The stability and screw sense of the α -helix in poly- β -benzyl-L-aspartate

1960 ◽  
Vol 259 (1296) ◽  
pp. 110-128 ◽  
Keyword(s):  
Optical Rotatory Dispersion ◽  
Molecular Models ◽  
X Ray Diffraction ◽  
X Ray ◽  
Left Handed ◽  
The Difference ◽  
Diffraction Patterns ◽  
The Stability ◽  
Α Helix ◽  
The Right

A number of polymers and copolymers containing β -benzyl-L-aspartate has been prepared and their optical rotatory dispersion in a variety of solvents has been measured. The results of these measurements together with studies of infra-red spectra, X-ray diffraction patterns, deuteration rates and molecular models lead to the following conclusions. (i) The α -helical form of poly- β -benzyl-L-aspartate is considerably less stable relative to the solvated randomly coiled form than that of poly- γ -benzyl-L-glutamate. (ii) The left-handed α -helix of poly- β -benzyl-L-aspartate is more stable than the right-handed one. (iii) The difference in stability between the two senses of α -helix is much less in the case of poly- β -benzyl-L-aspartate than in that of poly- γ -benzyl-L-glutamate or poly-L-alanine.

Evidence for cooling-rate-dependent icosahedral short-range order in a Cu–Zr–Al metallic glass

2014 ◽  
Vol 47 (6) ◽  
pp. 1906-1911 ◽  
Author(s):  
Helmut Hermann ◽  
Uta Kühn ◽  
Horst Wendrock ◽  
Valentin Kokotin ◽  
Björn Schwarz
Keyword(s):  
Metallic Glass ◽  
Cooling Rate ◽  
Short Range ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Dependent ◽  
Icosahedral Clusters ◽  
Thermal Displacements ◽  
The Difference ◽  
Diffraction Patterns

Samples of Cu47.5Zr47.5Al5metallic glass were prepared at different cooling rate,R. The dependence of the X-ray diffraction patterns onRwas analysed by comparing them with corresponding patterns of computer-simulated models generated at different cooling rates as well. The observed changes in the experimental diffraction patterns are reproduced by the simulations, showing an increasing fraction of icosahedral clusters with decreasing cooling rate. The difference of the fractions of icosahedrally coordinated atoms in mould-cast and rapidly quenched Cu47.5Zr47.5Al5averages to 3 (1)%. Different frozen-in thermal displacements and different density are ruled out as a possible origin for the experimental observations.

scholarly journals Preparation of CoFe2O4/SiO2Nanocomposites at Low Temperatures Using Short Chain Diols

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Thomas Dippong ◽  
Erika Andrea Levei ◽  
Oana Cadar
Keyword(s):  
Low Temperatures ◽  
Sol Gel ◽  
Silica Matrix ◽  
Short Chain ◽  
X Ray Diffraction ◽  
X Ray ◽  
Nanocrystallite Size ◽  
Methylene Groups ◽  
Diffraction Patterns ◽  
The Stability

The preparation of 70% CoFe2O4/30% SiO2(wt%) nanocomposites by sol-gel method using three short chain diols (1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol) as chelators was studied. The Fourier transformed infrared spectra and X-ray diffraction patterns were used to confirm the formation of nanocomposites. The X-ray diffraction analysis showed that the chain length of the carboxylates embedded in the silica matrix influences the formation of crystallized cobalt ferrite as single phase at low temperatures. The influence of the methylene groups number in the precursors and annealing temperature on the nanocrystallite size was revealed. The stability of the obtained compounds was determined by calculation of thermodynamic parameters.

Study of the Phases of Mg-Zn-La Magnesium Alloys at 150°C

2013 ◽  
Vol 750-752 ◽  
pp. 679-682 ◽  
Author(s):  
Ming Li Huang ◽  
Li Na Dong ◽  
Ying Ling Wang ◽  
Li Wei Quan
Keyword(s):  
Phase Equilibrium ◽  
Lattice Structure ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Binary Solid Solution ◽  
Two Phase ◽  
X Ray ◽  
The Difference ◽  
The Stability ◽  
T Phase

Alloys with different compositions in Mg-rich corner of Mg-Zn-La system at 150°C were prepared, and the phase equilibrium in Mg-Zn-La alloys were determined by scanning electron microscopy (SEM), electron probe microanalysis based on energy dispersive X-ray spectroscopy (EPMA-EDS) and X-ray diffraction (XRD). The stability, compositions and lattice structures of the intermetallic compounds of Mg-Zn-La alloys were identified. The results show that, there exists a ternary compound (T-phase) with constant La (about 8at%) and the changed ratio of Mg/Zn in the Mg-rich corner of Mg-Zn-La system. Though the ratio of (Mg, Zn)/La of T-phase is close to that of Mg/La of Mg12La, the T-phase was not the binary solid solution of Mg12La because of the difference of the lattice structure. It also reveals that T-phase is a stable phase, and it is in two-phase equilibrium of T-phase+Mg at 150°C.

scholarly journals The growth of decagonal Al–Co–Ni single crystals as a function of chemical composition

1997 ◽  
Vol 12 (9) ◽  
pp. 2274-2280 ◽  
Author(s):  
B. Zhang ◽  
M. Estermann ◽  
W. Steurer
Keyword(s):  
Single Crystals ◽  
Structural Changes ◽  
Ternary Systems ◽  
X Ray Diffraction ◽  
X Ray ◽  
Decagonal Phase ◽  
Different Types ◽  
Diffraction Patterns ◽  
The Stability ◽  
Diagram Analysis

Decaprismatic single crystals taken from a series of alloys of nominal compositions within Al65–77Co3–22Ni3–22 have been studied by means of x-ray diffraction techniques. The substitution of Co by Ni in increasing amounts changes the (pseudo)decagonal diffraction patterns drastically and indicates structural changes which range from a single-crystalline approximant via orientationally ordered nanodomain structures and quasiperiodic phases with different types of ordering phenomena, to a basic decagonal phase. A quantum phase diagram analysis shows a clear separation of the stability regions of the ternary systems described in this study and other decagonal phases.

THE XRD STUDY OF THE EFFECT OF SLIGHT CHANGE IN STRUCTURE ON THE SUPERCONDUCTIVITY OF Y-Ba-Cu-O SYSTEM MATERIAL

1987 ◽  
Vol 01 (07n08) ◽  
pp. 289-293 ◽  
Author(s):  
WANG HUAQIN ◽  
ZHANG SHIYUAN ◽  
JIN TONGZHENG ◽  
HAN SHIYING ◽  
QIU DIRONG ◽  
...  
Keyword(s):  
Single Phase ◽  
Crystal Symmetry ◽  
Epr Spectra ◽  
Processing Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Xrd Study ◽  
The Difference ◽  
Diffraction Patterns ◽  
Flowing Oxygen

In this paper the differences in diffraction intensities from some crystal planes in the X-ray diffraction patterns of high Tc Y-Ba-Cu-O system superconductors prepared by different processing conditions and the difference among various structure cells in references are interpreted using computer fitting. The results suggest that there exists two structure cells in the single phase YBa2Cu3O7−x samples. Both structure cells have the same crystal symmetry and almost the same lattice parameters, a=3.821Å, b=3.892Å and c=11.676Å, but the different distortion degree of Cu2-O plane. According to EPR spectra measured on the same samples, it is considered that the improvement of superconductivity for the samples prepared by two-step annealing in flowing oxygen may be related to concentration of the structure cell with more serious distortion on the Cu2-O plane.

scholarly journals LiCrO2 Under Pressure: In-Situ Structural and Vibrational Studies

Crystals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 2 ◽  
Author(s):  
Alka Garg ◽  
Daniel Errandonea ◽  
Julio Pellicer-Porres ◽  
Domingo Martinez-Garcia ◽  
Swayam Kesari ◽  
...  
Keyword(s):  
Research Work ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pressure Coefficients ◽  
Vibrational Studies ◽  
Diffraction Patterns ◽  
The Stability ◽  
Murnaghan Equation ◽  
Related Compounds

The high-pressure behaviour of LiCrO2, a compound isostructural to the battery compound LiCoO2, has been investigated by synchrotron-based angle-dispersive X-ray powder diffraction, Raman spectroscopy, and resistance measurements up to 41, 30, and 10 Gpa, respectively. The stability of the layered structured compound on a triangular lattice with R-3m space group is confirmed in all three measurements up to the highest pressure reached. The dependence of lattice parameters and unit-cell volume with pressure has been determined from the structural refinements of X-ray diffraction patterns that are used to extract the axial compressibilities and bulk modulus by means of Birch–Murnaghan equation-of-state fits. The pressure coefficients for the two Raman-active modes, A1g and Eg, and their mode-Grüneisen parameters are reported. The electrical resistance measurements indicate that pressure has little influence in the resistivity up to 10 GPa. The obtained results for the vibrational and structural properties of LiCrO2 under pressure are in line with the published results of the similar studies on the related compounds. Research work reported in this article contributes significantly to enhance the understanding on the structural and mechanical properties of LiCrO2 and related lithium compounds.

Chain arrangement and sense of the α-helix in poly-L-alanine fibres

1959 ◽  
Vol 249 (1256) ◽  
pp. 30-41 ◽  
Keyword(s):  
Optical Diffraction ◽  
Peptide Sequence ◽  
X Ray Diffraction ◽  
Repeat Distance ◽  
Left Handed ◽  
Diffraction Patterns ◽  
Α Helix ◽  
Limited Sequence ◽  
Good Agreement ◽  
Complete Account

The X-ray diffraction pattern of poly-L-alanine fibres has been compared with optical diffraction patterns of a-helices. With bond lengths and angles not significantly different from those found in simple compounds, good agreement is found with right-handed (but not with left-handed) helices. It is necessary to suppose that the direction of the peptide sequence of chains in the crystallites is random. Helices with a long repeat distance are found to pack in a way which produces a limited sequence of residues, spaced at 4.5 A, in which displacements from steric effects can be expected. It is shown how this may produce a meridian reflexion at 4.4 A, as observed. A complete account of all features of the packing is not given, however, and hardly seems to be practicable.

New Magnetic Metallic Glasses with Reduced Metalloid Content

1981 ◽  
Vol 8 ◽  
Author(s):  
R. C. O'handley ◽  
N. J. Grant
Keyword(s):  
Amorphous Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
Early Transition Metal ◽  
New Class ◽  
Class 1 ◽  
Diffraction Patterns ◽  
Late Transition ◽  
The Stability ◽  
Early Transition

ABSTRACTSeveral new magnetic amorphous alloys containing early transition metals (TE) and having reduced metalloid (M) content have been melt spun. Some properties of three examples of this new class, 1) Co80Nb14B6, 2) Co84Nb10B6, and 3) Fe81Nb5B14, are presented. The dominant late transition meta1 (TL) content assures an appreciable magnetic moment while the presence of an early transition metal significantly enhances the stability against crystallization. Crystallization temperatures are 1) 742K, 2) 698K, and 3) 762K for the three alloys, respectively. X-ray diffraction patterns show the materials to be amorphous and to exhibit a large-r correlation length (approximately 2.0 A) that is shorter than is typiclly observed in TL80M20 glasses containing more than one transition meta) species (approximately 2.3 − 2.5A). The coercivities of the glassy compositions range from 30 to 70 m0e.

scholarly journals Theoretical Investigations of a BN Polymorph with sp2 + sp3 Hybridizations

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1574
Author(s):  
Xinhai Yu ◽  
Riguge Su ◽  
Bei He ◽  
Binchang Ma
Keyword(s):  
Density Functional ◽  
Mechanical Anisotropy ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Theoretical Investigations ◽  
M Phase ◽  
The Difference ◽  
The Stability ◽  
Xrd Patterns

The crystal structure, mechanical anisotropy, elastic properties and electronic characteristics, as well as the stability, of P4/m BN are predicted by means of density functional theory. In this work, BN in the P4/m phase demonstrates mechanical and dynamical stability. Compared with the values of bulk B, E and G in the P4/m phase, the B of BN in the P4/m phase is greater than that of dz4 BN, while the G and E of P4/m BN are greater than those of Pnc2 BN and dz4 BN. The ratio of the bulk-to-shear modulus for P4/m BN is less than 1.75 and dz4 BN, dz2 BN and lzlz2 BN, indicating that P4/m BN is more brittle than dz4 BN, dz2 BN and lzlz2 BN. P4/m BN exhibits stronger mechanical anisotropy in G and E than Pbca BN, P42/mnm BN and Pm-3m BN but much weaker mechanical anisotropy than P4/mbm BN, B7N7, B11N11 and B15N15. In addition, P4/m BN is a quasi-direct bandgap semiconductor, and the difference between the direct and the indirect bandgap is 0.008 eV. In order to obtain further characteristics of P4/m BN for future synthetic verification, the X-ray diffraction (XRD) patterns for P4/m BN are also calculated. Given its properties, P4/m BN is a good candidate for photoelectric devices.

New structure, reconstruction, and behaviour of the coordination polymer framework [CuZn(CN)4]– towards hydrated alkali metal ions

2015 ◽  
Vol 93 (8) ◽  
pp. 913-919 ◽  
Author(s):  
Junpei Yamada ◽  
Shin-ichi Nishikiori
Keyword(s):  
Coordination Polymer ◽  
Crystal Structure Analysis ◽  
Atmospheric Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Square Channel ◽  
Unknown Structure ◽  
The Difference ◽  
Diffraction Patterns ◽  
Polymer Framework

A new framework structure of the coordination polymer [CuZn(CN)4]– has been discovered in the newly synthesized [Na(H2O)n][CuZn(CN)4] (n = 12.7; 1). X-ray crystal structure analysis revealed a 3D framework comprised of tetrahedral Cu(I) and Zn(II) centres with bridging cyanide ligands containing both octagonal and square channel cavities; these channels contain hydrated Na+ ions as guests. In open air, complex 1 is extremely unstable and loses water molecules to form [Na(H2O)n][CuZn(CN)4] (n = 5.2–6.8; 2) within 30 min. Powder X-ray diffraction patterns showed that this change results in the conversion of the framework of complex 1 to the same framework observed in [K(H2O)n][CuZn(CN)4]. The [CuZn(CN)4]– framework of [K(H2O)n][CuZn(CN)4] has a tridymite structure with hexagonal channel cavities occupied by hydrated K+ ions. Like 1, 2 is also unstable under atmospheric conditions, yielding [Na(H2O)n][CuZn(CN)4] (n = 3), which has an unknown structure. While the framework of [K(H2O)n][CuZn(CN)4] is structurally flexible and robust, the framework of 2 is unstable and fragile. This contrast comes from the difference between the nature of the hydrated K+ and Na+ ions present in the frameworks.

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