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At least 19 recordsLinked to original sources

PubMed2002

New applications of electron diffraction in the pharmaceutical industry: polymorph determination by using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques.

Electron diffraction has been recently used in the pharmaceutical industry to study the polymorphism in crystalline drug substances. While conventional X-ray diffraction patterns could not be used to determine the cell parameters of two forms of the microcrystalline GP IIb/IIIa receptor antagonist roxifiban, a combination of electron single-crystal and synchrotron powder diffraction techniques were able to clearly distinguish the two polymorphs. The unit-cell parameters of the two polymorphs were ultimately determined using new software routines designed to take advantage of each technique's unique capabilities. The combined use of transmission electron microscopy (TEM) and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large-unit-cell, micron-sized) polymorphic pharmaceutical compounds.

Amidines↗

PubMed2003

Protein crystal structure analysis from high-resolution X-ray powder-diffraction data.

Although high-resolution powder diffraction of proteins is in its infancy, we can easily see future developments of the method that will allow examination of protein structures that exceed 100 kDa. In particular, current data-collection technology scans the powder-diffraction pattern a few points at a time over a very narrow field of view. The use of high-resolution imaging technology and X-ray focusing optics should improve this 1000-fold or more, making it possible to use powder diffraction on a laboratory X-ray source to screen for the formation of protein/drug complexes and to determine their structures.

Animals↗

PubMed1999

Polymorph determination for the GP IIb/IIIa antagonist, roxifiban, using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques.

Unit cell parameters of two polymorphs of roxifiban have been determined by a combination of transmission electron microscopy (TEM) single-crystal and synchrotron X-ray powder diffraction techniques. While it was difficult to differentiate the two forms by their standard X-ray diffraction patterns, the high-resolution synchrotron patterns clearly showed striking differences. Unit cells for the two forms required the use of cell parameters derived from TEM diffraction patterns. The two unit cells are, not surprisingly, very similar except for a doubling of one of the axes for form II. The combined use of TEM and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large unit cell) polymorphs.

Amidines↗

PubMed2002

The Powder Diffraction File: present and future.

The International Centre for Diffraction Data (ICDD) produces the Powder Diffraction File (PDF). This paper discusses some of the seminal events in the history of producing this primary reference for powder diffraction. Recent key events that center on collaborative initiatives have led to an enormous jump in entry population for the PDF. Collective efforts to editorialize the PDF are ongoing and provide enormous added value to the file. Recently, the ICDD has created a new series of the PDF, designated PDF-4. These relational database structures are being used to house the PDF of the future. The design and benefits of the PDF-4 are described.

Journal Article↗

PubMed1999

Crystallization in Nonaqueous Media of Co- and Mn-Substituted Microporous Aluminophosphates Investigated by in Situ Synchrotron X-ray Powder Diffraction.

In situ synchrotron X-ray powder diffraction was used to investigate the crystallization of microporous transition metal-substituted aluminophosphates from nonaqueous media. The gels contained ethylene glycol and triethylamine as the template and were heated in quartz glass capillaries at temperatures up to 200 degrees C. The following crystalline products were formed: MnAPO-5, [AFI], CoAPO-5, [AFI], and AlPO(4)-5, [AFI]. Three nonaqueous systems were investigated in situ, where the crystallization of MAPO-5-type materials were followed. Solvothermal crystallization of MnAPO-5 and CoAPO-5 was studied, and the effect of adding HF as a mineralizing agent was investigated. Time-resolved powder diffraction data were collected using a translating imaging plate (TIP) camera, and crystallization curves were extracted using integrated diffraction peaks. Kinetic analysis of the crystallization curves was performed using an Avrami-type expression, alpha(t) = exp(-(kt)(n)()). Apparent activation energies were determined from Arrhenius plots: MnAPO-5, 94 kJ/mol; MnAPO-5(HF), 68 kJ/mol; CoAPO-5, 61 kJ/mol. Crystallization of CoAPO-5 is faster than for MnAPO-5, and the values for n obtained by fitting with the Avrami-type expression were significantly lower for CoAPO-5 than for MnAPO-5.

Journal Article↗

PubMed2002

New Powder Diffraction File (PDF-4) in relational database format: advantages and data-mining capabilities.

The International Centre for Diffraction Data (ICDD) is responding to the changing needs in powder diffraction and materials analysis by developing the Powder Diffraction File (PDF) in a very flexible relational database (RDB) format. The PDF now contains 136,895 powder diffraction patterns. In this paper, an attempt is made to give an overview of the PDF-4, search/match methods and the advantages of having the PDF-4 in RDB format. Some case studies have been carried out to search for crystallization trends, properties, frequencies of space groups and prototype structures. These studies give a good understanding of the basic structural aspects of classes of compounds present in the database. The present paper also reports data-mining techniques and demonstrates the power of a relational database over the traditional (flat-file) database structures.

Journal Article↗

PubMed2000

Octahedral deformations and cationic displacements in the ferroelectric PbHf(0.8)Ti(0.2)O(3): a neutron powder diffraction study from 10 to 770 K

Neutron powder diffraction data, collected over the temperature range 10-770 K, have been analysed in order to make a detailed characterization of the sequence of phase transitions occurring in the Hf-rich ferroelectric PbHf(0.8)Ti(0.2)O3, titanium hafnium lead oxide. Over the whole temperature range this compound undergoes two phase transitions, which involve cationic displacements and octahedral deformations (tilt and/or distortion) leading to strongly distorted perovskite-type structures. The first transition appears around 415 K between two ferroelectric rhombohedral phases: a low-temperature nonzero-tilt phase F(RL) (space group R3c) and an intermediate zero-tilt phase FRH (space group R3m). The second one, detected around 520 K, is associated with a ferroelectric to-paraelectric transition between the FRH phase and the Pc cubic phase (space group Pm3m). From high-resolution neutron powder diffraction data (diffractometer 3T2-LLB, Saclay, France, lambda = 1.2251 A), the crystallographic structure of the three successive phases has been accurately determined at the following temperatures: T = 10 K (FRL): space group R3c, Z = 6, a(hex) = 5.7827 (1), c(hex) = 14.2702 (4) A, V(hex) = 413.26 (2) A3; T = 150 K (F(RL)): space group R3c, Z = 6, a(hex) = 5.7871 (1), C(hex) = 14.2735 (4) A, V(hex) = 413.98 (3) A3; T = 290 K (FRL): space group R3c, Z = 6, a(hex) = 5.7943 (1), C(hex) = 14.2742 (5) A, V(hex) = 415.04 (3) A3; T = 440 K (F(RH)): space group R3c, Z = 6, a(hex) = 5.8025 (1), c(hex) = 14.2648 (4) A, V(hex) = 415.94 (3) A3; T = 520 K (Pc): space group Pm3m, Z = 1, a(cub) = 4.1072 (2) A, V(cub) = 69.29 (1) A3. In addition, a neutron powder thermodiffractometry experiment, performed between 290 and 770 K (diffractometer D1B-ILL, Grenoble, France, lambda = 2.533 A), has been used to study in situ the temperature-induced phase transitions. From sequential Rietveld refinements, the temperature dependence of the cation displacements and the rotation and/or distortion of oxygen octahedra was derived.

Journal Article↗

PubMed2000

The first protein crystal structure determined from high-resolution X-ray powder diffraction data: a variant of T3R3 human insulin-zinc complex produced by grinding.

X-ray diffraction analysis of protein structure is often limited by the availability of suitable crystals. However, the absence of single crystals need not present an insurmountable obstacle in protein crystallography any more than it does in materials science, where powder diffraction techniques have developed to the point where complex oxide, zeolite and small organic molecular structures can often be solved from powder data alone. Here, that fact is demonstrated with the structure solution and refinement of a new variant of the T(3)R(3) Zn-human insulin complex produced by mechanical grinding of a polycrystalline sample. High-resolution synchrotron X-ray powder diffraction data were used to solve this crystal structure by molecular replacement adapted for Rietveld refinement. A complete Rietveld refinement of the 1630-atom protein was achieved by combining 7981 stereochemical restraints with a 4800-step (d(min) = 3.24 A) powder diffraction pattern and yielded the residuals R(wp) = 3.73%, R(p) = 2.84%, R(F)(2) = 8.25%. It was determined that the grinding-induced phase change is accompanied by 9.5 and 17.2 degrees rotations of the two T(3)R(3) complexes that comprise the crystal structure. The material reverts over 2-3 d to recover the original T(3)R(3) crystal structure. A Rietveld refinement of this 815-atom protein by combining 3886 stereochemical restraints with a 6000-step (d(min) = 3.06 A) powder diffraction pattern yielded the residuals R(wp) = 3.46%, R(p) = 2.64%, R(F)(2) = 7.10%. The demonstrated ability to solve and refine a protein crystal structure from powder diffraction data suggests that this approach can be employed, for example, to examine structural changes in a series of protein derivatives in which the structure of one member is known from a single-crystal study.

Humans↗

PubMed2001

Identifying and indexing icosahedral quasicrystals from powder diffraction patterns.

We present a scheme to identify quasicrystals based on powder diffraction data and to provide a standardized indexing. We apply our scheme to a large catalog of powder diffraction patterns, including natural minerals, to look for new quasicrystals. Based on our tests, we have found promising candidates worthy of further exploration.

Journal Article↗

PubMed2000

Solving crystal structures from two-wavelength X-ray powder diffraction data - breaking the phase ambiguity in the noncentrosymmetric case

Direct methods of breaking phase ambiguities in protein crystallography have been introduced in powder diffraction analysis. This is aiming at ab initio solution of noncentrosymmetric structures using two-wavelength anomalous powder diffraction data. The known structure of the hydrogen bromide salt of leotidine (C(14)H(20)O(2)N(2).HBr) in space group P2(1)2(1)2(1) was used for simulating two-wavelength anomalous powder diffraction with the Br atom as anomalous scatterer. X-ray wavelengths are selected at lambda(1) = 0.920 and lambda(2) = 1.500 A. Unique reflections from the diffraction pattern of lambda(2) were able to locate the Br atom accurately. All overlapping diffraction peaks were uniformly partitioned to decompose into single reflections. Structure-factor amplitudes were then extracted. With these and the substructure of Br atoms, unique phases for centric reflections (hk0, h0l and 0kl) and phase doublets for noncentric reflections were obtained. The direct method was used to break the phase ambiguity leading to an interpretable electron-density map, from which five cycles of Fourier iteration yielded the complete structure.

Journal Article↗

PubMed1998

Multiple-wavelength powder diffraction using imaging plates at the Australian National Beamline.

The Australian powder diffractometer at the Photon Factory is capable of recording multiple powder-diffraction scans in less than 5 min per pattern using imaging plates in Debye-Scherrer geometry. This, coupled with incrementing the X-ray beam energy in suitably small steps (down to approximately 2 eV) between exposures, allows fast collection of anomalous diffraction data. Data collected from a copper oxide-based superconductor at energies near the Cu K-absorption edge are presented, along with an account of the technique used to extract multiple-exposure powder-diffraction data from imaging plates.

Journal Article↗

PubMed2001

Ab initio structure determination of BiPb2VO6 from powder diffraction data.

The crystal structure of BiPb2VO6 has been determined from powder diffraction data using a combination of direct methods and the novel approach of applying simulated annealing methods simultaneously to X-ray and neutron data; BiPb2VO6 is a polar, noncentrosymmetric, second harmonic generation active material and its crystal structure is one of the more complex to be solved ab initio from powder diffraction data.

Journal Article↗

PubMed2002

A hybrid Monte Carlo method for crystal structure determination from powder diffraction data.

A hybrid Monte Carlo algorithm for crystal structure determination from powder diffraction data is presented. The algorithm combines the key components of molecular dynamics and Monte Carlo simulations to achieve efficient sampling of phase space, allowing the crystal structure of capsaicin to be determined from powder diffraction data more effectively than by a simulated-annealing approach. The implementation of the algorithm, the choice of the simulation parameters and the performance of the algorithm are discussed.

Journal Article↗

PubMed2003

X-ray powder diffraction patterns for certain fluoroquinolone antibiotic drugs.

X-ray powder diffraction (XRD) data for six pure fluoroquinolone antibiotic drugs, ciprofloxacin, norfloxacin, enrofloxacin, ofloxacin, pefloxacin and sparfloxacin have been obtained using a powder diffractometer. The drugs were scanned from a Bragg angle (2theta) of 10 degrees to 70 degrees. The obtained data were tabulated in terms of the lattice spacing (A) and relative line intensities (I/I(I)). This new information may be useful for the identification of these drugs.

Anti-Infective Agents↗

PubMed2003

In situ monitoring of wet granulation using online X-ray powder diffraction.

PURPOSE: Polymorphic transformations during the wet granulation of a metastable polymorph of flufenamic acid were monitored in situ using online X-ray powder diffraction. The resulting data were used in testing a proposed process induced transformation rate model, which allows the extent and occurrence of polymorphic transformations during wet granulation to be controlled by adjusting the granulation time. METHODS: A small-scale, top mixing granulator was designed for compatibility with novel X-ray powder diffraction equipment (available from X-Ray Optical Systems of East Greenbush, NY). RESULTS: The unique polycapillary optic and X-ray source allowed the transformation of the metastable to the stable polymorph to be followed during the granulation. Following a diffraction peak each for the metastable and stable forms demonstrated that polymorphic transformations during the wetting phase of granulation follow the trends predicted by the model. CONCLUSIONS: The advanced online monitoring may allow real-time control of the process by the adjustment of process parameters, such as granulation time, and clearly qualifies as a PAT (process analytical technology).

Flufenamic Acid↗

PubMed2000

Ab initio structure determination and Rietveld refinement of a high-temperature phase of zirconium hydrogen phosphate and a new polymorph of zirconium pyrophosphate from in situ temperature-resolved powder diffraction data.

The collected in situ temperature-resolved synchrotron powder data revealed that the transformation of the recently reported three-dimensional tau-Zr(HPO4)2 to cubic ZrP2O7 goes through two intermediate phases. The first intermediate phase, rho-Zr(HPO4)2, is formed in a reversible phase transition at 598 K, which involves both rearrangement and disordering of the hydrogen phosphate groups of tau-Zr(HPO4)2. At 688 K condensation of the hydrogen phosphate groups leads to the formation of the second intermediate, a new polymorph of zirconium pyrophosphate (beta-ZrP2O7). Heating above 973 K results in the gradual transformation of beta-ZrP2O7 to cubic zirconium pyrophosphate (alpha-ZrP2O7). The crystal structures of the two intermediate phases were solved from the in situ powder diffraction data using direct methods and refined using the Rietveld method. Both phases are orthorhombic, space group Pnnm and Z = 2. The lattice parameters for the two phases are: p-Zr(HPO4)2: a = 8.1935 (2), b = 7.7090 (2), c = 5.4080 (1) A; beta-ZrP2O7: a = 8.3127 (5), b = 6.6389 (4), c = 5.3407 (3) A. The formation mechanism for the new zirconium pyrophosphate polymorph, beta-ZrP2O7, is discussed in relation to structurally restricted soft chemistry.

Diphosphates↗

PubMed2004

Shadowing and absorption corrections of high-pressure powder diffraction data: toward accurate electron-density determinations.

The shadowing of the primary beam and of reflections from a powder crystal sample enclosed in a diamond-anvil high-pressure cell (DAC) is described for unrestricted data-collection procedures. The corrections account for the shadowing of the data measured with point- or area-detector diffractometers and can be applied for any containers of environment devices enclosing a powdered sample. The general procedure for correcting the powder diffraction data can be applied for analysing and optimizing diffractometric procedures of data collection and provides facilities for collecting high-pressure powder diffraction data with the DAC positioned optimally and rotated to counteract the preferred-orientation and particle-size effects, and to increase the resolution of data. The quadrature effects of numerical integration for the accuracy of computed corrections have been analysed.

Journal Article↗

PubMed2001

Structure determination of two intercalated compounds VOPO4.(CH2)4O and VOPO4.OH-(CH2)2-O-(CH2)2-OH; synchrotron powder diffraction and molecular modelling.

The crystal structures of two intercalated compounds have been determined using a combination of synchrotron powder diffraction and molecular mechanics simulations: (1) vanadyl phosphate intercalated with tetrahydrofuran, VOPO(4).(CH(2))(4)O, and (2) vanadyl phosphate intercalated with diethylene glycol, VOPO(4).HO(CH(2))(2)O(CH(2))(2)OH. Both intercalates preserve the tetragonal space group P4/n, as found in the host structure VOPO(4).2H(2)O. (1): a = 6.208, c = 8.930 A, Z = 2, D(x) = 2.51 g cm(-3); (2): a = 6.223, c = 11.417 A, Z = 2, D(x) = 2.66 g cm(-3). Both intercalates exhibit the same type of orientational disorder in the arrangement of guest molecules, as observed in the same host compound intercalated with water. These two intercalates also exhibit, rather surprisingly, perfect ordering in layer stacking without the displacement disorder, characteristic of many intercalated layered structures. Thanks to this regularity in the arrangement of guests and layers, synchrotron powder diffraction could be used in the present structure determination. The present results also enabled the analysis of the effect of geometrical parameters characterizing the mutual host-guest complementarity and the effect of host-guest and guest-guest interaction on the crystal packing of intercalates.

Journal Article↗