Nitenpyram (NPM), a nitromethylene neonicotinoid (NN), has been used widely in agriculture as an insecticide and on pets for flea conctrol. It is important to understand its chemistry and photochemistry in the environment. NPM absorbs UV-Vis radiation in the actinic region and hence photodegradation is potentially a significant loss process. Its absorption cross sections in the actinic region above 290 nm in water were observed to decrease dramatically compared to those in non-aqueous solvents and in thin solid films. UV-Vis and IR spectra of NPM in D<sub>2</sub>O at pH 6 and 1 were studied to investigate this dramatic change of the NPM absorption spectrum in water. For comparison, those of ranitidine, which has a similar nitromethylene chromophore, were also measured, but did not show the dramatic reduction in absorption above 300 nm in water compared to organic solvents that was seen in NPM. Quantum chemical calculations on neutral and protonated NPM were used to elucidate the nature of the electronic transitions and the impacts of different protonation sites in the molecule on these transitions. Photolysis quantum yields of NPM in aqueous solutions were also measured using <i>o</i>-nitrobenzaldehyde as an actinometer in three wavelength regions: (1) a broadband radiation centered at 350 nm; (2) a broadband radiation centered at 313 nm; and (3) a low pressure mercury lamp at 254 nm. UPLC-MS/MS was used to followed the loss of NPM, and the photolysis products were studied using HPLC-MS and ESI-MS/MS. The implications of thee studies for the lifetimes of NPM in different media will be discussed.

Combined experimental and computational studies of the absorption spectra and photochemistry of nitenpyram and analogs

2019 Fall National Meeting

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