Structural characterization of the of inorganic and organic hydrotalcites

Layered double hydroxides are versatile materials used for intercalating bioactive molecules, both in pharmaceutical and cosmetic fields, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability, and/or obtaining modified release properties. Hydrotalcite is commercially available in its carbonate form, which is usually transformed into the nitrate form and finally exchanged by organic anions to obtain or regulate bioactivity or photo-activity effects (1). In this study all the steps of these transformations were characterized from the structural viewpoints by X-ray powder diffraction (XRPD) and automated electron diffraction tomography (ADT). ADT allowed shedding light on the nitrate position and conformation inside LDH. XRPD demonstrated at first that the presence of carbonate impurities is able to drive the intercalation of organic molecules into LDH, since CO32- contaminated samples tend to assume d-spacings roughly multiple of LDH-CO3 d-spacing. Finally XRPD was employed at in situ conditions to unravel the structural transformation occurring during the substitution of carbonate by nitrate ion and of the nitrate ion by organic anions. The carbonate-nitrate substitutions resulted to be very rapid (only few seconds) and only the use of a fast area detector, coupled to synchrotron radiation, allowed obtaining reliable patterns to perform XRPD refinement of the disordered structure at the sub-second time resolution. The nitrate-organic substitution resulted slower and depending on the chemical properties of the organic molecules

Résolution des structures cristallines par diffraction des rayons X et neutrons sur poudres en utilisant les méthodes d'optimisation globale

The main subject of this thesis is the resolution of crystal structures by X-ray and neutrons powder diffraction using global optimisation methods. The first subject is the order-disorder phenomena observed in some globular organic molecular solids. The second is the opiate family of neuropeptides. These neurotransmitters regulate sensory functions including pain and control of respiration in the central nervous system. The aim of our study was to try to determine the crystal structure of Leu-enkephalin and some of its sub-fragments. The determination of the crystal structures has been done performing Monte Carlo simulations. The third is the location of benzene in a sodium-X zeolite. The zeolite framework was already known and the benzene has been localized by simulated annaeling and by the use of maximum entropy maps.Ce travail de thèse s'articule autour la résolution des structures cristallines par diffraction des rayons X et neutrons sur poudres en utilisant les méthodes d'optimisation globale. Le premier sujet concerne les phénomènes d'ordre-désordre observés dans certains solides moléculaires organiques de type globulaire. Le deuxième est centré sur la famille des neuropeptides opiacés. Ces neurotransmetteurs régulent, au sein du système nerveux central, les fonctions sensitives telles que la douleur et la respiration. Le but de notre étude était de déterminer la structure cristalline de la Leu-enkephaline, sous sa forme complète ou fragmentée. Enfin, le troisième sujet d'étude est la localisation d'une molécule de benzène adsorbée sur des zéolithes X au sodium de structure déjà connue. Ce résultat a été obtenu par simulation et l'utilisation de cartes d'entropie maximale

Résolution des structures cristallines par diffraction des rayons X et neutrons sur poudres en utilisant les méthodes d'optimisation globale

Ce travail de thèse s'articule autour la résolution des structures cristallines par diffraction des rayons X et neutrons sur poudres en utilisant les méthodes d'optimisation globale. Le premier sujet concerne les phénomènes d'ordre-désordre observés dans certains solides moléculaires organiques de type globulaire. Le deuxième est centré sur la famille des neuropeptides opiacés. Ces neurotransmetteurs régulent, au sein du système nerveux central, les fonctions sensitives telles que la douleur et la respiration. Le but de notre étude était de déterminer la structure cristalline de la Leu-enkephaline, sous sa forme complète ou fragmentée. Enfin, le troisième sujet d'étude est la localisation d'une molécule de benzène adsorbée sur des zéolithes X au sodium de structure déjà connue. Ce résultat a été obtenu par simulation et l'utilisation de cartes d'entropie maximale.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

The Crystal Structure of Calcium Sebacate by X-ray Powder Diffraction Data

Sodium 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

In Situ X-ray Diffraction Study of Xe and CO2 Adsorption in Y Zeolite: Comparison between Rietveld and PCA-Based Analysis

New very fast and efficient detectors, installed both on laboratory instruments and synchrotron facilities, allow the monitoring of solid-state reactions from subsecond to minute scales with the production of large amounts of data. Traditional \u201cone-by-one\u201d pattern refinement needs complementary approaches, useful to handle hundreds to thousands of X-ray patterns. Principal-component analysis (PCA) has been applied to these fields in the last few years to speed up analysis with the specific goals of assessing data quality, identifying patterns where a reaction occurs, and extracting the kinetics. PCA is applied to the adsorption/desorption of Xe and CO2 within a Y zeolite. CO2 sequestration is a key issue in relation to climate change, while Xe is a critical raw material, and its purification is an important topic for the industry. At first, results were compared to traditional sequential Rietveld refinement. CO2-Y data were also compared with in situ single crystal data to investigate the different potentialities of PCA in the two cases. Two CO2 adsorption sites were confirmed, while three Xe sites were identified. CO2 showed a more linear adsorption trend with decreasing temperature, while Xe showed a more sigmoidal-like trend. Xe only showed site-dependent behavior in adsorption. Finally, PCA and correlation analysis, applied to analyze the parameters obtained from Rietveld refinement, highlighted finer details: in particular, this approach showed that the Y zeolite framework responded differently to CO2 and Xe adsorption

The Crystal Structure of Calcium Sebacate by X-ray Powder Diffraction Data

Sodium 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

The Peculiar H-Bonding Network of 4-Methylcatechol: A Coupled Diffraction and In Silico Study

The 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

XRF and XRPD data sets in ternary mixtures with high level micro-absorption and/or preferred orientations problems for phase quantification analysis

Micro-absorption (MA) and/or preferred orientations (PO) are two among the major problems affecting quantitative phase analysis (QPA) by X-ray Powder Diffraction Data (XRPD) in industrial samples such as minerals and ores, additives, cements, friction materials, coal combustion by-products. Typically XRPD data are coupled to elemental analysis by X-ray Fluorescence (XRF) to facilitate phase recognition and quantification when elements heavier than sodium are present. Graphite and urea are typical examples of large production industrial commodities showing such analytical problems. The present article provides a recipe to produce sets of data of increasing difficulty to test the performances of different approaches and/or software\u2019s for QPA by XRPD in graphite, zinc acetate and urea containing samples. Graphite, due to its platelet morphology, can exhibit orientation and was chosen because it is possible to control its PO degree by sieving. Simplex-centroid design augmented was used for the design of the experiments to select the mixtures with the more possible homogeneous exploration of the ternary experimental domains, from pure phase to equal-weighted mixtures. The different data sets collected on the four experimental domains by XRF and XRPD are provided and stored as a repository on Mendeley Data. Using the same approach, additional data sets sets with different composition and/or experimental setup can be added by us or any other contributor with the same DoE approach to create a wide open access data set of standardized X-ray powder diffraction and X-ray fluorescence data