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PubMed1999

Molecular structures of metal complexes with mefenamic acid.

The infrared spectra of Na and Ca complexes of mefenamic acid were investigated in the region between 4000 and 400 cm(-1). These spectra were compared with X-ray powder diffraction patterns of complexes. It is shown that the proposed structure for these complexes obtained from the infrared spectra was supported by X-ray powder diffraction measurements. Bands due to v(as)(COO)- and v(s)(COO)- stretching vibrations appear at about 1580 cm(-1) and in the range 1390-1400 cm(-1) in the infrared spectra of the samples, respectively. The values of NH deformation vibrations do not change in the spectra of mefenamic acid and its metal complexes. On the other hand, molecular mechanic calculations and conformational analysis of three compounds were also established in the present work. As a result of these theoretical studies, the atomic planes and the peak assignments of the powder diffraction patterns were determined. As a result of these experimental and theoretical investigations, it may be concluded that metal atoms are connected to the carboxyl group of the mefenamic acid.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1999

Paracetamol-propyphenazone interaction and formulation difficulties associated with eutectic formation in combination solid dosage forms.

Polymorphic behaviours of paracetamol and propyphenazone and interaction between these two compounds were investigated using differential scanning calorimetry (DSC), X-ray powder diffraction and Fourier transform-infrared (FT-IR)-spectroscopy. Binary mixtures containing various ratios of the compounds were prepared as physical and fused mixtures and analysed by DSC to study their thermal behaviours. Phase diagrams obtained from the melting endotherms of the binary mixtures demonstrated formation of an eutectic mixture at a paracetamol-propyphenazone combination of about 35:65 (w/w) with an eutectic temperature of 56 degrees C. The FT-IR spectroscopy revealed no chemical interaction due to eutectic formation, and a lower degree of crystallinity of the eutectic mixture than individual substances was observed by X-ray powder diffraction analysis. The DSC and X-ray powder diffraction data demonstrated a polymorphic change in propyphenazone as a result of melting of the compound. Tablets, containing both paracetamol and propyphenazone in a combination formulation and prepared using standard wet granulation technology, were found to have physical instability when packed in either polyvinylchloride// aluminium or polyvinylchloride/polyvinyldienechloride// aluminium blisters and stored for one month at 40 degrees C with either 75% relative humidity or without any humidity control. The instability of the tablets was more apparent under the high humidity condition.

Acetaminophen↗
PubMed2004

Characterization of complicated new polymorphs of chlorothalonil by X-ray diffraction and computer crystal structure prediction.

A simultaneous experimental and computational search for polymorphs of chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile) has been conducted, leading to the first characterization of forms 2 and 3. The crystal structure prediction study, using a specifically developed anisotropic atom-atom potential for chlorothalonil, gave as the global minimum in the lattice energy a structure that was readily refined against powder diffraction data to the known form 1 (P2(1)/a). The structure of form 2 was solved and refined from powder diffraction data, giving a disordered structure in the Rm (166) space group (Z = 3). It could also be refined against a P1 ordered model, starting from a low-energy hypothetical sheet structure found in the computational search. This shows that the disorder could be associated with the stacking of ordered sheets. The disordered structure for form 2 was later confirmed by single-crystal X-ray diffraction. The structure of form 3, determined from single-crystal diffraction, contains three independent molecules in the asymmetric unit in P2(1) (4) (Z = 6). Powder diffraction showed that this single-herringbone structure was similar to two low-energy structures found in the search. Further analysis confirmed that form 3 has a similar lattice energy and contains elements from both these predicted structures, which can be considered as good approximations to the form 3 structure.

Computer Simulation↗
PubMed1989

[X-ray diffractometry in the analysis of drugs and pharmaceutical forms].

As a consequence of the importance of solid drug substance characterization, analytical tools such as X-ray diffractometry (powder and single crystal methods) are usually employed in the pharmaceutical field. The diagnostic power of X-ray powder diffraction in identifying crystalline compounds, even in multicomponent mixtures, and in showing the non-crystalline ones, has brought about the usual characterization through the X-ray powder diffraction pattern of polymorphic, pseudopolymorphic, and amorphous drugs and of some drug-carrier systems such as solid dispersions, glass dispersions, solid surface dispersions, physical mixtures, eutectics, solid solutions, addition and inclusion compounds, etc. Moreover this technique is also used in the qualitative and quantitative analysis both of drug mixtures and dosage forms, and also in the study of relationships between crystal habit and technological characteristics of pharmaceutical formulations. Single crystal methods are employed for calculating the unit cell lenghts and angles, for indexing powder diffraction patterns, and for demonstrating the crystal and molecular structure of the drug. After a picture of the solid state properties and the X-ray characteristics, as well as of the interaction between X-rays and solid matter, the main pharmaceutical applications of X-ray diffraction are described.

Pharmaceutical Preparations↗
PubMed2000

Effect of compression force on the crystal properties of erythromycin acistrate tablets.

The crystal properties of compressed and powdered erythromycin acistrate tablets were studied by the X-ray powder diffraction (XRPD) method. Detailed analysis of X-ray powder diffraction line profiles was performed. Diffraction peak intensities and full width at half maximum (FWHM) values of the peaks corresponding to three different crystal lattice directions were determined. Crystallite size was calculated by Scherrer's equation using the data of integral breadth of the peaks. The preferred orientation of the crystallites is also discussed. According to the results, the crystallite size increased on the tablet surface after a small compression force (4 kN) in all crystal lattice directions studied. Even small compression forces caused recrystallization. With higher compression forces (8-18 kN) the crystallite size and the FWHM values remained rather constant. After the compression force of 18 kN the peaks in different crystal lattice directions behaved differently. In the lattice directions of diffraction maxima 2 and 3, the effect was the same with the small (4 kN) and the high compression force (22 kN). Further recrystallization occurred with 22 kN. However, in the crystal lattice direction of diffraction maximum 1 at the compression force of 8 kN the crystallite broke and crystallinity decreased. These were not seen in the powdered tablet samples. It could be concluded that the effect of compression force on the crystal properties of erythromycin acistrate tablets was seen on the tablet surface but not in the powdered tablets. Compression force also affected the preferred orientation of crystallites on the tablet surface and especially in the lattice direction of diffraction maximum 3. This was not seen in the powdered tablets.

Chemistry, Pharmaceutical↗
PubMed2002

Synthesis and crystal structure of Sr(2)AlH(7): a new structural type of alkaline earth aluminum hydride.

The title hydride and its deuteride were successfully synthesized. The heavy atom structure and hydrogen positions were determined respectively by X-ray powder diffraction and time-of-flight neutron powder diffraction. They crystallize with a new monoclinic structure in space group I2 (No. 5); cell parameters: a = 12.575(1) A, b = 9.799(1) A, c = 7.9911(8) A, beta = 100.270(4) degrees (hydride), a = 12.552(1) A, b = 9.7826(8) A, c = 7.9816(7) A, beta = 100.286(4) degrees (deuteride), Z = 8. Sr(2)AlH(7) is the first example that consists of isolated [AlH(6)] units and infinite one-dimensional twisted chains of edge-sharing [HSr(4)] tetrahedra along the crystallographic c axis.

Journal Article↗
PubMed1991

Solid state properties of an oral iron chelator, 1,2-dimethyl-3-hydroxy-4-pyridone, and its acetic acid solvate. I: Physicochemical characterization, intrinsic dissolution rate, and solution thermodynamics.

1,2-Dimethyl-3-hydroxy-4-pyridone (1), a crystalline oral iron chelator, forms an acetic acid solvate (2) on recrystallization from acetic acid and carbon tetrachloride. Compound 2 forms compact prisms, and 1 forms needles from water (mp 274 degrees C). The X-ray powder diffraction patterns of 1 and 2 differ, indicating distinct solid phases. Compound 2 has an extra DSC endotherm at 82 degrees C that is accompanied by a weight loss of 29% in TGA, corresponding to the desolvation of a 1:1 acetic acid solvate. Comparison of the solid-state 13C NMR of 1 and 2 revealed two additional peaks for 2 at 20.3 and 175.6 ppm, characteristic of -CH3 and -COOH, respectively, of acetic acid. The integrated intensities confirmed the 1:1 stoichiometry between 1 and acetic acid. However, 2 underwent desolvation in air at 25 degrees C as suggested by a change in its appearance to opaque crystals and as confirmed by X-ray powder diffraction, DSC, and TGA. Desolvation of 2 at 25 degrees C was a zero-order process with a rate constant of 6.9 mumol.h-1. X-ray powder diffraction showed that crystals or compacted discs of 1 are converted to 2 in contact with glacial acetic acid (A), whereas crystals or discs of 2 are converted to 1 in contact with water. The intrinsic dissolution rate (J) and the apparent solubility (Cs) of compacted discs of 1 and 2 were measured in water at 25 degrees C, and the following relations were determined: J(2)/J(1) = 1.39 and Cs(2)/Cs(1) = 1.70.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed2001

Dynamic in vitro calcification of bioprosthetic porcine valves: evidence of apatite crystallization.

OBJECTIVE: Calcification is the most important cause of structural deterioration of glutaraldehyde-fixed bioprosthetic valves. Devitalization of tissue favors calcium deposits in the shape of apatite crystals. Host factors influence the extent and progression of calcification, but the phenomenon can also occur in vitro in the absence of a viable milieu. Whether calcific deposits obtained in vitro are similar to those found in vivo is unknown. METHODS: Four porcine frame-mounted bioprostheses (St Jude Medical Bioimplant; St Jude Medical, Inc, St Paul, Minn) were tested in vitro by using a pulsatile accelerated calcification testing device at a frequency of 300 cycles per minute at 37 degrees C for 19 x 10(6) cycles with a rapid synthetic calcification solution (final product [calcium x phosphate], 130 mg/dL(2)). Three of the same type of xenografts explanted from human subjects because of calcific failure (time in place, 108 +/- 25.63 mo) served as control grafts. Each sample underwent gross and x-ray examination, histology, transmission and scanning electron microscopy, atomic absorption spectroscopy, electron microprobe analysis, and x-ray powder diffraction methods. RESULTS: All in vitro bioprostheses were heavily calcific, with intrinsic Von Kossa stain-positive deposits and a mean calcium content of 205.285 +/- 64.87 mg/g dry weight. At transmission electron microscopy, nuclei of calcification involved mostly collagen fibers and interfibrillar spaces and, more rarely, cell debris and nuclei. Electron microprobe analysis showed a Ca/P atoms ratio of 4.5:3, a value intermediate between hydroxyapatite and its precursor, octacalciumphosphate. X-ray powder diffraction showed a well-separated and sharp peak, which is typical of hydroxyapatite. Aggregates of plate-like crystals up to 8 microm in size were observed at scanning electron microscopy, with a typical tabular hexagonal shape consistent with apatite. The morphologic and chemical findings in human explants were similar. CONCLUSIONS: Intrinsic calcification of glutaraldehyde-fixed porcine valves was induced in vitro. Electron microprobe analysis and x-ray powder diffraction findings were in keeping with apatite crystallization, such as that occurring in valve xenografts implanted in vivo. The model may be of value to accelerate the screening of anticalcific agents and may reduce the need for animal experiments.

Apatites↗
PubMed2000

Structure of CnCn+2Cn-type (n = even) beta'-triacylglycerols.

The crystal structures of the beta' phase of CLC (1, 3-didecanoyl-2-dodecanoylglycerol) and MPM (1, 3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of beta'-CLC are a = 57.368 (6), b = 22.783 (2) and c = 5.6945 (6) A and the final R value is 0.175. The unit-cell parameters of beta'-MPM are a = 76.21 (4), b = 22.63 (1) and c = 5.673 (2) A and the final R(p) value is 0.057. Both the beta'-CLC and beta'-MPM molecules are crystallized in a chair conformation, having a bend at the glycerol moiety. The zigzag planes of the acyl chains are orthogonally packed, as is typical for a beta' phase. Furthermore, unit-cell parameters of some other members of the C(n)C(n+2)C(n)-type triacylglycerol series have been refined on their high-resolution X-ray powder diffraction pattern. Finally, the crystal structures are compared with the currently known structures and models of triacylglycerols.

Crystallography, X-Ray↗
PubMed2005

X-ray diffraction and Raman studies of the CuGeO3(III)-(IV) transformation under high pressures.

Both X-ray diffraction and Raman spectroscopy measurement were carried out on the same powder sample of CuGeO(3)(III) in a diamond anvil cell to high pressures at room temperature. The phase transformation of (III)-(IV) phase was observed at about 7GPa with both methods and the results were also in accord with previous powder diffraction and Raman measurements, respectively. However, the powder diffraction data were strikingly different from those reported in a recent single-crystal study on the phase (III). It is, therefore, evident that the phase transformations in CuGeO(3)(III) would be as complicated as those in CuGeO(3)(I) and that the monoclinic phase obtained from single-crystal phase (III) at approximately 7GPa is not the phase (IV) previously observed but rather a new phase (IVa) in CuGeO(3).

Minerals↗
PubMed1998

Structural Aspects of the Dehydration and Dehydroxylation of gamma-Titanium Phosphate, gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O.

The thermal transformations of gamma-titanium phosphate, gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O, have been studied using thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, and temperature-resolved in-situ powder diffraction. The transformation sequence goes from gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O over a new partially dehydrated form gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1) to the anhydrous form beta-Ti(PO(4))(H(2)PO(4)) and then through a two-step condensation process where layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), is formed first and finally cubic titanium pyrophosphate TiP(2)O(7). The dehydration of gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O and the dehydroxylation/condensation process from beta-Ti(PO(4))(H(2)PO(4)) to layered titanium pyrophosphate,Ti(PO(4))(H(2)P(2)O(7))(0.5), was followed in-situ. A new partially dehydrated phase, gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1), which forms at approximately 50 degrees C has been detected and characterized. The unit cell is monoclinic with the lattice parameters a = 23.670(1) Å, b = 6.264(1) Å, c = 5.036(1) Å, beta = 102.41(1) degrees, and Z = 4. Layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), which forms at 375 degrees C has been characterized. The unit cell is monoclinic with lattice parameters a = 16.271(3) Å, b = 6.319(1) Å, c = 5.122(1) Å, beta = 90.59(2) degrees, and Z = 4.

Journal Article↗
PubMed2000

Structures of

Crystal structures of [Pd(NH3)2X2] complexes, where X = Br or I, diamminediiodo-/-dibromopalladium(II), have been studied by X-ray powder diffraction. The series consists of five complexes: cis-[Pd(NH3)2Br2] (I) [a = 13.3202 (7), b = 12.7223 (6), c = 7.05854 (3) A, Z = 8, space group Pbca], trans-[Pd(NH3)2Br2] (II) [a = 6.7854 (3), b = 7.1057 (3), c = 6.6241 (2) A, alpha = 103.221 (3), beta = 102.514 (2), gamma = 100.386 (3) degrees, Z = 2, space group P1], beta-trans-[Pd(NH3)2Br2] (III) [a = 8.4315 (3), b = 8.4206 (3), c = 8.0916 (2) A, Z = 4, space group Pbca], cis-[Pd(NH3)2I2] (IV) [a = 13.9060 (8), b = 13.5035 (8), c = 7.5050 (4) A, Z = 8, space group Pbca], and beta-trans-[Pd(NH3)2I2] (V) [a = 8.8347 (5), b = 8.8410 (5), c = 8.6081 (2) A, Z = 4, space group Pbca]. Patterson synthesis and Rietveld refinement have been used for structural determination. Molecular structures with column- or parquet-type packing of flat complexes are characteristic of these substances. Corresponding cis- and beta-trans compounds are isostructural. The thermal transformations cis-->trans-->beta-trans (cis-->beta-trans in the case of iodine) are considered. Cl derivatives are also discussed. The transformations proceed irreversibly and are accompanied by decreasing specific volume. Owing to these features, they can be classified as chemical reactions. High-temperature X-ray powder diffraction was used to study the transformations in air. The set of data is consistent with a solid state transformation from cis to trans. According to this model, the columns of molecules remain intact during the process, and the transformation proceeds via the breaking of Pd...X and Pd...N intermolecular bonds. The powder diffraction data have been deposited in ICDD-JCPDS (45-0596, 46-0876, 46-0879, 47-1690, 48-1185).

Journal Article↗
PubMed1998

An eight-position capillary sample spinning stage for the diffractometer at BL20B at the Photon Factory.

An eight-position capillary sample spinning stage has been developed for use in conjunction with the versatile vacuum diffractometer (BIGDIFF) at BL20B at the Photon Factory. BIGDIFF is often used in its powder diffraction mode using powders mounted in capillaries and up to eight imaging plates to record the diffraction pattern from the sample. Using the multiple spinning stage a number of diffraction patterns can be recorded on the imaging plates if the imaging-plate cassette is moved behind the Weissenberg screen to a new position after exposure of the sample to the beam. Not only is this system more efficient in terms of time saved in the pumping-down process, but also it has the advantage of allowing the diffraction patterns of standards to be recorded, thereby calibrating both the angle scale of the diffractometer and the intensity scales of the imaging plates absolutely.

Journal Article↗
PubMed1998

A versatile X-ray diffraction station at LNLS (Brazil).

Versatility was a major consideration in the project to provide an X-ray diffraction station at LNLS. At least two techniques are possible at the station: powder diffraction and multiple single-crystal diffraction. A two-crystal monochromator based on monolithic elastic translators, developed at LNLS, with sagittal focusing by the second crystal, allows 10 mrad of a >/=2 keV monochromatic beam to be used on the diffractometer. The station is equipped with a fast scintillation detector, imaging plates, a high-energy-resolution pin-diode detector, an ionization chamber and a high-angular-resolution soller slit. The data collection and control hardware and software were also developed at LNLS. The theta-2theta goniometry for powder diffraction on this 1 m-diameter diffractometer is based on commercial rotation tables. The multiple single-crystal goniometry is realized by an independent elastic axis driven by differential micrometers for both high- and low-resolution angular movements. At least four independent axes can be positioned as necessary on the diffractometer table. Powder diffractograms and double-crystal rocking curves collected with the synchrotron beam show the expected quality.

Journal Article↗
PubMed1995

Crystallite orientation and anisotropic strains in thermally sprayed hydroxyapatite coatings.

Thermally sprayed hydroxyapatite powders and coatings have been studied using X-ray powder diffraction and scanning electron microscopy. Preferred orientation of the crystallites has been found on a number of coated plates using X-ray powder diffraction, and full profile fitting of the patterns from the extracted powders indicates anisotropically thermally strained crystallites. This is a result of rapid crystal regrowth and associated thermal gradients on deposition. Electron micrographs of some coatings show a consistent picture of columnar crystallites orientated perpendicular to the substrate surface.

Anisotropy↗
PubMed2004

Evaluation of photostability of solid-state nicardipine hydrochloride polymorphs by using Fourier-transformed reflection-absorption infrared spectroscopy - effect of grinding on the photostability of crystal form.

Photostability and physicochemical properties of nicardipine hydrochloride polymorphs (alpha- and beta-form) were studied by using Fourier-transformed reflection-absorption infrared spectroscopy (FT-IR-RAS) of the tablets, X-ray powder diffraction analysis, differential scanning calorimetry (DSC), and color difference measurement. It was clear from the results of FT-IR-RAS spectra after irradiation that nicardipine hydrochloride in the solid state decomposed to its pyridine derivative when exposed to light. The photostability of the ground samples of two forms was also measured in the same manner. The two crystalline forms of the drug changed to nearly amorphous form after 150 min grinding in a mixer mill. X-ray powder diffraction patterns of those ground samples showed almost halo patterns. The nicardipine hydrochloride content on the surface of the tablet was determined based on the absorbance at 1700 cm(-1) attributable to the C=O stretch vibration in FT-IR-RAS spectra before and after irradiation by fluorescent lamp (3500 lx). The photodegradation followed apparently the first-order kinetics for any sample. The apparent photodegradation rate constant of beta-form was greater than that of alpha-form. The ground samples decomposed rapidly under the same light irradiation as compared with the intact crystalline forms. The photodegradation rate constant decreased with increase of the heat of fusion.

Chemistry, Pharmaceutical↗
PubMed2004

The synchrotron powder diffractometer at beamline B2 at HASYLAB/DESY: status and capabilities.

The synchrotron powder diffraction beamline B2 at HASYLAB/DESY is described. The beamline is capable of high-resolution powder diffraction as well as time-resolved studies and offers several sophisticated ancillary equipments for special applications. A newly developed image-plate system allows for kinetic studies with good resolution in the minutes range. Numerous sample environments allow for various standard applications including structure solution, kinetic studies and in situ observations under flexible and well defined conditions. Representative examples are shown for these setups, which are also supported for experiments of external users.

Journal Article↗