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Acta Cryst. (2014). A70, C540
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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 such as solubility and dissolution rates, which depend on the crystal structure of the agrochemical itself, represents a way of optimizing the ratio between the amount of product used and its efficiency, improving its function and reducing its environmental impact. Hydrogen bonds play a crucial role in the spatial arrangement of the active molecules and the crystallization process. However, high accuracy and precision of the hydrogen atom positions can only be achieved through single crystal neutron diffraction (SND). SND experiments have been performed on three herbicides - isoproturon (IPU), pendimethalin (PDM), and diflufenican (DFF) - and the fungicide cyprodinil (CYP) [1][2]. All four structure refinements show a ten-time improvement in precision in the hydrogen atom positions compared to SXD with accurately determined nuclear positions. For cyprodinil, which crystallises as two polymorphs, A and B, differences in the hydrogen bonding network have been determined. Form A is governed by single, linear hydrogen bonds between two molecules, while the B form is characterized by the presence of dimers linked through pairs of hydrogen bonds, leading to a stable 8-membered ring. These differences in structure are reflected in the physical properties of the two polymorphs such as melting point and the observed slow inter-conversion that takes place during storage.

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Acta Cryst. (2014). A70, C1204
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Enzymes continue to expand their role in industry as a "green" option for the synthesis of value-added products. They are targeted for the design of drugs in pharmaceutical applications and also for protein engineering in industry to improve their efficiency, stability, and specificity. Knowledge of the exact mechanisms of enzymatic reactions may provide essential information for more effective drug design and enzyme engineering. For the first time, we are employing a joint X-ray/neutron (XN) protein crystallographic technique in combination with high-performance computing, including QM and QM/MM calculations, MD and Rosetta simulations, to investigate the mechanisms of several enzymes that are important to renewable energy and chemical synthesis. D-xylose isomerase (XI) is an enzyme which can be used to increase the production of biofuels from lignocellulosic biomass and also to synthesize rare sugars for pharmaceutical industry. XI catalyzes the reversible multi-stage sugar inter-conversion reaction facilitated by the presence of two divalent metal cations in its active site. It primarily catalyzes the isomerization of the aldo-sugar D-xylose to the keto-isomer D-xylulose, but can also epimerize L-arabinose into L-ribose, albeit much less efficiently. The reaction involves moving hydrogen atoms between the protein residues, sugar and water molecules, and can only be understood if hydrogen atoms are visualized at each reaction stage. We have obtained a number of joint XN structures of XI complexes representing snapshots along the reaction path with D-glucose, D-xylose and L-arabinose. The suggested reaction mechanism has been verified by QM calculations using the novel O(N) methodology. We are using this structural and mechanistic information to re-design XI to be more efficient on D-xylose and L-arabinose for biofuels and biomedical applications by employing QM/MM, MD, and Rosetta methodologies.

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Acta Cryst. (2014). A70, C1214
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Cryo-cooling of protein crystals is not often used in neutron crystallography. However cryo-temperatures are used to block the reaction processes at specific intermediate stages, and this has been widely used in X-ray studies (1); (2). In order to develop this area for joint neutron/X-ray applications, trypsin was chosen as a suitable system for which its interaction with the substrate succinyl-Ala-Ala-Pro-Arg-p-nitro-aniline could be studied (3). Here the neutron developments were carried out in parallel with complementary X-ray techniques, and also using in crystallo UV-visible and Raman spectroscopy. Various strategies for doing this have been tested. The installation of an N2-gas-cryostream system on the D19 single crystal diffractometer at the Institut Laue Langevin (ILL) and the development of a new carboloop mounting system, has opened new avenues to perform cryo-cooling experiments using a neutron source. Preliminary data collection carried out at the ILL and at the European Synchrotron Radiation Facility (ESRF), have confirmed the feasibility of the approach. A full description of the experimental procedures and results will be presented. As part of this a new carboloop mounting system has been developed that is suitable for both X-ray and neutron data collection. These mounts resolve the problems of activation and hydrogen incoherent scattering in neutron experiments We describe the use of these and their advantages over conventional X-ray mounting systems - including compatibility with standard magnetic goniometer heads and resistance to cryogenic temperatures.
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