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PubMed2006

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature.

The structure of 4-methylpyridine-N-oxide has been determined at 250, 100 and 10 K by combined synchrotron (C(6)H(7)NO) and neutron (C(6)D(7)NO) powder diffraction experiments. At 250 K the space group is I4(1)/amd and the tetragonal unit cell [a = b = 7.941 (2), c = 19.600 (5) A] contains eight equivalent molecules. At 100 K the structure is orthorhombic, with space group Fddd, a = 12.138 (2), b = 10.237 (2) and c = 19.568 (3) A. The 16 equivalent molecules are rotated by about 8 degrees around the c axis with respect to positions at high temperature. At 10 K the best structural model corresponds to a tetragonal unit cell with the space group P4(1), a = b = 15.410 (2) A and c = 19.680 (3) A. The 32 molecules (eight molecules in the asymmetric unit) show complex reorientations around the three cell axes. Whereas at 250 and 100 K the deuterated methyl groups are largely disordered, at 10 K they are ordered in-phase along infinite chains parallel to a and b. Face-to-face methyl groups along c are in an eclipsed configuration. The structure at 10 K suggests that the manifold of rotational tunnelling transitions could be due to inequivalent lattice sites for crystallographically independent methyl groups.

Journal Article↗
PubMed2005

A novel standard sample powder preparation method for quantitative analysis of polymorphs.

The purpose of this study was to improve the sensitivity and accuracy of the quantitative analysis of polymorphic mixtures. Calibration curve reliability has been improved through the advancement of standard mixture preparation techniques whereby samples at scales of several grams are homogeneously and accurately prepared without decrease in crystallinity. Crystalline powders are first micronized to anisotropic, nearly equal-sized (<10 microm) particles of almost random orientation in an air jet mill. These powders are then mixed in a vibration mill that includes rubber balls as mixing media. Using this technique, alpha and gamma forms of indomethacin (IMC) were prepared in various proportions from 0.5% to 50% alpha content and subjected to X-ray powder diffraction analysis. The validation data showed that these precisely prepared standard mixtures resulted in superior analytical sensitivity and accuracy compared to those prepared by agate mortar.

Calibration↗
PubMed2001

Extended polymorphism in copper(II) imidazolate polymers: a spectroscopic and XRPD structural study.

Copper(II) bisimidazolate affords five different polymorphs; of these, one was structurally characterized 40 years ago by standard single-crystal X-ray diffraction (Jarvis, J. A. J.; Wells, A. F. Acta Crystallogr. 1960, 13, 1027), while the remaining four, selectively prepared as pure polycrystalline phases, have been now studied by X-ray powder diffraction (XRPD) methods. Of the four new (blue, green, olive-green, and pink) phases, three were solved by the ab initio XRPD technique and refined by the Rietveld method, and the fourth phase (pink) could not be structurally characterized. Crystal data for [Cu(imidazolate)(2)](n): blue phase, a = 27.559(3) A, c = 5.3870(9) A, trigonal, R3 macro, Z = 54; green phase, a = 21.139(1) A, b = 19.080(1) A, c = 9.2842(8) A, orthorhombic, Ccca, Z = 20; olive-green phase, a = 11.7556(8) A, b = 23.422(2) A, c = 9.0727(9) A, beta = 104.993(5) degrees, monoclinic, C2/c, Z = 12. All polymorphs contain four-coordinate CuN(4) chromophores and (N,N')-exobidentate imidazolate ligands, but show different spectroscopic and structural properties, the latter ranging from 2D to different 3D networks of the PtS, sodalite, and moganite archetypes. The intermediacy of the [Cu(imidazole)(2)CO(3)]-H(2)O species in the synthesis of the blue polymorph has been confirmed by spectroscopic and thermal analyses. FTIR, Raman, and electronic spectra were correlated with the structural features revealed in the present work, and used to gain insight into the coordination geometry of copper(II) ions of the pink polymorph. In addition, the correct Raman spectrum for copper(II) bisimidazolate, common for all polymorphs, has been definitely determined.

Journal Article↗
PubMed2004

From nitrides to carbides: topotactic synthesis of the eta-carbides Fe3Mo3C and Co3Mo3C.

The molybdenum bimetallic interstitial carbides Fe(3)Mo(3)C and Co(3)Mo(3)C have been synthesized by temperature-programmed reaction (TPR) between the molybdenum bimetallic interstitial nitrides Fe(3)Mo(3)N and Co(3)Mo(3)N and a flowing mixture of CH(4) and H(2) diluted in Ar. These compounds have been characterized by X-ray diffraction, laser Raman spectroscopy, elemental analysis, energy dispersive analysis of X rays, thermal analysis (in air) and scanning electron microscopy (field emission). Their structures have been refined from X-ray powder diffraction data. These carbides crystallize in the cubic system, space group Fd3m[a= 11.11376(6) and 11.0697(3)[Angstrom] for Fe and Co compounds, respectively].

Journal Article↗
PubMed2003

Sialolith crystals localized intraglandularly and in the Wharton's duct of the human submandibular gland: an X-ray diffraction analysis.

The exact cause of the formation of sialoliths is unknown. Detailed knowledge of pathogenesis of sialolithiasis and composition of sialoliths is necessary to define new therapeutic procedures. The crystalline components of 23 sialoliths of human submandibular gland were investigated by X-ray powder diffraction analysis. All of the sialoliths localized in the ducts in the submandibular gland consisted of hydroxylapatite. However, in the sialoliths in the Wharton's duct, hydroxylapatite as well as whitlockite and brushite could be found in all except one case. Whitlockite was observed more often in the nucleus of the sialoliths and it was a common co-phase along with hydroxylapatite. The nucleus in one sialolith consisted of brushite and the cortex showed a co-phase of hydroxylapatite and brushite. The occurrence of whitlockite in the sialoliths in Wharton's duct may be due to a higher concentration of calcium and phosphate in saliva in this duct.

Adult↗
PubMed1999

The effect of polymorphism on powder compaction and dissolution properties of chemically equivalent oxytetracycline hydrochloride powders.

In South Africa, oxytetracycline is identified as an essential drug; many generic products are on the market, and many more are being developed. In this study, six oxytetracycline hydrochloride powders were obtained randomly from manufacturers, and suppliers were compared. It was found that compliance to a pharmacopoeial monograph was insufficient to ensure the optimum dissolution performance of a simple tablet formulation. Comparative physicochemical raw material analysis showed no major differences with regard to differential scanning calorimetry (DSC), infrared (IR) spectroscopy, powder dissolution, and particle size. However, the samples could be divided into two distinct types with respect to X-ray powder diffraction (XRD) and thus polymorphism. The two polymorphic forms had different dissolution properties in water or 0.1 N hydrochloride acid. This difference became substantial when the dissolution from tablets was compared. The powders containing form A were less soluble than that containing form B.

Calorimetry, Differential Scanning↗
PubMed1992

Scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction analyses of human salivary stones.

Ten salivary stones in the human submandibular gland were investigated by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction analyses. The stones usually showed a lamellar pattern. SEM observations revealed cubical, plate-like, granular, small and large granules, polyhedral or globular structures in these stones. By X-ray powder diffraction analysis, the main constituents of salivary stones were found to be apatite and whitlockite. SEM-EDS analyses showed that Ca and P were the major elements, frequently accompanied by Mg and S, and less frequently by Na, Al, Si, Cl, K, Fe, Cu and Zn. Ca/P molar ratios ranged from 1.00 to 2.00 with the average of 1.53, showing two maxima of about 1.50 and 1.60. The Ca/P molar ratio of about 1.50 corresponded to the value of whitlockite. The Ca/P molar ratio of 1.60 corresponded approximately to the value of apatite.

Adolescent↗
PubMed2002

Comparison of the mechanical properties of the crystalline and amorphous forms of a drug substance.

PURPOSE: To better understand the influence of long-range molecular order on the processing characteristics of an active pharmaceutical ingredient (API). METHODS: Crystalline and amorphous samples of a model drug substance were isolated and their "true" density, crystallinity, melting point, glass transition temperature, particle size distribution, and powder flow characteristics determined. Compacts of a standard porosity were manufactured from each form and their dynamic indentation hardness, quasi-static indentation hardness, tensile strength and "compromised tensile strength" determined. X-ray powder diffraction was used to confirm that no changes were induced by compact formation or testing. RESULTS: The crystalline and amorphous forms of the drug substance had relatively high melting and glass transition temperatures (approximately 271 and 142 degrees C, respectively) and were physically and chemically stable under the conditions of the testing laboratory. Consistent with this there was no evidence of crystallinity in the amorphous samples or vice versa before, during or after testing. The two API lots were effectively equivalent in their particulate properties (e.g. particle size distribution), although differences in their particle morphologies were observed which influenced powder flow behavior. The compacts of the bulk drug samples exhibited moderate ductility, elasticity, and strength, and high brittleness, in keeping with many other drug substance samples. A significantly greater compression stress was required to form the compacts of the crystalline material, and these sample materials were more ductile, less brittle and less elastic than those made from the amorphous API. There were no major differences in the tensile strength or the viscoelasticity of the compacts made from the crystalline and amorphous samples. CONCLUSIONS: The mechanical properties of compacted amorphous and crystalline samples of a drug substance have been measured and the contributions due to the molecular ordering of the crystalline form proposed. Small but significant differences in the mechanical properties were noted which could potentially affect the processing performance of API.

Chemical Phenomena↗
PubMed2002

Preparation and characterisation of ibuprofen-poloxamer 188 granules obtained by melt granulation.

The aim of this study was to prepare, by melt granulation, granules containing ibuprofen as a poorly water soluble model drug in order to improve its dissolution rate and its availability; lactose as a diluent and poloxamer 188 (Lutrol F68), as a new meltable hydrophilic binder, were used. The granules were prepared in a laboratory-scale high-shear mixer, using a jacket temperature of 50 degrees C and an impeller speed of 500 rpm. The particle size analysis shows that the main fraction was between 200 and 500 microm, while the determination of drug content indicated that ibuprofen was quite uniformly distributed in all the fractions. Scanning Electron Microscopy (SEM), image and fractal analysis revealed that the granules did not have a perfect spherical shape and a rugged surface (D(s)=2.6475). The in vitro dissolution tests showed an increase in the dissolution rate of granules compared to pure drug and physical mixture. The characterisation of the samples, performed by Differential Scanning Calorimetry (DSC) and X-ray powder diffraction (XRD), suggests that the improvement of dissolution rate could be correlated to the formation of a eutectic mixture between the drug and the binder. Stability studies indicated that the granule properties do not change, at least after 1 year of storage at 25 degrees C. In conclusion, the results of this work suggest that the melt granulation technique is an easy and fast method to improve the dissolution rate of ibuprofen, using poloxamer 188 as a new hydrophilic meltable binder.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Effect of pressure up to 5.5GPa on dry powder samples of chlorpropamide form-A.

The effect of pressure up to 5.5GPa on a dry powder sample of chlorpropamide (4-chloro-N-((propylamino)-carbonyl)-benzenesulfonamide), form-A (sp. gr. P2(1)2(1)2(1), a=9.066A, b=5.218A, c=26.604A), was studied in situ in a Merrill-Bassett diamond anvil cell using high-resolution X-ray powder diffraction (a synchrotron radiation source at SNBL ESRF, Grenoble). No evidence of the polymorphic transformation of chlorpropamide form-A to form-C was observed. The A-C polymorphic transition on tabletting previously reported by is therefore likely to be due to local heating effects. Similarly, the phase transitions of form-A reported by to be induced by pressure applied to a sample in its saturated ethanol solution (at 0.9 and at 2.0GPa) would appear to be solvent-mediated. In the dry sample, a phase transition may be supposed to occur at pressures above 4GPa, but this requires further studies.

Chlorpropamide↗
PubMed2005

Temperature-induced transformations in CoAPO-34 molecular sieve: a combined in situ X-ray diffraction and FTIR study.

Thermally induced processes of CoAPO-34, an aluminophosphate molecular sieve with chabasite-type structure, synthesized in the presence of morpholine as a structure-directing agent and HF as a mineralizing agent, have been studied by in situ X-ray synchrotron powder diffraction augmented with Fourier transform (FT) IR analysis. A time-resolved experiment was performed using a translating imaging plate system. At room temperature, the structure refinement by full-profile Rietveld analysis showed P-1 symmetry and the presence of one Al site with sixfold coordination. At around 400 degrees C, both fluorine and morpholine are lost, and the four-connected chabazite (CHA)-type topology is restored. Notwithstanding the metrically rhombohedral values of the cell parameters, the symmetry remains triclinic P-1. Inhomogeneous dealumination of the framework begins at 725 degrees C, accompanied by a strong triclinization of the unit cell and followed by the collapse of the structure above 775 degrees C. The insertion of cobalt ions within the CHA framework was monitored by FTIR spectroscopy, which showed that bridged Co(2+)-O(H)-P hydroxyls are present after morpholine removal.

Journal Article↗
PubMed2004

Diffraction techniques for nonlamellar phases of phospholipids.

A neutron diffraction method applicable to nonlamellar phases of substrate-supported lipid membranes is described and validated. When prepared on a flat substrate, the resulting nonlamellar phases have layered symmetry which provides some advantages over powder diffraction for detailed structure determination. This approach recently led to the detection of a rhombohedral phase and a distorted hexagonal phase of lipids. Here the determination of intensity and phase information for such phases is demonstrated by application to the hexagonal phase of diphytanoyl phosphatidylcholine (DPhPC). The hexagonal symmetry is used to verify the data reduction procedure for the intensities of the diffraction peaks. Diffraction intensities measured while varying the D2O/H2O ratio in the relative humidity was used to solve the phase problem. The neutron scattering length density distribution of the hexagonal phase was constructed and analyzed to elucidate the packing of the lipid molecules. The structure of DPhPC in the hexagonal phase is of interest in connection with its stalk structure in the rhombohedral phase. We also found that the incorporation of tetradecane into the DPhPC hexagonal phase is limited, similar to the case for dioleoyl phosphatidylethanolamine.

Neutron Diffraction↗
PubMed1991

Crystallization and preliminary X-ray diffraction studies of a flavoprotein, FP390, from a luminescent bacterium, Photobacterium phosphoreum.

A flavoprotein, FP390, obtained from a luminescent bacterium, Photobacterium phosphoreum, in the purification of luciferase has been crystallized by the vapor-diffusion procedure. Crystals obtained from polyethylene glycol 4000 solutions, whose X-ray photographs show powder diffraction patterns, were unsuitable for further crystallographic work. However, tetragonal crystals grown from potassium phosphate solution well diffracted X-rays beyond 3 A resolution. The space group of this crystal is P4(1)22 or P4(3)22 with unit-cell dimensions of a = b = 76.8 and c = 241 A. Assuming two or three molecules in an asymmetric unit, the value for the crystal volume per unit molecular mass, Vm, is calculated as 3.3 or 2.2 A3/Da, respectively. A total of 13,555 independent reflections for the native crystal was collected up to 3 A resolution using a Weissenberg camera attached to the synchrotron radiation source, the merging R factor being 0.077 for 79,335 measurements.

Bacterial Proteins↗
PubMed1988

Polymorphic differences in alpha- and beta-form crystals of 2R, 4S, 6-fluoro-2-methyl-spiro[chroman-4,4'-imidazoline]-2',5-dione (M79175) as determined by X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry.

Polymorphic differences in alpha- and beta-form crystals of 2R, 4S, 6-fluoro-2-methyl-spiro[chroman-4,4'-imidazoline]-2',5-dione (M79175; 1) were studied by X-ray diffractometry, infrared spectroscopy, and differential scanning calorimetry. X-ray powder diffraction indicated the longest spacing of the unit cells to be 14.9 and 12.4 A for the alpha- and beta-form crystals, respectively. The infrared spectra showed the absorption band assigned to NH streching vibration for the alpha-form crystals to be centered at 3250 cm-1 and that for the beta-form crystals to split into two peaks, at 3150 and 3425 cm-1. The enthalpies of fusion were 26.3 kJ/mol at 517.5 K and 31.3 kJ/mol at 501.0 K, respectively. Transformation from the beta- to alpha-form was observed at various heating rates, which were enhanced by the presence of a small amount of alpha-form crystals previously added to the beta-form. The former appeared to serve as a source of nuclei for the growth of both forms. These results confirm that the alpha-form crystal is more stable than the beta-form.

Calorimetry, Differential Scanning↗
PubMed2004

Structure determination of the intramolecular charge transfer state in crystalline 4-(diisopropylamino)benzonitrile from picosecond X-ray diffraction.

The molecular structure of photoexcited crystalline 4-(diisopropylamino)benzonitrile (DIABN) is determined by time-resolved X-ray diffraction with a time resolution of 70 ps. Spectroscopic results suggest that an ICT state with a lifetime of 3 ns is produced after photoexcitation. According to structural refinement of the X-ray data (powder diffraction), the torsional angle of the diisopropylamino group with respect to the plane of the phenyl ring of DIABN decreases from 14 degrees in the electronic ground state to 10 degrees in the equilibrated ICT state.

Journal Article↗
PubMed1996

The physical state of nafcillin sodium in frozen aqueous solutions and freeze-dried powders.

The purpose of this study was to develop a better understanding of the physical chemistry of freeze drying of lyotropic liquid crystals using nafcillin sodium as a model solute. Solutions and freeze-dried powders of nafcillin sodium were studied by polarized light microscopy, differential scanning calorimetry, x-ray powder diffraction, and water vapor adsorption. Differential scanning calorimetry thermograms of nafcillin sodium solutions contain a melting endotherm at approximately -5.5 degrees C and, depending on the concentration and heating rate, a crystallization exotherm immediately after this endotherm followed by the melting endotherm of ice. When the sample is annealed at -4 degrees C, both the endotherm and exotherm are eliminated, and a new endotherm appears at approximately -1 degree C on the shoulder of the ice-melting endotherm. The data are interpreted as melting of a liquid crystalline phase, followed by crystallization. X-ray powder diffractograms of unannealed freeze-dried nafcillin sodium are consistent with a lamellar liquid crystal. Diffractograms of annealed freeze-dried nafcillin sodium indicate crystalline material which is a different crystal form than the monohydrate starting material. Moisture adsorption isotherms of the freeze-dried annealed (crystalline) and unannealed (liquid crystalline) nafcillin sodium show different affinities for moisture compared to the crystalline starting material. Solid-state stability data demonstrate that the freeze-dried liquid crystalline form of nafcillin sodium is much less stable than the freeze-dried crystal-line material. The literature recognizes two types of solute behavior on freezing, where the solute either crystallizes from the freeze concentrate or remains amorphous. Lyotropic liquid crystal formation during freezing represents a separate category of freezing behavior, the physical chemistry of which is worthy of further investigation.

Calorimetry, Differential Scanning↗
PubMed2005

Polymorphism in micro-, submicro-, and nanocrystalline NaNbO3.

NaNbO(3) powders with various particle sizes (ranging from 30 nm to several microns) and well-controlled stoichiometry were obtained through microemulsion-mediated synthesis. The effect of particle size on the phase transformation of the prepared NaNbO(3) powders was studied using X-ray powder diffraction, Raman spectroscopy, and nuclear site group analysis based on these spectroscopic data. Coarsened particles exhibit an orthorhombic Pbcm (D(2h)(11), no. 57) structure corresponding to the bulk structure, as observed for single crystals or powders prepared by conventional solid-state reaction. The crystal symmetry of submicron powders was refined with the space group Pmc2(1) (C(2v)(2), no. 26). The reduced perovskite cell volumes of these submicron powders were most expanded compared to all the other structures. Fine particles with a diameter of less than 70 nm as measured from SEM observations showed an orthorhombic Pmma (D(2h)(5), no. 51) crystal symmetry. The perovskite formula cell of this structure was pseudocubic and was the most compact one. A possible mechanism of the phase transformation is suggested.

Journal Article↗
PubMed1999

Preparation of a microcrystalline suspension formulation of Lys(B28)Pro(B29)-human insulin with ultralente properties.

The monomeric analogue, Lys(B28)Pro(B29)-human insulin (LysPro), has been crystallized using similar conditions employed to prepare extended-acting insulin ultralente formulations. In the presence of zinc ions, sodium acetate and sodium chloride, but without phenolic preservative, LysPro surprisingly forms small rhombohedral crystals with similar morphology to human insulin ultralente crystals with a mean particle size of 20 +/- 1 microm. X-ray powder diffraction studies on the LysPro crystals prior to dilution in ultralente vehicle ([NaCl] = 1.2 M) revealed the presence of T(3)R(3)(f) hexamers. Consistent with human insulin ultralente preparations, LysPro crystals formulated as an ultralente suspension ([NaCl] = 0. 12 M) contain T(6) hexamers indicating that a conformational change occurs in the hexamer units of the crystals upon dilution of the salt concentration. The pharmacological properties of subcutaneously administered ultralente LysPro (ULP) were compared to ultralente human insulin (UHI) using a conscious dog model (n = 5) with glucose levels clamped at basal. There were no statistically significant differences between the kinetic and dynamic responses of ULP compared to UHI [C(max) (ng/mL): 3.58 +/- 0.76, ULP and 3.61 +/- 0. 66, UHI; T(max) (min): 226 +/- 30, ULP and 185 +/- 42, UHI; R(max) (mg/kg min): 11.2 +/- 1.9, ULP and 13.3 +/- 2.0, UHI; and T(Rmax) (min): 336 +/- 11, ULP and 285 +/- 57, UHI]. Although the Pro to Lys sequence inversion destabilizes insulin self-assembly and greatly alters the time action of soluble LysPro preparations, this modification has now been found neither to prevent the formation of ultralente crystals in the absence of phenolics nor to compromise the protracted activity of the insulin analogue suspension.

Animals↗