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Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials

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https://www.readbyqxmd.com/read/29927394/hydrophobic-dipeptides-the-final-piece-in-the-puzzle
#1
Carl Henrik Görbitz
The crystal structure of L-valyl-L-leucine acetonitrile solvate presented here adds to 24 previously reported structures of dipeptides constructed from the five nonpolar amino acids L-alanine, L-valine, L-isoleucine, L-leucine and L-phenylalanine. It thus constitutes the final piece in the 5 × 5 puzzle of hydrophobic dipeptide structures. This opportunity is taken to review the crystal packing arrangements and hydrogen-bonding preferences of a rather unique group of substances, with updated information on the various hydrogen-bonding patterns and the associated peptide conformations...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927393/a-crystallographic-and-thermal-study-of-pridinol-mesylate-and-its-monohydrated-solvate
#2
Pablo Gaztañaga, Ricardo Baggio, Daniel Roberto Vega
Herein are reported the crystal and molecular structures of the pridinol mesylate salt (C20 H25 NO+ ·CH3 O3 S- ) (I) and its monohydrated solvate form (C20 H25 NO+ ·CH3 O3 S- ·H2 O) (II). A comparison of both with the already reported structure of pure pridinol [1,1-diphenyl-3-piperidino-1-propanol, C20 H25 NO; Tacke et al. (1980). Chem. Ber. 113, 1962-1980] is made. Molecular structures (I) and (II) are alike in bond distances and bond angles, but differ in their spatial conformation, and, more relevant still, in their hydrogen-bonding motifs...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927392/structure-of-russellite-bi-2-wo-6-origin-of-ferroelectricity-and-the-effect-of-the-stereoactive-lone-electron-pair-on-the-structure
#3
Hiroki Okudera, Yuka Sakai, Kentaro Yamagata, Hiroaki Takeda
The structure of the low-temperature polar (orthorhombic) phase of russellite (Bi2 WO6 ) was examined on artificial specimens with precise single-crystal X-ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399-409] with powder neutron diffraction. The residual density attributable to a stereochemically-active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO4 2- slab along the b-axis direction...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927391/crystal-structure-analysis-of-a-star-shaped-triazine-compound-a-combination-of-single-crystal-three-dimensional-electron-diffraction-and-powder-x-ray-diffraction
#4
Tatiana E Gorelik, Jacco van de Streek, Herbert Meier, Lars Andernach, Till Opatz
The solid-state structure of star-shaped 2,4,6-tris{(E)-2-[4-(dimethylamino)-phenyl]ethenyl}-1,3,5-triazine is determined from a powder sample by exploiting the respective strengths of single-crystal three-dimensional electron diffraction and powder X-ray diffraction data. The unit-cell parameters were determined from single crystal electron diffraction data. Using this information, the powder X-ray diffraction data were indexed, and the crystal structure was determined from the powder diffraction profile. The compound crystallizes in a noncentrosymmetric space group, P21 21 21 ...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927390/crystal-structures-of-k-2-xsi-5-o-12-x-fe-2-co-zn-and-rb-2-xsi-5-o-12-x-mn-leucites-comparison-of-monoclinic-p2-1-c-and-ia-overline-3-d-polymorph-structures-and-inverse-relationship-between-tetrahedral-cation-t-si-and-x-o-bond-distances-and-intertetrahedral
#5
Anthony M T Bell, C Michael B Henderson
The leucite tectosilicate mineral analogues K2 X2+ Si5 O12 (X = Fe2+ , Co, Zn) and Rb2 X2+ Si5 O12 (X = Mn) have been synthesized at elevated temperatures both dry at atmospheric pressure and at controlled water vapour pressure; for X = Co and Zn both dry and hydrothermally synthesized samples are available. Rietveld refinement of X-ray data for hydrothermal K2 X2+ Si5 O12 (X = Fe2+ , Co, Zn) samples shows that they crystallize in the monoclinic space group P21 /c and have tetrahedral cations (Si and X) ordered onto distinct framework sites [cf...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927389/theory-of-order-disorder-phase-transitions-of-b-cations-in-ab-1-2-b-1-2-o-3-perovskites
#6
V P Sakhnenko, N V Ter-Oganessian
Perovskite-like oxides AB'1/2 B''1/2 O3 with two different cations in the B-sublattice may experience cation order-disorder phase transitions. In many cases the degree of cation ordering can be varied by suitable synthesis conditions or subsequent sample treatment, which has a fundamental impact on the physical properties of such compounds. Therefore, understanding the mechanism of cation order-disorder phase transition and estimation of the phase transition temperature is of paramount importance for tuning of properties of such double perovskites...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29927388/investigation-of-interactions-in-lewis-pairs-between-phosphines-and-boranes-by-analyzing-crystal-structures-from-the-cambridge-structural-database
#7
Milan R Milovanović, Jelena M Andrić, Vesna B Medaković, Jean Pierre Djukic, Sneǽana D Zarić
The interactions between phosphines and boranes in crystal structures have been investigated by analyzing data from the Cambridge Structural Database (CSD). The interactions between phosphines and boranes were classified into three types; two types depend on groups on the boron atom, whereas the third one involves frustrated Lewis pairs (FLPs). The data enabled geometric parameters in structures to be compared with phosphine-borane FLPs with classical Lewis pairs. Most of the crystal structures (78.1%) contain BH3 as the borane group...
June 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616997/crystal-structures-of-alkali-metal-group-1-citrate-salts
#8
Alagappa Rammohan, James A Kaduk
The crystal structures of 16 new alkali metal citrates were determined using powder and/or single crystal techniques. These structures and 12 previously determined citrate structures were optimized using density functional techniques. The central portion of a citrate ion is fairly rigid, while the conformations of the terminal carboxylate groups exhibit no preferences. The citrate-metal bonding is ionic. Trends in metal-citrate coordination are noted. The energy of an O-H...O hydrogen bond is proportional to the square root of the H...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616996/crystal-structure-phase-transition-and-structural-deformations-in-iron-borate-y-0-95-bi-0-05-fe-3-bo-3-4-in-the-temperature-range-90-500-k
#9
Ekaterina S Smirnova, Olga A Alekseeva, Alexander P Dudka, Vladimir V Artemov, Yan V Zubavichus, Irina A Gudim, Leonard N Bezmaterhykh, Kirill V Frolov, Igor S Lyubutin
An accurate X-ray diffraction study of (Y0.95 Bi0.05 )Fe3 (BO3 )4 single crystals in the temperature range 90-500 K was performed on a laboratory diffractometer and used synchrotron radiation. It was established that the crystal undergoes a diffuse structural phase transition in the temperature range 350-380 K. The complexity of localization of such a transition over temperature was overcome by means of special analysis of systematic extinction reflections by symmetry. The transition temperature can be considered to be Tstr ≃ 370 K...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616995/phase-transitions-in-ferroelectric-4-aminopyridinium-tetrachloroantimonate-iii-revisited
#10
Anna Gągor
New X-ray diffraction studies on the crystal structure of ferroelectric [4-NH2 C5 H4 NH][SbCl4 ] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vector q = βb*, β varying from 0.60 to 0.66 and monoclinic C2/c(0β0)s0 superspace group. Ferroelectric phase III is commensurate with q = 2\over 3b* and Cc(0β0)0 symmetry. Polar phase IV is incommensurately modulated with β varying from 0...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616994/accurate-and-precise-lattice-parameters-of-h-2-o-and-d-2-o-ice-ih-between-1-6-and-270-k-from-high-resolution-time-of-flight-neutron-powder-diffraction-data
#11
A Dominic Fortes
Accurate and precise lattice parameters for D2 O and H2 O varieties of hexagonal ice (ice Ih, space group P63 /mmc) have been obtained in the range 1.6 to 270 K. Precision of the lattice parameters (∼0.0002% in a and 0.0004% in c for D2 O, 0.0008% in a and 0.0015% in c for H2 O) is ensured by use of the time-of-flight method on one of the longest primary neutron flight-path instruments in the world, the High-Resolution Powder Diffractometer at the ISIS neutron source. These data provide a more precise description of the negative thermal expansion of the material at low temperatures than the previous synchrotron `gold standard' [Röttger et al...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616993/hydrocerussite-related-minerals-and-materials-structural-principles-chemical-variations-and-infrared-spectroscopy
#12
Oleg Siidra, Diana Nekrasova, Wulf Depmeier, Nikita Chukanov, Anatoly Zaitsev, Rick Turner
White lead or basic lead carbonate, 2PbCO3 ·Pb(OH)2 , the synthetic analogue of hydrocerussite Pb3 (OH)2 (CO3 )2 , has been known since antiquity as the most frequently used white paint. A number of different minerals and synthetic materials compositionally and structurally related to hydrocerussite have been described within the last two decades. Herein, a review is given of general structural principles, chemical variations and IR spectra of the rapidly growing family of hydrocerussite-related minerals and synthetic materials...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616992/ionic-network-analysis-of-tectosilicates-the-example-of-coesite-at-variable-pressure
#13
Melina Reifenberg, Noel W Thomas
The method of ionic network analysis [Thomas (2017). Acta Cryst. B73, 74-86] is extended to tectosilicates through the example of coesite, the high-pressure polymorph of SiO2 . The structural refinements of Černok et al. [Z. Kristallogr. (2014), 229, 761-773] are taken as the starting point for applying the method. Its purpose is to predict the unit-cell parameters and atomic coordinates at (p-T-X) values in-between those of diffraction experiments. The essential development step for tectosilicates is to define a pseudocubic parameterization of the O4 cages of the SiO4 tetrahedra...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616991/revisiting-the-i-overline-bf-1-structures-of-high-temperature-ca-rich-plagioclase-feldspar-a-single-crystal-neutron-and-x-ray-diffraction-study
#14
Shiyun Jin, Xiaoping Wang, Huifang Xu
The I{\overline 1} structures of four natural Ca-rich plagioclase feldspars formed at high temperature were analysed using single-crystal neutron and X-ray diffraction. The neutron time-of-flight Laue diffractometer at the ORNL Spallation Neutron Source (Tennessee, USA) combined with a single-crystal X-ray diffraction instrument were able to reveal some new details about these already intensively studied structures. The split oxygen atoms refined from the neutron diffraction data show the underlying mechanism of Ca-Na ordering and the anisotropic P{\overline 1} ordering along the c-axis...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616990/aromaticity-of-benzene-derivatives-an-exploration-of-the-cambridge-structural-database
#15
Irena Majerz, Teresa Dziembowska
The harmonic oscillator model of aromaticity (HOMA) index, one of the most popular aromaticity indices for solid-state benzene rings in the Cambridge Structural Database (CSD), has been analyzed. The histograms of HOMA for benzene, for benzene derivatives with one formyl, nitro, amino or hydroxy group as well as the histograms for the derivatives with two formyl, nitro, amino or hydroxy groups in ortho, meta and para positions were investigated. The majority of the substituted benzene derivatives in the CSD are characterized by a high value of HOMA, indicating fully aromatic character; however, the distribution of the HOMA value from 1 to about 0 indicates decreasing aromaticity down to non-aromatic character...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616989/a-method-for-visualization-of-the-variation-of-noncovalent-interactions-in-crystal-structures-of-conformational-polymorphs
#16
Anton V Savchenkov, Viktor N Serezhkin
A method for clear visualization of the variation of noncovalent interactions in crystal structures of conformational polymorphs is developed and introduced. The first stage of the method establishes the characteristics of all, without exception, noncovalent interactions in all crystal structures under discussion. This is possible using a strict and objective method of construction of Voronoi-Dirichlet polyhedra within the framework of the stereoatomic model of crystal structures. The second stage of the method then involves plotting of diagrams, showing the relation between parameters characterizing interatomic interactions and chosen geometric parameters of molecules...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616988/crystal-growth-structure-and-characterization-of-er-6-b-4-o-15-as-self-activated-eye-safe-laser-material-within-the-near-infrared-waveband
#17
Yan Wang, Wei Zhang, Ziyi Li, Jianfu Li, Zhaojie Zhu, Zhenyu You, Chaoyang Tu
A new rare-earth borate Er6 B4 O15 was synthesized by a solid-state reaction technique. The crystal was obtained by a flux method. Single-crystal X-ray diffraction analysis revealed that the crystal structure is composed of ErO6 polyhedra sharing edges and BO3 groups. The absorption, near-infrared fluorescence spectra and the fluorescence decay curve of Er: 4 I13/2 energy level in the Er6 B4 O15 crystal were measured at room temperature. The absorption peak was located at 977 nm with absorption cross section of 1...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/29616987/the-crystal-structure-of-fe-2-pimic6-anthco-2-ch-3-cn-%C3%A2-fe-2-pimic6-anthco-2-ch-3-cn-0-9-ch-2-cl-2-0-1-%C3%A2-fe-2-pimic6-anthco-2-oh-2-%C3%A2-0-75ch-3-cn-a-crystallographer-s-nightmare-or-a-fascinating-case-of-disorder
#18
Sabine Becker
Refinement of large crystal structures as well as that of disordered structures can be challenging. If both features come together, structure refinement has the potential of becoming a crystallographer's nightmare. Here, the refinement of the large and highly disordered structure of [Fe2 (PIMIC6)(AnthCO2 )(CH3 CN)]·[Fe2 (PIMIC6)(AnthCO2 )(CH3 CN)0.9 (CH2 Cl2 )0.1 ]·[Fe2 (PIMIC6)(AnthCO2 )(OH2 )]·0.75CH3 CN [(1), PIMIC6 is a phenol-imine-based macrocycle, AnthCO2 is an anthracene acid anion] is described and discussed...
April 1, 2018: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/28981007/first-line-antituberculosis-drug-pyrazinamide-its-pharmaceutically-relevant-cocrystals-and-a-salt
#19
Kashyap Kumar Sarmah, Trishna Rajbongshi, Sourav Bhowmick, Ranjit Thakuria
A few pyrazinamide (Pyz) cocrystals involving hydroxybenzoic/cinnamic acid derivatives [2,4-dihydroxybenzoic acid (24DHBA); 2,6-dihydroxybenzoic acid (26DHBA); 3,5-dihydroxybenzoic acid (35DHBA) and nutraceutical molecule ferulic acid (FRA)] and the first example of a molecular salt with p-toluenesulfonic acid (pTSA) have been prepared and characterized using various solid-state techniques. A high-temperature cocrystal polymorph of Pyz·FRA has been characterized from the endothermic peaks observed using differential scanning calorimetry...
October 1, 2017: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
https://www.readbyqxmd.com/read/28981006/investigations-of-the-phase-relations-among-e1-e2-and-c-bar-bf-1-structures-of-na-rich-plagioclase-feldspars-a-single-crystal-x-ray-diffraction-study
#20
Shiyun Jin, Huifang Xu
The subsolidus phase relations of plagioclase feldspar solid solution have been puzzling mineralogists and petrologists for decades, mainly due to the complicated structures of intermediate plagioclase at low temperature. The crystal structures of 12 Na-rich plagioclase samples are investigated by single-crystal X-ray diffraction analyses. The samples studied cover a compositional range from An21 to An49 (An is anorthite, CaAl2 Si2 O8 ), as well as a wide variety of origins, from extremely slow-cooled gabbroic rocks to pegmatite and metamorphic rocks...
October 1, 2017: Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
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