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

现场用作炸药、杀虫剂和药品的大量有机化合物涉及氮取代芳香族化合物的使用。这些化合物在农业和射击场使用后，或从工业和家庭排放后，可进入水环境。众所周知，这些化合物可以在氧气存在下发生反应的水中形成聚合物。目前的模式是，这些化合物的聚合只有在水中溶解氧气的条件下才会发生。然而，初步证据表明，在没有氧气的情况下也可以发生偶联反应，这可能对它们在地下水和其他低氧浓度水域的毒性有重要影响。本项目的主要目的是为微生物还原硝基芳香族污染物产生的活性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还原(生物)转化为芳香胺。这项研究将探索携带硝基还原酶基因的厌氧微生物的某些分类群是否因硝基芳香化合物的生物还原而变得丰富。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族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)。第三种假设是芳香胺被金属氧化形成的自由基的偶联。预计偶联反应的程度取决于硝基芳香族结构。只有一个硝基的化合物的偶联可能仅限于二聚体；而具有多个硝基的结构可以继续偶联以形成大的聚合物。随着硝基芳香族污染物的持续供应，预计还会发生广泛的偶联反应，这将使活性中间体的生产得以持续。同位素标记的模型化合物(15N，13C和14C)将被用来帮助阐明在没有氧气的情况下形成的腐植酸类物质的结构。初步数据表明，与原始的硝基芳香化合物相比，二聚体具有更高的毒性，因此有理由在本项目中对其微生物和水生毒性进行详细评估。该项目将对风险评估、绿色综合、高中STEM教育、将少数族裔纳入科教企业以及研究小组的长期目标产生影响。偶氮染料非常适合STEM项目，因为浓度是可见的。

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.