bluuebunny/crossref_metadata_2025 huggingface dataset:
AIn2S4(A= Mn-Ni): New synthesis methods and structural characterization
Authors: Bolletta Juan , Alonso José , Carbonio Raúl , De Paoli Juan
Published: November 2015

Ternary chalcogenides with the spinel crystal structure have been widely studied for the last 60 years. These compounds are more covalent and allow different interactions between ions when compared to corresponding oxides while maintaining the versatility of the spinel structure. Particularly, spinels with formula AIn2S4(A= Mn-Ni) are found to be semiconductors with a large band gap (~2.0 eV), showing mainly antiferromagnetic interactions at temperatures below 100 K. These properties are dependent on the distribution of cations between octahedral and tetrahedral sites in the structure and also on the synthesis method. Syntheses of these compounds have been extensively reported, involving long heating periods of mixtures of elements or binary sulfides inside evacuated quartz ampoules, lasting for up to two weeks or longer. We report two new, faster synthesis methods for polycrystalline samples of indium thiospinels avoiding evacuated ampoules. Polycrystalline FeIn2S4and MnIn2S4samples were synthesized from stoichiometric mixtures of binary sulfides, heating in a constant gas flow of 1% H2in Ar at 1073 K for 6 and 24 hours respectively. Polycrystalline samples of FeIn2S4, CoIn2S4and NiIn2S4have also been synthesized in a piston-cylinder press, from stoichiometric mixtures of the binary sulfides, at a pressure of 3.5 GPa at 1173 K for 1 hour. From x-ray powder diffraction data all crystal structures were refined by means of Rietveld analysis. Refined cell parameters are in agreement with previous reports. Different degrees of inversion were obtained for each sample. NiIn2S4and both FeIn2S4samples are in accordance with previous reports, while MnIn2S4and CoIn2S4differ from reported values [1]. FeIn2S4and MnIn2S4synthesized in H2/Ar flux were characterized by Raman spectroscopy to further assess cation distribution. In addition, their thermal stability in air was tested by Thermogravimetric Analysis (TGA).
Structural studies of biomass degrading enzyme systems
Authors: Lunin Vladimir , Alahuhta Markus , Beckham Gregg , Brunecky Roman , Taylor Larry , Donohoe Bryon , Xu Qi , Vander Wall Todd , Bomble Yannick , Himmel Michael
Published: November 2015

Renewable energy today comprises wind, photovoltaics, geothermal, and biofuels. Biomass is the leading source of renewable, sustainable energy used for the production of liquid transportation fuels. While the focus is shifting today from the ethanol towards next generation or advanced biofuels the real challenge however remains the same: reducing the recalcitrance of biomass to deconstruction, which yields the sugars needed for further processing. NREL's Biosciences Center conducts studies of the fundamental nature of the plant cell wall; as well as those enzyme systems utilized in Nature to deconstruct it. These systems could be classified in two ways: the "free enzymes" and the "cellulosomes." Cellulosomes are self-assembling, multi-enzyme machinery that can include dozens and hundreds of catalytic domains and cellulose binding modules interconnected by linker peptides. We will present a structural overview of the biomass degrading enzymes from fungi using Trichoderma reesei and Penicillum funiculosum as examples. The bacterial cellulosome system discussed will be from a thermophile Clostridium thermocellum and bacterial free enzyme example will be the hyperthermophile, Caldicellulosiruptor bescii. To study these systems, we combined classical biochemistry and molecular biology, mass spectrometry, electron microscopy, high throughput robotics, macromolecular crystallography, and molecular dynamics. We seek to understand the properties and structure of biomass and plant cell walls, the structure-function relationships of the relevant hydrolytic enzymes, and the ways these enzymes interact with and alter the biomass during the degradation. Thorough understanding of the details of the molecular machinery at work has led to the development of improved enzyme cocktails that have reduced the cost of biomass conversion to renewable fuels so that today, this technology is becoming competitive with traditional fossil fuels.
Effect of Lone Pair Cations on the Orientation of Crystallographic Shear Planes in Anion-Deficient Perovskites
Authors: Batuk Dmitry , Abakumov Artem , Hadermann Joke
Published: November 2015

Anion deficiency in perovskite-based ferrites containing lone pair cations Pb2+ and Bi3+ can be accommodated by the formation of crystallographic shear (CS) planes. In this contribution, using (Pb1-zSrz)1-xFe1+xO3-y as a model system, we demonstrate that the lone pair cations are not only responsible for the formation of the CS planes, but also control their orientation. The isovalent substitution of Pb2+ by stereochemically inactive Sr2+ highlights the influence of the A-cation electronic structure owing to very close ionic radii of these cations. Employing a combination of transmission electron microscopy and X-ray and neutron powder diffraction, we have systematically investigated the structure evolution of the compounds with changing P/Sr ratio. Two compositional ranges with distinct orientations of the CS planes have been identified in the system: 0.05 ≤ z ≤ 0.2, where the CS planes orientation systematically varies but stays close to (203)p, and 0.3 ≤ z ≤ 0.45 with the (101)p CS planes. The incommensurate structure of Pb0.792Sr0.168Fe1.040O2.529, a representative compound of the first range, has been refined from the neutron powder diffraction data (S.G. X2/m(α0γ), X = [1/2,1/2,1/2,1/2], a = 3.9512(1)Å, b = 3.9483(1)Å, c = 3.9165(1)Å, β = 93.268(2)0, q = 0.0879(1)a* + 0.1276(1)c*, RF = 0.023, RP = 0.029, T = 900K). Comparing the CS structures in both compositional ranges, we demonstrate that the orientation of the CS planes is primarily governed by a specific bonding configuration of the lone pair cations with the anions.
The first protein Structure Determinations
Authors: Rossmann Michael
Published: November 2015

Max Perutz had been studying the structure of haemoglobin for 21 years using highly original and creative techniques, when I arrived in Cambridge in the summer of 1958. Most recently he had explored the use of isomorphous replacement by substituting specific amino acids with heavy metal compounds. Together with Ann Cullis, he had collected three dimensional diffraction data on native haemoglobin crystals and on three heavy atom derivatives. But now Max needed help in analyzing this data. I had had experience in determining three small aromatic hydrocarbon structures as a graduate student with J.M. Robertson at the University of Glasgow using only mechanical hand calculators, a slide rule and Beevers-Lipson strips. At the University of Minnesota, as a post doc with Bill Lipscomb, I had learned how to program one of the earliest commercial computers and solved a plant terpenoid structure in three dimensions. Thus, when I joined Max's lab, I was soon busy programming the bran new "home build" EDSAC2 computer to determine and refine the heavy atom parameters for phase determination by isomorphous replacement. When we calculated the 5.5Å resolution horse oxy haemoglobin electron density map in the summer of 1959 we were amazed to see that the two polypeptide chains of haemoglobin each had the same fold as that of myoglobin, another oxygen carrying protein determined by John Kendrew at 6Å resolution two years earlier at the Cavendish. John and his group were extending the structure of myoglobin to 2Å resolution. The high resolution map of myglobin was calculated using my Fourier program the week after the low resolution haemoglobin map. We then saw the atomic structure of α-helices as had been predicted by Linus Pauling. Seeing evolution for the first time at a molecular level has inspired my thinking and choice of research topics ever since. In the following few years, stimulated by these discoveries , David Blow (who had returned from the US later that summer after two years of post-doc studies) and I developed the single isomorphous replacement method, the use of anomalous dispersion for phase determination, phase combination procedures and, most importantly, molecular replacement.
Chiral Channels in Molecular Co-Crystals: Structures on the Path to Tris(carboxyphenyl)arenes
Authors: Wiscons Ren , Rowsell Jesse , Zeller Matthias
Published: November 2015

Porous molecular crystals that retain their structure in the absence of trapped solvent molecules are rare, given the flexibility of most non-covalent interactions. The crystal structure of microporous 1,3,5-tris(4-carboxyphenyl)benzene (tcpb) is notable for its large void volume and thermal stability, which stems from a complex polycatenation of its hydrogen-bonded network. Our group is exploring the crystallography of derivatives of this model compound with an eye towards tuning the dimensions and polarity of its pore structure. In one synthetic pathway, tritolylarenes are prepared as intermediates. We have discovered that even these molecules, which have no hydrogen-bond forming groups, tend towards complex crystal packings that exhibit disorder, aperiodicity, and solvent-filled voids. Additional exploration of co-crystals of these propeller shaped entities produced a pseudohexagonal columnar structure assembled from π-stacked helices. These helices enclose channels containing disordered tetrafluoroborate counterions, suggesting the possibility of ion exchange properties.
The effect of cold rolling on the crystal structure of Mg and MgH2
Authors: Lang Julien , Huot Jacques
Published: November 2015

Hydrogen could have a leading role as an energy carrier in the future. As a storage medium, metal hydrides are interesting from a fundamental as well as practical point of view. Hydrogen storage applications have been the main driving force of research on these materials but lately uses such as thermal storage are considered. Magnesium and magnesium alloys are interesting as a hydrogen storage material since they are low cost and have a high gravimetric capacity (7.6 wt. %). As a preparation technique, cold rolling has been recently shown to be an equivalent to high energy ball milling for magnesium hydride [1]. In this presentation we will review the use of x-ray and neutron diffraction to study the effect of cold rolling on magnesium and magnesium hydride's crystal structure. Cold rolling on magnesium plate produced a highly textured material. When performed on magnesium hydride, cold rolling reduced the crystallite size down to nanometer scale. The impact of texture and naocrystallinity on hydrogen storage behaviours will also be discussed.
Structural Characterization of Heteroepitaxial Growth of AlxGa1-xSb/GaSb by LPE
Authors: Lopez Primavera , Martinez Javier , Juarez Gabriel , Diaz Joel
Published: November 2015

The heteroepitaxial AlxGa1-xSb/GaSb (001) growth with different x aluminum content, from 0.05 to 0.2 prepared by Liquid Phase Epitaxy (LPE) is presented. The interest in this study is due to the layers of AlxGa1-xSb systems should be well matched for fabrication of sources and detectors operating in the 1.3-1.6 micron range. The layered structure obtained was characterized mainly by high-resolution X-ray diffraction and reciprocal space mapping. In the case of x = 0.05 aluminum content, the relaxation is minimal, and almost without deviation respect to GaSb. As the aluminum content increases above 0.05, the relaxation is larger and deviation from GaSb substrate too. Crystallographic tilt is detected by a shift of layer diffraction maximum on reciprocal space maps. Deviation changes the intensity of layer respect to substrate peak in rocking curves and hence the estimation of thickness of layer obtained from them. A correction for estimated thickness of layers is obtained from mapping.
A proton wire water channel revealed in the crystal structure of isatin hydrolase
Authors: Bjerregaard-Andersen Kaare , Sommer Theis , Jensen Jan , Jochimsen Bjarne , Etzerodt Michael , Morth Jens Preben
Published: November 2015

Two high resolution crystal structures of isatin hydrolase (IH) from the Baltic seabed bacteria Labrenzia aggregata are presented. The crystals structure capture both the apo and the product state. This hydrolase present a new fold and the first metal-dependent hydrolase with this fold to be functionally characterized[1]. The Isatin hydrolase catalyze the reaction that convert isatin to isatinate and belongs to a novel family of metalloenzymes that include bacterial kynurenine formamidase (KynB) also recently published, however hoste a binclear zink site in the active site[2] as compared to a single manganese in IH. The product state, mimicked by thioisatinate, has captured an additional water molecule that bridges the thioisatinate to a water channel and that could act as a proton wire and thus allows the proton to be released during the hydrolysis reaction only when the product is formed. The functional proton wire is therefore locked by thioisatinate and represents a unique catalytic feature trapped and visualized. Biochemical evidence for the proton wire is also presented as single point mutation from S225C enhances the Vmax of the enzyme. Ser-225 is the only side chain residue that is included in the proton wire. The molecular basis for thioisatinate recognition allows stronger and more confident identification of orthologous genes encoding isatin hydrolases within the prokaryotic kingdom. The isatin hydrolase orthologues found in human gut bacteria raise the question as to whether the indole-3-acetic acid degradation pathway is present in human gut flora.
The Crystalline Sponge Method: Synthetic and Crystallographic Guidelines
Authors: Ramadhar Timothy , Zheng Shao-Liang , Chen Yu-Sheng , Clardy Jon
Published: November 2015

Synthetic and crystallographic guidelines for the crystalline sponge method based upon the analysis of rapidly-synthesized crystal sponges using high-flux synchrotron radiation are presented [1]. The synthetic procedure for the zinc-based metal-organic framework (MOF) used in preliminary crystal sponge reports [2, 3] has been modified to afford suitable sponges in 3 days instead of 2 weeks. These sponges were tested on some small molecules, with two being difficult cases for in-house diffraction analysis in regards to data quality and determination of space group. These issues were readily resolved by the use of high-flux synchrotron radiation with <1 hour data collection times. None of the structures required the use of electron density removal programs to treat solvent accessible voids. The crystalline sponge systems analyzed in this study are the highest-quality structures of this class presented to date that meets chemical crystallographic standards. As a result of these studies, a set of guidelines for the crystallographic process were developed, and the single crystal to single crystal transformation process for these systems was also analyzed. The presented guidelines will be helpful for those interested in using the crystalline sponge method to fully elucidate the structures of non-crystallizable compounds at in-house diffraction or synchrotron facilities, and will aid in obtaining data that meet the standards of chemical crystallography.
Open Meeting of the Commission on International Tables for Crystallography
Authors: Brock Carolyn
Published: November 2015

The development of the seriesInternational Tables for Crystallographysince the 2011 Congress in Madrid will be discussed. The series includes eight published volumes with a ninth expected before the end of 2014 and definite plans for a tenth. A new edition of Volume A (Space-group symmetry, Editor Mois Aroyo) is nearly ready. A great deal of work has been done on the associated onlineSymmetry Database. Volume A1 (Symmetry relations between space groups, 2011, editors Hans Wondratschek and Ulrich Müller) is the companion volume. Work on a revision of theBrief Teaching Editionwill begin once the new Volume A is finished. Volume B (Reciprocal space, 2010; Editor Gervais Chapuis, who succeeded Uri Shmueli in 2011) and Volume C (Mathematical, physical and chemical tables, 2006, Editor Richard Welberry) are undergoing revisions, which will be major. The volumes will be reorganized with those topics connected to reciprocal space in B and those connected to direct space in C. A new edition of Volume D (Physical properties of crystals, Editor André Authier) was completed in 2013. A new edition of Volume F (Crystallography of biological macromolecules, Editors Eddy Arnold, Daniel Himmel, and Michael Rossmann) appeared in 2012. A new Volume H onPowder diffraction(Editors Chris Gilmore, Jim Kaduk, and Henk Schenk) is nearing completion. A new Volume I onXAFS(Editors Chris Chantler, Federico Boscherini, and Bruce Bunker) is in the planning stage. The Commission on Magnetic Structures is developing plans for a volume. In the meantime Danny Litvin's compilation of 1-, 2-, and 3-dimensional magnetic subperiodic groups and space groups was published as an e-book by the IUCr in 2013. Ideas for future developments will be welcome.
Effects of Annealing and X-ray Exposure in (Y,Co)-Codoped CeO2 Probed by XAFS
Authors: Wu Tai-Sing , Jeng Horng-Tay , Chang Shih-Lin , Soo Yun-Liang
Published: November 2015

Local structures surrounding Co dopoant atoms in (Y,Co) codoped CeO2 nanocrystals prepared by a chemical method followed by a series of thermal annealing and x-ray exposure have been probed using x-ray absorption fine structure (XAFS) techniques. These material systems are of great interest for catalytic applications. Our x-ray results show systematic variation of local structures surrounding Co atoms due to thermal annealing at different temperatures. It was also found that x-ray exposure with sufficient incident photon energy can substantially neutralize the structural effects of annealing. A theoretical model based on calculation using the Vienna ab initio Simulation Package (VASP) was proposed to identify relevant dopant locations that lead to the observed XAFS results and to explain the migration of Co in the CeO2 host due to the x-ray and thermal treatments. Manipulation of dopant atoms using x-ray exposure may provide unprecedented opportunities for tuning the physical properties of these materials for catalytic applications.
Measurement of chiroptical properties of nickel sulfate hexahydrate with G-HAUP
Authors: Taniguchi Takuya , Ishikawa Kazuhiko , Nakagawa Kenta , Tanaka Masahito , Asahi Toru
Published: November 2015

A crystal, which belongs to a lower crystal system than cubic one, exhibits optical anisotropies. The optical anisotropies originate from the difference in refraction and absorption between orthogonally linearly polarized lights. When molecules forming a crystal are enantiomers with the same chirality or form helical structures with the same handedness, the crystal shows chiroptical properties, which originate from the difference in refraction and absorption between right and left circularly polarized lights. The four optical phenomena are called linear birefringence (LB), linear dichroism (LD), circular birefringence (CB) and circular dichroism (CD), respectively. It had been difficult to measure CB and CD in chiral crystals with optical anisotropies because the signals of the anisotropies are three or four orders of magnitude larger than those of chiroptical properties. The Generalized High Accuracy Universal Polarimeter (G-HAUP) [1] enables us to simultaneously measure LB, LD, CB and CD of any anisotropic crystal. Nickel sulfate (NS) is achiral in the solution state. However, in the crystalline state, it forms hexahydrate and exhibits chirality since molecules are put in helical arrangements. The NS crystal belongs to an enantiomorphous space group, P41212 or P43212. Many researchers have reported the optical properties of NS crystal because large and good-quality crystals are readily grown. However, we consider the LB, LD, CB and CD in NS crystal should be simultaneously and completely investigated. The purpose of this study is to obtain LB, LD, CB and CD along the a axis with G-HAUP and compare the CB and CD with the results along the c axis. We measured optical rotatory power (ORP) along the c axis with G-HAUP, which agrees with the previous results [2,3]. We then prepared for some samples with chirality and anisotropy. We measured LB, LD, CB and CD spectra, respectively and will demonstrate the relation between their optical properties and structures.
Three-Dimensional Analyses of Morphology of Polymer Spherulites by X-ray Computerized Tomography
Authors: Nguyen-Dung Tien , Nishikawa Yukihiro , Hashimoto Masato , Tosaka Masatoshi , Sasaki Sono , Sakurai Shinichi
Published: November 2015

We report 3-dimensional structural analyses of huge spherulites of poly(oxyethylene) (PEG) by the X-ray computerized tomographic (CT) observation in blends of PEG and amorphous poly(lactide). The formation of the huge spherulites is characteristic of PEG and its direct observation by the X-ray CT is reported here for the first time. Slit-shaped cracks were clearly observed by the X-ray CT. Not only the straight cracks but also curved ones were found and it seemed that they overall formed a set of spokes. Furthermore, the scanning electron microscopic observation revealed that the cracks were parallel to bundles of lamellar crystallites. From those observations, we conclude that a set of radial cracks observed under the X-ray CT is a signature of a huge spherulite. Several aspects of an axialite structure are presented and a good agreement with the intuitively proposed structural model is obtained.
The new phase GdFe0690Si1940as a structural intermediate of GdSi2and GdFe2Si2
Authors: Vinokur Anastasiya , Fredrickson Daniel
Published: November 2015

Intermetallic phases are solid state compounds formed between metals that exhibit a wide structural variety and a myriad of important properties such as magnetism, catalysis, and superconductivity. Developing their properties requires an ability to control or guide their crystal structures, which can be wildly elaborate, involving thousands of atoms per unit cell. One principle for approaching this problem is the recognition that many of the most complex phases encountered in intermetallics can be understood in terms of fragments of simpler structures. The challenge of tailoring of intermetallics then lies in understanding the driving forces for the insertion of interfaces into simple structures to build complexity. We present the synthesis and the crystal structure of a new phase that sheds light on this issue, GdFe0690Si1940. It shares structural motifs with two neighboring phases in the Gd-Fe-Si system with common structure types, GdSi2(AlB2-type) and GdFe2Si2(ThCr2Si2-type). GdFe0690Si1940arises as the hexagonal nets of GdSi2are cut perpendicular to the a axis by square nets, forming distinct slabs. The surroundings of the Fe square nets locally resemble slabs of the GdFe2Si2structure, but the Fe content of the nets varies, depending on the presence of an Fe/Si mixed site. GdFe0690Si1940thus represents an intermediate point between the GdSi2and GdFe2Si2phases. This viewpoint offers the possibility of a series of crystal structures linking GdSi2and GdFe2Si2, representing a continuum of GdFexSi2phases with varying degrees of Fe incorporation, which we are now exploring synthetically.
General Synthetic Route and Structural Characterization of New 3d-4f Materials
Authors: Vega Andres , Baldo Bianca , Paredes-García Veronica , Spodine Evgenia , Venegas-Yazigi Diego
Published: November 2015

Within the field of coordination chemistry, the crystal engineering has been applied mainly through the design and synthesis of Metal-Organic Materials (MOMs), which are attractive not only by the wide variety of architectures and topologies that they present, but also by the potential applications in catalysis, ion exchange, molecular adsorption, fluorescence, nonlinear optics, and magnetism. From a structural and synthetic point of view, the literature shows that a wide variety of MOMs ranging from 0D to 3D structures have been rationally designed and synthesized by the appropriate selection of the metal centers and organic building blocks, as well as of the reaction pathways.1-3 In this work, we present the a general synthetic route and the structural characterization to a new MII(3d)-M'III(4f) (M = Co, Ni ; M' = Ce) MOMs. The assembly of paramagnetic ions of transition metal centers together with simple and versatile ligands permits to obtain this new heterometallic three dimensional structures. From a structural point of view, the 3D MOM, present a cubic structure and crystallizes in the Fm-3m spatial group. Details of synthetic methodology and structural characteristic of the synthesized MOM should be discussed. Figure 1: Lanthanide ions are cubically surrounded by transitions ions which defines a covalent cubic tridimensional lattice. Acknowledgements: The authors acknowledge financial support from FONDECYT 1130643 and Financiamiento Basal, FB0807. B.B. thanks UNAB Doctoral Scholarship 2013 and CONICYT Fellowship.
Cation disorder in CZTS materials from anomalous diffraction at KMC-2 (BESSY)
Authors: Többens Daniel , Neldner Kai , Valle-Rios Laura , Schorr Susan
Published: November 2015

The compound semiconductor Cu2ZnSnS4 (CZTS) is a promising alternative for absorber layers in thin film solar cells, as it has a nearly ideal band gap of about 1.5 eV, a high absorption coefficient for visible light, and contains only earth abundant and non-toxic elements. Besides chemical composition and phase purity, the efficiency of CZTS thin film solar cells depends strongly on the concentration of Cu- and Zn-antisites and copper vacancies in the kesterite-type structure. However, Cu(I) and Zn(II) are isoelectric and thus cannot be distinguished by conventional X-ray diffraction. In prior work we determined Cu-Zn-distribution successfully from neutron scattering [1]. Here we present experiments utilizing anomalous X-ray diffraction on the K-edges of Cu and Zn. Anomalous scattering coefficients are heavily wavelength-dependent close to the absorption edges of the respective element. This is utilized for contrast enhancement. Usage of multiple wavelengths above, below and between the absorption edges of Cu and Zn ensures significant overdetermination, so that the Cu-, Zn-, and vacancy concentrations can be refined reliably for the independent crystallographic sites. Experiments were conducted at the diffraction end station of the KMC-2 beamline [2] at BESSY (Berlin, Germany). KMC-2 provides X-ray radiation with both very stable energies and intensities. The accessible energy range of 4 – 14 keV is ideally suited for the K-edges of Cu (8979 eV) and Zn (9659 eV). A 6-circle goniometer in psi-geometry allows both powder and grazing incidence diffraction, so that bulk samples and thin films can be measured. The instrument can be equipped with either a scintillation point detector (Cyberstar) or an area detector (Bruker Vantec), allowing to optimize resolution and intensity to the needs of the experiment.
X-ray powder diffraction use in forensic analysis in Brazilian context
Authors: Oliveira Larissa , Thyone Cassio , Speziali Nivaldo
Published: November 2015

The forensic analysis of evidences must be able to extract maximum of information from small quantities of samples, while preserving as much material as possible for future tests. In this case, the accuracy and speed are vital in order to obtain relevant and trustful results. Among the many types of materials that are subject of a criminal investigation, a great quantity of them can be analyzed by using the X-ray powder diffraction (XPD) technique [1] [2] [3]: inorganic, organic and metals. It's required that the material should be solid and crystalline or partially crystalline. The huge advantages lie in the fact that it is a nondestructive technique and the unique characterization is possible because each compound has its own specific pattern, like a `fingerprint'. It was not found any publication about the use of the XPD by the Brazilian laboratories that is dedicated to forensic analysis. The aim of this work is to show the versatility of the technique and the great cost-beneficial that this technique can offer. Many Brazilian laboratories situated in universities possess the equipment and can eventually help the investigations along with the police. This partnership can provide advances in technology and can encourage the fundamental and applied science students to contribute with the Forensic Science in Brazil, increasing the quality and variety of the national scientific research.
Influence of Various Carbonates on the Hydration of Portalnd Cement
Authors: Meden Anton , Medvescek Simona , Kaucic Venceslav
Published: November 2015

Over the last 20 years, the effects of using limestone in Portland cement (PC) have been well studied. The benefits of limestone as a partial replacement for PC are well established. Its economic and environmental advantages of reducing CO2 emissions are well known. For a long time, the limestone has been considered as an inert filler. Recently it has been concluded that limestone serves both as an inert filler and also reacts to a limited extend. The reactivity depends on its fineness (specific surface)[1] and content [2,3]. The question arose, whether a) it is the availability of excess carbonate ion in the hydration system, which determines the degree of influence on the hydration process or b) does the system have its internal capacity to include carbonate ions and the increased availability (more carbonate ions in the solution, embedding the hydrating particles) would not have a significant effect. So the question was if the more soluble carbonates would have more pronounced effect on the hydration of the Portland cement than the limestone, which is only slightly soluble. The influence of slightly soluble (CaCO3, MgCO3, dolomite), medium soluble (Li2CO3) and highly soluble (K2CO3 and KHCO3) carbonates on the hydration of Portland cement was studied using Rietveld analysis. The results indicated that the amount of reacted carbonate in cement hydration at a 15% addition of slightly or medium soluble carbonates does not exceed 5% and is not affected by their solubility; at a 15% addition of the highly soluble carbonate K2CO3 the amount of reacted carbonate is around 6% leading to the conclusion that the system behaves according to the option b). The fugure presents the quantitative analysis of cement hydration at 3, 7, 28 and 90 days of hydration and temperatures of 25 and 400C.
Synthesis and Catalytic Properties of Gold(III) Complexes with Triazine Ligand
Authors: Lo Chui-Man
Published: November 2015

Gold catalysts were found to have high catalytic activities.[1] They can be stabilized by ligands such as triazine, bipyridine, or terpyridine.[2] It was found to be an effective catalyst in the addition of nucleophiles to triple bonds. In relation to this work, we have adopted 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine 1 to form the gold(III) complex 2.[3] The gold(III) complex 2 was characterized and it demonstrated catalytic hydration of aromatic alkyne (yield 10~80%). We have optimized the condition with the use of a mixture of water and methanol (v:v, 1:5) as the solvent system with catalytic amount of sulfuric acid. The reaction was carried out at 65 °C for 1 hour unless specify. The catalytic results were compared with KAuCl4.
Reduction of Cu2+in exchanged Ag+natural clinoptilolite: structural study
Authors: Concepcion-Rosabal Beatriz , Penton-Madrigal Arbelio , Rodriguez-Iznaga Inocente , Estevez-Rams Ernesto , Petranovskii Vitalii
Published: November 2015

Modified zeolites with cations, clusters and metallic nanoparticles are of interest due to the possibility to develop materials with new properties [1]. A study concerning the thermal reduction under hydrogen flow of mixed bimetallic system Cu2+ and Ag+ exchanged natural clinoptilolite Tasajeras deposit, Cuba is presented. The influence of silver in the reduction of Cu2+ was studied. X-Ray diffraction experiments on natural clinoptilolite, as well as on ion-exchanged monometallic and bimetallic samples were performed. The peak intensities of the exchanged samples, are changed as a result of the ion exchange, and they are fundamentally associated with differences in nature, amount and position of the extra-framework ions in the channels of the natural zeolites [2, 3]. The fig 1 shows the magnitude of the Fourier Transform (FT) for the EXAFS signals of the natural clinoptilolite exchanged with Cu2+ and of the natural clinoptilolite exchanged with both Cu2+ and Ag+ and reduced at 150 oC . The TF of the experimental EXAFS signal of metallic Cu, has been also added. The amplitude of the peak at 1.82 Å, associated with the coordination of Cu2+ with 4 oxygen atoms, decreases upon Cu was added. A detailed analysis of the graph reveals also that for the exchanged and reduced samples a peak at 2.58 Å begins to emerge. This maximum coincides with the first maximum of the metallic Cu and may be associated with the formation of small clusters of Cu. The addition of Ag+ favors the decrease of the reduction temperature of Cu2+. The reduction of Cu2+ and Ag+ cations shows existence of notable interinfluence between both cations during this process. The Cu2+ reduction is favored by the presence of Ag+. The aggregation of the reduced highly dispersed species both for copper and silver is limited in this bimetallic system. The introduction of Ag+ as the second cation in the copper exchanged zeolites appears to be an efficient tool for the control of the size of the resultant reduced nanoparticles.
Symmetry Relations Between Space Groups in Layered Germanate Structures: Modeling Crystal Structures
Authors: Flores-Sanchez Nelly , Rosales Ivonne , Bucio Lauro
Published: November 2015

Structural models for the new layered germanates ScInGe2O7 and ScFeGe2O7 were analyzed within the framework of symmetry relations between space groups. These compounds were supposed to be hettotypes of the thortveitite mineral, (Sc,Y)2Si2O7, which was considered as the aristotype. Thortveitite crystallizes in the monoclinic system, and the symmetry is described by the space group type C2/m. Other monoclinic hettotypes for the thortveitite are FeInGe2O7 (PDF 01-070-8447, ICSD - 94487), space group C2/m (No. 12); TbInGe2O7 (PDF 01-072-6515, ICSD - 96360), space group C2/c (No. 15); and FeYGe2O7 (PDF 01-072-6099, ICSD - 95935), space group P21/m (No. 11). All these space groups are related by symmetry. By the use of these relations, we proposed starting models for the crystal structures of ScInGe2O7 and ScFeGe2O7. For ScInGe2O7 this was found to be isostructural to FeInGe2O7 reported by our laboratory [1]. The structural data for this compound were obtained by conventional Rietveld refinement of the powder diffraction data of X-rays, using the GSAS program and EXPGUI [2, 3] interface. For ScFeGe2O7 the symmetry related structural model was found in the triclinic system by symmetry reduction from the space group C2/m (unique axis b) to the triclinic space group P1 (figure 1). Rietveld refinement was performed reaching to the following results: lattice parameters a = 5.3434 (8), b = 5.3145 (8), c = 4.8732 (7 ) Å, α = 99 468 (2), β = 97 257 (2), γ = 104 609 (2)0, V = 130.03 (5) A3, Z = 1; WRp = 0.047, Rp = 0.04 and reduced χ2 of 2.176 for 64 variables. This study was sponsored by CONACyT project CB-2011/167624.
Study of Ti-V-Cr metal hydrides by neutron powder diffraction
Authors: Bibienne Thomas , Flacau Roxana , Bobet Jean-Louis , Huot Jacques
Published: November 2015

Metal hydrides are interesting materials from a fundamental as well as practical point of view. In particular, Ti-based BCC solid solutions are considered as promising candidates for mobile applications because of their high volumetric capacities and room temperature operation. However, the slow kinetics of the first hydrogenation, the so-called activation step, is an important hurdle in the use of these alloys for practical applications. It has recently been shown that doping a Ti-V-Cr composition with Zr7Ni10 leads to a fast activation kinetic without heating treatment [1]. We studied the effect of this doping on two new Ti-V-Cr compositions: 52Ti-12V-36Cr and 42Ti-21V-37Cr. Two different doping methods were investigated: i) a single-melt synthesis where the raw materials (i.e. Ti, V, Cr, Zr and Ni) chunks were mixed and arc-melted; ii) co-melt synthesis where 52Ti-12V-36Cr and 7Zr-10Ni were arc-melted independently and thereafter re-melted together. Using only X-ray diffraction for structural identification does not provide information about hydrogen localization. Therefore, neutron diffraction is essential for complete determination of this class of hydrides. The peculiarity of the present alloys is that, for neutron diffraction, the scattering lengths of the elements almost cancel. Therefore, the neutron pattern of as-cast alloy shows very small Bragg peaks but the advantage is that the hydride is very easy to see and analyze. We performed in-situ neutron diffraction experiments during dehydrogenation of these materials to see the transition from the dihydride to monohydride. These measurements were complementary to X-ray and synchrotron radiation diffraction and enabled a better crystal structure determination of these alloys
Crystal wafer as a wavelength monitor
Authors: Wright Jonathan
Published: November 2015

For accurate synchrotron data collection it is important to know the precise X-ray wavelength and to be able to monitor this value. Due to the high heat load on the X-ray optics from modern sources significant drifts may occur. Any change in wavelength is reflected as a change in the unit cell parameters derived from the data and this is especially problematic for measurements of strain. A conceptually simple device has been developed to allow measurements and monitoring of the X-ray wavelength by measuring the transmission of a silicon single crystal wafer in transmission. As the crystal is rotated in the beam different hkl reflections are diffracted leading to a loss of intensity in the transmitted beam. By measuring the incident and transmitted intensity the angles of all of these peaks can be measured with high precision while rotating the crystal, with a setup rather similar to a conventional EXAFS experiment. A similar device has also recently been developed for polychromatic experiments [1]. For high energy X-rays the wafer can be left in the beam throughout the experiment and individual reflections can be scanned to monitor the wavelength as a function of time. The rich diffraction pattern which can be recorded in this geometry should contain a wealth of information as all single rocking curves are measured with high resolution on an absolute scale in comparison to the crystal absorption. The figure shows an example scan collected at 42 keV using a silicon wafer.
Aperiodic atomic ordering in PMN recovered from the anomalous x-ray scattering
Authors: Kopecký Miloš , Kub Jiří , Fábry Jan , Šourek Zbyněk
Published: November 2015

Various imaging techniques with atomic resolutions have been developed to study 3D arrangement of atoms in sub-nanometer and nanometer scale. The method presented is based on the measurement of the anomalous portion of x-ray scattering in large volume of the reciprocal space. It can be shown that, by analogy to x-ray holography with atomic resolution, the anomalous diffuse scattering provides information on both the amplitude and the phase of the scattered wave. The sample was PbMg1/3Nb2/3O3 (PMN), which belongs to relaxor ferroelectrics. Although the short and intermediate range chemical ordering is responsible for its relaxor behaviour, the real arrangement of cations remains unclear so far. The intensities of x-ray scattering in a large 3D volume of the reciprocal space were measured using an intense x-ray radiation generated by the synchrotron facility. Anomalous x-ray scattering has been obtained as a difference of intensity maps collected at two energies. The energy E1 just below the Nb K absorption edge was chosen in order to get a strong anomalous component in the scattering from Nb atoms. The data acquired at the energy E2 far from the absorption edge were used as the reference. The measured 3D pattern of anomalous scattering, including both discrete diffraction peaks and continuous x-ray diffuse scattering, allows us to reconstruct numerically an average environment around Nb atoms. The reconstructed real-space images clearly show a systematic local ordering of Mg2+ and Nb5+ cations. This ordering is more significant close to the central reference Nb atom but it is still apparent at the distance of about 3 nm giving thus an idea on the average size of ordered regions. More distant sites are occupied randomly with probabilities of occurrence of Mg2+ and Nb5+ cations given by their relative fraction in the sample. It is possible to determine conditioned probabilities of site occupancies by the given type of atom provided that the central site is occupied by Nb and to get information on the structure model of the ordered regions in the crystal.
Improvement and Upgrade of Small-Angle X-ray Scattering Beamlines at the Photon Factory
Authors: Shimizu Nobutaka , Mori Takeharu , Ohta Hiromasa , Nagatani Yasuko , Saijyo Shinya , Takagi Hideaki , Kamijyo Ai , Kosuge Takashi , Igarashi Noriyuki
Published: November 2015

Three small-angle X-ray scattering (SAXS) beamlines, BL-6A, BL-10C and new BL-15A2 are available at the Japanese synchrotron facility, Photon Factory (PF). We are recently improving and upgrading the SAXS beamlines at the PF in order to support new measurements and construct a high-throughput experimental system. BL-6A is a bending magnet beamline and the wavelength is fixed at 1.5 angstrom. This beamline had two detectors, PILAUS 300K (Dectris) for SAXS/GI-SAXS and PILATUS 100K (Dectris) for WAXD experiment, respectively, and the simultaneous measurement using these detectors are available. We installed a new experimental stage and replaced PILATUS 300K with PILATUS3 1M in this March. Therefore, the range of an applicable camera length spread to 0.25 ~ 2.5 m, and the detectable angle area expanded in the small-angle region. BL-10A is also a bending magnet beamline and the wavelength has been fixed at 1.488 angstrom. We replaced almost all the optical and experimental components of this beamline with new ones in this March. A fixed-exit double-crystal monochromator, a focusing mirror and a mirror bender were newly installed in this beamline. We will be able to change the energy from 6 to 14 keV. Although the photon flux at the sample position will not change after this upgrade, the area of the beam at the focal point will decrease to 40 % on the basis of the raytracing calculation. The camera length spread from 2 m to 3m in a new experimental stage with the camera tube. PILATUS3 2M and 200K (Dectris) were also installed as a detector. The commissioning will be started from this May, and the beamline will be re-opened from this June. In order to control all new devices and make the user-operation easier, we newly developed GUI software for the beamline control and the experiment. We are also developing the solution sample mixer and changer at BL-15A2 for the high-throughput Bio-SAXS measurement. We will present the current status of these beamline refurbishment.
HEIMDAL: A novel materials science neutron powder diffractometer at ESS
Authors: Holm Sonja , Bertelsen Mads , Singh Anar , Schefer Jürg , Lefmann Kim , Christensen Mogens
Published: November 2015

Developing new materials is the most challenging task for the future demands due to limitations in energy, resources but also environmental damage. Improvements in material performances are reached for example by the incorporation of advanced ceramics and polymers into heterogeneous systems. Their performances usually depend on the interplay between properties defined by the atomic, nano/mesoscopic and microscopic structure. In-situ and in-operandi investigations will be in the focus of such investigations. The instrument HEIMDAL proposed for the European spallation neutron source ESS will offer here perfect prospects, as the instrumental resolution of this powder diffractometer can widely be adapted taking either full advantage of the broad pulse of ESS (2.86ms) offering highest intensity, or using a fraction of the pulse for highest resolution. A thermal and a cold guides pointing to the same virtual source extend the spatial window of the instrumental from an atomic scale (0.3Å-1≤Q≤50Å-1) to a nano/meso scale, 0.002Å-1≤Q≤0.1Å-1 by adding a narrow-band SANS instrument behind. Our chopper system allows switching the different operation modes electronically. Traditionally such structural information has been collected in separated experiments such as powder diffraction (PD), wide angle diffraction scale, small angle diffraction and direct space imaging techniques (sub-micronic to millimeter scale), whereas HEIMDAL can offer these options in its final stage at the same time at therefore for absolutely identical experimental conditions. The top-loading geometry foreseen not only accepts auxiliary from the ESS pool (cryogenics, pressure cells, magnets) but also allows implementing bulky brought-in user equipment. It can be pretested off-line at the instrument, but already fully connected to the HEIMDAL electronics. Figure 1: a) Operation modes of the HEIMDAL b) Layout of the instrument HEIMDAL
Building brain network in electron density map determined by micro-CT
Authors: Saiga Rino , Takekoshi Susumu , Nakamura Naoya , Takeuchi Akihisa , Uesugi Kentaro , Suzuki Yoshio , Mizutani Ryuta
Published: November 2015

In macromolecular crystallography, an electron density distribution is traced to build a model of the target molecule. We applied this method to model building for electron density maps of a brain network. Human cerebral tissue was stained with heavy atoms [1]. The sample was then analyzed at the BL20XU beamline of SPring-8 to obtain a three-dimensional map of X-ray attenuation coefficients representing the electron density distribution. Skeletonized wire models were built by placing and connecting nodes in the map [2], as shown in the figure below. The model-building procedures were similar to those reported for crystallographic analyses of macromolecular structures, while the neuronal network was automatically traced by using a Sobel filter. Neuronal circuits were then analytically resolved from the skeletonized models. We suggest that X-ray microtomography along with model building in the electron density map has potential as a method for understanding three-dimensional microstructures relevant to biological functions.