Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Powder Diffraction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76Linked to original sources
PubMedDate not supplied

Preparation and characterization of a new polymorphic form and a solvate of glibenclamide.

A new crystalline form and a solvate of glibenclamide were prepared and characterized by hot-stage microscopy, DSC, IR, scanning electron microscope, X-ray powder diffraction and dissolution studies. From I, III and the solvate which melt at 174.4, 153.2 and 109.3 degrees C, were obtained by crystallization. Significant differences between the three forms in the X-ray and IR spectra were observed. Polymorphic transformation was observed for the least stable form (III) to the most stable one (form I) upon storage at different temperatures and trituration. The dissolution profiles showed significant differences between the three forms, with form III having the highest dissolution rate.

Calorimetry, Differential Scanning↗
PubMed1998

Identification of zinc phosphide in a falsely labeled rodenticide bait.

"Kela" is a commercial rodenticide bait commonly used in Israel, made of wheat grains, which, according to its label, contains chlorophacinone. This product was involved in the death case of a man in which the victim's female companion was accused of assisting in this suicide and was subsequently convicted. Analysis of the wheat grains revealed zinc phosphide, whose use is restricted to authorized exterminators only, instead of chlorophacinone. Zinc phosphide was identified using microscopic examination, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and X-ray powder diffraction (XRD).

Aged↗
PubMed1996

Formation of hydrated calcium oxalates in the presence of poly-L-aspartic acid.

The effect of poly-L-aspartic acid (PA) on the crystal structure of calcium oxalate crystals grown after spontaneous nucleation was evaluated as a function of relative supersaturation and calcium:oxalate ratio in a buffered salt solution, with pH and ionic strength in the range of normal human urine. PA was used as a model for naturally occurring acidic urine proteins that have been shown to inhibit nucleation and growth of calcium oxalate crystals. The crystals grown were characterized by optical microscopy and X-ray powder diffraction. It was observed that calcium oxalate monohydrate was the preferred crystalline form in the absence of added PA, and it was the only crystalline form obtained at most conditions tested without PA. However, the presence of PA favored the formation of calcium oxalate dihydrate crystals, when present in adequate quantities. The quantity of PA required to affect this change in preferred crystal structure was increased at higher supersaturations and at lower calcium:oxalate ratios, exhibiting a non-linear dependence on both variables. PA was also shown to be a kinetic inhibitor of calcium oxalate dihydrate crystallization. Aspartic acid monomer was found to cause no change in the preferred structure of calcium oxalate monohydrate at mass concentrations well beyond those required with PA to obtain 100% calcium oxalate dihydrate, indicating the critical importance of the polymeric nature of PA for this effect on crystal structure.

Calcium Oxalate↗
PubMed2006

Structural determination of the stable and meta-stable forms of atomoxetine HCl using single crystal and powder X-ray diffraction methods.

Stratteratrade mark is the first FDA-approved nonstimulant medication for the treatment of Attention Deficit Hyperactivity Disorder (ADHD) in children, adolescents, and adults. Two polymorphic forms and an amorphous form of the active pharmaceutical ingredient, atomoxetine HCl, were discovered during drug development. The thermodynamically stable polymorphic form was selected for the commercial product. The stable form readily grows as crystals suitable for single crystal diffraction. The meta-stable crystal form is isolated by rapid crystallization, providing crystals that are too small for routine single crystal methods; consequently its structure was determined by X-ray powder diffraction.

Atomoxetine Hydrochloride↗
PubMed2002

Structure solution of a novel aluminium methylphosphonate using a new simulated annealing program and powder X-ray diffraction data.

The structure of a novel layered aluminium methylphosphonate, formula Al2(CH3PO3)3, has been solved from laboratory X-ray powder diffraction data by simulated annealing of five independent structural sub-units, revealing a combination of four- and five-fold coordinated aluminiums within the inorganic lamellae that is unique for this kind of solid.

Algorithms↗
PubMed1998

[The powder X-ray diffraction analysis with Fourier spectrum of Chinese material medica Cortex Cinnamomi].

OBJECTIVE: To develop a method for the identification of Chinese medicinal materials in diffraction space. METHOD: Using powder X-ray diffraction analysis to obtain the Fourier spectrum of 10 samples of Cortex Cinnamomi. RESULTS: The analysis shows that each of the 10 samples has its own Fourier pattern topology and characteristic peaks which are connected with its chemical composition. CONCLUSION: Cortex Cinnamomi can be identified successfully according to its topology and characteristic peaks.

Cinnamomum↗
PubMed2003

[The study on fingerprint of compound ginseng injection by powder X-ray diffraction].

OBJECTIVE: To establish the fingerprint of "Compound Ginseng Injection", including Ginseng and Pericarpium Citri Reticulatae (Chenpi) raw material, their intermediate and injection by powder X-ray diffraction. METHOD: Powder X-ray diffraction was used to analyze Ginseng and Chenpi raw material, their intermediate and injection, contrasted and analyzed the graphs to establish the fingerprint. RESULT: The fingerprint of Ginseng and Chenpi raw material, their intermediate and injection was established. Furthermore, the fingerprint of them showed an excellent recurrence and stability. CONCLUSION: Powder X-ray diffraction method can be used to control the quality of "Compound Ginseng Injection".

Citrus↗
PubMed2006

Hydrated Cs+-exchanged MFI zeolites: location and population of Cs+ cations and water molecules in hydrated Cs6.6MFI from in and ex situ powder X-ray diffraction data as a function of temperature and other experimental conditions.

Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97-106) to hydrated analogues, we have determined the crystal structures of members of the Cs(6.6)H(0.3)MFI.xH(2)O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs(+) cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H(2)O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (approximately 1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H(2)O)(n) clusters and one (H(2)O)(4) cluster in the MFI channel system: Cs2(H(2)O)(5) centered at x/y/z approximately -0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H(2)O)(4) centered at approximately 0.056/0.240/0.889 (the zigzag channel openings), Cs3(H(2)O)(2) centered at approximately 0.228/0.25/0.899 (in the zigzag channel), and the (H(2)O)(4) cluster (in the zigzag channel) bonded to Cs1 and Ow1. (H(2)O)(4) and Cs3(H(2)O)(2) exclude each other. The Cs2(H(2)O)(5) clusters are connected through weak Ow5...Ow5' hydrogen bonds (2.88 A) and form polymeric chains in the straight channel direction (010). During progressive hydration this Cs2 cation enlarges its hydration shell, stepwise, from Cs2(H(2)O)(2) to Cs2(H(2)O)(3), to Cs2(H(2)O)(4), and finally to a Cs2(H(2)O)(5) cluster. During the dehydration process, these extraframework species migrate, and it is shown that for varying total H(2)O/uc loadings the individual populations of the Cs(+) cations and H(2)O molecules strongly depend on experimental and measurement (in situ vs ex situ) conditions. The shapes of the channels change also; except for T > 150 degrees C, in all the Cs(6.6)H(0.3)MFI.xH(2)O phases, the straight channel D10R (double 10-ring) pore openings (1.16 < epsilon < 1.23) become strongly elliptical. The framework structure of all the investigated phases conforms to orthorhombic Pnma space group symmetry. Hydration and dehydration in Cs(6.6)MFI are fully reversible processes. From a knowledge of the Cs(+) locations, we are able to estimate, by computer simulations, the positions of H(2)O molecules in Cs(6.6)H(0.3)MFI.28H(2)O. The maximum theoretically possible water loading in an hypothetical and idealized cationless [Cs(6.6)H(0.3)]MFI structure amounts to 48 H(2)O/uc (nine independent water species), which is in fair agreement with existing high-pressure data (47 H(2)O/uc). This value is to be compared with the water saturation capacity obtained in a structural refinement of sealed-tube diffraction data of a proton-exchanged H(6.9)MFI.38H(2)O (seven independent water molecules). In the crystal structure of this H-ZSM-5 phase, the straight channel openings are almost circular (epsilon = 1.08). From this we conclude that the main factor responsible for the flexibility of the MFI framework is the presence of the Cs(H(2)O)(n)() clusters residing in, or close to, the straight channel double 10-rings.

Journal Article↗
PubMed2004

Synthesis, crystal structure from single-crystal and powder X-ray diffraction data, and thermal behavior of mixed potassium lanthanide squarates: thermal transformations of layered [Ln(H2O)6]K(H2C4O4)(C4O4)2 into pillared LnK(C4O4)2 (Ln = Y, La, Gd, Er).

A new series of mixed potassium and rare-earth squarates, [Ln(H(2)O)(6)]K(H(2)C(4)O(4))(C(4)O(4))(2) (Ln = Y, La, Gd, Er), has been synthesized and structurally characterized from single-crystal X-ray diffraction and spectroscopic analyses. The yttrium-based compound crystallizes with a monoclinic symmetry, space group C2/c [a = 8.3341(2) A, b = 37.7094(9) A, c = 11.7195(3) A, beta = 90.3959(9) degrees , V = 3683.1(2) A(3), Z = 8]. The structure is built from layers maintained together via hydrogen bonds. Within a layer, squarate ligands act as linkers between lanthanide and potassium cations. The thermal decomposition of the precursors has been studied by powder thermodiffractometry and thermal analyses. It is shown that crystalline intermediate phases are formed during the degradation. Among them, unprecedented mixed anhydrous squarates, LnK(C(4)O(4))(2), could be isolated. The crystal structure of the Y compound has been solved ab initio from X-ray powder diffraction data, using direct-space methods [a = 6.2010(5) A, c = 11.639(1) A, V = 447.55 A(3), Z = 2]. The structure consists of layers of edge-sharing YO(8) and KO(8) antiprisms, pillared by mu(8)-squarate groups. The end of the precursor decomposition is marked by the formation of cubic sesquioxides Ln(2)O(3), including lanthanum oxide.

Journal Article↗
PubMed2006

The crystal structure of Zr2NiD4.5.

The crystal structure of Zr2NiD4.5 has been determined by a combination of synchrotron radiation powder X-ray diffraction, electron diffraction and powder neutron diffraction data. Deuterium ordering results in a triclinic supercell given by asuper=6.81560 (7), bsuper=8.85137 (9), csuper=8.88007 (10) A, alphasuper=79.8337 (8), betasuper=90.0987 (9), gammasuper=90.3634 (9) degrees, which relates to the non-super unit cell as asuper=-a, bsuper=-b-c, csuper=-b+c. The centrosymmetric and fully ordered deuterium sublattice was determined by simulated annealing and Rietveld refinement. Deuterium was found to occupy three types of tetrahedral sites: two that are coordinated by four Zr atoms and one that is coordinated by three Zr atoms and one Ni atom. All D-D distances are longer than 2 A. The feasibility of the crystal structure was supported by density functional theory calculations.

Journal Article↗
PubMed2000

Ce4

The yellow-orange oxonitridosilicate oxide Ce4[Si4O4N6]O was obtained by the reaction of cerium metal with Si(NH)2 and SiO2 in a radiofrequency furnace at 1560 degrees C. The crystal structure was determined by single-crystal X-ray diffraction (a = 1033.67(6) pm, P2,3, Z = 4, R1 = 0.0412, wR2 = 0.0678) and powder neutron diffraction. In the solid there are complex cations [Ce4O]10+ that are enveloped by a hyperbolical layer structure [Si4O4N6]10-. The layer is built up by corner-sharing SiON3 tetrahedra of Q3 type. The oxygen atoms of the SiON3 tetrahedra are terminally bound to Si, while all nitrogen atoms bridge two neighboring Si centres. The crystallographic differentiation of O and N was unequivocally possible by a careful evaluation of the single-crystal X-ray diffraction data combined with lattice-energy calculations by using the MAPLE concept (Madelung part of lattice energy). Furthermore the results were confirmed by the chemical analyses. Subsequently, the determined N/O distribution and their crystallographic ordering was proved by neutron powder diffraction. In accordance with the molar ratio Si:(O,N) = 2:5 the [Si4O4N6]10- network may be classified as a layer silicate. In this specific case a hyperbolically corrugated topology of the layers is observed; this is correlated to periodic nodal surface (PNS) representatives.

Journal Article↗
PubMed2000

Comparative evaluation of the degree of indomethacin crystallinity by chemoinfometrical Fourier-transformed [corrected] near-infrared spectroscopy and conventional powder X-ray diffractometry.

A chemoinfometrical method for evaluating the degree of crystallinity based on Fourier-transformed [corrected] near-infrared (FT-NIR) spectroscopy was established and compared with the conventional powder X-ray diffraction method. Powder X-ray diffraction profiles and FT-NIR spectra were recorded for 11 kinds of standard materials with various degrees of crystallinity obtained by physically mixing crystalline and amorphous indomethacin (IMC). Chemoinfometric analysis was performed on the FT-NIR spectral data sets by multiple linear regression (MLR) (MLR-Set-Up Search program). The crystalline and amorphous forms showed significant NIR spectral peaks. MLR analysis was performed based on normalized NIR spectra sets for standard samples of known crystallinity. A calibration equation was determined to minimize the root mean square error of prediction. The predicted crystallinity values were reproducible and had a smaller standard deviation. The values of crystallinity predicted by X-ray powder diffractometry and FT-NIR spectrometry suggested a satisfactory correlation between the 2 techniques. The results indicated that FT-NIR spectroscopy provides for an accurate quantitative analysis of crystallinity compared with conventional X-ray diffractometry.

Calorimetry, Differential Scanning↗
PubMed2006

Understanding the structural properties of a dendrimeric material directly from powder X-ray diffraction data.

Complete structure determination of an early-generation dendrimeric material has been carried out directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. This work represents the first application of modern direct-space techniques for structure determination from powder X-ray diffraction data in the case of a dendrimeric material and paves the way for the future application of this approach to enable complete structure determination of other dendrimeric materials that cannot be prepared as single crystal samples suitable for single crystal X-ray diffraction studies.

Letter↗
PubMed2000

Powder and single-crystal X-ray diffraction study of the structure of

From powder pattern indexing it has been demonstrated that [Y(H(2)O)](2)(C(2)O(4))(CO(3))(2), yttrium oxalate carbonate, crystallizes with orthorhombic symmetry, space group C222(1), a = 7. 8177 (7), b = 14.943 (1), c = 9.4845 (7) A, V = 1108.0 (1) A(3), Z = 4. This unit cell displays a doubling of the c parameter, arising from weak diffraction lines observed in the powder diffraction pattern, with respect to results reported in the literature. The crystal structure has been solved ab initio using direct methods from powder data and has been confirmed by additional single-crystal data collected with a CCD area detector. The overall crystal structure is similar for both unit cells, except that an alternation of the carbonate groups in the direction parallel to the screw axis is displayed in the larger cell, while with the suggested half unit cell (space group C2mm) the carbonate groups would show only one orientation. The unit-cell determination strategy from single-crystal diffraction, collected with Nonius CAD-4 and Nonius Kappa CCD diffractometers, is discussed with respect to the results extracted from the powder diffraction pattern. The study demonstrates the power and usefulness of the full trace of a powder pattern for the detection of subtle structure details.

Journal Article↗
PubMed2001

Quantitative determination of binary and tertiary calcium carbonate mixtures using powder X-ray diffraction.

The ability to determine the calcium carbonate polymorphic ratio of calcite, aragonite and vaterite in a mixture is important for a variety of applications, particularly the fields of biomineralisation and crystal engineering. Raman spectroscopy and powder X-ray diffraction were used to quantitatively determine the polymorphic composition of both binary and tertiary mixtures of calcium carbonate. It was found that the quantitative detection limits of powder X-ray diffraction were superior to both Raman and infrared spectroscopy.

Calcium Carbonate↗
PubMed2004

Ab initio structure determination of the hygroscopic anhydrous form of alpha-lactose by powder X-ray diffraction.

Annealing of alpha-lactose monohydrate at 408 K yielded a mixture of this compound with hygroscopic anhydrous alpha-lactose. A powder X-ray diffraction pattern of this mixture was recorded at room temperature. The starting structural model of hygroscopic alpha-lactose was found by a Monte Carlo simulated-annealing method. The final structure was obtained through Rietveld refinements, with soft restraints on interatomic bond lengths and bond angles, and crystalline energy minimization to locate the H atoms of the hydroxy groups. The crystalline cohesion is achieved by networks of O-H...O hydrogen bonds that differ from those of the monohydrate phase. The width of the Bragg peaks is interpreted by a phenomenological microstructural approach in terms of isotropic size effects and anisotropic strain effects.

Hydrogen Bonding↗