Equilibrium argon adsorption from the gas phase on mesoporous MCM-41 silica of hexagonal structure is directly studied by in situ synchrotron powder X-ray diffraction (XRD) measurements at SPring-8. The diffraction intensity data is analyzed by extending the previously developed analytical formula for the crystal structure factors of MCM-41 to account for argon adsorbed in the pores. It is clearly observed that argon adsorbs in layers on the pore walls at low gas pressures and exhibits sudden capillary condensation as the gas pressure increased. The proposed method of interpretation of XRD data allows one to calculate the density ratio between the silica wall and condensed argon, the pore size, and the pore wall fluctuation/roughness, together with the thickness of the adsorbed layer as a function of the gas pressure. The results of in situ XRD experiments are compared with the results of argon adsorption volumetric experiments. The adsorption data are interpreted with the quench solid density functional theory (QSDFT), which takes into account the pore wall roughness. The perfect agreement of the QSDFT isotherm predicted from the adsorption data and the XRD recalculated isotherm suggests that the adsorption porosimetry and XRD measurements can be reconciled provided a proper interpretation of the experimental data.
Five anhydrous polymorphs (forms I−V) and one hydrate of furosemide−nicotinamide 1:1 cocrystal were discovered, and their solid-state properties were characterized using X-ray powder diffraction and differential scanning calorimetry. The crystal structures of forms I−IV were determined from the X-ray powder diffraction data and showed the structural differences between forms, which are mainly attributable to molecular conformations and supramolecular synthons. The slurry conversion experiments revealed that the order of thermodynamic stability of the polymorphs at 25 °C is I > III > II > V > IV. Dynamic vapor sorption analysis and X-ray single-crystal structure determination of the hydrate were conducted to study the dehydration mechanism. We observed structural similarities between the hydrate and its dehydrate, form IV, such as lattice parameters (except the a-axis length), synthons between furosemide and nicotinamide molecules, and the molecular conformation of furosemide; after dehydration, however, the a-axis contracted and nicotinamide molecules were displaced, along with the pyridine ring twisting.
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