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1.
Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. II. Influence of side‐chain structure
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Aleksandr Perevedentsev Paul N. Stavrinou Paul Smith Donal D. C. Bradley 《Journal of Polymer Science.Polymer Physics》2015,53(21):1492-1506
Solution‐crystallization is studied for two polyfluorene polymers possessing different side‐chain structures. Thermal analysis and temperature‐dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X‐ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar‐zigzag chain conformation termed the β‐phase, which is observed for certain linear‐side‐chain polyfluorenes, is necessary for the formation of so‐called polymer‐solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side‐chains prevents formation of the β‐phase conformation and results in non‐solvated, i.e. melt‐crystallization‐type, polymer crystals. Unlike non‐solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β‐phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter‐chain interactions. The presented results clarify the fundamental differences between the β‐phase and other conformational/crystalline forms of polyfluorenes. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1492–1506 相似文献
2.
Dirk Grote Dr. Christopher Finke Simone Kossmann Frank Neese Prof. Dr. Wolfram Sander Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4496-4506
The photochemistry of 2‐iodo‐3,4,5,6‐tetrafluorophenyl azide ( 7 d ) has been investigated in argon and neon matrices at 4 K, and the products characterized by IR and EPR spectroscopy. The primary photochemical step is loss of a nitrogen molecule and formation of phenyl nitrene 1 d . Further irradiation with UV or visible light results in mixtures of 1 d with azirine 5 d ′, ketenimine 6 d ′, nitreno radical 2 d , and azirinyl radical 9 . The relative amounts of these products strongly depend on the matrix and on the irradiation conditions. Nitreno radical 2 d with a quartet ground state was characterized by EPR spectroscopy. Electronic structure calculations in combination with the experimental results allow for a detailed understanding of the properties of this unusual new type of organic high‐spin molecules. 相似文献
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Michael Kampf Rainer Richter Jan Griebel Anke Weller Reinhard Kirmse 《无机化学与普通化学杂志》2005,631(4):698-708
Synthesis, Structures, EPR and ENDOR Investigations on Transition Metal Complexes of N, N‐diisobutyl‐N′‐(2, 6‐difluoro)benzoyl selenourea The synthesis and the structures of the NiII and PdII complexes of the ligand N, N‐diisobutyl‐N′‐(2, 6‐difluoro)benzoylselenourea HBui2dfbsu are reported. The ligands coordinate bidentately forming bis‐chelates. The structure of the ligand could not be obtained, however, the structure of its O‐ethyl ester will be reported. Attempts to prepare the CuII complex result only in the formation of oily products. However, the CuII complex could be incorporated into the corresponding NiII and PdII compounds. From this diamagnetically diluted powder and single‐crystal samples were obtained being suitable for EPR‐ENDOR measurements. We report X‐ and Q‐band EPR investigations on the systems [Cu/Ni(Bui2dfbsu)2] and [Cu/Pd(Bui2dfbsu)2] as well as a single‐crystal X‐band EPR study for [Cu/Ni(Bui2dfbsu)2]. The obtained 63, 65Cu and 77Se hyperfine structure tensors allow a determination of the spin‐density distribution within the first coordination sphere. In addition, orientation selective 19F Q‐band pulse ENDOR investigations on powder‐samples of [Cu/Ni(Bui2dfbsu)2] have been performed. The hyperfine structure tensors of two intramolecular 19F atoms could be determined. According to the small 19F couplings only a vanishingly small spin‐density of < 1 % was obtained for these 19F atoms. 相似文献
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Back Cover: Breslow Intermediates from Aromatic N‐Heterocyclic Carbenes (Benzimidazolin‐2‐ylidenes,Thiazolin‐2‐ylidenes) (Angew. Chem. Int. Ed. 27/2018)
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Dr. Mathias Paul Dr. Nils E. Schlörer Dr. Jörg‐M. Neudörfl Prof. Dr. Albrecht Berkessel 《Angewandte Chemie (International ed. in English)》2018,57(27):8332-8332
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1,1′‐Bis(trimethylsilylamino)ferrocene reacts with trimethyl‐ and triethylgallium to give the μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetraalkyldigallanes. These were converted into the 1,3‐bis(trimethylsilyl)‐2‐alkyl‐2‐pyridine‐1,3,2‐diazagalla‐[3]ferrocenophanes, of which the ethyl derivative was characterized by X‐ray structural analysis. Treatment of gallium trichloride with N,N′‐dilithio‐1,1′‐bis(trimethylsilylamino)ferrocene affords μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetrachlorodigallane along with bis(trimethylsilyl)‐2,2‐dichloro‐1‐aza‐3‐azonia‐2‐gallata‐[3]ferrocenophane as a side product, and both were structurally characterized by X‐ray analysis. The solution‐state structures of the new gallium compounds and aspects of their molecular dynamics in solution were studied by NMR spectroscopy (1H, 13C, 29Si NMR). 相似文献
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Inside Cover: A Rotational BODIPY Nucleotide: An Environment‐Sensitive Fluorescence‐Lifetime Probe for DNA Interactions and Applications in Live‐Cell Microscopy (Angew. Chem. Int. Ed. 1/2016)
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Dr. Dmytro Dziuba Dr. Piotr Jurkiewicz Dr. Marek Cebecauer Prof. Dr. Martin Hof Prof. Dr. Michal Hocek 《Angewandte Chemie (International ed. in English)》2016,55(1):2-2
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Dual‐color fluorescence cross‐correlation spectroscopy (dcFCCS) allows one to quantitatively assess the interactions of mobile molecules labeled with distinct fluorophores. The technique is widely applied to both reconstituted and live‐cell biological systems. A major drawback of dcFCCS is the risk of an artifactual false‐positive or overestimated cross‐correlation amplitude arising from spectral cross‐talk. Cross‐talk can be reduced or prevented by fast alternating excitation, but the technology is not easily implemented in standard commercial setups. An experimental strategy is devised that does not require specialized hardware and software for recognizing and correcting for cross‐talk in standard dcFCCS. The dependence of the cross‐talk on particle concentrations and brightnesses is quantitatively confirmed. Moreover, it is straightforward to quantitatively correct for cross‐talk using quickly accessible parameters, that is, the measured (apparent) fluorescence count rates and correlation amplitudes. Only the bleed‐through ratio needs to be determined in a calibration measurement. Finally, the limitations of cross‐talk correction and its influence on experimental error are explored. 相似文献
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Stefan Schneider Ashwani Vij Jeffrey A. Sheehy Fook S. Tham Thorsten Schroer Karl O. Christe Karl O. Christe Karl O. Christe 《无机化学与普通化学杂志》2001,627(4):631-637
The reaction of KPO2F2 with the strong Lewis acid SbF5 was studied as a potential pathway to the unknown PO2+ cation. The resulting product has the desired PO2SbF6 composition but consists of an eight‐membered, antimony‐oxygen‐phosphorus‐bridged ring that was characterized by vibrational and NMR spectroscopy, ab initio methods, and a single crystal x‐ray diffraction study. The preferred formation of the ring and its mechanism are discussed. 相似文献
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Dr. Xianjun Tan Jenny Melkersson Shiqun Wu Prof. Lingzhi Wang Prof. Jinlong Zhang 《Chemphyschem》2016,17(17):2630-2639
Surface‐enhanced Raman spectroscopy (SERS) is an attractive tool for the sensing of molecules in the fields of chemical and biochemical analysis as it enables the sensitive detection of molecular fingerprint information even at the single‐molecule level. In addition to traditional coinage metals in SERS analysis, recent research on noble‐metal‐free materials has also yielded highly sensitive SERS activity. This Minireview presents the recent development of noble‐metal‐free materials as SERS substrates and their potential applications, especially semiconductors and emerging graphene‐based nanostructures. Rather than providing an exhaustive review of this field, possible contributions from semiconductor substrates, characteristics of graphene enhanced Raman scattering, as well as effect factors such as surface plasmon resonance, structure and defects of the nanostructures that are considered essential for SERS activity are emphasized. The intention is to illustrate, through these examples, that the promise of noble‐metal‐free materials for enhancing detection sensitivity can further fuel the development of SERS‐related applications. 相似文献
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Inside Back Cover: Initial Carbon–Carbon Bond Formation during the Early Stages of the Methanol‐to‐Olefin Process Proven by Zeolite‐Trapped Acetate and Methyl Acetate (Angew. Chem. Int. Ed. 51/2016)
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Dr. Abhishek Dutta Chowdhury Dr. Klaartje Houben Dr. Gareth T. Whiting Prof. Dr. Mohamed Mokhtar Prof. Dr. Abdullah M. Asiri Prof. Dr. Shaeel A. Al‐Thabaiti Prof. Dr. Suliman N. Basahel Prof. Dr. Marc Baldus Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2016,55(51):15929-15929
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Inside Back Cover: Self‐Assembly of Measles Virus Nucleocapsid‐like Particles: Kinetics and RNA Sequence Dependence (Angew. Chem. Int. Ed. 32/2016)
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Dr. Sigrid Milles Dr. Malene Ringkjøbing Jensen Dr. Guillaume Communie Damien Maurin Dr. Guy Schoehn Prof. Rob W. H. Ruigrok Dr. Martin Blackledge 《Angewandte Chemie (International ed. in English)》2016,55(32):9441-9441
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Novel, high‐sensitivity and high‐resolution spectroscopic methods can provide site‐specific nuclear information by exploiting nuclear magneto‐optic properties. We present a first‐principles electronic structure formulation of the recently proposed nuclear‐spin‐induced Cotton–Mouton effect in a strong external magnetic field (NSCM‐B). In NSCM‐B, ellipticity is induced in a linearly polarized light beam, which can be attributed to both the dependence of the symmetric dynamic polarizability on the external magnetic field and the nuclear magnetic moment, as well as the temperature‐dependent partial alignment of the molecules due to the magnetic fields. Quantum‐chemical calculations of NSCM‐B were conducted for a series of molecular liquids. The overall order of magnitude of the induced ellipticities is predicted to be 10?11–10?6 rad T?1 M ?1 cm?1 for fully spin‐polarized nuclei. In particular, liquid‐state heavy‐atom systems should be promising for experiments in the Voigt setup. 相似文献
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Ping Ding Dorith Wunnicke Prof. Heinz‐Jürgen Steinhoff Prof. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14385-14396
Nucleobase‐directed spin‐labeling by the azide‐alkyne ‘click’ (CuAAC) reaction has been performed for the first time with oligonucleotides. 7‐Deaza‐7‐ethynyl‐2′‐deoxyadenosine ( 1 ) and 5‐ethynyl‐2′‐deoxyuridine ( 2 ) were chosen to incorporate terminal triple bonds into DNA. Oligonucleotides containing 1 or 2 were synthesized on a solid phase and spin labeling with 4‐azido‐2,2,6,6‐tetramethylpiperidine 1‐oxyl (4‐azido‐TEMPO, 3 ) was performed by post‐modification in solution. Two spin labels ( 3 ) were incorporated with high efficiency into the DNA duplex at spatially separated positions or into a ‘dA‐dT’ base pair. Modification at the 5‐position of the pyrimidine base or at the 7‐position of the 7‐deazapurine residue gave steric freedom to the spin label in the major groove of duplex DNA. By applying cw and pulse EPR spectroscopy, very accurate distances between spin labels, within the range of 1–2 nm, were measured. The spin–spin distance was 1.8±0.2 nm for DNA duplex 17 ( dA*7,10 ) ?11 containing two spin labels that are separated by two nucleotides within one individual strand. A distance of 1.4±0.2 nm was found for the spin‐labeled ‘dA‐dT’ base pair 15 ( dA*7 ) ?16 ( dT*6 ). The ‘click’ approach has the potential to be applied to all four constituents of DNA, which indicates the universal applicability of the method. New insights into the structural changes of canonical or modified DNA are expected to provide additional information on novel DNA structures, protein interaction, DNA architecture, and synthetic biology. 相似文献
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Prof. Dr. Thomas M. Klapötke Franz A. Martin Norbert T. Mayr Jörg Stierstorfer 《无机化学与普通化学杂志》2010,636(15):2555-2564
3,5‐Diamino‐1,2,4‐triazole ( 1 , guanozol) was protonated with diluted hydrochloric acid, nitric acid, as well as perchloric acid forming 3,5‐diamino‐1,2,4‐triazolium chloride hemihydrate ( 2 ), 3,5‐diamino‐1,2,4‐triazolium nitrate ( 3 ) and 3,5‐diamino‐1,2,4‐triazolium perchlorate ( 4 ), respectively. In a second step 4 reacted with potassium dinitramide forming 3,5‐diamino‐1,2,4‐triazolium dinitramide ( 5 ) and low soluble potassium perchlorate. Compounds 2 – 5 were characterized by low temperature single X‐ray diffraction, IR and Raman as well as multinuclear NMR spectroscopy, mass spectrometry and differential scanning calorimetry. The heats of formation of 1 – 5 were calculated by the CBS‐4M method to be 81.1 ( 1 ), 124.7 ( 2 ), –76.1 ( 3 ), –25.2 ( 4 ) and 138.7 ( 5 ) kJ·mol–1. With these values as well as the X‐ray densities several detonation parameters were calculated using both computer codes EXPLO5.03 and EXPLO5.04. In addition, the sensitivities of 1 – 5 were determined by the BAM drophammer and friction tester as well as a small scale electrical discharge device. 相似文献
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Stefan Henkel Melanie Ertelt Prof. Dr. Wolfram Sander 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7585-7588
4‐Oxocyclohexa‐2,5‐dienylidene is a highly reactive triplet ground state carbene that is hydrogenated in solid H2, HD, and D2 at temperatures as low as 3 K. The mechanism of the insertion of the carbene into dihydrogen was investigated by IR and EPR spectroscopy and by kinetic studies. H or D atoms were observed as products of the reaction with H2 and D2, respectively, whereas HD produces exclusively D atoms. The hydrogenation shows a very large kinetic isotope effect and remarkable isotope selectivity, as was expected for a tunneling reaction. The experiments, therefore, provide clear evidence for both hydrogen tunneling and the rare deuterium tunneling in an intermolecular reaction. 相似文献
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