1,721,000 research outputs found
Rationalization of liquid assisted grinding intercalation yields of organic molecules into layered double hydroxides by multivariate analysis
No full textThe Liquid Assisted Grinding (LAG) method for the fast and facile preparation of organic-intercalated Layered Double Hydroxide (LDH) nanocomposites allowing the production of low cost, stable and efficient functional materials, is here employed to rationalize the features of the organic compounds that most likely undergo easy intercalation. LAG method was exploited to determine in a short time which molecules can be successfully intercalated into LDH. A straightforward rationalization of the intercalation yield results was not possible since no individual feature (such as bulkiness or pK(a)) could alone describe the intercalation behaviour of the whole set of molecules. Therefore, Principal Component Analysis (PCA) together with the use of molecular descriptors to classify molecules, were mutuated from the chemometric approach, widely used in analytical chemistry and applied successfully, for the first time, to a novel area of materials science. A set of molecular descriptors were chosen to cover different features of the molecule (physicochemical, topological, geometrical etc.) and then screened by statistical methods to understand which descriptors affected the intercalation yield. Then PCA allowed us to highlight the presence of various mechanisms, involved in the LAG intercalation and to separate the samples along PC3 as a function of yield. Finally, the classification tree method allowed us to understand the various mechanisms of intercalation and to classify molecules in groups, related to their yield. These groups can be used to estimate the expected yield as a function of the molecular descriptors. The molecules more apt to LAG have medium-low molecular weight, high flexibility and low refractivity. Conversely large and hydrophobic molecules and, surprisingly, small but rigid molecules have a small success rate concerning LAG intercalation. The behaviour of this last class of molecules, that should be in principle easily intercalated by LAG but which was identified by the present study as a difficult case, was thus tested using two molecules and the prediction of the chemometric study was confirmed
Chemical selectivity in structure determination by the time dependent analysis of in situ XRPD data: a clear view of Xe thermal behavior inside a MFI zeolite
No full textPCA Analysis of In Situ X-ray Powder Diffraction and Imaging Data Shedding New Light on Solid-State Transformations: The Crystallization of Low Temperature Eutectic Mixtures
No full textEutectic mixtures are usually studied by differential scanning calorimetry (DSC), able to identify the transition temperatures, possible hysteresis, and investigate the energetic features of transformations. However, DSC is not able to give compositional, structural, or morphological information. A new approach is proposed exploiting powder X-ray diffraction (XRPD) and imaging to overcome the issues posed to diffraction by the presence of an amorphous liquid phase. Principal component analysis (PCA) is applied blindly to in situ XRPD data from both solid and liquid phases in an approach called differential scanning diffraction (DSD), with PCA scores being the reaction coordinate of melting or crystallization steps. PCA was used in a similar way to analyze the imaging data in what was named differential scanning imaging (DSI). Exploiting this approach, the structural and morphological changes during phase transitions can be characterized by XRPD and imaging respectively, complementarily to the energetic effects probed by DSC. Melting and crystallization points can be identified together with the hysteresis between downward and upward temperature ramps, by the structural and morphological viewpoints. A three-component mixture (NaBr, KCl, and water), with wide industrial applications, was studied to describe the behavior around the eutectic composition and examine how small mixture changes can affect the transition temperature and the freezing/melting behaviors. The phase composition at the solid state was elucidated and a new phase of NaBr was identified and its lattice parameters were obtained by XRPD. DSD and DSI resulted complementary to traditional DSC data with many potential applications in solid state chemistry and materials science
Epoxy resins composites for X-ray shielding materials additivated by coated barium sulfate with improved dispersibility
No full textEpoxy resins additivated by barium sulfate proved to be promising low cost, easy workable and environmentally
friendly alternative to lead and steel as X-ray shielding materials, but the composites tends to be stratified, with
the additive accumulating in the bottom side of the sample. This sedimentation process has been, at first, studied
by in situ X-ray powder diffraction, thermogravimetric techniques and X-ray tomography and then inhibited by
exploiting finer barite sources, implementing a grinding procedure, combined to a surface modification of the
inorganic additives. Stearic acid and sodium dodecyl sulfate were used to coat barite surface, using a liquid
assisted grinding (LAG) approach. The functionalized additives resulted more compatible with the resin and their
dispersion within the polymer resulted much improved. The produced composite samples were then studied by
optical and electron microscopy, X-ray radiography, X-ray diffraction, thermogravimetric analysis and tensile
strength test. The use of a finer additive and the grinding procedure allowed to limit the sedimentation and
induced a marked hardening of the samples, with the drawback of a reduction of their plasticity. Stearic acid
coating was able to eliminate sedimentation maintaining good mechanical properties
POSS as building-blocks for the preparation of polysilsesquioxanes through an innovative synthetic approach
No full textMonitoring the Formation of H-MCM-22 by a Combined XRPD and Computational study of the Decomposition of the Structure Directing Agent
No full textThe Crystal Structure of Calcium Sebacate by X-ray Powder Diffraction Data
No full textSodium sebacate salts have several industrial applications as additives, lubricants, and a metal self-healing promoter in general industry, and some derivatives also have wide applications in cosmetics and pharmaceutical fields. Calcium sebacate formation and precipitation can be detrimental for the systems where sodium sebacate is used. It is thus important to investigate their crystallization features. Sodium and calcium sebacate were prepared, purified, and crystallized with different approaches to carry out a full X-ray diffraction powder diffraction structural analysis since suitable single crystals cannot be obtained. The calcium sebacate crystal structure was solved by simulated annealing. Calcium ions form layers connected by straight “all trans” sebacate molecules, a conformation that is also suggested by Fourier-transform infrared spectroscopy FTIR data. Water molecules are caged within calcium layers. The crystal structure is characterized by the calcium layers bent by 10.65° with respect to the plane where sebacate chains lie, different from other dicarboxilic salts, such as cesium suberate, where the layers are perpendicular to the cation planes. The sodium sebacate crystal structure resulted in being impossible to be solved, despite several crystallization attempts and the different data collection approaches. FTIR spectroscopy indicates marked differences between the structures of calcium and sodium sebacate, suggesting a different type of metal coordination by carboxyls. Calcium sebacate shows a bis-bidentate chelating and bridging configuration ((κ2)−(κ1−κ1)−μ3−Carb), while for sodium sebacate, FTIR spectroscopy indicates an ionic interaction between sodium and the carboxyls. A thermogravimetric analysis TGA was carried out to assess the hydration states of the two salts. Calcium sebacate shows, as expected, a total weight loss of ca. 7%, corresponding to the single water molecule located in the crystal structure, while sodium sebacate shows no weight loss before total combustion, indicating that its structure is not hydrated. Scanning electron microscopy SEM images show different morphologies for calcium and sodium salts, probably a consequence of the different interactions at the molecular lever suggested by FTIR and TGA. The used approach can be extended to fatty acid salt in general, a still under-explored field because of the difficulty of growing suitable single crystals
Conformational and Intermolecular Interaction Analysis of Tiaprofenic Acid: A X-Ray Powder Diffraction and First Principle Modeling Analysis
No full text(±)-tiaprofenic acid (TA), marketed as (Surgam®), belongs to the family of NSAIDs, with the peculiarity of a reduced incidence of ulcer induction in rats compared with parent drugs. However, some adverse effects were observed, and better knowledge of its interaction with biologic substrates is needed. Unfortunately, unlike most commercial NSAIDs, suitable single crystals for an X-ray diffraction study could not be obtained. To fill the gap, the crystal structure of TA was solved by X-ray powder diffraction, and the molecular interactions stabilizing the structure were analyzed by Hirshfeld surface and energy framework analysis. TA crystallizes in the P21/c space group, with its two enantiomers in the asymmetric unit, further confirming the peculiarity of the crystal structure and the difficulty of solving it. TA packing is characterized by alternating enantiomers connected through hydrogen bonds, forming chains, arranged in layers, stabilized by π-stacking. First principle modeling revealed several stable conformations within 4kJ mol−1 of the global minimum and the relaxed potential energy scans revealed modest (8kJ mol−1 to 15kJ mol−1) energy barriers. Such flat energy landscape suggests flexible and dynamic behavior of tiaprofenic acid in solution and in vivo conditions, with multiple suitable docking sites
The Peculiar H-Bonding Network of 4-Methylcatechol: A Coupled Diffraction and In Silico Study
No full textThe crystal structure of 4-methylcatechol (4MEC) has, to date, never been solved, despite its very simple chemical formula C7O2H8 and the many possible applications envisaged for this molecule. In this work, this gap is filled and the structure of 4MEC is obtained by combining X-ray powder diffraction and first principle calculations to carefully locate hydrogen atoms. Two molecules are present in the asymmetric unit. Hirshfeld analysis confirmed the reliability of the solved structure, since the two molecules show rather different environments and H-bond interactions of different directionality and strength. The packing is characterised by a peculiar hydrogen bond network with hydroxyl nests formed by two adjacent octagonal frameworks. It is noteworthy that the observed short contacts suggest strong inter-molecular interactions, further confirmed by strong inter-crystalline aggregation observed by microscopic images, indicating the growth, in many crystallization attempts, of single aggregates taller than half a centimetre and, often, with spherical shapes. These peculiarities are induced by the presence of methyl group in 4MEC, since the parent compound catechol, despite its chemical similarity, shows a standard layered packing alternating hydrophobic and polar layers. Finally, the complexity and peculiarity of the packing and crystal growth features explain why a single crystal could not be obtained for a standard structural analysis
Multivariate versus traditional quantitative phase analysis of X-ray powder diffraction and fluorescence data of mixtures showing preferred orientation and microabsorption
Full text linkIn materials and earth science, but also in chemistry, pharmaceutics and engineering, the quantification of elements and crystal phases in solid samples is often essential for a full characterization of materials. The most frequently used techniques for this purpose are X-ray fluorescence (XRF) for elemental analysis and X-ray powder diffraction (XRPD) for phase analysis. In both methods, relations between signal and quantity do exist but they are expressed in terms of complex equations including many parameters related to both sample and instruments, and the dependence on the active element or phase amounts to be determined is convoluted among those parameters. Often real-life samples hold relations not suitable for a direct quantification and, therefore, estimations based only on the values of the relative intensities are affected by large errors. Preferred orientation (PO) and microabsorption (MA) in XRPD cannot usually be avoided, and traditional corrections in Rietveld refinement, such as the Brindley MA correction, are not able, in general, to restore the correct phase quantification. In this work, a multivariate approach, where principal component analysis is exploited alone or combined with regression methods, is used on XRPD profiles collected on ad hoc designed mixtures to face and overcome the typical problems of traditional approaches. Moreover, the partial or no known crystal structure (PONKCS) method was tested on XRPD data, as an example of a hybrid approach between Rietveld and multivariate approaches, to correct for the MA effect. Particular attention is given to the comparison and selection of both method and pre-process, the two key steps for good performance when applying multivariate methods to obtain reliable quantitative estimations from XRPD data, especially when MA and PO are present. A similar approach was tested on XRF data to deal with matrix effects and compared with the more classical fundamental-parameter approach. Finally, useful indications to overcome the difficulties of the general user in managing the parameters for a successful application of multivariate approaches for XRPD and XRF data analysis are given
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