3 years ago

DDT Polymorphism and the Lethality of Crystal Forms

DDT Polymorphism and the Lethality of Crystal Forms
Michael D. Ward, Qiang Zhu, Jingxiang Yang, C. T. Hu, Xiaolong Zhu, Bart Kahr
DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane), a contact insecticide with a rich and controversial history since its activity was discovered in 1939, has long been thought to be monomorphic. Herein we report the discovery and characterization of a second polymorph, designated Form II, which can be isolated as single crystals, but converts very slowly at room temperature to the form reported previously, now designated as Form I. Computations based on an evolutionary algorithm for crystal structure prediction revealed that Forms I and II are among the four lowest energy crystal structures of fifty calculated. A preliminary study of the contact insecticidal activity toward fruit flies (Drosophila melanogaster) indicates that Form II is more active, suggesting opportunities for more effective solid-state formulations that would allow reduced amounts of DDT, thereby minimizing environmental impact. A new polymorph of DDT has been discovered, provoking questions about the lethality of different crystal forms and the mode of action of this most prominent insecticide. Graphic: Insect walking on DDT crystals, from the film Doomsday for Pests (1946, Sherwin-Williams Research Laboratories).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201703028

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