Relationships between molecular geometry, crystal packing, and thermal motion: temperature-dependent studies of three crystal forms of 4-hydroxybiphenyl

1986 ◽  
Vol 90 (22) ◽  
pp. 5631-5640 ◽  
Author(s):  
Carolyn Pratt Brock ◽  
Gaye L. Morelan
Keyword(s):  
Crystal Packing ◽  
Molecular Geometry ◽  
Thermal Motion ◽  
Temperature Dependent ◽  
Crystal Forms

The low-resolution 3D-structure of porin, a channel-forming protein in E. coliouter membranes

1983 ◽  
Vol 41 ◽  
pp. 440-441
Author(s):  
A. Engel ◽  
D.L. Dorset ◽  
A. Massalski ◽  
J.P. Rosenbusch
Keyword(s):  
Crystal Packing ◽  
3D Structure ◽  
Gram Negative Bacteria ◽  
Protein Ratio ◽  
Crystal Forms ◽  
Large Molecules ◽  
Functional Studies ◽  
Voltage Dependent ◽  
Planar Membranes ◽  
Hexagonal Arrays

Porins represent a group of channel forming proteins that facilitate diffusion of small solutes across the outer membrane of Gram-negative bacteria, while excluding large molecules (>650 Da). Planar membranes reconstituted from purified matrix porin (OmpF protein) trimers and phospholipids have allowed quantitative functional studies of the voltage-dependent channels and revealed concerted activation of triplets. Under the same reconstitution conditions but using high protein concentrations porin aggregated to 2D lattices suitable for electron microscopy and image processing. Depending on the lipid-to- protein ratio three different crystal packing arrangements were observed: a large (a = 93 Å) and a small (a = 79 Å) hexagonal and a rectangular (a = 79 Å b = 139 Å) form with p3 symmetry for the hexagonal arrays. In all crystal forms distinct stain filled triplet indentations could be seen and were found to be morphologically identical within a resolution of (22 Å). It is tempting to correlate stain triplets with triple channels, but the proof of this hypothesis requires an analysis of the structure in 3 dimensions.

Disazo (Bishydrazone) pigments based on acetoacetanilides

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Robert Christie ◽  
Adrian Abel
Keyword(s):  
Crystal Packing ◽  
Molecular Geometry ◽  
Coupling Reactions ◽  
Dominant Group ◽  
Color Strength ◽  
Decomposition Products ◽  
Organic Pigments ◽  
Yellow Pigments ◽  
Structure Investigations ◽  
Coupling Components

Abstract Disazoacetoacetanilide pigments, more commonly known as diarylide yellows, are the most important group of yellow classical organic pigments. They were commercialized in the early 20th century many years after the introduction of the structurally related monazoacetoacetanilides (Hansa yellows). The molecules adopt the bis-ketohydrazone tautomeric form. X-ray single crystal structure investigations have provided an insight into the influence of the molecular geometry and crystal packing arrangements in the solid state on the properties of the pigments in application. The synthesis of diarylide pigments is relatively straightforward, the conditions essentially following those used for the corresponding monoazo pigments, so that the products are economically priced. In the case of these disazo pigments, suitable aromatic amines (1 mol) are bis-diazotized and the resulting bis-diazonium salts reacted with acetoacetanilide coupling components (2 mol), the two azo coupling reactions occurring at the same time. They are by far the dominant group of yellow pigments used in printing inks, well-suited for most standard process yellow inks. They were formerly important in the coloration of plastics but are no longer recommended for polymers processed above 200 °C, under which conditions toxic decomposition products are formed. Diarylide yellow pigments are characterized by high color strength, good to excellent solvent fastness, and good chemical stability, although they generally show inferior lightfastness.

Crystal structure of Tetracyclo[5,3,1,12,6,04,9]dodecane (iceane)

1977 ◽  
Vol 30 (8) ◽  
pp. 1837 ◽  
Author(s):  
DPG Hamon ◽  
CL Raston ◽  
GF Taylor ◽  
JN Varghese ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Rigid Body ◽  
Least Squares ◽  
Title Compound ◽  
Molecular Geometry ◽  
Thermal Motion ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Hexagonal Close Packed

The crystal structure of the title compound, C12H18, has been determined at 295 K by X-ray diffraction and refined by full-matrix least squares to a residual of 0.049 for 216 ?observed? reflections; molecular geometry has been corrected for the effects of thermal motion using a rigid body approximation. Crystals are hexagonal, P63/m, a = 6.582(1), c = 11.843(3) Ǻ, Z = 2, the molecules occupying a hexagonal close- packed array.

Structural phase transitions, and Br...N and Br...Br interactions in 1-phenyl-2-methyl-4-nitro-5-bromoimidazole

2004 ◽  
Vol 60 (3) ◽  
pp. 333-342 ◽  
Author(s):  
Maciej Kubicki
Keyword(s):  
Phase Transitions ◽  
Crystal Packing ◽  
Structural Phase ◽  
Molecular Geometry ◽  
Second Phase ◽  
Triclinic Space Group ◽  
Space Group ◽  
Β Phase ◽  
Α Phase ◽  
Second Order Transition

Crystals of C10H8N3O2Br undergo two reversible phase transitions between 295 and 100 K. The first, of an order–disorder nature, is a second-order transition and takes place continuously over a wide temperature range. This transition is connected with the doubling of the length of the c axis of the unit cell and with the change of the space group from P21/m with Z′ = 1/2 (room-temperature α-phase) to P21/c, Z′ = 1 (β-phase, 200–120 K). During this transition the molecule loses the C s symmetry of the α-phase. The second transition takes place between 118 and 115 K, and is accompanied by a change of the crystal symmetry to the triclinic space group P\bar 1 (low-temperature γ-phase). This second phase transition is accompanied by the twinning of the crystal. Neither the molecular geometry nor the crystal packing shows any dramatic changes during these phase transitions. Halogen bonds C—Br...N and dihalogen interactions Br...Br play a crucial role in determining the crystal packing and compete successfully with other kinds of weak intermolecular interactions.

THE CRYSTALLINE FORM OF 1,3,5,7-TETRANITRO-1,3,5,7-TETRAZACYCLOOCTANE (HMX)

1962 ◽  
Vol 40 (12) ◽  
pp. 2278-2299 ◽  
Author(s):  
M. Bedard ◽  
H. Huber ◽  
J. L. Myers ◽  
George F Wright
Keyword(s):  
Electrical Property ◽  
Absorption Spectra ◽  
Crystalline Form ◽  
Dielectric Constants ◽  
Temperature Dependent ◽  
Crystal Forms ◽  
The Difference ◽  
Absorption Frequencies

The absorption spectra and dielectric constants of three of the four polymorphs of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) have been examined. The difference in absorption frequencies shows that these crystal forms are more distinctive than are most polymorphs. Likewise the distortion polarizations of HMX-I, -II, and -III are markedly different whereas identical distortion polarizations have been found among typical polymorphic systems. The distortion polarizations of HMX-II and -III also are unique because they are appreciably temperature dependent, although this electrical property ought to be temperature independent. Because of these unique behaviors we have postulated that the so-called HMX polymorphs actually are lattice-caged conformational modifications.

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