One-dimensional composite host–guest structure in BaVS3

A detailed synchrotron X-ray diffraction (XRD) study performed with a single crystal of BaVS3 (barium vanadium trisulfide) in the temperature range between 10 and 295 K is reported. Aside from the known tetragonal–orthorhombic (240 K) and orthorhombic–monoclinic (69 K) phase transitions, in the 130 < T ≤ 295 K range the overall structure can be viewed as a host–guest (H–G) composite. The BaS3 matrix is the host, while the V-chains form the guest. The two subsystems lock in at T LOCK = 130 ± 20 K. This temperature is marked by a symmetry change from orthorhombic to monoclinic. This results in the formation of twins, implying a structural phase transition identified here for the first time. From the refined structural data, it is possible to follow, starting already at 295 K downwards, the stepwise transformation of VS6 octahedra into VS5 tetragonal pyramids as the origin of the structure evolution. The new findings will yield a better understanding of the complex electronic phase diagram of BaVS3.

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Structural Evolution of BaVS3 Under Pressure

Zeitschrift für Naturforschung B ◽

10.1515/znb-2008-0611 ◽

2008 ◽

Vol 63 (6) ◽

pp. 661-667 ◽

Cited By ~ 1

Author(s):

Alka B. Garg ◽

Viswanathan Vijayakumar ◽

Amitava Choudhury ◽

Hans D. Hochheimer

Keyword(s):

Structural Transition ◽

Ambient Pressure ◽

Structural Phase ◽

Structural Evolution ◽

Structural Phase Transitions ◽

X Ray Diffraction ◽

Pressure Derivative ◽

One Dimensional ◽

A Value ◽

Murnaghan Equation

Results of a high-pressure angle dispersive X-ray diffraction and electrical resistance study on quasi one-dimensional BaVS3 are reported. They show that no structural transition occurs up to 26 GPa. However, there is evidence of gradual disordering indicated by the broadening of the diffraction lines. p-V data fitted to a Birch-Murnaghan equation of state yields a value of the room-temperature, ambient-pressure bulk modulus of 77.3 GPa with a pressure derivative of 4.03. It is proposed that under compression structural phase transitions resulting from static displacements of V ions that are observed at low temperature are suppressed. Instead, a partial “polymerization” of V ions that is dynamic in nature and allows enhanced hopping conduction, starts near 3 GPa and saturates above 15 GPa.

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Spektroskopische und strukturelle Aspekte der Protonierung von Tetraaza[14]annulen-Dianionen / Spectroscopic and Structural Aspects of the Protonation of Tetraaza[14]annulene Dianions

Zeitschrift für Naturforschung B ◽

10.1515/znb-1996-0908 ◽

1996 ◽

Vol 51 (9) ◽

pp. 1255-1266 ◽

Cited By ~ 4

Author(s):

H. Schumann ◽

B. Neumann ◽

H.- G. Stammler

Keyword(s):

Structural Data ◽

X Ray Diffraction ◽

Space Group ◽

Crystal System ◽

Additional Information ◽

R Factor ◽

Vis Spectroscopy ◽

First Time ◽

Structural Aspects ◽

C Nmr

The effects of increasing protonation upon two [ 14]annulene dianions prepared by reaction of LiCH3 with 5,14-dihydro-6,8,15,17-tetramethyldibenzo[b,i][l,4,8,l l]tetraazacyclotetradecine (IIIb) and 5,14-dihydro-6,17-dimethyl-8,15-diphenyldibenzo[b,i][l,4,8,l 1 ]tetraazacyclotetradecine (IIIc) have been studied by 1H, 13C NMR and UV-VIS spectroscopy in solution. The crystal structures of the diprotonated macrocycle IIIb x 2 HPF6 (lIb) and of the neutral macrocycle IIIc have been determined by X-ray diffraction. For lIb, the crystal system is monoclinic with a space group of P21/n: a = 12.019(3), b = 13.864(6), c = 33.547(9) Å, β = 99.82(2)°, Z = 8 . The final R factor is 0.083 for 5520 observed reflections (745 variables). For IIIc, the crystal system is triclinic with a space group of P1̄: a = 9.923(8), b = 11.633(9), c = 14.318(12) Å, ct = 110.50(6)°, β = 98.86(7)°, 7 = 103.12(6)°, Z = 2. The final R factor is 0.081 for 2174 observed reflections and 191 variables. Comparison of these structural data together with those obtained from the literature for the deprotonated macrocycle IVb and a wide variety of substituted [ 14]annule derivatives allows for the first time a discussion of protonation effects upon the highly π-conjugated pentadiimidato moiety. Additional information is derived from NMR and UV-VIS data.

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Synthesis, Structure, and Dielectric Properties of (3-Nitroanilinium) (18-Crown) (PF6)

Crystals ◽

10.3390/cryst10111028 ◽

2020 ◽

Vol 10 (11) ◽

pp. 1028

Author(s):

Le Wang ◽

Liu-lei Qin ◽

Yang Liu ◽

Peng Wang ◽

Hui-ting Xu ◽

...

Keyword(s):

Variable Temperature ◽

Structural Phase ◽

Dielectric Measurements ◽

Slow Evaporation ◽

X Ray Diffraction ◽

Temperature Dependent ◽

Scanning Calorimetry ◽

One Dimensional ◽

X Ray ◽

Potential Energy Calculations

(3-Nitroanilinium) (18-crown) (PF6) (1), which is an organic-inorganic hybrid containing one-dimensional chains of hydrogen-bonded supramolecular cations, was synthesized under slow evaporation conditions and subjected to differential scanning calorimetry, temperature-dependent dielectric measurements, and variable-temperature single-crystal X-ray diffraction analysis. These analyses revealed the occurrence of a reversible structural phase transition [P21/n P21/c] at 223 K and a dielectric anomaly, which, based on the results of structural analysis and potential energy calculations, was attributed to the synergistic effect between the pendulum-like motion of the nitro group in the supramolecular cation, (3-nitroanilinium)(18-crown), and the order-disorder motion of PF6− anions.

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Phase Transition Study of CaB6 under High Pressure

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.705.97 ◽

2013 ◽

Vol 705 ◽

pp. 97-100

Author(s):

Jia Wang ◽

Gang Peng ◽

Bao Jia Wu

Keyword(s):

Phase Transition ◽

High Pressure ◽

Structural Phase ◽

X Ray Diffraction ◽

X Ray ◽

Conductivity Change ◽

Electronic Phase ◽

Transition Study ◽

Abnormal Conductivity

Phase transition of CaB6 sample under high pressure was studied by in situ electrical conductivity measurements and synchrotron X-ray diffraction up to 26GPa. Three anomalies in conductivity change were found respectively at 3.7, 12.4 and 21.9GPa. X-ray diffraction reveals that CaB6 transforms from Pm3m to orthogonal structure at 12.32GPa and hence the abnormal conductivity change at 12.4GPa can be attributed to the structural phase transition. The other two anomalies were considered as pressure-induced electronic phase transition in the pressure range of our measurements.

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X-ray diffraction analysis of homodimeric yeast hexokinases

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314095898 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C410-C410

Author(s):

Bartholomeus Kuettner ◽

Karina Kettner ◽

Thomas Kriegel ◽

Norbert Sträter

Keyword(s):

Protein Concentration ◽

Glucose Repression ◽

Structural Data ◽

X Ray Diffraction ◽

Yeast Saccharomyces Cerevisiae ◽

X Ray ◽

Sequence Identity ◽

First Time ◽

Hexokinase Isoenzymes ◽

Yeast Hexokinase

Yeast hexokinases are described in textbooks as classical open/close-switch monomeric enzymes. The hexokinase isoenzymes ScHxk1 and ScHxk2 of the budding yeast Saccharomyces cerevisiae share 77 % sequence identity. They exist in either an open or closed conformation, however, the published states were not of the same isoform. Crystal structures of the hexokinase KlHxk1 of the milk yeast Kluyvermyces lactis demonstrated open/close states of the same yeast hexokinase isoenzyme for the first time. KlHxk1 has 70 or 73 % sequence identity with ScHxk1 or 2, respectively. ScHxk2 and KlHxk1 contain an N-terminal binding stretch for the transcriptional repressor Mig1 which is the structural link to their function in glucose repression. They also exhibit monomer-dimer equilibria depending on protein concentration and phosphorylation of an N-terminal serine residue (S15). Experimental evidence for an expected ring-shaped homodimer of ScHxk2 was still missing to explain the phosphorylation-dependent oligomerization as demonstrated for KlHxk1 (figure). Structural data of other yeast glucose kinases were also limited in order to support a similar phenomenon. Therefore, we comparatively explored the oligomeric structure of ScHxk2 and K. lactis glucokinase 1 (KlGlk1) by means of X-ray diffraction in solution and in the crystalline state. The crystal structure of ScHxk2 was solved at high resolution (<1.5Å), and small-angle X-ray data of ScHxk2 were collected. Data analysis indicated that all three glucose-phosphorylating enzymes share a similar oligomeric architecture.

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Tubulin structure at intermediate resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100140634 ◽

1995 ◽

Vol 53 ◽

pp. 852-853

Author(s):

K. H. Downing ◽

S. G. Wolf ◽

E. Nogales

Keyword(s):

High Resolution ◽

Structural Data ◽

Therapeutic Drug ◽

Zinc Ions ◽

Two Dimensional ◽

X Ray Diffraction ◽

X Ray ◽

Negative Stain ◽

Functional Mechanisms ◽

Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

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Materials to the lichen flora of Samurskiy Ridge (high mountainous Dagestan)

Novosti sistematiki nizshikh rastenii ◽

10.31111/nsnr/2018.52.2.397 ◽

2018 ◽

Vol 52 (2) ◽

pp. 397-406

Author(s):

A. B. Ismailov ◽

G. P. Urbanavichus

Keyword(s):

North Caucasus ◽

Lichenicolous Fungi ◽

Greater Caucasus ◽

Altitudinal Range ◽

The North ◽

New Findings ◽

Mountainous Landscapes ◽

First Time ◽

Lichen Flora

The lichens and lichenicolous fungi of high mountainous landscapes of Samurskiy Ridge were studied in altitudinal range 2400–3770 m a. s. l. for the first time and 112 species are recorded. Among them 33 species, 10 genera (Arthrorhaphis, Baeomyces, Calvitimela, Epilichen, Lambiella, Psorinia, Rufoplaca, Sagedia, Sporastatia, Tremolecia) and 4 families (Anamylopsoraceae, Arthrorhaphidaceae, Baeomycetaceae, Hymeneliaceae) are new for Dagestan, six species (Buellia uberior, Carbonea atronivea, Lecanora atrosulphurea, Lecidea fuliginosa, L. swartzioidea, Rhizoplaca subdiscrepans) are reported for the first time for the Greater Caucasus and two species (Acarospora subpruinata and Rhizocarpon postumum) — for the North Caucasus. Most of the new findings were collected from 3500–3770 m a. s. l.

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Quartz Crystallite Size and Moganite Content as Indicators of the Mineralogical Maturity of the Carboniferous Chert: The Case of Cherts from Eastern Asturias (Spain)

Minerals ◽

10.3390/min11060611 ◽

2021 ◽

Vol 11 (6) ◽

pp. 611

Author(s):

Celia Marcos ◽

María de Uribe-Zorita ◽

Pedro Álvarez-Lloret ◽

Alaa Adawy ◽

Patricia Fernández ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Crystallite Size ◽

Archaeological Sites ◽

X Ray Diffraction ◽

X Ray ◽

Transmission Electron ◽

Infrared And Raman Spectroscopy ◽

First Time ◽

Geological Formations

Chert samples from different coastal and inland outcrops in the Eastern Asturias (Spain) were mineralogically investigated for the first time for archaeological purposes. X-ray diffraction, X-ray fluorescence, transmission electron microscopy, infrared and Raman spectroscopy and total organic carbon techniques were used. The low content of moganite, since its detection by X-ray diffraction is practically imperceptible, and the crystallite size (over 1000 Å) of the quartz in these cherts would be indicative of its maturity and could potentially be used for dating chert-tools recovered from archaeological sites. Also, this information can constitute essential data to differentiate the cherts and compare them with those used in archaeological tools. However, neither composition nor crystallite size would allow distinguishing between coastal and inland chert outcrops belonging to the same geological formations.

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First Report on the Geologic Occurrence of Natural Na–A Zeolite and Associated Minerals in Cretaceous Mudstones of the Paja Formation of Vélez (Santander), Colombia

Crystals ◽

10.3390/cryst11020218 ◽

2021 ◽

Vol 11 (2) ◽

pp. 218

Author(s):

Carlos Alberto Ríos-Reyes ◽

German Alfonso Reyes-Mendoza ◽

José Antonio Henao-Martínez ◽

Craig Williams ◽

Alan Dyer

Keyword(s):

Natural Zeolite ◽

Scanning Electron Micrographs ◽

Total Sulfur ◽

Zeolite A ◽

X Ray Diffraction ◽

X Ray ◽

Mineral Phases ◽

The World ◽

Porosity And Permeability ◽

First Time

This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world.

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The Effect of Surfactant-Modified Montmorillonite on the Cross-Linking Efficiency of Polysiloxanes

Materials ◽

10.3390/ma14102623 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2623

Author(s):

Monika Wójcik-Bania ◽

Jakub Matusik

Keyword(s):

Total Pore Volume ◽

Cross Linking ◽

X Ray Diffraction ◽

X Ray ◽

Transmission Electron ◽

The Cross ◽

Chain Lengths ◽

First Time ◽

Substituent Influence ◽

Benzyl Substituent

Polymer–clay mineral composites are an important class of materials with various applications in the industry. Despite interesting properties of polysiloxanes, such matrices were rarely used in combination with clay minerals. Thus, for the first time, a systematic study was designed to investigate the cross-linking efficiency of polysiloxane networks in the presence of 2 wt % of organo-montmorillonite. Montmorillonite (Mt) was intercalated with six quaternary ammonium salts of the cation structure [(CH3)2R’NR]+, where R = C12, C14, C16, and R’ = methyl or benzyl substituent. The intercalation efficiency was examined by X-ray diffraction, CHN elemental analysis, and Fourier transform infrared (FTIR) spectroscopy. Textural studies have shown that the application of freezing in liquid nitrogen and freeze-drying after the intercalation increases the specific surface area and the total pore volume of organo-Mt. The polymer matrix was a poly(methylhydrosiloxane) cross-linked with two linear vinylsiloxanes of different siloxane chain lengths between end functional groups. X-ray diffraction and transmission electron microscopy studies have shown that the increase in d-spacing of organo-Mt and the benzyl substituent influence the degree of nanofillers’ exfoliation in the nanocomposites. The increase in the degree of organo-Mt exfoliation reduces the efficiency of hydrosilylation reaction monitored by FTIR. This was due to physical hindrance induced by exfoliated Mt particles.

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