Orientability of Rigid Rodlike Molecules in Solution and Controlled Preparation of Model Systems

1988 ◽  
Vol 134 ◽  
Author(s):  
Jeffrey A. Odell ◽  
Andrew Keller ◽  
Edward D.T. Atkins ◽  
Miklos J. Nagy ◽  
Jose Luis Feijoo ◽  
...  
Keyword(s):  
Rotational Diffusion ◽  
Model Systems ◽  
Specific Reference ◽  
X Ray Diffraction ◽  
Rigid Rods ◽  
Colloid Science ◽  
Rigid Rod ◽  
Separate Line ◽  
The Individual ◽  
Controlled Preparation

ABSTRACTA survey is presented of our works on orientability of poly(p-phenylene-benzbisthiazole) (PBT) as a model for rigid rods. It starts with the solid state with specific reference to diffraction by the individual molecule. It is followed by behaviour in semidilute solutions, demonstrating increase of orientability with increasing rod alignment, with vastly higher absolute values (as expressed by rotational diffusion coefficient) than anticipated from existing theory. The origin of the discrepancy, as identified by simulations, lies in the inappropriateness of the application of mean constraints, a recognition which should have wider implications. The relaxation from the highly oriented state, also in solution, has been followed and the elementary rotational jump of rods identified, with a new method relying on in situ (synchrotron) X-ray diffraction. As a separate line, we are announcing a new model system, ellipsoidal latices of predesigned axial ratios, with wide ranging potential for the study of rigid rod behaviour in polymer and colloid science.

Layer Spacing of Montmorillonites Modified with Rigid Rods

2007 ◽  
Vol 7 (12) ◽  
pp. 4546-4551
Author(s):  
Lorena Solar ◽  
Rodrigo Navarro ◽  
Clara Gómez ◽  
Helmut Reinecke
Keyword(s):  
Interlayer Distance ◽  
X Ray Diffraction ◽  
Layer Spacing ◽  
X Ray ◽  
Modified Montmorillonite ◽  
Rigid Rods ◽  
Montmorillonite Clays ◽  
Rigid Rod ◽  
Clay Layers ◽  
Oriented Parallel

The dependence of the interlayer distance in modified montmorillonite clays on the length of rigid rod molecules used for clay organophilization is studied. Therefore, a series of fully aromatic compounds of different length functionalized with a terminal amine group has been synthesized and transformed into the corresponding ammonium salts. The interlayer distance is determined by X-ray diffraction, the quantity of the modifier incorporated in the clay is obtained by thermogravimetric analysis. It is shown that the distance between layers in the modified clay does not depend on the length of the modifier used. This fact leads to the conclusion that rigid rods must be oriented parallel to the clay layers. On the other hand, the molar percentage of modifier molecules incorporated in the clay structure depends on the length of the rigid rods in the sense that shorter molecules are considerably easier to incorporate than longer ones.

scholarly journals First and Second Dissociation Enthalpies in Bi-Component Crystals Consisting of Maleic Acid and L-Phenylalanine

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5714
Author(s):  
Inês O. Feliciano ◽  
Daniela P. Silva ◽  
M. Fátima M. Piedade ◽  
Carlos E. S. Bernardes ◽  
Manuel E. Minas da Piedade
Keyword(s):  
Hydrogen Bonds ◽  
Maleic Acid ◽  
Solution Calorimetry ◽  
Model Systems ◽  
X Ray Diffraction ◽  
Enthalpy Changes ◽  
Dissociation Enthalpy ◽  
Structural Differences ◽  
The Individual ◽  
Stepwise Dissociation

The energetics of the stepwise dissociation of a A:B2 bi-component crystal, according to A:B2(cr) → A:B(cr) + B(cr) and A:B(cr) → A(cr) + B(cr), was investigated using MA:Phe2 and MA:Phe (MA = maleic acid; Phe = L-phenylalanine) as model systems. The enthalpy changes associated with these sequential processes and with the overall dissociation reaction A:B2(cr) → A(cr) + 2B(cr) were determined by solution calorimetry. It was found that they are all positive, indicating that there is a lattice enthalpy gain when MA:Phe2 is formed, either from the individual precursors or by adding Phe to MA:Phe. Single-crystal X-ray diffraction (SCXRD) analysis showed that MA:Phe2 is best described as a protic salt containing a maleate anion (MA−) and two non-equivalent L-phenylalanine units, both linked to MA− by NH···O hydrogen bonds (H-bond): one of these units is protonated (HPhe+) and the other zwitterionic (Phe±). Only MA− and HPhe+ molecules are present in the MA:Phe lattice. In this case, however, NH···O and OH···O H-bonds are formed between each MA− unit and two HPhe+ molecules. Despite these structural differences, the enthalpy cost for the removal of the zwitterionic Phe± unit from the MA:Phe2 lattice to yield MA:Phe is only 0.9 ± 0.4 kJ mol−1 higher than that for the dissociation of MA:Phe, which requires a proton transfer from HPhe+ to MA− and the rearrangement of L-phenylalanine to the zwitterionic, Phe±, form. Finally, a comparison of the dissociation energetics and structures of MA:Phe and of the previously reported glycine maleate (MA:Gly) analogue indicated that parameters, such as the packing coefficient, density, hydrogen bonds formed, or fusion temperature, are not necessarily good descriptors of dissociation enthalpy or lattice enthalpy trends when bi-component crystals with different molecular composition are being compared, even if the stoichiometry is the same.

Modellsysteme für die Gallium-Extraktion, I. Struktur und Moleküldynamik von Aluminium- und Galliumtris(oxinaten) / Model Systems for Gallium Extraction, I. Structure and Molecular Dynamics of Aluminium and Gallium Tris(oxinates)

1991 ◽  
Vol 46 (7) ◽  
pp. 901-911 ◽  
Author(s):  
Hubert Schmidbaur ◽  
Josef Lettenbauer ◽  
Dallas L. Wilkinson ◽  
Gerhard Müller ◽  
Otto Kumberger
Keyword(s):  
Ammonium Acetate ◽  
Elevated Temperatures ◽  
Model Systems ◽  
X Ray Diffraction ◽  
Metal Chlorides ◽  
H Nmr ◽  
Lower Temperature ◽  
The Individual ◽  
Influence Of Substituents ◽  
Steric Influence

Tris(oxinato) complexes of aluminium(III) and gallium(III) have been prepared from 8-oxyquinoline (OxH) and its six C-methylated derivatives from aqueous solutions of the metal chlorides or nitrates and an ammonium acetate buffer. Crystalline monohydrates or (upon precipitation with methanol) mono-methanol adducts are obtained. Single crystal X-ray diffraction studies reveal a meridional tris(chelate) structure for the two (isomorphous) tris(oxinates) Al(Ox)3 · MeOH and Ga(Ox)3 · MeOH with distinct differences in the individual dimensions. (The MeOH molecules form strong hydrogen bonds with one of the oxygen atoms.) For these species and those of the substituted ligands 3-MeOx, 4-MeOx, 5-MeOx, 6-MeOx, and 7-MeOx a similar meridional structure was confirmed by low temperature 1H NMR spectroscopy, which showed three inequivalent sets of ligands in each case. The collaps of these signals at elevated temperatures indicates a ligand-equilibrating process, with the mechanism probably comprising a dissociation of a pyridine function from the metal, to give a fluctional pentacoordinate species with free rotation about the intact M—O bond, and an M—N recombination at a random octahedral site. For the 2-MeOx ligands, however, the facial structure is preferred at lower temperature, but with the meridional isomer present as a component of an equilibrium. This indicates the strong steric influence of substituents in 2-position of the 8-oxy-quinoline.

Strain Measurement by X-ray Diffraction Methods

1949 ◽  
Vol 1 (3) ◽  
pp. 211-224
Author(s):  
G. B. Greenough
Keyword(s):  
Strain Measurement ◽  
Plastic Anisotropy ◽  
Stress And Strain ◽  
Routine Method ◽  
X Ray Diffraction ◽  
Strain Measurements ◽  
X Ray ◽  
The Past ◽  
Polycrystalline Metals ◽  
The Individual

SummaryMany papers have been written on the measurement of strain by X-ray diffraction methods and on the interpretation of these strains in terms of stresses. Whereas, during the past few years, the experimental methods of determining the strains have. remained largely unchanged, research has shown that the older techniques for calculating stresses from strains are not always valid.In this paper an attempt is made to describe some of the principles of strain measurement by X-ray diffraction methods to those who are unfamiliar with the methods. The types of stress and strain systems which may exist in polycrystalline metals are then considered, particular attention being paid to the effect of the elastic and plastic anisotropy of the individual crystals. Some indication is given as to how the earlier methods of interpreting X-ray strain measurements should be modified, but no rigid routine method is proposed for use in a general case.

scholarly journals Combined XRD-paramagnetic 13C NMR spectroscopy of 1,2,3-triazoles for revealing copper traces in a Huisgen click-chemistry cycloaddition. A model case

2019 ◽  
Vol 25 (1) ◽  
pp. 98-106
Author(s):  
Daniel Canseco-González ◽  
José Luis Rodríguez de la O ◽  
José Enrique Herbert-Pucheta
Keyword(s):  
Click Chemistry ◽  
13C Nmr Spectroscopy ◽  
Model Systems ◽  
Paramagnetic Nmr ◽  
Resonance Spectroscopy ◽  
X Ray Diffraction ◽  
Model Case ◽  
Purification Methods ◽  
Paramagnetic Metal ◽  
Torsional Angles

AbstractCopper-catalyzed Alkyne-Azide Cycloaddition (CuAAC) click chemistry robustness has been demonstrated over recent years to produce 1,2,3-triazoles with excellent yields at mild conditions with simple purification methods. However, the consequences of having copper paramagnetic traces in final products, which complicate spectroscopic assignments and can produce inaccurate conclusions, has been scarcely discussed. Herein we present a strategy that combines X-Ray Diffraction (XRD) with 13C- paramagnetic Nuclear Magnetic Resonance spectroscopy, in order to demonstrate the presence of paramagnetic metal traces at standard Huisgen synthesis and purification conditions. We also demonstrate that the derivatization of 1,4-disubstituted-1,2,3-triazoles to produce 1,3,4,-trisubstituted-1,2,3.triazolium salts, promotes an efficient removal of Cu(II/I) moieties. Evidence of paramagnetic metal moieties is given using XRD structural analysis of abnormalities in torsional angles between substituents and the 1,2,3-triazole center, in parallel to 13C- paramagnetic NMR chemical shift and line width analysis. As model systems to demonstrate the importance of characterizing paramagnetic traces, we present the synthesis of novel 1-((3s,5s,7s)-adamantan-1-yl)-4-cyclopropyl-1H-1,2,3-triazole and its derivatized 1-((3s,5s,7s)-adamantan-1-yl)-4-cyclopropyl-3-methyl-1H-[1,2,3]-triazol-3-ium triflate salt.

Characterization of bulk crystals of transition metal doped ZnO for spintronic applications

2003 ◽  
Vol 799 ◽  
Author(s):  
M. H. Kane ◽  
R. Varatharajan ◽  
Z. C. Feng ◽  
S. Kandoor ◽  
J. Nause ◽  
...  
Keyword(s):  
Transition Metal ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Absorption Bands ◽  
Growth Technique ◽  
Undoped Material ◽  
Doped Zno ◽  
Metal Doped ◽  
The Individual

ABSTRACTIn this work, we report on the material properties of ZnO doped with Mn, Co, and Fe grown by a modified melt growth technique. X-ray diffraction measurements show that transition metals can be incorporated on Zn sites; an increase in the lattice parameter is apparent with increasing doping level. UV-visible transmission and reflectance measurements have also been performed. Absorption bands in the visible regime are distinctive to the individual transition metal dopants. A noticeable shift in the optical band edge has been observed from these Mn/Co/Fe-doped ZnO crystals in comparison with the undoped material. ZnO may also provide a suitable platform for the incorporation of transition metal elements through high temperature near equilibrium growth processes; however, further work is required in order to employ these materials for spintronic applications.

scholarly journals 1P291 Humidity-controlled preparation of frozen-hydrated biological samples for cryogenic coherent X-ray diffraction imaging using XFEL(27. Bioimaging,Poster)

2013 ◽  
Vol 53 (supplement1-2) ◽  
pp. S154
Author(s):  
Yuki Takayama ◽  
Masayoshi Nakasako ◽  
Tomotaka Oroguchi ◽  
Yuki Sekiguchi ◽  
Amane Kobayashi ◽  
...  
Keyword(s):  
Biological Samples ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Imaging ◽  
Controlled Preparation

scholarly journals XRD Characterization of the Structure of Graphites and Carbon Materials Obtained by the Low-Temperature Graphitization of Coal Tar Pitch

2015 ◽  
Vol 17 (2) ◽  
pp. 87 ◽  
Author(s):  
Ch.N. Barnakov ◽  
G.P. Khokhlova ◽  
A.N. Popova ◽  
S.A. Sozinov ◽  
Z.R. Ismagilov
Keyword(s):  
Low Temperature ◽  
Carbon Materials ◽  
Coal Tar ◽  
Structural Phase ◽  
Coherent Scattering ◽  
Amorphous Structure ◽  
Coal Tar Pitch ◽  
X Ray Diffraction ◽  
Needle Coke ◽  
The Individual

The structure of some commercial graphites and carbon materials (CMs) obtained by the low-temperature catalytic graphitization of coal tar pitch with iron salt, needle coke, foamed graphite as the catalysts has been studied. The study was performed using the X-ray diffraction technique with reflections from base plane and their decomposition into two components corresponding to the structural phases of graphite which have different XRD characteristics. Various CMs were compared with respect to the structural phase ratio, distance between polyarene layers in these phases, and sizes of the coherent scattering regions. The (004) reflection provided a better fit of some properties of graphites to the calculated XRD characteristics as compared to calculation from the (002) reflection. In the case of carbonization of coal tar pitch with investigated catalyst additions, prepared carbon materials have a higher degree of graphitization and a crystallite size greater than in the other case of carbonization of the individual pitch. The highest catalytic activity is shown by foamed graphite. It was found that the use of foamed graphite as the catalyst at 800-900 ºC produced carbon materials possessing a crystalline structure with interplanar spacing close to that in commercial graphites, while in the absence of catalyst the coal tar pitch material has an amorphous structure.

scholarly journals Modelling nonlinear dynamics of interacting tipping elements on complex networks: the PyCascades package

2021 ◽  
Author(s):  
Nico Wunderling ◽  
Jonathan Krönke ◽  
Valentin Wohlfarth ◽  
Jan Kohler ◽  
Jobst Heitzig ◽  
...  
Keyword(s):  
Dynamical Systems ◽  
Open Source Software ◽  
Software Package ◽  
Model Systems ◽  
Stochastic Dynamical Systems ◽  
Moisture Recycling ◽  
Modelling Framework ◽  
Different Types ◽  
Open Source Software Package ◽  
The Individual

AbstractTipping elements occur in various systems such as in socio-economics, ecology and the climate system. In many cases, the individual tipping elements are not independent of each other, but they interact across scales in time and space. To model systems of interacting tipping elements, we here introduce the PyCascades open source software package for studying interacting tipping elements (10.5281/zenodo.4153102). PyCascades is an object-oriented and easily extendable package written in the programming language Python. It allows for investigating under which conditions potentially dangerous cascades can emerge between interacting dynamical systems, with a focus on tipping elements. With PyCascades it is possible to use different types of tipping elements such as double-fold and Hopf types and interactions between them. PyCascades can be applied to arbitrary complex network structures and has recently been extended to stochastic dynamical systems. This paper provides an overview of the functionality of PyCascades by introducing the basic concepts and the methodology behind it. In the end, three examples are discussed, showing three different applications of the software package. First, the moisture recycling network of the Amazon rainforest is investigated. Second, a model of interacting Earth system tipping elements is discussed. And third, the PyCascades modelling framework is applied to a global trade network.

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