Spotted wing drosophila (SWD) is an invasive species of fruit fly that are detrimental to California agriculture. N,N-diethyl-m-toluamide (m-DEET) is a common insect repellent that can be used to deter many species of fruit fly, including SWD. In an attempt to explore better repellency, a structural examination of m-DEET and its interactions with odorant binding proteins is underway. The amide bond in m-DEET and DEET analogs is a key component to the molecule’s structural conformation. The amide bond is in resonance between two structural conformations, one with free rotation about the amide bond and one with a double bond, restricting rotation and causing a planar geometry. This restricted rotation is observed by the chemical exchange of the hydrogen atoms on the carbon atoms adjacent to the nitrogen atom. Examination of DEET analogs has shown that the degree of double bond character can be modulated by steric interactions and the electronic properties of the substituents bound to the aromatic ring as well as the amine. This effect can be enhanced or reduced by the chemical environment the molecules are in. A solvent commonly used for NMR studies is deuterated chloroform, which has a relatively low polarity and is a poor representation of the chemical environment in which m-DEET interacts with its biological targets, so a range of solvents have been used to examine the solvent effect on DEET analogs. This solvent effect on the resonance of the amide bond in DEET analogs are compared experimentally between deuterated chloroform, deuterated acetone, and deuterated dimethyl sulfoxide as the solvents for VT-1H-NMR. The more polar solvents result in an increase in the double bond character of the amide bond. An accurate insight into the understanding of the solvent influence on the conformation of these molecules can potentially aide to the development of SWD repellents.

Solvent effect and electronic modulation of amide bond resonance in DEET analogs

256th National Meeting (2018)

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