The intermolecular interactions in concentrated (5 M) aqueous imidazole solutions have been investigated by combining neutron diffraction with isotopic substitution, total X-ray scattering and empirical potential structure refinement (EPSR) simulations using a box containing 5530 water and 500 imidazole molecules. The structural model with the best fit was used to generate radial distribution functions and spatial density functions. The local volume surrounding imidazole molecules is dominated by water, due to strong hydrogen-bonding between the nitrogen moieties of imidazole and water molecules; within a radius of 6.4 Å from the central imidazole molecule there are, on average, 17 water and only 3 imidazole molecules. Even though imidazole interacts with water it appears to disrupt hydrogen bonding in the surrounding water network only minimally. Hydrogen-bonding between imidazole molecules is negligible. The most probable positions of imidazole nearest-neighbours are above and below the plane of the aromatic ring. At low distances (up to B3.5-3.8 Å) these nearest neighbours were found to prefer parallel orientation of the molecular planes, indicating hydrophobic (p-p) stacking. At longer distances (up to B5 Å), imidazole neighbours assume both parallel and edgeto-face orientations. Overall, hydrated imidazole molecules are the most probable structural motif in aqueous solutions, with very few direct imidazole-imidazole interactions.

X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization.

<p>X-ray phase contrast imaging (XPCI) of anti-solvent crystallization of lovastatin from an acetone/water solution was carried out in a concentric flow mixing device, using water as the anti-solvent. Spinodal decomposition of the solution is observed to give rise to ‘oiled out’ phases that undergo heterogeneous nucleation at the interface with the flowing solution. Heterogeneous nucleation is also observed on the walls of the reactor walls in the form of what appears to be Stranski–Krastanov growth of plate-like crystals. XPCI together with Eulerian video magnification forms a powerful tool for the spatio-temporal analysis, revealing mechanistic details of a non-equilibrium process such as anti-solvent crystallization.</p>

<p>X-ray phase contrast imaging (XPCI) of anti-solvent crystallization of lovastatin from an acetone/water solution was carried out in a concentric flow mixing device, using water as the anti-solvent. Spinodal decomposition of the solution is observed to give rise to ‘oiled out’ phases that undergo heterogeneous nucleation at the interface with the flowing solution. Heterogeneous nucleation is also observed on the walls of the reactor walls in the form of what appears to be Stranski–Krastanov growth of plate-like crystals. XPCI together with Eulerian video magnification forms a powerful tool for the spatio-temporal analysis, revealing mechanistic details of a non-equilibrium process such as anti-solvent crystallization.</p>