Resonant x-ray diffraction as a tool to calculate mixed valence ratios: Application to Prussian Blue materials

An approach is proposed here to calculate mixed valence ratios in molecular compounds. Synchrotron x-ray powder diffraction experiments were conducted to determine the Fe(+3)/Fe(+2) ratio in Prussian Blue compounds, which were elected as an example of the use of this approach. As a result, a resonant x-ray diffraction measurement provided direct evidence that the vacant [Fe(CN)(6)] group was randomly absent from similar to 31% of the structure, which was indicated by structural differences caused by variations in the anomalous dispersion term. These findings are very important for a deeper understanding of the changes occurring in properties during in situ compositional variations. (c) 2008 American Institute of Physics.

Composition of the first coordination sphere of Ni2+ in concentrated aqueous NiBr2 solutions by x-ray diffraction

Two concentrated solutions of NiBr2 have been examined by x-ray diffraction. The Fourier transformed scattering data indicate inner complex formation between Ni2 + and Br- ions. Average numbers of bonded bromide ions per nickel atom have been determined for each solution and the reliability of the complexation numbers as well as of the other structural parameters has been critically examined. © 1985 American Institute of Physics.

X-ray diffraction investigation of Co(II) ions in borosilicate glasses

The radial distribution functions of cobalt glasses with 6%, 8%, and 14% CoO are compared with those of suitable cobalt-free borosilicate matrices leading to difference distribution curves representative of the cobalt structural arrangement. Analysis of the curves indicates that cobalt ions are surrounded by approximately four oxygen neighbors at the distance expected for fourfold coordination. © 1986 American Institute of Physics.

High temperature X-ray diffraction study of the U4O9 formation on UO2 sintered plates

The surface oxidation of UO2 sintered plates at 170-275 ° C was studied in situ by high temperature X-ray diffractometry. At very low oxygen concentration, UO2 is oxidized to U4O9, while at 300°C and argon-20 vol% oxygen it is oxidized up to U3O7. X-ray diffraction profiles of the UO2, U4O9 and U3O7 phases were well characterized during the transformations. The activation energy for the transformation of UO2 to U4O9, obtained from X-ray diffraction data, was found to be 117 ± 9 kJ/mol and 90 ± 14 kJ/mol for the β-(311) and α-(200) reflections, respectively. © 1991.

Crystallization and X-ray diffraction data analysis of oxyhemoglobin-I from the catfish Liposarcus anisitsi (pisces)

Hemoglobin remains, despite the enormous amount of research involving this molecule, as a prototype for allosteric models and new conformations. Functional studies carried out on Hemoglobin-I from the South-American Catfish Liposarcus anisitsi [1] suggest the existence of conformational states beyond those already described for human hemoglobin, which could be confirmed crystallographically. The present work represents the initial steps towards that goal.

Quantitative phase analysis from X-ray diffraction in Y-TZP dental ceramics: A critical evaluation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Crystallization and preliminary X-ray diffraction studies of an L-amino-acid oxidase from Lachesis muta venom

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Crystallization and preliminary X-ray diffraction analysis of a novel sphingomyelinase D from Loxosceles gaucho venom

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Crystallization and preliminary X-ray diffraction analysis of endoglucanase III from Trichoderma harzianum

Endoglucanases are enzymes that hydrolyze cellulose and are important components of the cellulolytic complex. In contrast to other members of the complex, they cleave internal beta-1,4-glycosidic bonds in the cellulose polymer, allowing cellulose to be used as an energy source. Since biomass is an important renewable source of energy, the structural and functional characterization of these enzymes is of interest. In this study, endoglucanase III from Trichoderma harzianum was produced in Pichia pastoris and purified. Crystals belonging to the orthorhombic space group P212121, with unit-cell parameters a = 47.54, b = 55.57, c = 157.3 angstrom, were obtained by the sitting-drop vapour-diffusion method and an X-ray diffraction data set was collected to 2.07 angstrom resolution.

Copper ore type definition from Sossego Mine using X-ray diffraction and cluster analysis technique

This paper presents the classification of 110 copper ore samples from Sossego Mine, based on X-ray diffraction and cluster analysis. The comparison based on the position and the intensity of the diffracted peaks allowed the distinction of seven ore types, whose differences refer to the proportion of major minerals: quartz, feldspar, actinolite, iron oxides, mica and chlorite. There was a strong correlation between the grouping and the location of the samples in Sequeirinho and Sossego orebodies. This relationship is due to different types and intensities of hydrothermal alteration prevailing in each body, which reflect the mineralogical composition and thus the X-ray diffractograms of samples.

Preparation and characterization of chloroaluminum phthalocyanine-loaded solid lipid nanoparticles by thermal analysis and powder X-ray diffraction techniques

Solid lipid nanoparticles (SLN) without drug and SLN loaded with chloroaluminum phthalocyanine (AlClPc) were prepared by solvent diffusion method in aqueous system and characterized by thermal analyses and X-ray diffraction (XRD) in this study. Determination of particle size, zeta potential (ZP), and encapsulation efficiency were also evaluated. SLN containing AlClPc of nanometer size with high encapsulation efficiency and ZP were obtained. The results indicated that the size of SLN loaded with AlClPc is larger than that of the inert particle, but ZP is not changed significantly with incorporation of the drug. In differential scanning calorimetry (DSC) curves, it was observed that the melting point of stearic acid (SA) isolated and in SLN occurred at 55 and 64 degrees C, respectively, suggesting the presence of different polymorphs. DSC also shows that the crystallinity state of SLN was much less than that of SA isolated. The incorporation of drug in SLN may have been favored by this lower crystallinity degree of the samples. XRD techniques corroborated with the thermal analytic techniques, suggesting the polymorphic modifications of stearic acid.

The T-2 phase in the Nb-Si-B system studied by ab initio calculations and synchrotron X-ray diffraction

The solid solution based on Nb5Si3 (Cr5B3 structure type, D8(l), tl32, 14/mcm, No140, a=6.5767 angstrom, c=11.8967 angstrom) in the Nb-Si-B system was studied from the structural and thermodynamic point of view both experimentally and by ab initio calculations. Rietveld refinement of powder X-ray synchrotron data allowed to determine the boron to silicon substitution mechanism and the structural parameters. Ab initio calculations of different ordered compounds and selected disordered alloys allowed to obtain in addition to the enthalpy of formation of the solution, substitution mechanism and structural parameters which are in excellent agreement with the experimental data. The stability of the phase is discussed. (C) 2012 Elsevier Inc. All rights reserved.

X-ray diffraction and theoretical investigation of the Gedunin crystal structure

The Gedunin compound (C28H34O6) is a natural product extracted from Trichilia pallida that has shown a wide activity. The crystallographic structure shows two conformers in the asymmetric unit, which differ in a rotation of the furan group. To understand this molecular arrangement, the density functional calculations. Molecular Electrostatic Potential (MEP) and thermodynamic function calculation have been performed at the B3LYP/6-311++g(d,p) level. Both conformers were optimized and the agreement with the experimental structure was very good, making possible further theoretical analysis of the structure. The inter-conversion between two conformers depends on the energy barrier. This process is studied in the vacuum and shows two transition states with a low energetic barrier for a potential energy curve scanning rigid around furan group: 4.37 kcal/mol and 16.52 kcal/mol. As the first transition state has a notably lower energetic barrier, the preferred inter-conversion pathway between the conformers involves the first rather than the second transition state. Understanding this transition state in detail led us to perform its optimization, showing an energetic barrier around 3.66 kcal/mol. The negative free energy and low enthalpy confirm that the process is spontaneous and exothermic. The results show that this requirement makes the existence of the two conformers in the asymmetric unit possible. The structure of molecules in the asymmetric unit is better understood when the MEP is used on the interaction between molecules. For Gedunin, both molecules have shown MEP with well-defined regions, and this behavior contributes to the observed link between molecules and for the negative regions complementing positive regions of another molecule. (C) 2011 Elsevier B.V. All rights reserved.

Crystallization and preliminary X-ray diffraction of malate dehydrogenase from Plasmodium falciparum

The expression, purification, crystallization and preliminary X-ray diffraction characterization of malate dehydrogenase (MDH) from the malarial parasite Plasmodium falciparum (PfMDH) are reported. In order to gain a deeper understanding of the function and role of PfMDH, the protein was purified to homogeneity. The purified protein crystallized in space group P1, with unit-cell parameters a = 72, b = 157, c = 159 angstrom, a = 105, beta = 101, ? = 95 degrees. The resulting crystals diffracted to a maximal resolution of 2.24 angstrom and the structure has been solved by molecular replacement, with 16 monomers in the asymmetric unit. The 16 monomers are arranged into four independent tetramers, in agreement with previous reports demonstrating the tetrameric solution state of PfMDH. The X-ray structure of PfMDH is expected to clarify the differences in catalysis by PfMDH compared with other MDH family members and to provide a basis for the structure-based design of specific PfMDH inhibitors as well as general MDH inhibitors.

Crystallization and preliminary X-ray diffraction analysis of three myotoxic phospholipases A2 from Bothrops brazili venom

Two myotoxic and noncatalytic Lys49-phospholipases A2 (braziliantoxin-II and MT-II) and a myotoxic and catalytic phospholipase A2 (braziliantoxin-III) from the venom of the Amazonian snake Bothrops brazili were crystallized. The crystals diffracted to resolutions in the range 2.562.05 angstrom and belonged to space groups P3121 (braziliantoxin-II), P6522 (braziliantoxin-III) and P21 (MT-II). The structures were solved by molecular-replacement techniques. Both of the Lys49-phospholipases A2 (braziliantoxin-II and MT-II) contained a dimer in the asymmetric unit, while the Asp49-phospholipase A2 braziliantoxin-III contained a monomer in its asymmetric unit. Analysis of the quaternary assemblies of the braziliantoxin-II and MT-II structures using the PISA program indicated that both models have a dimeric conformation in solution. The same analysis of the braziliantoxin-III structure indicated that this protein does not dimerize in solution and probably acts as a monomer in vivo, similar to other snake-venom Asp49-phospholipases A2.