预计还会发生广泛的偶联反应，这将允许反应中间体的连续生产。同位素标记的模型化合物（15N， 13C和14C）将用于帮助阐明在无氧条件下形成的腐殖质样物质的结构。初步数据表明，二聚体的毒性比原来的硝基芳香族化合物更高，因此在本项目中对其微生物和水生毒性进行了详细的评估。该项目将对风险评估、绿色综合、高中STEM教育、将少数民族纳入科教企业以及研究小组的长期目标产生影响。偶氮染料很适合用于STEM项目，因为浓度在视觉上是可观察到的。

1510698FieldNumerous organic compounds that are used as explosives, pesticides, and pharmaceuticals involve the use of nitrogen substitute aromatic compounds. These compounds can enter into aquatic environments after use in agriculture and firing ranges or from industrial and household discharges. It is known that these compounds may form polymers in waters reactive in the presence of oxygen. The current paradigm is that the polymerization of these compounds only occurs under conditions with oxygen dissolved in the aqueous waters. However, preliminary evidence has shown coupling reactions can also occur in the absence of oxygen which may have important implications to their toxicity in ground waters and other waters with low oxygen concentrations. The main focus of this project is to provide a mechanistic basis for the anaerobic coupling reactions between reactive intermediates derived from the microbial reduction of nitroaromatic pollutants. In anaerobic environments, the nitroaromatic compounds will undergo reductive (bio)transformation to aromatic amines via nitroso- and hydroxylamine-intermediates. The research will explore whether certain taxonomic groups of anaerobic microorganisms with nitroreductase genes become enriched as a consequence of the bioreduction of nitroaromatic compounds. Next the project will test three hypothesized mechanisms of coupling. The first two involve nucleophilic attacks on nitrosobenzene intermediates by either aromatic hydroxylamines or amines, forming azoxy (Ar-N+(O-)=N-Ar) or azo bonds (Ar-N=N-Ar), respectively. The third hypothesis is the coupling of radicals formed from the oxidation of aromatic amines by metals. The extent of the coupling reactions is expected to depend on the nitroaromatic structure. Coupling of compounds with just one nitro group may be limited to dimers; whereas, structures with multiple nitro groups can continue coupling to form large polymers. Extensive coupling reactions are also expected with a continuous supply of nitroaromatic pollutants which would allow for a continuous production of reactive intermediates. Isotopically labeled model compounds (15N, 13C and 14C) will be used to help elucidate the structure of humic-like substances formed in the absence of O2. Preliminary data indicate that dimers have an increased toxicity compared to the original nitroaromatic compounds justifying a detailed evaluation of their microbial and aquatic toxicity in this project. The project will have impacts on risk assessment, green synthesis, high school STEM education, inclusion of minorities in the scientific and educational enterprises, and the long term goals of the research group. Azo dyes lend themselves nicely to STEM projects because concentration is visually observable.