-
AAPS PharmSciTech Sep 2013A series of blends of polydimethylsiloxane (PDMS) and indomethacin (IMC), containing 20-80 wt.% IMC were obtained and characterized by differential scanning calorimetry,...
A series of blends of polydimethylsiloxane (PDMS) and indomethacin (IMC), containing 20-80 wt.% IMC were obtained and characterized by differential scanning calorimetry, Fourier transform-infrared spectroscopy, and powder X-ray diffraction in order to observe the mutual influence of the two components. The main thermal transitions of PDMS remained un-changed. Both the solvent (tetrahydrofuran, THF) and the PDMS influenced the crystalline form of IMC. The blends were subsequently re-dissolved in THF, with or without cross-linking reagents added and precipitated into diluted aqueous solutions of siloxane-based surfactants. The resulted nanoparticles were analyzed by dynamic light scattering and scanning electron microscopy. Most of the particles had diameters between 200 and 300 nm. The surfactants, the IMC content and the cross-linking influenced the particles size and polydispersity, as well as the nanoparticle yield. The maximum drug release from selected aqueous formulations was 30%.
Topics: Anti-Inflammatory Agents, Non-Steroidal; Dimethylpolysiloxanes; Indomethacin; Microscopy, Electron, Scanning; Nanoparticles; Powder Diffraction; Spectroscopy, Fourier Transform Infrared
PubMed: 23761264
DOI: 10.1208/s12249-013-9989-2 -
Journal of Applied Crystallography Apr 2024NdGa hydride and deuteride phases were prepared from high-quality NdGa samples and their structures characterized by powder and single-crystal X-ray diffraction and...
NdGa hydride and deuteride phases were prepared from high-quality NdGa samples and their structures characterized by powder and single-crystal X-ray diffraction and neutron powder diffraction. NdGa with the orthorhombic CrB-type structure absorbs hydrogen at hydrogen pressures ≤ 1 bar until reaching the composition NdGaH(D), which maintains a CrB-type structure. At elevated hydrogen pressure additional hydrogen is absorbed and the maximum composition recovered under standard temperature and pressure conditions is NdGaH(D) with the LaGaH-type structure. This structure is a threefold superstructure with respect to the CrB-type structure. The hydrogen atoms are ordered and distributed on three fully occupied Wyckoff positions corresponding to tetrahedral (4, 8) and trigonal-bipyramidal (8) voids in the parent structure. The threefold superstructure is maintained in the H-deficient phases NaGaH(D) until 1.6 ≥ ≥ 1.2. At lower H concentrations, coinciding with the composition of the hydride obtained from hydrogenation at atmospheric pressure, the unit cell of the CrB-type structure is resumed. This phase can also display H deficiency, NdGaH(D) (1.1 ≥ ≥ 0.9), with H(D) exclusively situated in partially empty tetrahedral voids. The phase boundary between the threefold superstructure (LaGaH type) and the onefold structure (NdGaH type) is estimated on the basis of phase-composition isotherms and neutron powder diffraction to be = 1.15.
PubMed: 38596740
DOI: 10.1107/S1600576724000554 -
Acta Crystallographica. Section E,... Oct 2022The triclinic structures of poly[(μ-4,4'-bi-phenyldi-carboxyl-ato)di-μ-hydroxido-dicobalt], [Co(CHO)(OH)] , and...
Structures of dicobalt and dinickel 4,4'-bi-phenyldi-carboxyl-ate di-hydroxide, (OCCHCHCO)(OH), = Co and Ni, and di-ammonium 4,4'-bi-phenyldi-carboxyl-ate from powder diffraction data.
The triclinic structures of poly[(μ-4,4'-bi-phenyldi-carboxyl-ato)di-μ-hydroxido-dicobalt], [Co(CHO)(OH)] , and poly[(μ-4,4'-bi-phenyldi-carboxyl-ato)di-μ-hydroxido-dinickel], [Ni(CHO)(OH)] , were established using laboratory X-ray powder diffraction data. These structures, as well as that of poly[(μ-4,4'-bi-phenyldi-carboxyl-ato)di-μ-hydroxido-dimanganese], [Mn(CHO)(OH)] , were optimized using density functional techniques. The structure of di-ammonium 4,4'-bi-phenyldi-carboxyl-ate, 2NH ·CHO , was also solved using laboratory powder data. The Mn and Co compounds are isostructural: the octa-hedral MO groups share edges to form chains running parallel to the -axis. These chains share corners (OH groups) to link into layers lying parallel to the plane. The hydroxyl groups do not participate in hydrogen bonds. The structure of (NH)BPDC consists of alternating layers of BPDC and ammonium ions lying parallel to the plane. Each hydrogen atom of the ammonium ions in (NH)BPDC participates in a strong N-H⋯O hydrogen bond.
PubMed: 36250126
DOI: 10.1107/S2056989022009288 -
Materials (Basel, Switzerland) Jun 2023The ordered CaTaGaSiO and disordered LaGaSiO crystals of the lantangallium silicate family were grown via the Czochralski method. The independent coefficients of thermal...
The ordered CaTaGaSiO and disordered LaGaSiO crystals of the lantangallium silicate family were grown via the Czochralski method. The independent coefficients of thermal expansion of crystals αc and αa were determined using X-ray powder diffraction based on the analysis of X-ray diffraction spectra measured in the temperature range of 25~1000 °C. It is shown that, in the temperature range of 25~800 °C, the thermal expansion coefficients are linear. At temperatures above 800 °C, there is a nonlinear character of the thermal expansion coefficients, associated with a decrease in the Ga content in the crystal lattice.
PubMed: 37374653
DOI: 10.3390/ma16124470 -
Cellulose (London, England) Apr 2014Previous studies of calculated diffraction patterns for cellulose crystallites suggest that distortions that arise once models have been subjected to MD simulation are...
Previous studies of calculated diffraction patterns for cellulose crystallites suggest that distortions that arise once models have been subjected to MD simulation are the result of both microfibril twisting and changes in unit cell dimensions induced by the empirical force field; to date, it has not been possible to separate the individual contributions of these effects. To provide a better understanding of how twisting manifests in diffraction data, the present study demonstrates a method for generating twisted and linear cellulose structures that can be compared without the bias of dimensional changes, allowing assessment of the impact of twisting alone. Analysis of unit cell dimensions, microfibril volume, hydrogen bond patterns, glycosidic torsion angles, and hydroxymethyl group orientations confirmed that the twisted and linear structures collected with this method were internally consistent, and theoretical powder diffraction patterns for the two were shown to be effectively indistinguishable. These results indicate that differences between calculated patterns for the crystal coordinates and twisted structures from MD simulation can result entirely from changes in unit cell dimensions, and not from microfibril twisting alone. Although powder diffraction patterns for models in the 81-chain size regime were shown to be unaffected by twisting, suggesting that a modest degree of twist is not inconsistent with experimental data, it may be that other diffraction techniques are capable of detecting this structural difference. Until such time as definitive experimental evidence comes to light, the results of this study suggest that both twisted and linear microfibrils may represent an appropriate model for cellulose Iβ.
PubMed: 24729665
DOI: 10.1007/s10570-013-0051-z -
Journal of Applied Crystallography Feb 2020A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small...
A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small-angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin-echo small-angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from α-FeO powder samples. The resulting -spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample.
PubMed: 32047407
DOI: 10.1107/S160057671901611X -
Powder Diffraction 2020The National Institute of Standards and Technology (NIST) certifies a suite of Standard Reference Materials (SRMs) to evaluate specific aspects of instrument performance...
The National Institute of Standards and Technology (NIST) certifies a suite of Standard Reference Materials (SRMs) to evaluate specific aspects of instrument performance of both X-ray and neutron powder diffractometers. This report describes SRM 660c, the fourth generation of this powder diffraction SRM, which is used primarily for calibrating powder diffractometers with respect to line position and line shape for the determination of the instrument profile function (IPF). It is certified with respect to lattice parameter and consists of approximately 6 g of lanthanum hexaboride (LaB) powder. So that this SRM would be applicable for the neutron diffraction community, the powder was prepared from an isotopically enriched B precursor material. The microstructure of the LaB powder was engineered specifically to yield a crystallite size above that where size broadening is typically observed and to minimize the crystallographic defects that lead to strain broadening. A NIST-built diffractometer, incorporating many advanced design features, was used to certify the lattice parameter of the LaB powder. Both Type A, statistical, and Type B, systematic, uncertainties have been assigned to yield a certified value for the lattice parameter at 22.5 °C of = 0.415 682 6 ± 0.000 008 nm (95% confidence).
PubMed: 33311851
DOI: 10.1017/s0885715620000068 -
Acta Crystallographica. Section A,... May 2014This article proposes a new theory of X-ray scattering that has particular relevance to powder diffraction. The underlying concept of this theory is that the scattering...
This article proposes a new theory of X-ray scattering that has particular relevance to powder diffraction. The underlying concept of this theory is that the scattering from a crystal or crystallite is distributed throughout space: this leads to the effect that enhanced scatter can be observed at the `Bragg position' even if the `Bragg condition' is not satisfied. The scatter from a single crystal or crystallite, in any fixed orientation, has the fascinating property of contributing simultaneously to many `Bragg positions'. It also explains why diffraction peaks are obtained from samples with very few crystallites, which cannot be explained with the conventional theory. The intensity ratios for an Si powder sample are predicted with greater accuracy and the temperature factors are more realistic. Another consequence is that this new theory predicts a reliability in the intensity measurements which agrees much more closely with experimental observations compared to conventional theory that is based on `Bragg-type' scatter. The role of dynamical effects (extinction etc.) is discussed and how they are suppressed with diffuse scattering. An alternative explanation for the Lorentz factor is presented that is more general and based on the capture volume in diffraction space. This theory, when applied to the scattering from powders, will evaluate the full scattering profile, including peak widths and the `background'. The theory should provide an increased understanding of the reliability of powder diffraction measurements, and may also have wider implications for the analysis of powder diffraction data, by increasing the accuracy of intensities predicted from structural models.
PubMed: 24815975
DOI: 10.1107/S205327331400117X -
Acta Crystallographica. Section E,... Feb 2017The crystal structure of the title compound, 3Rb·CHO·HO, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density...
The crystal structure of the title compound, 3Rb·CHO·HO, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The hy-droxy group participates in an intra-molecular hydrogen bond to the deprotonated central carboxyl-ate group with graph-set motif (5). The water mol-ecule acts as a hydrogen-bond donor to both terminal and central carboxyl-ate O atoms. The three independent rubidium cations are seven-, six- and six-coordinate, with bond-valence sums of 0.84, 1.02, and 0.95, respectively. In the extended structure, their polyhedra share edges and corners to form a three-dimensional network. The hydro-phobic methyl-ene groups occupy channels along the axis.
PubMed: 28217348
DOI: 10.1107/S2056989017000743 -
Materials (Basel, Switzerland) Apr 2019A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl's original procedure of reducing...
A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl's original procedure of reducing Tl(I)-iodide by sodium liquid ammonia solutions. The powder diffraction pattern obtained by the high temperature synthesis using classical solid-state techniques allowed a model-independent unambiguous structure solution and refinement of tetragonal distorted NaTl (Rp = 0.0179, wRp = 0.0246, R = 0.0477, wR = 0.0527, GooF = 1.24).
PubMed: 31027267
DOI: 10.3390/ma12081356