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PubMed2002

Solution-mediated phase transformation of anhydrous to dihydrate carbamazepine and the effect of lattice disorder.

This paper describes the kinetics of the solution-mediated phase transformation of the anhydrous monoclinic polymorph of carbamazepine (CBZ(A)) to the dihydrate crystal form (CBZ(D)). Monitoring both solution concentration and solid phase composition identified the steps and mechanisms that control the kinetic processes, and regulate the concentration of drug achieved during dissolution of the metastable solid phase, CBZ(A). The results show that the kinetics and the rate-controlling step for the transformation depend on grinding and storage conditions of CBZ(A). Grinding CBZ(A) shortened the transformation times and changed the rate-controlling step from crystallization of CBZ(D) to dissolution of CBZ(A). Grinding may cause various degrees of disorder in the form of lattice defects and/or amorphous regions. These disordered regions promote the anhydrous to dihydrate transformation by facilitating the surface nucleation of CBZ(D) on freshly ground CBZ(A) and on amorphous CBZ. The concentration-time profiles revealed aging effects on the solution-mediated transformation of ground CBZ(A) that were undetectable by diffraction and thermal analysis. These results have significant consequences on the concentration-time profiles of active pharmaceutical ingredients during dissolution of metastable solid phases, crystalline or amorphous.

Calorimetry, Differential Scanning↗
PubMed2002

Protein dynamics studied by neutron scattering.

This review of protein dynamics studied by neutron scattering focuses on data collected in the last 10 years. After an introduction to thermal neutron scattering and instrumental aspects, theoretical models that have been used to interpret the data are presented and discussed. Experiments are described according to sample type, protein powders, solutions and membranes. Neutron-scattering results are compared to those obtained from other techniques. The biological relevance of the experimental results is discussed. The major conclusion of the last decade concerns the strong dependence of internal dynamics on the macromolecular environment.

Bacteriorhodopsins↗
PubMed2006

Preparation of a solid dispersion of felodipine using a solvent wetting method.

A straightforward solvent wetting method was used to prepare felodipine solid dispersions in the presence of various carriers. Dichloromethane is not needed when HPMC solid dispersions were produced using the solvent wetting method. The amount of ethanol used to prepare solid dispersions did not have a significant effect on the dissolution rate of felodipine. The results of X-ray diffraction and thermal analysis indicated that the drug was in the amorphous state when PVP, HPMC, and poloxamer were used as carriers. The dissolution rates of felodipine in PVP, HPMC, or poloxamer solid dispersions were much faster than those for the corresponding physical mixtures. However, dissolution profiles were found to depend on the carrier used; the dissolution rate of felodipine increased slowly for solid dispersions prepared using HPMC, whereas rapid initial dissolution rates were observed for solid dispersions prepared using PVP or poloxamer. Increases in dissolution rates were partly dependent on the ratios of felodipine to carrier. No significant changes in crystal form were observed by X-ray diffraction or thermal analysis, and no significant changes in dissolution rate were observed when sorbitol and mannitol were used as carriers.

Calcium Channel Blockers↗
PubMed2005

Structure and synthesis of SSZ-63: toward an ordered form of zeolite beta.

The synthesis, characterization, and structure elucidation of the borosilicate zeolite SSZ-63 are described. SSZ-63 is synthesized using the 1-cyclodecyl-1-methylpyrrolidinium cation as a structure-directing agent. The structural model for SSZ-63 was determined by comparison of its powder X-ray diffraction pattern with those of zeolite beta and its polytype structures. Whereas conventional zeolite beta may be described as a random intergrowth of polytypes A and B, SSZ-63 is more accurately described as a random intergrowth of polytypes B and C(H) (the hypothetical polytype C proposed by Higgins). Polytype C(H) is essentially an ordered intergrowth (of polytypes A and B) in which one of the crystallographic projections is equivalent to those in polytype A and another projection is equivalent to those in polytype B. Unlike zeolite beta, which possesses significant disorder related to layer shifts along both the a- and b-crystallographic axes, the structure of SSZ-63 has little disorder associated with the translations of layers in the a-direction. DIFFaX simulations of the powder diffraction patterns, electron diffraction, and high-resolution transmission electron microsocopy data all support the proposed model.

Journal Article↗
PubMed2006

Iron-oxide-modified nanosized diamond: preparation, characterization, and catalytic properties in methanol decomposition.

Nanosized diamond (UDD), obtained by a detonation procedure, was modified with iron from the corresponding acetylacetonate precursor under various pretreatment conditions. Nitrogen physisorption, X-ray diffraction, temperature-programmed reduction, and FTIR and Mössbauer spectroscopy were used for their characterization. The samples' catalytic behavior in methanol decomposition was also studied. The physicochemical and catalytic properties of the obtained materials (Fe/UDD) were compared with those of other iron-oxide-modified mesoporous supports with different nature and functionality (MCM-48 silica and CMK-1 carbon). The highest catalytic activity and stability was achieved with air-pretreated Fe/UDD.

Adsorption↗
PubMed2005

Layered copper hydroxide n-alkylsulfonate salts: synthesis, characterization, and magnetic behaviors in relation to the basal spacing.

A series of hybrid inorganic-organic copper(II) hydroxy n-alkylsulfonate with a triangular lattice, Cu(2)(OH)(3)(C(n)H(2)(n)(+1)SO(3)) (n = 6, 8, 10), are prepared by anion exchange, starting from copper hydroxy nitrate Cu(2)(OH)(3)NO(3). These compounds show a layered structure as determined by X-ray diffraction, with interlayer distances of 14.3-34.8 A in alternation with interdigitated bilayer packing. Magnetic properties have been investigated by means of dc and ac measurements. All the compounds show similar metamagnet behaviors, with a Neel temperature of about 11 K. A subtle difference in the ac magnetic susceptibility among the compounds is understood by the existence of hydrogen bonding between the sulfonate headgroup and the hydroxide anion. A detailed molecular structure of the alkyl chains incorporated to the inorganic copper hydroxide layer is also discussed from the FTIR data.

Copper↗
PubMed2004

Solid state NMR studies and density functional theory (DFT) calculations of conformers of quercetin.

This work presents the first comparative analysis of two crystallographic modifications of quercetin (3,3',4',5,7-penta-hydroxyflavone). The existence of dihydrate and unhydrated forms of quercetin in the solid state is confirmed by several experimental techniques e.g. X-ray diffraction of powders, DSC, TGA, and NMR. Our studies allow an understanding of the complexity of quercetin samples obtained from different sources. A PASS-2D experiment is employed to establish principal values of 13C chemical shift tensors for both modifications. Solid state NMR spectroscopy and DFT GIAO calculations provide unique information about NMR shielding and electron density distribution for different conformers. It has been concluded that changes of conformation and hydrogen bonding pattern have great influence on bond order parameters of quercetin. Theoretical calculations and experimental data do not exclude the existence of the syn conformer of quercetin, which so far was not considered in the condensed phase.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Fibrillar beta-lactoglobulin gels: Part 1. Fibril formation and structure.

As a prelude to experimental and theoretical work on the mechanical properties of fibrillar beta-lactoglobulin gels, this paper reports the structural characterization of beta-lactoglobulin fibrils by electron and atomic force microscopy (AFM), infrared and Raman spectroscopy, and powder X-ray diffraction. Aggregates formed by incubation of beta-lactoglobulin in various alcohol-water mixtures at pH 2, and in water-trifluoroethanol (TFE) at pH 7, were found to be wormlike (approximately 7 nm in width and <500 nm in length), with a "string-of-beads" appearance. Longer (approximately 7 nm in width, and >1 microm in length), smoother, and seemingly stiffer fibrils formed on heating aqueous beta-lactoglobulin solutions at pH 2 and low ionic strength, although there was little evidence for the higher-order structures common in most amyloid-forming systems. Time-lapse AFM also revealed differences in the formation of these two fibril types: thermally induced aggregation occurring more cooperatively, in keeping with a nucleation and growth process. Only short stiff-rods (<20 nm in length) formed on heating beta-lactoglobulin at pH 7, and only complex three-dimensional "amorphous"aggregates in alcohols other than TFE at this pH. Studies of all of the pH 2 fibrils from beta-lactoglobulin, by Raman and infrared spectroscopy confirmed beta-sheet as mediating the aggregation process. Interestingly, however, some evidence for de novo helix formation for the solvent-induced systems was obtained, although it remains to be seen whether this is actually incorporated into the fibril-structure. In contrast to other amyloid systems, X-ray powder diffraction provided no evidence for extensive repeating "crystalline" structures for any of the pH 2 beta-lactoglobulin fibrils. In relation to amyloid, the lactoglobulin fibrils bear more resemblance to protofilaments than to higher-order fibril structures, these latter appearing more convincingly for thermally induced insulin fibrils (pH 2) also included in the AFM study.

Amyloid↗
PubMed2004

Protein dynamics in solution and powder measured by incoherent elastic neutron scattering: the influence of Q-range and energy resolution.

Incoherent elastic neutron scattering (IENS) has been widely used to measure intramolecular atomic mean square displacements (MSDs) of proteins in powder and in solution. The instrumental energy resolution and the wave vector transfer (Q-range) determine, respectively, the time and length scales of observable motions. In order to investigate contributions of diffusive motions to MSDs measured by this method, we calculated the elastic intensity for several simple scattering functions. We showed that continuous translational diffusion contributes to MSDs in a Q-range where the energy width of the scattering function is of the order of the instrumental energy resolution. We discuss the choice of instruments adapted to focus on intramolecular motions in the presence of solvent or global macromolecular diffusion. The concepts developed are applied to interpret experimental data from H(2)O- and D(2)O-hydrated proteins. Finally, analogies between the Gaussian approximation in IENS and the Guinier approximation in small-angle scattering are discussed.

Computer Simulation↗
PubMed2001

Batch Pb2+ and Cu2+ removal by electric furnace slag.

An evaluation of the application of electric furnace slag (EFS) as an adsorbent to remove Pb2+ and Cu2+ from industrial effluents is presented. The paper examines phase composition of EFS by using X-ray diffraction of powder. In the batch experiments, parameters studied include the effect of initial concentration of lead and copper ions, temperature, and contact time. Over the temperature range studied (293-313 K) the results of adsorption experiments could be fitted by using both Langmuir and Freundlich models and thermodynamic values of deltaG0, deltaH0 and deltaS0 corresponding to each adsorption process were calculated. Satisfactory conformity between experimental data and the model-predicted values was expressed by the correlation coefficient (R2). Both Langmuir and Freundlich models described the Pb2+ and Cu2+ sorption processes adequately, with correlation coefficient (R2) values ranging from 0.9760 to 0.9994. Data from this study indicated the potential use of the tested electric furnace slag, a by-product from "Felis" foundry in Sisak, Croatia, as Pb2+ and Cu2+ sorbents from the industrial effluents.

Adsorption↗
PubMed2004

Structural study of Cu(2-x)Se alloys produced by mechanical alloying.

The crystalline structures of the superionic high-temperature copper selenides Cu(2-x)Se (0 < x < 0.25) produced using mechanical alloying were investigated using X-ray diffraction (XRD). The measured XRD patterns showed the presence of peaks corresponding to the crystalline superionic high-temperature alpha-Cu(2)Se phase in the as-milled sample, and its structural data were determined by means of a Rietveld refinement procedure. After heat treatment in argon at 473 K for 90 h, this phase transforms to the superionic high-temperature alpha-Cu(1.8)Se phase, whose structural data were also determined by Rietveld refinement. In this phase, a very low occupation of the trigonal 32(f) sites ( approximately 3%) by Cu ions is found. In order to explain the evolution of the phases in the samples, two possible mechanisms are suggested: (i). the high mobility of Cu ions in superionic phases and (ii). the important diffusive processes in the interfacial component of samples produced by mechanical alloying.

Alloys↗
PubMed1992

Physicochemical properties of salts of p-aminosalicylic acid. I. Correlation of crystal structure and hydrate stability.

The potassium (K), sodium (NA), calcium (CA), and magnesium (MG) salts of p-aminosalicylic acid were obtained, and their thermal behavior was characterized by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Their crystal and molecular structures were determined by single-crystal X-ray diffraction after powder patterns had shown them to be nonisomorphous. Different degrees of hydration were observed for the solid salts, and an assessment of hydrate stability to dehydration was made from thermogravimetric studies. The onset temperature of dehydration (Tt) of each salt varied within the series and exhibited correlation with X-ray determined structure. The observed onset of dehydration of MG and CA was higher than that of NA and is consistent with stronger ion-dipole interactions for the divalent salts. Crystallographic determination of the bond lengths between the metal ion and the water oxygens were 2.4 and 2.9 A for NA, between 2.0 and 2.1 A for MG, and 2.4 A for CA. The open nature and presence of a channel feature in the structure of the sodium salt may have facilitated escape of water molecules from the crystal. Particle presentation (e.g., size, crystallinity) was also shown to affect dehydration behavior.

Aminosalicylic Acid↗
PubMed2004

On the mechanism of nanopore filling of SAPO-5 molecular sieve by nitrogen molecules.

SAPO-5 molecular sieve was synthesized according to patent literature and characterized with X-ray diffraction, electron microscopy (SEM, TEM), and solid state magic angle spinning NMR spectroscopy. The material of particles in the micrometer region was found to consist of ca. 20 nm microcrystallites packed in mostly parallel orientation to ca. 200 nm sized agglomerates. The nitrogen adsorption isotherm was measured at 77.6 K over ca. 7 decades of pressure up to pore saturation. The course of the isotherm is interpreted to consist of filling of the nanopores (diameter, 0.73 nm) up to 2N(2)/unit cell, subsequent multilayer adsorption on the outer surface of the agglomerates, and, finally, pore condensation in the interparticle adsorption space. The nanopore adsorption can be quantitatively reproduced with the statistical mechanical model of a quasi one-dimensional lattice gas taking intermolecular interactions into account. The evaluated energy parameters are of physically reasonable magnitude and agree with literature data. The multilayer part of the adsorption isotherm can be well represented by the Brunauer-Emmett-Teller model yielding a specific outer space area (63 m(2) g(-)(1)) which is consistent with estimated geometrical and pore size analysis data.

Adsorption↗
PubMed2006

A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite.

Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30-50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered.

Calcium↗
PubMed2000

Boron - Carbon Order in CeB(2)C(2).

Powder neutron diffraction studies show that boron and carbon atoms alternate in the planar pi-conjugated layers in CeB(2)C(2) and its lanthanide analogues, rather than being paired as was previously reported. Long and short B-C bonds correspond to the idealized arrangement of single and double bonds shown in the picture.

Journal Article↗
PubMed2001

A new 1 --> infinity [Ni7] cluster in LaNi7In6 and distorted bcc indium cubes in LaNiIn4.

LaNiIn4 and LaNi7In, were prepared by reaction of the elements in an arc melting furnace and subsequent annealing at 870 K for five weeks. Both compounds were investigated by X-ray diffraction on powders and single crystals and the structures were refined from single-crystal data: Cmcm, a = 448.2(1), b = 1689.5(4). c = 722.1(1) pm, wR2 = 0.0340, 472 F2 values, 24 variables for LaNiIn4, and Ibam, a = 806.6(2). b = 924.8(2). c = 1246.5(2) pm. wR2 = 0.0681. 726 F2 values and 40 variables for LaNi7In,. LaNiIn4 adopts the YNiAl4-type structure. The nickel and indium atoms form a three-dimensional infinite [NiIn4] polyanion in which the lanthanum atoms fill distorted hexagonal channels. No Ni-Ni contacts occur. The indium substructure consists of distorted bcc-like indium cubes. LaNi7In6 crystallizes with a peculiar new structure type. The nickel atoms build a 1 --> infinity [Ni7] cluster unit with Ni-Ni distances ranging from 249 to 269 pm. The cluster units are enveloped by indium atoms. These larger units show an orthorhombic rod packing with the lanthanum atoms filling the space between the rods. Several nickel clusters in ternary rare earth metal nickel indides and the structural relations of the LaNi7In6 structure with the cubic NaZn13 type are discussed.

Journal Article↗