A concerted approach for a better understanding and control of the polymorphism of benzamide molecular crystals - synthesis as well as experimental and theoretical characterisation

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The aim of this project is to increase the understanding of polymorphism and nucleation of benzamide, which was developed during the first project period of the SPP 1415. Additionally, we strive to extend our studies to related molecular systems. During the first funding period we found to our surprise that benzamide exhibits a strong amphiphilic character. This opens up promising avenues for structurally similar molecules like pharmaceuticals and their precursors. Sodium benzoate was shown to display an unusual micelle like packing, indicating similar molecular interactions for benzamide and sodium benzoate. For the oncoming period we plan to focus our research efforts on heterogeneous nucleation processes for both systems. We intend to unravel specific structural motives of the pre-organisation of amphiphilic molecules at polar/unpolar interfaces as well as the influence of tensides and the formation of nuclei starting to grow from molecular monolayers at the interfaces. We also plan to investigate the potential of forming micellar aggregates as possible precursor and will follow their self-organisation into mesocrystals. In the case of sodium benzoate the experimentally observed transformation occurs in the solid-state and is slow allowing for easy access with in-situ analytics. We believe sodium benzoate to be an ideal system to study the hierarchical processes during the nucleation and growth mechanism. Therefore, we will use a coordinated approach combining synthesis, theory and experimental characterisation. As such the competence of all three groups involved is essential. The Breu group need to develop synthetic methods allowing for a nucleation which occurs at the interfaces as selectively as possible. The atomistic simulations carried out in the Zahn group will help to understand the relevant molecular interactions and is able to suggest possible scenarios of the selforganisation at the interfaces. The Senker group will contribute with NMR spectroscopic experiments, providing direct access to the molecular assembly at the interfaces and the micelles, respectively. They are also suited to validate the structural motives derived from the MD simulations. The thus derived insight into the nucleation phenomenon serves the long term goal to reach a general control of polymorphism in molecular crystals.