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131.
Novel semiflexible polyazomethines containing chromophoric units into azomethine mesogenic core have been synthesised by condensation of a flexible dialdehyde with mesogenic diamines containing fluorene, antraquinone, pyrimidine, azobenzene and benzophenone. The thermotropic behaviour of the resulting polyazomethines was assessed by differential scanning calorimetry, polarised light microscopy and investigations of the miscibility relations. While the pure polyazomethines showed a birefringent viscous texture difficult to be ascribed, by mixing with a liquid crystal dimer, clear Schlieren or marbled textures were observed, indicating a nematic mesophase. The polymers exhibited violet, blue or yellow light emission. 相似文献
132.
The New Data for the Reaction of Arylenedioxy Trihalogenophosphoranes with Alkyl- and Arylacetylenes
Vladimir F. Mironov Alfiya A. Shtyrlina Ravil R. Petrov Tamara A. Baronova Fedor F. Alekseev Elena N. Varaksina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1381-1385
The new data concerning the reaction between substituted arylenedioxy trihalogenophosphoranes and monoalkyl- or arylacetylenes are summarized. The reaction leads to formation of six-membered heterocycles-2-oxo-4-R-benzo[ e ]-1,2-oxaphosphorin-3-enes. The substituent effects in the phosphorane and acetylene molecules on the ipso -substitution and halogenation regiochemistry are discussed. The ipso -substitution of tert -butyl group on chlorine and the exchange of bromine on chlorine and iodine on hydrogen have been observed, along with formation of benzophosphorines. The interaction of tetrachloro- ortho -benzoquinone with phosphorus trichloride and arylacetylenes is proposed as a new modification of the reaction leading to the formation of benzo[ e ]-1,2-oxaphosphorines. The structures of some benzo[ e ]-1,2-oxaphosphorines are determined by the single crystal X-ray diffraction. 相似文献
133.
Vasily S. Minkov Evgeny A. Kapustin Elena V. Boldyreva 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):416-420
The title compound, betaine 0.77‐perhydrate 0.23‐hydrate, (CH3)3N+CH2COO−·0.77H2O2·0.23H2O, crystallizes in the orthorhombic noncentrosymmetric space group Pca21. Chiral molecules of hydrogen peroxide are positionally disordered with water molecules in a ratio of 0.77:0.23. Betaine, 2‐(trimethylazaniumyl)acetate, preserves its zwitterionic state, with a positively charged ammonium group and a negatively charged carboxylate group. The molecular conformation of betaine here differs from the conformations of both anhydrous betaine and its hydrate, mainly in the orientation of the carboxylate group with respect to the C—C—N skeleton. Hydrogen peroxide is linked via two hydrogen bonds to carboxylate groups, forming infinite chains along the crystallographic a axis, which are very similar to those in the crystal structure of betaine hydrate. The present work contributes to the understanding of the structure‐forming factors for amino acid perhydrates, which are presently attracting much attention. A correlation is suggested between the ratio of amino acid zwitterions and hydrogen peroxide in the unit cell and the structural motifs present in the crystal structures of all currently known amino acids perhydrates. This can help to classify the crystal structures of amino acid perhydrates and to design new crystal structures. 相似文献
134.
Dr. Emilio M. Pellegrino Prof. Luigi Cerruti Prof. Elena M. Ghibaudi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4330-4335
The present reflection on the development of research on carbon nanotubes (CNTs) stems from the publication of the report “Realizing the Promise of Carbon Nanotubes” by the US National Nanotechnology Initiative in 2015. The report is a critical assessment of the state‐of‐art of CNT research and highlights some unresolved issues related with this field. Starting from the results of this assessment, we carried out an analysis of the publications’ pool in CNTs and related domains, by exploiting bibliometric tools. We focused on the item of competition/collaboration between disciplines and nations, with the purpose of evaluating the position of chemistry (as a discipline) as well as the position of the main European countries and the European Union (EU) as a whole in the context of CNT research. The results of such analysis outline very clearly the interdisciplinary landscape wherein CNT research is situated and show the highly competitive place occupied by EU in the field. 相似文献
135.
Alexander P. Filippov Elena V. Belyaeva Tamara K. Meleshko Alexander V. Yakimansky 《Journal of Polymer Science.Polymer Physics》2014,52(23):1539-1546
A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546 相似文献
136.
Toward Fluorescence‐Based High‐Throughput Screening for Enantiomeric Excess in Amines and Amino Acid Derivatives
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Elena G. Shcherbakova Dr. Valentina Brega Dr. Tsuyoshi Minami Sara Sheykhi Prof. Dr. Tony D. James Prof. Dr. Pavel Anzenbacher Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10074-10080
A highly accurate and reliable screening method for enantiomeric excess of amine derivatives in the presence of water is reported. The fluorescence‐based screening system has been realized by self‐assembly of chiral diol‐type dyes (BINOL, VANOL and VAPOL), 2‐formylphenylboronic acid, and chiral amines forming iminoboronate esters. The structure and chirality of the amine analytes determine the stability of the diastereomeric iminoboronate esters, which in turn display differential fluorescence. The fluorescence signal reflects the enantiomeric purity of the chiral amines and was utilized in high‐throughput arrays. The arrays were able to recognize enantiomeric excess of amines, amino esters, and amino alcohols. In addition to qualitative analysis, quantitative experiments were successfully performed. Studies of the role of additives such as water or citrate were carried out to gain insight into the stability of the iminoboronate esters. It is shown that the above additives destabilize less stable esters while the stable esters remain unchanged. Thus, the presence of water and citrate leads to increased difference between the diastereomeric iminoboronates and contributes to the enantiodiscrimination of the chiral amines. 相似文献
137.
138.
We consider a transmission problem on a polygonal partition for the two-dimensional conductivity equation. For suitable classes of partitions we establish the exact behaviour of the gradient of solutions in a neighbourhood of the vertexes of the partition. This allows to prove shape differentiability of solutions and to establish an explicit formula for the shape derivative. 相似文献
139.
Elena Perju Simon J. Dünki Dorina M. Opris 《Journal of polymer science. Part A, Polymer chemistry》2016,54(18):2940-2948
A synthetic strategy to polydimethylsiloxanes and polymethylsiloxanes containing thiol functions as end‐ or side‐groups, respectively, is presented. Such polymers are important starting materials for elastomeric networks and postpolymerization modifications. The synthesis starts either with vinyl end‐functionalized polydimethylsiloxanes or with polymethylvinylsiloxanes. The vinyl groups are reacted either with thioacetic acid or with a thioacetic acid/butanethiol mixture via a UV‐initiated thiol‐ene reaction to form the respective thioester quantitatively within few minutes. The thioesters are subsequently deprotected to the respective thiols by reduction with LiAlH4. The resulting thiol containing polysiloxanes can be used for the formation of networks or another functionalization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2940–2948 相似文献
140.
Unraveling σ and π Effects on Magnetic Anisotropy in cis‐NiA4B2 Complexes: Magnetization,HF‐HFEPR Studies,First‐Principles Calculations,and Orbital Modeling
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Dr. Gaëlle Charron Dr. Elena Malkin Dr. Guillaume Rogez Dr. Luke J. Batchelor Dr. Sandra Mazerat Dr. Régis Guillot Dr. Nathalie Guihéry Dr. Anne‐Laure Barra Dr. Talal Mallah Dr. Hélène Bolvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16850-16862
By using complementary experimental techniques and first‐principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2v, has been investigated. Four complexes have the general formula [Ni(bpy)X2]n+ (bpy=2,2′‐bipyridine; X2=bpy ( 1 ), (NCS?)2 ( 2 ), C2O42? ( 3 ), NO3? ( 4 )). In the fifth complex, [Ni(HIM2‐py)2(NO3)]+ ( 5 ; HIM2‐py=2‐(2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2‐py. Analysis of the high‐field, high‐frequency electronic paramagnetic resonance (HF‐HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from ?1 to ?10 cm?1. First‐principles SO‐CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3 , on one hand, and 4 and 5 , on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters (D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg‐like orbitals and is due to the difference in the σ‐donor strength of NO3? and bpy or HIM2‐py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g‐like orbitals; and 2) the anisotropy of complexes 1 – 3 arises from the small splitting of the t2g‐like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. 相似文献