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61.
Piotr Król Bożena Król Stanisław Pikus Maciej Kozak 《Colloid and polymer science》2006,285(2):169-175
Small angle X-ray scattering and differential scanning calorimetry methods were employed to characterise the internal order of structural phases present in polyurethane coatings obtained as a result of water evaporation from anionomer dispersions. Those anionomers were produced in the reaction of aromatic, cycloaliphatic and aliphatic diisocyanates with polyoxyethylene glycol, 2,2-bis-(hydroxymethyl)propionic acid and 1,6-hexamethylenediamine. The decisive effects were found from ionic and polar structures within the rigid urethane and urea segments on the ordered arrangement degree of the supermolecular structures in the obtained anionomers. That becomes apparent in differential scanning calorimetry thermograms and contributes to improved thermal stability of the produced polyurethane coatings. 相似文献
62.
In order to eliminate the errors of the TG method with a static layer, and to determine the influence of the heating rate, the composition of the carrier gas and the particle size of the solids, a method of thermal gas evolution from a fluidized bed (FTGE) with continuous and linear increase of temperature was worked out and the thermal decomposition of diammonium hydrogen phosphate was followed. This method gives reproducible results and makes possible the determination of the apparent activation energies and kinetic parameters.
Some parts presented at the IIIrd Analytical Conference, Budapest, 1970 相似文献
Zusammenfassung Um die Fehler der TG Methode unter fixierten Verhältnissen zu eliminieren, den Einfluß der Temperaturerhöhung, der Zusammensetzung des Trägergases und des Ausmaßes der Festkörper zu klären, wurde eine thermogasanalytische Methode im fluidisierten Bett (FTGE) mit kontinuierlichem und linearem Temperaturanstieg entwickelt und die thermische Zersetzung des Diammonium-biphosphates verfolgt. Man erhielt mit dieser Methode reproduzierbare Ergebnisse. Sie ist zur Bestimmung der scheinbaren Aktivierungsenergien und kinetischer Parameter geeignet.
Résumé Dans le but d'éliminer les erreurs des procédés thermogravimétriques avec couches fixes, et de mettre en évidence l'influence de la vitesse d'échauffement de la composition du gaz porteur et de la dimension des solides, on a développé une méthode d'analyse des gaz dégagés, avec lit fluidifié et élévation de la température continue et linéaire. On a suivi ainsi la décomposition thermique de (NH4)2HPO4. Cette méthode donne des résultats reproductibles et rend possible la détermination des énergies d'activation apparentes et des paramètres cinétiques.
, , . . , .
Some parts presented at the IIIrd Analytical Conference, Budapest, 1970 相似文献
63.
Reaction of trimethylsilyl-protected cytosine with methyl iodide afforded N1-methylated product. Subsequent treatment with ethanol resulted in cleavage of the protection group forming [(MeCyt)2H]I (4). Identity of was confirmed by microanalysis, mass spectrometry, 1H and 13C NMR spectroscopy and by single-crystal X-ray diffraction analysis. Crystals of consist of dimeric [(MeCyt)2H]+ cations and I- anions. These ions are arranged in the crystal such that there is a strong base stacking (mean stacking distance 3,467 angstroms) and, furthermore, pi interactions between I- and cytosine rings (mean distance 3,737 angstroms). The dimeric [(MeCyt)2H]+ cations are centrosymmetric having three strong hydrogen bonds, namely two terminal N4-H...O' ones (N4...O' 2.815(4) angstroms) and a central N3-H...N3' (N3...N3' 2.813(4) angstroms) one. Quantum chemical calculations on the DFT level of theory show that the gas phase structure of the dimeric cation exhibits two different terminal N-HO hydrogen bonds, a stronger (N4...O' 2.722 angstroms) and a weaker one (N4'...O 2.960 angstroms). The central N3-HN3[prime or minute] hydrogen bond (N3...N3' 2.852 angstroms) was characterized to have an unsymmetrically located proton and a typical double minimum potential with a very low activation barrier. The interaction energy between [(MeCyt)H]+ and MeCyt yielding [(MeCyt)2H]+ was calculated to be -42.4 kcal mol(-1)(ZPE and BSSE corrected). Comparison with the interaction energy (calculated on the same level of the theory) between cytosine and guanine yielding the triply hydrogen-bonded Watson-Crick dimer (-24.2 kcal mol(-1)) revealed a much higher stability of the hydrogen bonds in [(MeCyt)2H]+. 相似文献
64.
The binary system Li2Se-In2Se3 was investigated in the range of 40 to 100 mol% In2Se3 by thermoanalytical and X-ray methods. The system is characterized by two eutectic points. Beside the two binary components
and the known ternary compound LiInSe2 another ternary compound crystallizes in this binary system at 83.3 mol% In2Se3. This compound was identified as LiIn5Se8. In contrast to (Cu, Ag)IB5
IIIC8
VI compounds such as CuIn5S8 [1] it does not crystallize in the spinel structure. LiIn5Se8 shows a stratified structure. The melting point was determined to be at 810°C. Starting from room temperature up to the melting
point no phase transitions were observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
65.
Use of molecular dynamics in the design and structure determination of a photoinducible beta-hairpin
Kräutler V Aemissegger A Hünenberger PH Hilvert D Hansson T van Gunsteren WF 《Journal of the American Chemical Society》2005,127(13):4935-4942
The study presented here consists of three parts. In the first, the ability of a set of differently substituted diazobenzene-based linkers to act as photoswitchable beta-turn building blocks was assessed. A 12-residue peptide known to form beta-hairpins was taken as the basis for the modeling process. The central (beta-turn) residue pair was successively replaced by six symmetrically ((o,o), (m,m), or (p,p)) substituted (aminomethyl/carboxymethyl or aminoethyl/carboxyethyl) diazobenzene derivatives leading to a set of peptides with a photoswitchable backbone conformation. The folding behavior of each peptide was then investigated by performing molecular dynamics simulations in water (4 ns) and in methanol (10 ns) at room temperature. The simulations suggest that (o,o)- and (m,m)-substituted linkers with a single methylene spacer are significantly better suited to act as photoswitchable beta-turn building blocks than the other linkers examined in this study. The peptide containing the (m,m)-substituted linker was synthesized and characterized by NMR in its cis configuration. In the second part of this study, the structure of this peptide was refined using explicit-solvent simulations and NOE distance restraints, employing a variety of refinement protocols (instantaneous and time-averaged restraining as well as unrestrained simulations). We show that for this type of systems, even short simulations provide a significant improvement in our understanding of their structure if physically meaningful force fields are employed. In the third part, unrestrained explicit-solvent simulations starting from either the NMR model structure (75 ns) or a fully extended structure (25 ns) are shown to converge to a stable beta-hairpin. The resulting ensemble is in good agreement with experimental data, indicating successful structure prediction of the investigated hairpin by classical explicit-solvent molecular dynamics simulations. 相似文献
66.
Lindén AA Hermanns N Ott S Krüger L Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):112-119
Eight different flavin derivatives have been synthesized and the electronic effects of substituents in various positions on the flavin redox chemistry were investigated. The redox potentials of the flavins, determined by cyclic voltammetry, correlated with their efficiency as catalysts in the H2O2 oxidation of methyl p-tolyl sulfide. Introduction of electron-withdrawing groups increased the stability of the reduced catalyst precursor. 相似文献
67.
报道了深圳市南山区714名0 ̄6岁儿童头发中6种必需微量和宏量元素的水平,分析了不同年龄、性别儿童6种元素的异常状况,研究结果表明,儿童头发中锌、铜、铁、钙和锰元素缺乏状况相当严重总缺乏率占89.9%。 相似文献
68.
Alexandra Tsybizova Christopher Brenig Christoph Kieninger Bernhard Kräutler Peter Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(25):7252-7264
Aryl-cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential ‘antivitamins B12’. Here, the first cationic aryl-cobinamides are described, which were synthesized using the newly developed diaryl-iodonium method. The aryl-cobinamides were obtained as pairs of organometallic coordination isomers, the stereo-structure of which was unambiguously assigned based on homo- and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt-center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas-phase bond dissociation energies (BDEs) of the coordination-isomeric phenyl- and 4-ethylphenyl-cobinamides were determined by ESI-MS threshold CID experiments, furnishing (Co−C )-BDEs of 38.4 and 40.6 kcal mol−1, respectively, for the two β-isomers, and the larger BDEs of 46.6 and 43.8 kcal mol−1 for the corresponding α-isomers. Surprisingly, the observed (Co−C )-BDEs of the Coβ-aryl-cobinamides were smaller than the (Co−C )-BDE of Coβ-methyl-cobinamide. DFT studies and the magnitudes of the experimental (Co−C )-BDEs revealed relevant contributions of non-bonded interactions in aryl-cobinamides, notably steric strain between the aryl and the cobalt-corrin moieties and non-bonded interactions with and among the peripheral sidechains. 相似文献
69.
B. Henc P.W. Jolly R. Salz S. Stobbe G. Wilke R. Benn R. Mynott K. Seevogel R. Goddard C. Krüger 《Journal of organometallic chemistry》1980,191(2):449-475
A series of 1 : 1 adducts have been prepared by treating the bis-η3-allyl complexes of nickel, palladium and platinum with tertiary phosphines. Investigations of their structure in solution as well as in the crystal have shown that both 18-electron (η3-allyl)2ML complexes as well as 16-electron (η1-allyl)-(η3-allyl)ML complexes may be formed. 相似文献
70.
In situ pulsed force mode scanning force microscopy (PFM-SFM) images of phase separated solid-supported lipid bilayers are discussed with the help of computer simulations. Simultaneous imaging of material properties and topography in a liquid environment by means of PFM-SFM is severely hampered by hydrodynamic damping of the cantilever. Stiffness and adhesion images of solid-supported membranes consisting of cholesterol, sphingomyelin, and 1,2-dioleyl-phosphatidylcholine obtained in aqueous solution exhibit contrast inversion of adhesion and stiff. ness images depending on parameters such as driving frequency, amplitude, and trigger setting. Simulations using a simple harmonic oscillator model explain experimental findings and give a deeper insight into the way PFM-SFM experiments have to be performed in order to obtain interpretable results and hence pave the way for reliable material contrast imaging at high speed. 相似文献