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Synthesis, Infrared Spectroscopy and Crystal Structure Determination of a New Decavanadate

GUILHERME, Luciana Rebelo; MASSABNI, Antonio Carlos; DAMETTO, Alessandra Cristina; CORREA, Rodrigo de Souza; ARAUJO, Alexandre Suman de
Fonte: SPRINGER/PLENUM PUBLISHERS Publicador: SPRINGER/PLENUM PUBLISHERS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Synthesis, infrared spectroscopy and crystal structure of a new potassium decavanadate decahydrate, K(6)[V(10)O(28)] 10H(2)O, has been reported The infrared spectrum is dominated by decavanadate polyanion and water bands The X-ray crystallography analysis found the compound crystallizes in a triclinic system with the parameters a = 10 5334 (4) angstrom, b = 10 6600 (4) angstrom, c = 17 7351 (5) angstrom, alpha = 76 940 (2)degrees, beta = 75 836 (2)degrees, gamma = 64 776 (2)degrees, V = 1,729 86 (11) A(3), Z = 2, space group P (1) over bar The polyanion consists of ten [VO(6)] octahedra sharing edges, in which the V-O distances are in good agreement with those reported for other decavanadates The crystal structure is stabilized by potassium cations and water molecules forming a complex pattern of hydrogen bonding and short contact ionic interactions; Capes; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

THE CRYSTAL STRUCTURE OF A MICROLITE-GROUP MINERAL WITH A FORMULA NEAR NaCaTa(2)O(6)F FROM THE MORRO REDONDO MINE, CORONEL MURTA, MINAS GERAIS, BRAZIL

ANDRADE, Marcelo B.; Atencio, Daniel; MENEZES FILHO, Luiz A. D.; ELLENA, Javier
Fonte: MINERALOGICAL ASSOC CANADA Publicador: MINERALOGICAL ASSOC CANADA
Tipo: Artigo de Revista Científica
ENG
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We present electron-microprobe and single-crystal X-ray-diffraction data for a microlite-group mineral with a formula near NaCaTa(2)O(6)F from the Morro Redondo mine, Coronel Murta, Minas Gerais, Brazil. On the basis of these data, the formula is A(Na(0.88)Ca(0.88)Pb(0.02)square(0.22))(Sigma 2.00) (B)(Ta(1.70)Nb(0.14)Si(0.12)As(0.04))(Sigma 2.00) (X)[(O(5.75)(OH)(0.25)](Sigma 6.00) (Y)(F(0.73)square(0.27))(Sigma 1.00). According to the new nomenclature for the pyrochlore-supergroup minerals, it is intermediate between fluornatromicrolite and "" fluorcalciomicrolite"". The crystal structure, F (d3) over barm, a = 10.4396(12) angstrom, has been refined to an R(1) value of 0.0258 (wR(2) = 0.0715) for 107 reflections (MoK alpha radiation). There is a scarcity of crystal-chemical data for pyrochlore-supergroup minerals in the literature. A compilation of these data is presented here.; FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[2008/04984-7]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[2009/09125-5]

Insights into the role of oligomeric state on the biological activities of crotoxin: crystal structure of a tetrameric phospholipase A(2) formed by two isoforms of crotoxin B from Cratalus durissus terrificus venom

Marchi-Salvador, Daniela P.; Correa, Luiz C.; Magro, Angelo J.; Oliveira, Clayton Z.; Soares, Andreimar M.; Fontes, Marcos R. M.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 883-891
ENG
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Crotoxin B (CB or Cdt PLA(2)) is a basic Asp49-PLA(2) found in the venom of Crotalus durissus terrificus and it is one of the subunits that constitute the crotoxin (Cro). This heterodimeric toxin, main component of the C. d. terrificus venom, is completed by an acidic, nontoxic, and nonenzymatic component (crotoxin A, CA or crotapotin), and it is related to important envenomation effects such as neurological disorders, myotoxicity, and renal failure. Although Cro has been crystallized since 1938, no crystal structure of this toxin or its subunits is currently available. In this work, the authors present the crystal structure of novel tetrameric complex formed by two dimers of crotoxin B isoforms (CB1 and CB2). The results suggest that these assemblies are stable in solution and show that Ser1 and Glu92 of CB1 and CB2, respectively, play an important role in the oligomerization. The tetrameric and dimeric conformations resulting from the association of the isoforms may increase the neurotoxicity of the toxin CB by the creation of new binding sites, which could improve the affinity of the molecular complexes to the presynaptic membrane.

Synthesis, Infrared Spectroscopy and Crystal Structure Determination of a New Decavanadate

Guilherme, Luciana Rebelo; Massabni, Antonio Carlos; Dametto, Alessandra Cristina; Correa, Rodrigo de Souza; de Araujo, Alexandre Suman
Fonte: Springer/plenum Publishers Publicador: Springer/plenum Publishers
Tipo: Artigo de Revista Científica Formato: 897-901
ENG
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661.3008%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Synthesis, infrared spectroscopy and crystal structure of a new potassium decavanadate decahydrate, K-6[V10O28] 10H(2)O, has been reported The infrared spectrum is dominated by decavanadate polyanion and water bands The X-ray crystallography analysis found the compound crystallizes in a triclinic system with the parameters a = 10 5334 (4) angstrom, b = 10 6600 (4) angstrom, c = 17 7351 (5) angstrom, alpha = 76 940 (2)degrees, beta = 75 836 (2)degrees, gamma = 64 776 (2)degrees, V = 1,729 86 (11) A(3), Z = 2, space group P (1) over bar The polyanion consists of ten [VO6] octahedra sharing edges, in which the V-O distances are in good agreement with those reported for other decavanadates The crystal structure is stabilized by potassium cations and water molecules forming a complex pattern of hydrogen bonding and short contact ionic interactions

THE CRYSTAL-STRUCTURE OF BENZOYL-HISTIDINE MONOHYDRATE

Frohlich, R.; Arni, R. K.; Bozopoulos, A.; Kavounis, C. A.
Fonte: R Oldenbourg Verlag Publicador: R Oldenbourg Verlag
Tipo: Artigo de Revista Científica Formato: 816-817
ENG
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The crystal structure of benzoyl-histidine monohydrate (BYLH hereafter), C-13H-12N-3O-3. H2O was determined from three dimensional data of 3012 independent reflections measured on a Enraf-Nonius (CAD4) single crystal diffractometer. The compound crystallizes in the orthorhombic space group P2(1)2(1)2(1) with cell dimensions alpha = 7.102(1) angstrom, b = 13.783(3) angstrom, c = 14.160(4) angstrom, V = 1385.92 angstrom-3, F.W. = 277.28, F(000) = 584 Q(calc) = 1.32 g cm-3 and Z = 4.The structure was solved with direct methods. All positional and anisotropic thermal parameters were refined by full-matrix least-squares calculations. The final reliability factor was R = 0.040, while the weighted one was Rw = 0.034. The H atoms found in the difference Fourier map were refined isotropically.The compound consists of a histidine molecule bound to a benzoyl group. There is also a cocrystallized water molecule stabilized through a hydrogen bridge.The 5-membered ring of the histidine has its tautomeric form, after the transfer of the H atom from the N(delta) to the N(epsilon) atom of the ring. There is an sp2 conformation around C6 while the conformation around C3 is that of sp3. The histidine ring forms with the benzene ring a dihedral angle of 109.8(1)-degree.All angle values and bond distances agree very well with the expected values in the literature.

Kinetics and crystal structure of human purine nucleoside phosphorylase in complex with 7-methyl-6-thio-guanosine

Silva, Rafael G.; Pereira, José H.; Canduri, Fernanda; De Azevedo Jr., Walter F.; Basso, Luiz A.; Santos, Diógenes S.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 49-58
ENG
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Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of nucleosides and deoxynucleosides, generating ribose 1-phosphate and the purine base, which is an important step of purine catabolism pathway. The lack of such an activity in humans, owing to a genetic disorder, causes T-cell impairment, and drugs that inhibit this enzyme may have the potential of being utilized as modulators of the immunological system to treat leukemia, autoimmune diseases, and rejection in organ transplantation. Here, we describe kinetics and crystal structure of human PNP in complex with 7-methyl-6-thio-guanosine, a synthetic substrate, which is largely used in activity assays. Analysis of the structure identifies different protein conformational changes upon ligand binding, and comparison of kinetic and structural data permits an understanding of the effects of atomic substitution on key positions of the synthetic substrate and their consequences to enzyme binding and catalysis. Such knowledge may be helpful in designing new PNP inhibitors. © 2005 Elsevier Inc. All rights reserved.

Crystal structure of Jararacussin-I: The highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes

Ullah, A.; Souza, T. A C B; Zanphorlin, L. M.; Mariutti, R. B.; Santana, V. S.; Murakami, M. T.; Arni, R. K.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 128-132
ENG
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Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 Å resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity. © 2012 The Protein Society.

Synthesis, characterisation and magnetic properties of copper(II) complexes with 3-hydroxypicolinic acid (HpicOH): the crystal structure of [Cu(picOH)(2)(BPE)](2) . [Cu(picOH)(2)(BPE)(2)] . 8H(2)O

Girginova, PI; Paz, FAA; Nogueira, HIS; Silva, NJO; Amaral, VS; Klinowski, J; Trindade, T
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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A novel 1D coordination polymer, [Cu(picOH)2(BPE)] (IIa), and neutral [Cu(picOH)2(BPE)2] (IIb) complexes, can be simultaneously isolated (structure II) when neutral [Cu(picOH)2] (I) species are axially bridged by 1,2-bis(4-pyridyl)ethane (BPE) molecules. The compound has been characterised structurally using single-crystal X-ray diffraction, elemental analysis, infrared and Raman spectroscopies and thermoanalytical measurements. In both structures the 3-hydroxypicolinate ligands are coordinated to the Cu2C centres through their typical N,O-chelating coordination, with the increase of coordination number in II leading to a typical Jahn–Teller distorted octahedral coordination geometry. Although the structure of I has already been reported, we have re-determined its single-crystal structure at the low temperature of 180(2) K for comparative purposes. The magnetic properties of both compounds have also been investigated.

5.841 Crystal Structure Refinement, Fall 2006; Crystal Structure Refinement

Mueller, Peter
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
EN-US
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666.4092%
This course in crystal structure refinement examines the practical aspects of crystal structure determination from data collection strategies to data reduction and basic and advanced refinement problems of organic and inorganic molecules.

The crystal structure of gatehouseite

Elliott, P.; Pring, A.
Fonte: Mineralogical Society Publicador: Mineralogical Society
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
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The crystal structure of the manganese phosphate mineral gatehouseite, ideally Mn2+5(PO4)2(OH)4, space group P212121, a = 17.9733(18), b = 5.6916(11), c = 9.130(4) Å, V = 933.9(4) Å3, Z = 4, has been solved by direct methods and refined from single-crystal X-ray diffraction data (T = 293 K) to an R index of 3.76%. Gatehouseite is isostructural with arsenoclasite and with synthetic Mn2+5(PO4)2(OH)4. The structure contains five octahedrally coordinated Mn sites, occupied by Mn plus very minor Mg with observed distances from 2.163 to 2.239 Å. Two tetrahedrally coordinated P sites, occupied by P, Si and As, have distances of 1.559 and 1.558 Å. The structure comprises two types of building unit. A strip of edge-sharing Mn(O,OH)6 octahedra, alternately one and two octahedra wide, extends along [010]. Chains of edge- and corner-shared Mn(O,OH)6 octahedra coupled by PO4 tetrahedra extend along [010]. By sharing octahedron and tetrahedron corners, these two units form a dense three-dimensional framework, which is further strengthened by weak hydrogen bonding. Chemical analyses by electron microprobe gave a unit formula of (Mn4.99Mg0.02)Σ5.01(P1.76Si0.20As0.07)Σ2.03O8(OH)3.97.; P. Elliott and A. Pring

Description and crystal structure of maghrebite, MgAl₂(AsO₄)₂(OH)₂•8H₂O, from Aghbar, Anti-Atlas, Morocco: first arsenate in the laueite mineral group; Description and crystal structure of maghrebite, MgAl(2)(AsO(4))(2)(OH)(2)(.)8H(2)O, from Aghbar, Anti-Atlas, Morocco: first arsenate in the laueite mineral group

Meisser, Nicolas; Brugger, Joel; Krivovichev, Sergey V.; Armbruster, Thomas; Favreau, Georges
Fonte: E Schweizerbartsche Verlags Publicador: E Schweizerbartsche Verlags
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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663.936%
Maghrebite, MgAl2(AsO4)2(OH)2•8H2O, is a new mineral occurring at the Aghbar open pit mine, Bou Azzer district, Anti-Atlas, Morocco. Maghrebite is associated with quartz, erythrite, arseniosiderite, wendwilsonite and cabalzarite, and results from the weathering of a Variscan hydrothermalCo-Ni-As-(Cu-U-Mo) vein. Maghrebite forms lozenge-shaped prismatic crystals up to 0.2 mm in length. It is colorless, translucent with vitreous luster. Dmeas is 2.60(1) g/cm3, Dcalc (crystal structure) 2.46 g/cm3. The new mineral is biaxial negative without pleochroism. Measured 2V angle is 87 (3)_; the refractive indices measured at 589 nm are: a ¼ 1.562 (2), b ¼ 1.574 (2), g ¼ 1.586 (2) with the following orientation a // b; b ^ c ¼ 28.8_ and g ^ a ¼ 25.5_. The empirical chemical formula is (Mg0.96Co0.01Ca0.01)P¼0.98(Al1.94Fe3þ 0:06)P¼2.00(As2.01Si0.01)P¼2.02H18.0O18.02. Maghrebite is triclinic, P_1, Z ¼ 1, with a ¼ 5.436 (2)A ° , b ¼ 10.500 (3)A ° , c¼7.075 (2)A ° , a ¼97.701 (7)_, b¼ 110.295 (5)_, g¼ 102.021 (6)_ and V¼ 361.0 (2)A ° 3. The six strongest lines in the X-ray powder diffraction pattern are [d in A ° (I)(hkl)]: 9.9 (100) (010), 6.4 (90) (001), 4.90 (80) (_101), 3.198 (60) (002), 2.885 (60) (_131) and 2.622 (60) (13-1). The structure was solved by direct methods and refined to R1¼0.045 on the basis of 1064 unique observed reflections. The structure is based upon [Al(AsO4)(OH)(H2O)3]_ layers parallel to (010) and interlinked by [Mg(H2O)6]þ octahedra. In addition...

Crystal structure of pseudojohannite, with a revised formula, Cu₃(OH)₂[(UO₂)₄O₄(SO₄)₂](H₂O)₁₂; Crystal structure of pseudojohannite, with a revised formula, Cu(3)(OH)(2)[(UO(2))(4)O(4)(SO(4))(2)](H(2)O)(12)

Plasil, Jakub; Fejfarova, Karla; Wallwork, Kia S.; Dusek, Michal; Skoda, Radek; Sejkora, Jiri; Cejka, Jiri; Veselovsky, Frantisek; Hlousek, Jan; Meisser, Nicolas; Brugger, Joel
Fonte: Mineralogical Society of America Publicador: Mineralogical Society of America
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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The crystal structure of pseudojohannite from White Canyon, Utah, was solved by charge-flipping from single-crystal X-ray diffraction data and refined to an Robs = 0.0347, based on 2664 observed reflections. Pseudojohannite from White Canyon is triclinic, P1̄, with a = 8.6744(4), b = 8.8692(4), c = 10.0090(5) Å, α = 72.105(4)°, β = 70.544(4)°, γ = 76.035(4)°, and V = 682.61(5) ų, with Z = 1 and chemical formula Cu₃(OH)₂[(UO₂)₄O₄(SO₄)₂](H₂O)₁₂. The crystal structure of pseudojohannite is built up from sheets of zippeite topology that do not contain any OH groups; these sheets are identical to those found in zippeites containing Mg²+, Co²+, and Zn2+. The two Cu²+ sites in pseudojohannite are [5]- and [6]-coordinated by H₂O molecules and OH groups. The crystal structure of the pseudojohannite holotype specimen from Jáchymov was refined using Rietveld refinement of high-resolution powder diffraction data. Results indicate that the crystal structures of pseudojohannite from White Canyon and Jáchymov are identical.; Jakub Plášil, Karla Fejfjfarová, Kia Sheree Wallwork, Michal Dušek, Radek Škoda, Jiří Sejkora, Jiří Čejka, František Veselovský, Jan Hloušek, Nicolas Meisssser, and Joël Brugger

Description and crystal structure of domerockite, Cu₄(AsO₄)(AsO₃OH)(OH)₃·H₂O, a new mineral from the Dome Rock Mine, South Australia; Description and crystal structure of domerockite, Cu(4)(AsO(4))(AsO(3)OH)(OH)(3)(.)H(2)O, a new mineral from the Dome Rock Mine, South Australia

Elliott, P.; Kolitsch, U.; Willis, A.; Libowitzky, E.
Fonte: Mineralogical Society Publicador: Mineralogical Society
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Domerockite, Cu₄(AsO₄)(AsO₃OH)(OH)₃·H₂O, is a new mineral from the Dome Rock Mine, South Australia. It occurs as aggregates of bluish green, equant to short prismatic and tabular crystals up to 0.3 mm long and 0.2 mm across. Domerockite is translucent, with a vitreous lustre and pale green streak. It displays no fluorescence under UV irradiation. The mineral is brittle with an uneven fracture, a Mohs hardness of ∼3 and a calculated density of 4.44 g/cm³ (based on the structure refinement). Optically, it is biaxial negative, with α = 1.798(4), β = 1.814(4), γ = 1.817(4), 2V(calc). = 46°; pleochroism is very weak; X pale greenish yellow, Y greenish blue, Z greenish blue; absorption X < Y = Z; orientation is uncertain. Chemical analysis by electron microprobe gave CuO 52.04, ZnO 0.78, BaO 0.11, As₂O₅37.67, P₂O₅0.32, SiO₂0.24, H₂O 8.84, total 100.00 wt.%, with H₂O calculated by difference. The empirical chemical formula is (Cu₃.₉₄, Zn₀.₀₆)Σ₄.₀₀H₀.₉₁(As₁.₉₇, P₀.₀₃, Si₀.₀₂)Σ₂.₀₂O₈(OH)₃.₀₀˙H₂O based on 12 oxygen atoms. Domerockite is triclinic, space group P1, with a = 5.378(11), b = 8.962(18) c = 9.841(2) Å, α = 75.25(3), β = 83.56(3), γ = 79.97(3)°...

Hylbrownite, Na₃MgP₃O₁₀·12H₂O, a new triphosphate mineral from the Dome Rock Mine, South Australia: description and crystal structure; Hylbrownite, Na(3)MgP(3)O(10)(.)12H(2)O, a new triphosphate mineral from the Dome Rock Mine, South Australia: description and crystal structure

Elliott, P.; Brugger, J.; Caradoc-Davies, T.; Pring, A.
Fonte: Mineralogical Society Publicador: Mineralogical Society
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
664.40836%
Hylbrownite, ideally Na₃MgP₃O₁₀·12H₂O, the second known triphosphate mineral, is a new mineral species from the Dome Rock mine, Boolcoomatta Reserve, Olary Province, South Australia, Australia. The mineral forms aggregates and sprays of crystals up to 0.5 mm across with individual crystals up to 0.12 mm in length and 0.02 mm in width. Crystals are thin prismatic to acicular in habit and are elongate along [001]. Forms observed are {010}, {100}, {001}, {210} and {201}. Crystals are colourless to white, possess a white streak, are transparent, brittle, have a vitreous lustre and are nonfluorescent. The measured density is 1.81(4) g cm⁻³; Mohs' hardness was not determined. Cleavage is good parallel to {001} and to {100} and the fracture is uneven. Hylbrownite crystals are nonpleochroic, biaxial (−), with α = 1.390(4), β = 1.421(4), γ = 1.446(4) and 2V(calc). = 82.2°. Hylbrownite is monoclinic, space group P2₁/n, with a = 14.722(3), b = 9.240(2), c = 15.052(3) Å, β = 90.01(3)°, V = 2047.5(7) ų, (single-crystal data) and Z = 4. The strongest lines in the powder X-ray diffraction pattern are [d (Å)(I)(hkl)]: 10.530(60)(101,101), 7.357(80)(200), 6.951(100)(111, 111), 4.754(35)(103, 103), 3.934(40)(022), 3.510(45)(303...

CRYSTAL STRUCTURE OF 5,6,8,12b-TETRAHYDRODIOXOLO[4,5-g]ISOINDOLO[1,2-a]ISOQUINOLIN-8-ONE (C17H13NO3)

Cassels, Bruce K.; Castro-Castillo, Vicente; Galdámez, Antonio
Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
EN
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The title compound was prepared by cyclization of 2-(3,4-methylenedioxyphenyl)ethyl-3-hydroxyisoindolin-1-one in concentrated hydrochloric acid. The compound crystallizes in the orthorhombic space group Pca21 (No. 29) with a = 27.034(5) Å, b = 4.5093(9) Å, c = 10.667(2)Å, V = 1300.4(4) Å3 and Z = 4. The crystal consists of a single enantiomer. The molecule consists of two essentially flat moieties forming an dihedral angle of 116.3(2)º. The crystal structure has intermolecular C-H⋅⋅⋅O interactions resulting in chains that run along the crystallographic c-axis.; V. C.-C. is the recipient of a MeceSup (UMCE-0204) fellowship. M. T. Garland and A. Ibáñez are thanked for the X-ray measurements and FONDAP Grant Nº 11980002 for the purchase of the Bruker SMART CCD single crystal diffractometer. This work was supported in part by CONICYT grant AT-23070040 and ICM grant P05-001-F.

Ti02-Doped Zirconia: Crystal Structure, Monoclinic-Tetragonal Phase Transition, and the New Tetragonal Compound Zr3Ti08

Troitzsch, Ulrike
Fonte: American Ceramic Society Publicador: American Ceramic Society
Tipo: Artigo de Revista Científica
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Zirconia samples with up to 27 mol% TiO2 were synthesized at low and elevated pressures, significantly extending the range of ZrO 2-TiO2 solid solution compared with previous crystal structure studies of monoclinic and tetragonal zirconia (<17.5 mol%). Cr

Crystal structure of c5321 : a protective antigen present in uropathogenic Escherichia coli strains displaying an SLR fold

Urosev, Dunja; Ferrer Navarro, Mario; Pastorello, Ilaria; Cartocci, Elena; Costenaro, Lionel; Zhulenkovs, Dmitrijs; Maréchal, Jean-Didier; Leonchiks, Ainars; Reverter i Cendrós, David; Serino, Laura; Soriani, Marco; Daura i Ribera, Xavier
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2013 ENG
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Background: Increasing rates of antimicrobial resistance among uropathogens led, among other efforts, to the application of subtractive reverse vaccinology for the identification of antigens present in extraintestinal pathogenic E. coli (ExPEC) strains but absent or variable in non-pathogenic strains, in a quest for a broadly protective Escherichia coli vaccine. The protein coded by locus c5321 from CFT073 E. coli was identified as one of nine potential vaccine candidates against ExPEC and was able to confer protection with an efficacy of 33% in a mouse model of sepsis. c5321 (known also as EsiB) lacks functional annotation and structurally belongs to the Sel1-like repeat (SLR) family. Herein, as part of the general characterization of this potential antigen, we have focused on its structural properties. Results: We report the 1.74 Å-resolution crystal structure of c5321 from CFT073 E. coli determined by Se-Met SAD phasing. The structure is composed of 11 SLR units in a topological organisation that highly resembles that found in HcpC from Helicobacter pylori, with the main difference residing in how the super-helical fold is stabilised. The stabilising effect of disulfide bridges in HcpC is replaced in c5321 by a strengthening of the inter-repeat hydrophobic core. A metal-ion binding site...

The crystal structure of disordered (Zr,Ti)O 2 solid solution including srilankite: evolution towards tetragonal ZrO 2 with increasing Zr

Troitzsch, Ulrike; Christy, Andrew; Ellis, David
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
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Crystal structure data are presented for seven synthetic samples of disordered zirconium-titanate solid solution (Zr,Ti)O2, ranging in composition from xTi=0.43 to 0.67, thus covering compounds such as ZrTiO4, Zr5Ti7 O24, and ZrTi2O6 (srilankite). The compounds, synthesized at high temperatures and various pressures in their respective stability fields, are well crystallized and of homogeneous composition. The resulting structure data are less scattered compared to previous studies that were based on compounds synthesized metastably at low temperatures and room pressure. The compounds have the structure of scrutinyite (α-PbO2) with space group Pbcn, Z = 4, unit cell parameters a = 4.8495(3) Å, b = 5.4635(3) Å, c = 5.0462(3) Å at xTi=0.425 to a = 4.7112(2) Å, b = 5.4944(1) Å, c = 4.9962(1) Å at xTi=0.666. The first structure refinement of pure, synthetic srilankite is presented, which is in good agreement with that of the natural counterpart. Structural trends observed in disordered zirconium-titanate solid solution along the binary join ZrO2 -TiO2 are relatively smooth and continuous, except for rapid lengthening of an unshared octahedral edge which is anomalously short in scrutinyite-structure TiO2. The shortness of this edge may explain the observed instability of this structure with the relatively small Ti as the dominant cation. With increasing Zr content...

The synthesis and crystal structure of CaAlFSiO4 , the Al-F analog of titanite

Troitzsch, Ulrike; Ellis, David
Fonte: Mineralogical Society of America Publicador: Mineralogical Society of America
Tipo: Artigo de Revista Científica
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663.10516%
Aluminum-rich titanites [Ca(Ti,Al)(O,F)SiO4] with X(Al) > 0.53 [X(Al)=Al/(Al+Ti)], including the pure end-member CaAlFSiO4, were synthesized for the first time in a high-pressure experimental study. The crystal structure of CaAlFSiO4 was determined by Rietveld analysis of an X-ray powder diffraction pattern. CaAlFSiO4 is monoclinic, belongs to the space group A2/a, and has the unit-cell dimensions a = 6.9149(2) Å, b = 8.5064(1) Å, c = 6.4384(2) Å, and β = 114.684(2)°. The unit-cell volume is less than 93% of CaTiOSiO4, which is consistent with the natural occurrence of Al-rich titanite in high-P rocks. Although previous studies suggested that titanite with X(Al) > 0.5 is possibly not stable, this study demonstrates that complete solid solution occurs between CaTiOSiO4 and CaAlFSiO4. The similarity of the crystal structures of titanite and CaAlFSiO4 explains why in natural Al-rich titanite the end-member CaAlFSiO4 generally dominates over the hypothetical end-member CaAlOHSiO4, which under geological conditions is stable in a different crystal structure.

The Crystal Structure of Ni 13 Sn 8 P 3 Elucidated from HREM

Garcia-Garcia, F Javier; Larsson, Ann-Kristin
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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The crystal structure of Ni13Sn8P3 was elucidated from High Resolution Electron Microscopy Images. It was tound to be a superstructure of the B8-type (NiAs-type) structure with Sn and P atoms ordered at the hexagonally closepacked array and Ni atoms in all octahedral and in two out of every eleven trigonal bipyramidal sites. The structure motif within a NiSn B8-type matrix comprises triangles of P atoms with two of the three edges capped by Ni atoms in trigonal bipyramidal sites. This motif is repeated along the [01̄1]B8 zone axis so that the structure can be envisaged as pairs of face-sharing Ni centered Edshammar polyhedra corner-connected along [01̄1]B8. The reciprocal lattice (H) can be described as H = G + mq1 + nq2 (where G refers to the Bragg reflections of the underlying B8-type structure, q1 = 1/11 [112̄1]B8, q2 = 1/22 [6̄515]B8 and m and n are integers. The resultant triclinic (P1̄) unit cell parameters are a = 6.456 Å, b = 21.291 Å, c = 13.247 Å, α = 81.052°, β = 56.260° and γ = 68.221°.