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PubMed2006

The usefulness of simple X-ray powder diffraction analysis for counterfeit control--the Viagra example.

Counterfeit and illegally manufactured drugs become a very important problem all over the world, hence, a search for new fast, easy, reliable and not expensive methods of drugs screening is essential. We describe the use of X-ray powder diffraction method for the fast screening of tablets for counterfeit medicines identification. The original Viagra tablets and some counterfeit and/or imitations of Viagra were used as example. We demonstrate the application of diffraction method for discrimination of tablets coatings and for identification of differences in drug composition. The X-ray diffraction method turns out to be very fast and reliable for detecting counterfeits and imitation, and it correctly predicts the presence or absence of active substance and/or particular excipients.

Excipients↗
PubMed2006

The 136-atom structure of ZrP2O7 and HfP2O7 from powder diffraction data.

There has been considerable debate in the literature about the true room-temperature structure of ZrP2O7 and related materials. In this article we describe how a combination of information from solid-state 31P NMR and powder diffraction data can be used to determine the structure of this 136 unique-atom material. The structure has been solved using a combination of simulated annealing and Rietveld refinement performed simultaneously on X-ray and neutron diffraction data. Despite the close to cubic metric symmetry of the material, we show how its true orthorhombic structure (space group Pbca) can be refined to a high degree of precision.

Journal Article↗
PubMed1988

Additional evidence from x-ray powder diffraction patterns that icosahedral quasi-crystals of intermetallic compounds are twinned cubic crystals.

Analysis of the measured values of Q for the weak peaks (small maxima, usually considered to be background fluctuations, "noise") on the x-ray powder diffraction curves for 17 rapidly quenched alloys leads directly to the conclusion that they are formed by an 820-atom or 1012-atom primitive cubic structure that by icosahedral twinning produces the so-called icosahedral quasi-crystals.

Journal Article↗
PubMed2001

Sodium 4-(2-pyridinyldiazenyl)resorcinolate monohydrate and ammonium 2,4-dinitro-1-naphthalenolate from powder diffraction data.

The crystal structures of two dyestuffs, Na(+).C(11)H(8)N(3)O(2)(-).H(2)O, (I), and NH(4)(+).C(10)H(5)N(2)O(5)(-), (II), were determined from X-ray powder diffraction data. In both structures, translationally related anions form stacks, and cations fill interstack channels. A comparison of the diffuse reflectance spectra of crystalline (I) and (II) with the absorption spectra of their aqueous solutions demonstrates that the geometry of their anions does not change significantly upon transfer from the crystalline to the solution state.

Journal Article↗
PubMed2000

Rapid characterization of complex structural phase transitions using powder diffraction and an area detector.

The use of a high-intensity and well collimated X-ray beam from a third-generation synchrotron source, combined with an area detector with online readout capabilities, allows high-quality powder patterns to be obtained with exposure times of only a few seconds. Powder measurements of a rare-earth manganate perovskite (Nd(0.43)Sr(0.57)MnO(3)) were performed in the temperature range 105-200 K, and the data were of sufficient quality to be able to extract, via Rietveld refinement, accurate values for the lattice constants and atomic parameters. The temperature dependence of the Mn-O-Mn bond angles and Mn-O distances obtained in this manner illustrate the well known correlation between the distortion of the MnO(6) octahedra and the onset of orbital ordering. The success of this study, for which only two hours of synchrotron beam time was required, indicates the enormous improvements in efficiency and throughput which area detectors are bringing to powder diffraction experiments.

Journal Article↗
PubMed1996

Structure Determination of a Complex Tubular Uranyl Phenylphosphonate, (UO(2))(3)(HO(3)PC(6)H(5))(2)(O(3)PC(6)H(5))(2).H(2)O, from Conventional X-ray Powder Diffraction Data.

The three-dimensional structure of a complex tubular uranyl phosphonate, (UO(2))(3)(HO(3)PC(6)H(5))(2)(O(3)PC(6)H(5))(2).H(2)O, was determined ab initio from laboratory X-ray powder diffraction data and refined by the Rietveld method. The crystals belong to the space group P2(1)2(1)2(1), with a = 17.1966(2) Å, b = 7.2125(2) Å, c = 27.8282(4) Å, and Z = 4. The structure consists of three independent uranium atoms, among which two are seven-coordinated and the third is eight-coordinated. These metal atoms are connected by four different phosphonate groups to form a one-dimensional channel structure along the b axis. The phenyl groups are arranged on the outer periphery of the channels, and their stacking forces keep the channels intact in the lattice. The determination of this structure which contains 50 non-hydrogen atoms in the asymmetric unit, from conventional X-ray powder data, represents significant progress in the application of powder techniques to structure solution of complex inorganic compounds, including organometallic compounds.

Journal Article↗
PubMed2006

Structures of the cation-deficient perovskite Nd(0.7)Ti(0.9)Al(0.1)O3 from high-resolution neutron powder diffraction in combination with group-theoretical analysis.

The crystal structures of Nd(0.7)Ti(0.9)Al(0.1)O3, taken to represent the ideal Nd(2/3)TiO3, have been elucidated from 4 to 1273 K using high-resolution neutron powder diffraction in combination with group-theoretical analysis. The room-temperature structure is monoclinic in C2/m, on a cell with a = 7.6764 (1), b = 7.6430 (1), c = 7.7114 (1) A, beta = 90.042 (2) degrees . Pertinent features are the layered ordering of the A-site Nd cations/vacancies along the z axis and out-of-phase tilting of the (Ti/Al)O6 octahedra around both the x and z axes. From about 750 to 1273 K, the octahedra are tilted around just one axis (x axis) perpendicular to the direction of the cation ordering, giving rise to an orthorhombic structure with space-group symmetry Cmmm.

Journal Article↗
PubMed2001

Structure of beta-trimyristin and beta-tristearin from high-resolution X-ray powder diffraction data.

The crystal structures of beta-1,2,3-tritetradecanoylglycerol (beta-trimyristin or beta-MMM) and beta-1,2,3-trioctadecanoylglycerol (beta-tristearin or beta-SSS) have been determined from high-resolution synchrotron X-ray powder diffraction data. Grid search and Rietveld refinement have been used to determine and refine the structure, respectively. Both substances crystallize in space group P1; with Z = 2. The unit-cell parameters for beta-MMM are a = 12.0626 (6), b = 41.714 (1), c = 5.4588 (3) A, alpha = 73.388 (4), beta = 100.408 (5) and gamma = 118.274 (4) degrees. For beta-SSS the unit-cell parameters are a = 12.0053 (7), b = 51.902 (2), c = 5.4450 (3) A, alpha = 73.752 (5), beta = 100.256 (6) and gamma = 117.691 (5) degrees. Soft-distance restraints have been applied to the molecules during refinement. For beta-MMM the final R(p) value obtained is 0.053 and for beta-SSS the final R(p) value is 0.041.

Journal Article↗
PubMed1995

A Mössbauer and X-ray powder diffraction study of some ferrous hematinics.

Iron deficiency anemia is a relatively common illness that can arise from a number of different causes. Three ferrous salts are usually used in its treatment: ferrous fumarate, gluconate, and sulfate. They are administered orally and are relatively well tolerated. These hematinics have been studied by Mössbauer spectroscopy and X-ray powder diffraction, and can easily be distinguished by both techniques. It was found that the two ferrous sulfates studied (Eckerd and SmithKline Beckman Co.) most closely resemble the monohydrate by comparison of the X-ray powder pattern with those of the JCPDS. Both the ferrous fumarate (Femiron) and gluconate (Spring Valley) had approximately 10% ferric iron present. To the authors' knowledge, this is the first reported Mössbauer spectrum for ferrous fumarate.

Ferrous Compounds↗
PubMed1996

Structural and Quantum Chemical Study of Bi(5)(3+) and Isoelectronic Main-Group Metal Clusters. The Crystal Structure of Pentabismuth(3+) Tetrachlorogallate(III) Refined from X-ray Powder Diffraction Data and Synthetic Attempts on Its Antimony Analogue.

Pentabismuth(3+) tetrachlorogallate(III), (Bi(5)(3+))(GaCl(4)(-))(3), has been synthesized by reducing a BiCl(3)-GaCl(3) melt with bismuth metal and the crystal structure refined from X-ray (Cu Kalpha(1)) powder diffraction data. The structure was found to belong to space group R-3c, with the lattice parameters a = 11.871(2) Å and c = 30.101(3) Å (Z = 6). It is isostructural with the previously characterized Bi(5)(AlCl(4))(3). An attempt to synthesise the antimony analogue Sb(5)(GaCl(4))(3) by reducing a SbCl(3)-GaCl(3) mixture with gallium metal produced a black solid phase. The gallium content of this phase is consistent with the stoichiometry Sb(5)(GaCl(4))(3), and the Raman spectrum of the phase dissolved in SbCl(3)-GaCl(3) comprises strong, low-frequency bands attributable to Sb-Sb stretch vibrations in Sb(5)(3+) or another reduced antimony species. Quantum chemical analyses have been performed for the isoelectronic, trigonal pyramidal closo-clusters Sn(5)(2-), Sb(5)(3+), Tl(5)(7-), Pb(5)(2-), and Bi(5)(3+), both with extended Hückel (eH) and Hartree-Fock (HF) methods. The HF calculations were performed with and without corrections for the local electron-electron correlation using second-order Møller-Plesset perturbation theory (MP2). All theoretical results are compared and evaluted with respect to experimental cluster structures and vibrational frequencies. The results from the calculations agree well with available experimental data for the solid-state structures and vibrational spectra of these cluster ions, except for the Tl(5)(7-) ion. Isolated Tl(5)(7-) is suggested to be electronically unstable because of the high charge density. The Sb(5)(3+) cluster ion is indicated to be stable. According to the calculations, Sn(5)(2-) and Pb(5)(2-) may be described in terms of edge-localized bonds without substantial electron density between the equatorial atoms, whereas Sb(5)(3+) and Bi(5)(3+) have electron density evenly distributed over all M-M vectors. Furthermore, the theoretical results give no support for a D(3h) --> C(4v) fluxionality of these clusters.

Journal Article↗
PubMed2005

Structural analysis of a melaminium polyphosphate from X-ray powder diffraction and solid-state NMR data.

The crystal structure of the environmentally friendly flame retardant melaminium polyphosphate (MPoly) (2,4,6-triamino-1,3,5-triazinium x PO(3))(n)was determined by a direct-space global optimization technique from X-ray powder diffraction data. Solid-state NMR was used to corroborate the proposed hydrogen-bonding model and to determine the average degree of polymerization (n > 100). An analysis of the crystal structure of MPoly reveals aspects of molecular geometry and packing that are characteristic for melamine-containing compounds and polyphosphate salts. A comparison of MPoly with the crystal structures of its precursors melaminium orthophosphate (MP) and melaminium dihydrogenpyrophosphate (MPy) provides insight in the mechanism of the endothermic dehydration processes that takes place in the reaction path MP --> MPy --> MPoly. Solid-state NMR characterization of various samples of the same batch showed inhomogeneities in the MPoly composition. Various quantities of orthophosphates were found, which cannot be assigned to be MP.

Journal Article↗
PubMed1999

Structure determination of lithium chloroacetate, lithium bromoacetate and lithium iodoacetate by powder diffraction.

Most halogenoacetates of alkali salts readily undergo a thermally induced polymerization reaction to poly-(hydroxyacetic acid) in the solid state. The lithium salts represent a remarkable exception. The crystal structures of lithium chloroacetate, lithium bromoacetate and lithium iodoacetate were determined ab initio from synchrotron powder diffraction data. The three compounds are isostructural and differ considerably from the structures of sodium chloroacetate and silver chloroacetate, two compounds that undergo polymerization. Most likely, the strong polarizing effect of the small lithium cation is responsible for the unfavorable crystal structure in which each lithium cation is coordinated to four O atoms from four different halogenoacetate molecules. Lithium chloroacetate: a = 9.3882 (9), b = 4.8452 (4), c = 9.0119 (7) Å, beta = 94.330 (5) degrees; lithium bromoacetate: a = 9.7165 (11), b = 4.8610 (6), c = 9.0228 (11) Å, beta = 93.946 (5) degrees; lithium iodoacetate: a = 10.1812 (10), b = 4.8922 (8), c = 9.0468 (10) Å, beta = 93.251 (5) degrees, all crystallizing in space group P2(1)/c with Z = 4.

Journal Article↗
PubMed2006

Crystal structure of carnidazole form II from synchrotron X-ray powder diffraction: structural comparison with form I, the hydrated form and the low energy conformations in vacuo.

The crystal structure of carnidazole form II, O-methyl [2-(2-methyl-5-nitro-1H-imidazole-1-yl)ethyl]thiocarbamate, has been determined using synchrotron X-ray powder diffraction in combination with simulated annealing and whole profile pattern matching, and refined by the Rietveld method. For structure solution, 12 degrees of freedom were defined: one motion group and six torsions. Form II crystallizes in space group P2(1)/n, Z=4, with unit cell parameters after Rietveld refinement: a=13.915(4), b=8.095(2), c=10.649(3) A, beta=110.83(1) degrees, and V=1121.1(5) A3. The two polymorphic forms, as well as the hydrate, crystallize in the monoclinic space group P2(1)/n having four molecules in the cell. In form II, the molecules are held together by forming two infinite zig-zag chains via hydrogen bonds of the type N--H...N, the same pattern as in form I. A conformational study of carnidazole, at semiempirical PM3 level, was performed using stochastic approaches based on modification of the flexible torsion angles. The values of the torsion angles for the molecules of the two polymorphic forms and the hydrate of carnidazole are compared to those obtained from the conformational search. Form I and form II are enantiotropic polymorphic pairs this agrees with the fact that the two forms are conformational polymorphs.

Calorimetry, Differential Scanning↗
PubMed2001

Structure determination of two metal-organic complexes from high-resolution synchrotron powder diffraction data.

The crystal structures of [1,2-bis(2,6-diisopropylphenylimino)acenaphthene-N,N']carbonylchlororhodium(I) (1) and [N,N'-ethylene-bis(3-methylsalicylideneiminato)-O,N,N',O'](tetrahydrofurfuryl)-cobalt(II) (2) have been determined from high-resolution synchrotron X-ray powder diffraction data. Compound 1 is the first neutral Rh complex, in contrast with findings in the literature, containing a bidentate nitrogen ligand, and compound 2 is the first three-dimensional structure of a (five-coordinated) tetrahydrofurfurylcobalt(III) complex. Grid-search and Rietveld refinement have been used to determine and refine the structures, respectively. Crystals of 1 are orthorhombic, space group Pbca, Z = 8, with cell parameters a = 21.729 (2), b = 27.376 (3), c = 11.580 (1) A. Crystals of 2 are monoclinic, space group P2(1)/n, Z = 4, a = 16.6701 (6), b = 9.4170 (4), c = 13.7088 (7) A and beta = 96.520 (3) degrees. Chemical diagrams for the two compounds are given. Soft restraints were applied during Rietveld refinement; for 1 converging to R(p) = 8.4%, R(w) = 11.0%, GoF = 2.3, and for 2 converging to R(p) = 8.5%, R(w) = 11.4%, GoF = 7.6.

Journal Article↗
PubMed1985

X-ray powder diffraction and microscopic analysis of crystalluria in dogs with ethylene glycol poisoning.

Most of the urinary crystals in 2 dogs intoxicated with ethylene glycol had prismatic (rod-like, hippurate-like), and to a less extent, hemp seed or spindle shapes. Using X-ray powder diffraction and optical analysis, these crystals were identified as calcium oxalate monohydrate. A few crystals of calcium oxalate dihydrate (envelope shape) were also observed in the urine sediment. Their presence was confirmed by the appearance of weak X-ray peaks having interplanar spacings ranging from 0.617 to 0.620 nm, which are thought to correspond to the 200 X-ray reflection of calcium oxalate dihydrate. Thus, the 6-sided hippurate-like crystals in the urine of ethylene glycol-poisoned dogs are actually calcium oxalate monohydrate.

Animals↗
PubMed2001

Temperature-dependent neutron powder diffraction study of the Ba(OD)(2) polymorphs: a new low-temperature phase.

The structural behaviour of both low-temperature beta- and high-temperature alpha-Ba(OD)(2), barium dihydroxide-d, was investigated at temperatures between 10 and 552 K by neutron powder diffraction. While the beta phase (P2(1)/n) remains stable to the lowest temperature investigated, the quenchable alpha phase (Pnma) shows a reversible orthorhombic-to-monoclinic phase transition between 100 and 150 K. The structure of the new alpha(m) phase (P2(1)/n) is quite similar to that of the alpha phase. This behaviour is unusual as a metastable phase transforms to another metastable phase. The Pnma <--> P2(1)/n low-temperature phase transition is driven by an order-disorder mechanism, mainly caused by one of the D atoms, which is disordered on positions off the mirror plane, mimicking a special position on the mirror plane in the orthorhombic phase. Refinements of the alpha phase above the phase transition indicate this disorder across the mirror plane through a conspicuously high isotropic displacement parameter if compared to the other D atoms. At low temperature the energy of the vibration is lowered and the D atom is frozen at a general position in a correlated way, thus violating the mirror plane and reducing the space-group symmetry.

Journal Article↗
PubMed2001

Hydrothermal synthesis and ab initio structural resolution from X-ray powder diffraction of a new open framework Cu(II) carboxyethylphosphonate: Na[Cu(O3P-(CH2)2-CO2)].

Na[Cu(O3P-(CH2)2-CO2)], or MIL-39 (for Material of Institut Lavoisier), was synthesized hydrothermally at 443 K for 72 h under autogenous pressure. Its three-dimensional open structure was determined from X-ray powder diffraction. MIL-39 is monoclinic, it crystallizes in the space group P2(1)/m, (No. 11) with the following cell parameters at 293 K: a = 8.808(1) A, b = 6.4149(8) A, c = 5.3418(8) A, beta = 105.75(1) degrees, Z = 2. Its framework contains double rows built from isolated distorted CuO5 square pyramids linked by PO3C tetrahedral groups from (O3P-(CH2)2-CO2)3- organic moieties. At the other end of these latter moieties, the carboxylate group links two different Cu polyhedra of two neighboring chains. These connections define two types of channels along [010].

Journal Article↗
PubMed2003

New insights into an old reaction. High-resolution x-ray powder diffraction of Wiberg's aminoalane intermediate.

In accordance with the procedure described by E. Wiberg, Me(3)Al-NH(3) was heated as a bulk material in inert atmosphere to give a colorless liquid which slowly loses methane. Close to the end of this elimination reaction, the melt crystallized to give a microcrystalline powder of (Me(2)AlNH(2))(x)(). The structure of this intermediate has been solved by the method of high-resolution X-ray powder diffraction. The compound crystallizes in the monoclinic space group C2/c with the cell parameters of a = 15.0047(6) A, b = 8.7500(2) A, c = 24.4702(8) A, and beta = 107.290(2) degrees, with eight trimers (Me(2)AlNH(2))(3) per unit cell. These trimers crystallize in a boat conformation in contrast to the known trimers of the same composition where a twist-boat conformation had been found by single crystal determination. Different conformers of (Me(2)AlNH(2))(3) have been investigated by theoretical methods (HF/6-31G(d), B3LYP/6-31G(d), B3LYP/6-311G(d,p), MP2(fc)/6-31G(d), and MP2(fc)/6-311G(d,p)). The twist-boat and the chair conformer correspond to minima at the potential energy surface, whereas the boat conformer corresponds to a first-order transition state (relative energies of 0.45-2.56 kJ/mol (boat) and 6.66-11.91 kJ/mol (chair)). Relaxed scans of the potential energy surface at the HF/6-31G(d) and B3LYP/6-31G(d) levels have shown that the boat conformer (C(s)() symmetry) connects two enantiomers of the twist-boat form (C(2) symmetry).

Journal Article↗