scholarly journals Rhombohedral trap for studying molecular oligomerization in membranes: application to daptomycin

Soft Matter ◽  
2019 ◽  
Vol 15 (21) ◽  
pp. 4326-4333 ◽  
Author(s):  
Ming-Tao Lee ◽  
Wei-Chin Hung ◽  
Huey W. Huang
Keyword(s):  
Rhombohedral Phase ◽  
Unit Cell ◽  
Hexagonal Unit Cell

Diffraction of daptomycin/Ca/Br-DOPG complex trapped in the hexagonal unit cell of rhombohedral phase.

THE NON-MARTENSITIC DIFFUSIONLESS TRANSITION IN MANGANESE ARSENIDE AT ABOUT 40 °C

1958 ◽  
Vol 36 (8) ◽  
pp. 1017-1021 ◽  
Author(s):  
Z. S. Basinski ◽  
W. B. Pearson
Keyword(s):  
Crystal Structure ◽  
Plastic Deformation ◽  
Strain Energy ◽  
Unit Cell ◽  
Discontinuous Change ◽  
Manganese Arsenide ◽  
Hexagonal Unit Cell ◽  
Higher Temperature ◽  
Crystal Grains

We have investigated the nature of the transition at about 40 °C in manganese arsenide. It is already well known that the transition involves a discontinuous change of the length of the a axis of the hexagonal unit cell, and that there is no change of crystal structure. The transition is accompanied by a loss of ferromagnetism of MnAs on proceeding to higher temperature. We find that the transformation takes place by a novel diffusionless non-martensitic mechanism. It appears that plastic deformation of MnAs is impossible and so, instead of the change following the martensitic pattern, the strain energy of the transformation is minimized by a fragmentation of the crystal grains into pencil-like subgrains whose direction lies parallel to the c axis of the crystals.

Crystal chemistry of ettringite

1962 ◽  
Vol 33 (256) ◽  
pp. 59-64 ◽  
Author(s):  
Duncan McConnell ◽  
Joseph Murdoch
Keyword(s):  
Crystal Chemistry ◽  
Simple Form ◽  
Unit Cell ◽  
Crystal Chemical ◽  
Aluminium Sulphate ◽  
Hexagonal Unit Cell ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Anionic Groups ◽  
Oxygen Atoms

Summary Crystal-chemical calculations are based on three chemically analysed samples of ettringite and their respective unit-cell dimensions and specific gravities. The large hexagonal unit cell is deduced to contain 384 oxygen atoms, 64 cations with co-ordination number 6 or more, and 48 cations with co-ordination number 4 or less. Some substitution of cations with co-ordination number 3 apparently takes place, and any excess above 192 H2O takes place in the form of substitution of (H4O4) for XO4 anionic groups. The isomorphism is extremely complex but can be generalized in simple form as 16[A4(XO4)3(H2O)12], where A represents atoms with six-fold co-ordination (Ca, Na, Al) and X represents atoms with four-fold coordination (S, Si, H4, and possibly some of the Al). It is implied that an isostructural series of silicon-containing calcium aluminium sulphate hydrates might exist, the extreme compositions of which are: 6CaO.Al2O3.3SO3.3SiO2.24H2O and 6CaO.Al2O3.3SO3.30H2O.

Röntgenographische und IR-Spektroskopische Untersuchung der Substitution von Phosphat- durch Sulfat-Ionen im Fluorapatit-Gitter / X-rayand IR Spectroscopic Investigation of the Phosphate Substitution by Sulfate Ions in the Fluoroapatite Lattice

1979 ◽  
Vol 34 (8) ◽  
pp. 1124-1127 ◽  
Author(s):  
Maria C. Apella ◽  
Enrique J. Baran
Keyword(s):  
Ir Spectra ◽  
Spectroscopic Investigation ◽  
Unit Cell ◽  
Spectroscopic Methods ◽  
Sulfate Ions ◽  
X Ray ◽  
Hexagonal Unit Cell ◽  
Ir Spectroscopic

Phases of composition Ca10-z;Naz(PO4)6-z;(SC)4)xF2, obtained during the substitution of PO43- by SO42- ions in the Ca10(PO4)6F2 lattice have been investigated by means of X-ray and IR spectroscopic methods. The stepwise introduction of SO42- ions produces an increasing distorsion of the lattice, although the parameters of the "pseudo-hexagonal" unit cell are practically invariant. The not well defined IR spectra are greatly dependent of the oxoanion present in largest concentration

The högbomite polytypes

1963 ◽  
Vol 33 (262) ◽  
pp. 563-580 ◽  
Author(s):  
Duncan McKie
Keyword(s):  
Single Crystal ◽  
Unit Cell ◽  
Stacking Sequence ◽  
X Ray ◽  
Hexagonal Unit Cell ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

SummarySingle crystal X-ray examination has shown that högbomite forms a series of polytypes, designated nH or nR, with hexagonal or rhombohedral lattices and hexagonal unit-cell dimensions a 5·72 Å, c 4·6 × n Å. The polytypes arise by variation, in a manner as yet undetermined, of the stacking sequence of approximately close-packed oxygen layers with interstitial cations on fourfold and on sixfold sites; the composition of 1/nth of a unit-cell may be represented as R2+1.0_1.6T4+0.2-0.4R3+3.7-4.3O2-7.6-8.0(OH)-0-0.4,, where R2+ = Zn, Fe, Mg, and R2+ = Fe, Al. The polytypes so far observed are 4H, 5H, 6H, 15H, 15R, and 18R. Minerals structurally related to högbomite are nigerite (3H) and taaffeite (4H). A new occurrence of högbomite, polytype 5H, with composition Ti1·7Fe1·6Mg6·3Al18·8Si0·2O40, is described from a spinel-free paragenesis in a magnesian skarn at Mautia Hill, Tanganyika. Another new occurrence in an aluminous xenolith in the Cashel gabbro in Co. Galway, Ireland, is recorded. X-ray powder data are given for two of the polytypes.

Painite, a new mineral from Mogok, Burma

1957 ◽  
Vol 31 (236) ◽  
pp. 420-425 ◽  
Author(s):  
G. F. Claringbull ◽  
Max H. Hey ◽  
C. J. Payne
Keyword(s):  
Unit Cell ◽  
New Mineral ◽  
Space Group ◽  
Hexagonal Unit Cell

SummaryA singly terminated transparent, deep-garnet-red crystal originally weighing 1·7g. from a gem gravel from Mogok, Burma, proves to be a new mineral having Al2O3 76·2, SiO2 5·6, B2O3 2·2, CaO 15·7, H2O 0·7, Fe2O3 and MnO traces, total 100·4. Sp. gr. 4·01; ω 1·8159, ɛ 1·7875; H 8. The hexagonal unit cell has a 8·725, c 8·46 Å., space group P63, P63/m or P63 22, and contains approximately 38 O. The name painite is proposed in honour of A. C. D. Pain who recognized the unusual nature of the crystal.

Synthesis and crystal structure of Na3.5Cr1.5Co0.5(PO4)3 phosphate

2006 ◽  
Vol 21 (3) ◽  
pp. 210-213 ◽  
Author(s):  
Mohamed Chakir ◽  
Abdelaziz El Jazouli ◽  
Jean-Pierre Chaminade
Keyword(s):  
Crystal Structure ◽  
Three Dimensional ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Synthesis And Crystal Structure ◽  
Space Group ◽  
X Ray ◽  
Hexagonal Unit Cell ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

A new Nasicon phosphates series [Na3+xCr2−xCox(PO4)3(0⩽x⩽1)] was synthesized by a coprecipitation method and structurally characterized by powder X-ray diffraction. The selected compound Na3.5Cr1.5Co0.5(PO4)3 (x=0.5) crystallizes in the R3c space group with the following hexagonal unit-cell dimensions: ah=8.7285(3) Å, ch=21.580(2) Å, V=1423.8(1) Å3, and Z=6. This three-dimensional framework is built of PO4 tetrahedra and Cr∕CoO6 octahedra sharing corners. Na atoms occupy totally M(1) sites and partially M(2) sites.

scholarly journals The rise and fall of Weber indices

2018 ◽  
Vol 51 (4) ◽  
pp. 1221-1225 ◽  
Author(s):  
Massimo Nespolo
Keyword(s):  
Electron Microscopy ◽  
Critical Analysis ◽  
Unit Cell ◽  
Reciprocal Space ◽  
The Other ◽  
Metal Science ◽  
Hexagonal Unit Cell ◽  
Other Hand ◽  
The One

Weber indices were introduced to provide a unique expression of a lattice direction with respect to the four-axis setting used for hexagonal and rhombohedral crystals. They are in general fractional indices, even in the case of a primitive hexagonal unit cell, but they are often carelessly reduced to integer values. This corresponds, on the one hand, to taking as direction indices the nodes of a lattice further from the origin and, on the other hand, to adopting a hybrid indexing between direct and reciprocal space. A critical analysis of the drawbacks of Weber indices is presented, which justifies the reluctance of crystallographers to adopt them, despite a more widespread use in fields like electron microscopy and metal science.

The Crystal Structure of Potassium Hexafluoroplatinate (IV)

1951 ◽  
Vol 4 (3) ◽  
pp. 406 ◽  
Author(s):  
DP Mellor ◽  
NC Stephenson
Keyword(s):  
Crystal Structure ◽  
Unit Cell ◽  
Space Group ◽  
Hexagonal Unit Cell ◽  
Fluoro Complex

The crystal structure of potassium hexafluoroplatinate (IV) has been determined. The structure is based on a hexagonal unit cell whose dimensions are a=5.76 Ǻ, 0=4.64 Ǻ. There is one molecule per cell and the space group is D33d-C3m. The Pt-F distance in the slightly irregular octahedral fluoro complex is 1.91 Ǻ.

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