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101.
Johanna M. Spörl Antje Ota Ronald Beyer Thomas Lehr Alexandra Müller Frank Hermanutz Michael R. Buchmeiser 《Journal of polymer science. Part A, Polymer chemistry》2014,52(9):1322-1333
Reversible‐addition fragmentation‐transfer (RAFT) polymerization of acrylonitrile (AN) was performed with 2‐(2‐cyano‐2‐propyl‐dodecyl)trithiocarbonate as RAFT agent and azobis(isobutyronitrile) as initiator. Linear polyacrylonitrile (Mn = 133,000 g/mol, PDI = 1.34) was prepared within 7 h in 86% isolated yield. High‐yield copolymerization with methyl methacrylate (MMA) was performed and copolymerization parameters were determined according to Kelen and Tüdös at 90 °C in ethylene carbonate yielding rAN = 0.2 and rMMA = 0.42. The molecular weights, polydispersity indices (PDIs), and MMA content of the copolymer were adjusted in a way that precursor fibers could be prepared via wet spinning. These precursor fibers had round cross‐sections and a dense morphology, showing tenacities of 40–50 cN/tex and elastic moduli of 900–1000 cN/tex at a fineness of 1 dtex and an elongation of 13–17%. Precursor fibers were oxidatively stabilized and then carbonized at different temperatures. A maximum tensile strength of 2.5 GPa was reached at 1350 °C. Thermal analysis, infrared and Raman spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and tensile testing were used to characterize the resulting carbon fibers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1322–1333 相似文献
102.
103.
High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA
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Dr. Ignacio Vayá Dr. Johanna Brazard Dr. Miquel Huix‐Rotllant Dr. Arun K. Thazhathveetil Prof. Frederick D. Lewis Dr. Thomas Gustavsson Prof. Dr. Irene Burghardt Dr. Roberto Improta Dr. Dimitra Markovitsi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4904-4914
The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)n. Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)n structures with those reported previously for alternating (GC)n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence. 相似文献
104.
Direct Aryloxylation/Alkyloxylation of Dialkyl Phosphonates for the Synthesis of Mixed Phosphonates
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Dr. Hai Huang Johanna Denne Dr. Chou‐Hsun Yang Prof. Dr. Haobin Wang Prof. Dr. Jun Yong Kang 《Angewandte Chemie (International ed. in English)》2018,57(22):6624-6628
A strategy for the direct functionalization strategy of inertial dialkyl phosphonates with hydroxy compounds to afford diverse mixed phosphonates with good yields and functional‐group tolerance has been developed. Mechanistic investigations involving both NMR studies and DFT studies suggest that an unprecedented highly reactive PV species (phosphoryl pyridin‐1‐ium salt), a key intermediate for this new synthetic transformation, is generated in situ from dialkyl phosphonate in the presence of Tf2O/pyridine. 相似文献
105.
Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser 总被引:6,自引:0,他引:6
Namjou K Cai S Whittaker EA Faist J Gmachl C Capasso F Sivco DL Cho AY 《Optics letters》1998,23(3):219-221
We report what we believe are the first spectroscopic measurements to be made with a room-temperature quantum-cascade distributed-feedback laser. Using wavelength modulation spectroscopy, we detected N(2)O and CH(4) in the chemical fingerprint wavelength range near 8microm . The noise equivalent absorbance for our measurement was 5 parts in 10(5), limited by excess amplitude modulation on the laser output, which corresponds to a 1-Hz bandwidth detection limit of 250 parts N(2)O in 10(9) parts N(2) in a 1-m path length. 相似文献
106.
107.
The high-pressure iron borate α-FeB2O4 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. The monoclinic iron borate crystallizes with eight formula units in the space group P21/c with the lattice parameters a=715.2(2), b=744.5(2), c=862.3(2) pm, and β=94.71(3)°. The compound is built up exclusively from corner-sharing BO4-tetrahedra, isotypic to the monoclinic phases β-SrGa2O4, CaAl2O4-II, and CaGa2O4. Additionally, the structure is closely related to the orthorhombic compound BaFe2O4. The structure consists of layers of six-membered rings, which are interconnected to a three-dimensional network. The iron cations are coordinated by six and seven oxygen atoms. Next to synthesis and crystal structure of the new high-pressure borate, structural coherences to other structure types are discussed. 相似文献
108.
Andersson J Li S Lincoln P Andréasson J 《Journal of the American Chemical Society》2008,130(36):11836-11837
The dramatically different DNA-binding properties of the two isomeric forms of a photochromic spiropyran have been demonstrated, enabling photoswitched DNA binding. The closed, UV-absorbing form shows no signs of interaction with DNA. Upon UV exposure the spiropyran is isomerized to the open form that binds to DNA by intercalation. The process is fully reversible as the corresponding dissociation process is induced by visible light. 相似文献
109.
Mechanochemical Synthesis of 3d Transition‐Metal–1,2,4‐Triazole Complexes as Precursors for Microwave‐Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties
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Franziska A. Brede Dr. Johanna Heine Prof. Dr. Gerhard Sextl Prof. Dr. Klaus Müller‐Buschbaum 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2708-2718
The complexes [MCl2(TzH)4] (M=Mn ( 1 ), Fe ( 2 ); TzH=1,2,4‐1H‐triazole) and [ZnCl2(TzH)2] ( 3 ) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4‐1H‐triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave‐assisted reaction or by thermal conversion. For manganese, the conversion directly yielded [MnCl2TzH] ( 4 ), whereas for the iron‐containing precursor, [FeCl2TzH] ( 6 ), was formed via the intermediate coordination polymer [FeCl(TzH)2]Cl ( 5 ). For cobalt, the isotypic polymer [CoCl(TzH)2]Cl ( 7 ) was obtained, but exclusively by a microwave‐induced reaction directly from CoCl2. The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain‐like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from “low‐k” to “high‐k” with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to “low‐k” materials with very low dielectric constants up to 50 °C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition‐metal ions. 相似文献
110.
Golovanov AP Blankley RT Avis JM Bermel W 《Journal of the American Chemical Society》2007,129(20):6528-6535
A new NMR approach is presented for observing in vitro multicomponent protein-protein-ligand(s) interactions, which should help to understand how cellular networks of protein interactions operate on a molecular level and how they can be controlled with drugs. The method uniquely allows at least two polypeptide components of the mixture to be simultaneously closely monitored in a single sample, without increased signal overlap, and can be used to study complex (e.g., sequential, competitive, cooperative, allosteric, induced, etc.) binding events, witnessed by two polypeptides independently. One polypeptide is uniformly labeled with 15N and another with 15N and 13C. The 1H-15N correlation spectra are recorded for each of these molecules separately, discriminated on the basis of the type of 13C'/12C' atom attached to the amide group nitrogen. Any changes to the state of the two differently isotopically labeled molecules will be reported individually by fingerprint signals from amide groups, e.g., as unlabeled ligands are added. To our knowledge, no other technique currently exists which can monitor complex binding events in similar detail. The proposed method can be combined easily with traditional protein NMR techniques and incorporated in a variety of applications. 相似文献