Four crystalline polymorphs of the proinsecticide chlorfenapyr [4-bromo-2-(4-chlorophenyl)-1-ethoxymethyl-5-trifluoromethyl-1H-pyrrole-3-carbonitrile] have been identified and characterized by polarized light optical microscopy, differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, and electron diffraction. Three of the four structures were considered polytypic. Chlorfenapyr polymorphs show similar lethality against fruit flies (Drosophila melanogaster) and mosquitoes (Anopheles quadrimaculatus) with the least stable polymorph showing slightly higher lethality. Similar activities may be expected to be consistent with structural similarities. Knockdown kinetics, however, depend on an internal metabolic activating step, which further complicates polymorph-dependent bioavailability.
Photography was employed for the quantitation and differentiation of G- and V-series nerve agent mimics with the use of self-propagating cascades. Fluoride anion and thiols, released from a G-nerve agent mimic (i.e., diisopropyl fluorophosphate) and a V-nerve agent mimic (i.e., demeton-S-methyl), respectively, were used to initiate self-propagating cascades that amplify fluorescence signals exponentially in a ratiometric manner. A homemade LEGO dark-box, a cell phone, and 96-well plates were employed to collect photographs of the fluorescence response to the analytes. The photographic images were digitally processed in the 1931 xyY color space using a watershed and morphological erosion algorithm to generate chromaticity vs concentration calibration curves. We show that the two different amplification routines are selective for their analyte class and thus successfully discriminated the G- and V-series nerve agent mimics. Further, accurate concentrations of the analytes are determined using the chromaticity and LEGO approach given herein, thus demonstrating a simple and on-site constructible/portable device for use in the field.
