Experimental and Theoretical Studies of the Environmental Sensitivity of the Absorption Spectra and Photochemistry of Nitenpyram and Analogs
Experimental and Theoretical Studies of the Environmental Sensitivity of the Absorption Spectra and Photochemistry of Nitenpyram and Analogs
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DOI：
10.1021/acsearthspacechem.9b00179
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发表时间：
2019-09-19
影响因子：
3.4
通讯作者：
Finlayson-Pitts, Barbara J.
中科院分区：
文献类型：
--
作者：
Ezell, Michael J.;Wang, Weihong;Finlayson-Pitts, Barbara J.
新烟碱类（NN）农药已广泛使用，在很大程度上取代了其他农药，如氨基甲酸酯。因此，有必要在分子水平上了解它们在各种介质，特别是水中的环境命运。在这里，我们报告的研究nitroenamine NN，烯啶虫胺（NPM），在水溶液中的光化区域以上290 nm的吸收截面观察到显着减少相比，在非水溶剂中。量子化学计算表明，向NPM中的叔胺氮添加质子会破坏发色团的共轭，将吸收转移到较短的波长，这与实验一致。然而，令人惊讶的是，将质子添加到仲胺氮导致其立即转移到NO2基团，保持共轭。这就解释了为什么雷尼替丁（RAN）的紫外吸收，它有一个类似的发色团，但只有仲胺氮，没有显示出类似的大蓝移在水中。NPM水溶液中的光解量子产率在254 nm处测得为phi= 0.18 +/- 0.07，对于以313 nm为中心的宽带辐射为（9.4 +/- 1.6）x 10（-2），对于以350 nm为中心的宽带辐射为（5.2 +/- 1.1）x 10（-2）（误差为2 sigma）。水溶液中的主要产物是固体光解中也形成的亚胺和水中光解所特有的羧酸衍生物。将水中较大的量子产率与减少的吸收截面相结合，计算出的NPM寿命在太阳天顶角为35度时仅为5分钟，典型的是4月1日北纬40度。该产品在光化区域不吸收，因此相对于光解将是长寿命的。
Neonicotinoid (NN) pesticides have widespread use, largely replacing other pesticides such as the carbamates. Hence, there is a need to understand their environmental fates at a molecular level in various media, especially water. We report here the studies of a nitroenamine NN, nitenpyram (NPM), in aqueous solution where the absorption cross sections in the actinic region above 290 nm are observed to dramatically decrease compared to those in nonaqueous solvents. Quantum chemical calculations show that addition of a proton to the tertiary amine nitrogen in NPM breaks the conjugation in the chromophore, shifting the absorption to shorter wavelengths, consistent with experiment. However, surprisingly, adding a proton to the secondary amine nitrogen leads to its immediate transfer to the NO2 group, preserving the conjugation. This explains why the UV absorption of ranitidine (RAN), which has a similar chromophore but only secondary amine nitrogens, does not show a similar large blue shift in water. Photolysis quantum yields in aqueous NPM solutions were measured to be phi= 0.18 +/- 0.07 at 254 nm, (9.4 +/- 1.6) x 10(-2) with broadband radiation centered at 313 nm and (5.2 +/- 1.1) x 10(-2) for broadband radiation centered at 350 nm (errors are 2 sigma). The major products in aqueous solutions are an imine that was also formed in the photolysis of the solid and a carboxylic acid derivative that is unique to the photolysis in water. Combining the larger quantum yields in water with the reduced absorption cross sections results in a calculated lifetime of NPM of only 5 min at a solar zenith angle of 35 degrees, typical of 40 degrees N latitude on April 1. The products do not absorb in the actinic region and hence will be long-lived with respect to photolysis.