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Antonietta Di Pumpo - (successfully completed PhD and awaiting graduation)

Hydrogen bonding structure and polymorphism in agrochemicals

The term polymorphism indicates the ability of a substance to crystallise in different crystal structures, which show different physical properties, such as colour, solubility, density, melting point and electric or thermal conductivity.
Polymorphism of crystals, crystal habit and crystal growth are important factors that must be controlled for any commercial crystallization process. Pharmaceuticals and agrochemicals are two of the most industrially-important, active-molecule systems for which the physical properties are strongly correlated to their crystal structure. While pharmaceuticals have attracted more academic interest to date, the market for agrochemicals is also very considerable, amounting to $15 bn annually. Given the potential significant toxicity of some agrochemicals, the ability to control physical properties, in particular solubility and dissolution rates, which depend on the crystal structure of the agrochemical itself, represents a way of optimising the ratio between the amount of product used and its efficiency, improving its function and reducing its environmental impact.
An example of how the polymorphic behaviour affects the commercial use and application of an agrochemical is the fungicide Cyprodinil. This fungicide exists in two forms, modifications A and B, which differ from one another because of a different hydrogen bonding networks. Upon storage, the metastable form B undergoes a slow conversion to the other form, causing particle aggregation, which then blocks the nozzles of delivery equipment, reducing the ability to spray the compound effectively onto crops. My research focuses on the extensive characterization of the hydrogen bonds responsible for the different crystal packing among polymorphs. Such knowledge represents the most valuable tool for the stabilization of a preferred polymorph and for the design of multi-component systems, which exhibit specific and desired physical properties. The determination of the hydrogen bonding network is achieved through X-ray and neutron diffraction, both on single crystal and powder.

Weller, M. T., Weber, O. J., Henry, P. F., Di Pumpo, A. M. and Hansen, T. C., Complete structure and cation orientation in the perovskite photovoltaic methylammonium lead iodide between 100 and 352 K. Chemical Communications, 51 (20), 4180-4183, 2015.

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