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排序方式: 共有562条查询结果,搜索用时 312 毫秒
91.
92.
Jakob Knelles Dr. Stuart Beardsworth Korinna Bader Dr. Johanna R. Bruckner Andrea Bühlmeyer Robert Forschner Kevin Schweizer Dr. Wolfgang Frey Prof. Dr. Frank Giesselmann Prof. Dr. Yann Molard Prof. Dr. Sabine Laschat 《Chemphyschem》2019,20(17):2210-2216
A series of tetraguanidinium tetraphenylethene (TPE) arylsulfonates with different chain lengths was prepared via ionic self-assembly of tetraguanidinium TPE chloride and the respective methyl arylsulfonates. Liquid crystalline properties were studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. Tetraguanidinium TPE arylsulfonates with chain lengths of C8–C12 displayed hexagonal columnar mesophases over a broad temperature range, while derivatives with longer chains showed oblique columnar phases. In solution all compounds displayed aggregation-induced emission behaviour. Temperature-dependent luminescence spectra of the bulk phase of the tetraguanidinium TPE arylsulfonate with C14 side chains revealed a strong luminescence both in the solid state and the oblique columnar mesophase. The emission behaviour was rationalized by a unique combination of restriction of intramolecular rotation of the TPE core, Coulomb interaction between the guanidinium cations and π–π interactions of the anionic arylsulfonate moieties. 相似文献
93.
We present photoluminescence spectroscopy of blend thin films of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) with electron-donating copolymers under hydrostatic pressure. The photoluminescence spectrum of F8BT redshifts by 530+/-60 meV over pressures of 0.1 MPa-8.8 GPa. That of the interfacial charge-transfer exciton redshifts by 270-370 meV over a similar pressure range. Despite the relatively small shift of the charge-transfer exciton, the excited state dynamics at the molecular heterojunction are strongly enhanced due to the decreasing intermolecular distance, leading to favored exciplex emission. 相似文献
94.
95.
Orchestrating the Biosynthesis of an Unnatural Pyrrolysine Amino Acid for Its Direct Incorporation into Proteins Inside Living Cells 下载免费PDF全文
Michael Ehrlich Michael J. Gattner Bastien Viverge Johanna Bretzler Dr. David Eisen Michael Stadlmeier Dr. Milan Vrabel Prof. Dr. Thomas Carell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7701-7704
We here report the construction of an E. coli expression system able to manufacture an unnatural amino acid by artificial biosynthesis. This can be orchestrated with incorporation into protein by amber stop codon suppression inside a living cell. In our case an alkyne‐bearing pyrrolysine amino acid was biosynthesized and incorporated site‐specifically allowing orthogonal double protein labeling. 相似文献
96.
A simple “green synthesis” of noble metal nanoparticles by direct reaction between Dextran‐graft‐lactone copolymers and metal salts without the need to separately add reducing and stabilizing agents was carried out. The effects of the composition, molecular weights of copolymers and solvents on the characteristics of the nanoparticles were considered. The amphiphilic character of the copolymers seems to be an important factor in the results of the synthesis. According to the results, general correlations between experimental parameters of synthesis and characteristics of the obtained nanoparticles were established. Techniques such as, transmission electron microscopy, scanning electron microscopy, UV–visible spectroscopy, Zeta Potential, dynamic light scattering and Fourier transform Infrared Spectroscopy, were used for the characterization of the products. The results indicate the possibility of control of the characteristics of the nanostructured material. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
97.
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
98.
99.
High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA 下载免费PDF全文
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
100.
Direct Aryloxylation/Alkyloxylation of Dialkyl Phosphonates for the Synthesis of Mixed Phosphonates 下载免费PDF全文
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