排序方式: 共有217条查询结果,搜索用时 15 毫秒
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Kottysch T Ahlborn C Brotzel F Richert C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(16):4017-4028
The 5-position of pyrimidines in DNA duplexes offers a site for introducing alkynyl substituents that protrude into the major groove and thus do not sterically interfere with helix formation. Substituents introduced at the 5-position of the deoxyuridine residue of dU:dA base pairs may stabilize duplexes and reinforce helices weakened by a low G/C content, which would otherwise lead to false negative results in DNA chip experiments. Here we report on a method for preparing oligonucleotides with a 5-alkynyl substituent at a 2'-deoxyuridine residue by on-support Sonogashira coupling involving the fully assembled oligonucleotide. A total of 25 oligonucleotides with 5-alkynyl substituents were prepared. The substituents either decrease the UV melting point of the duplex with the complementary strand or increase it by up to 7.1 degrees C, compared with that of the unmodified control duplex. The most duplex-stabilizing substituent, a pyrenylbutyramidopropyne moiety, is likely to intercalate but does not prevent sequence-specific base pairing of the modified deoxyuridine residue or the neighboring nucleotides. It also increases the signal for a target strand when employed on a small oligonucleotide microarray. The ability to tune the melting point of a DNA dodecamer duplex with a single side chain over a temperature range of >11 degrees C may prove useful when developing DNA sequences for biomedical applications. 相似文献
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An infinite plate on the halfspace is treated as a typical soil–structure interaction problem. Based on an analytical solution in the wavenumber– and frequency domain the dynamic flexibility is obtained using contour integration. The force–displacement relationship is transformed into the time domain by means of a rational approximation technique and the fractional calculus. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Carolin Albrecht Thomas Krüger Christoph Wagner Tobias Rüffer Heinrich Lang Dirk Steinborn Prof. Dr. 《无机化学与普通化学杂志》2008,634(14):2495-2503
On the Reactivity of Titanocene Complexes [Ti(Cp′)2(η2‐Me3SiC≡CSiMe3)] (Cp′ = Cp, Cp*) towards Benzenedicarboxylic Acids Titanocene complexes [Ti(Cp′)2(BTMSA)] ( 1a , Cp′ = Cp = η5‐C5H5; 1b , Cp′ = Cp* = η5‐C5Me5; BTMSA = Me3SiC≡CSiMe3) were found to react with iodine and methyl iodide yielding [Ti(Cp′)2(μ‐I)2] ( 2a / b ; a refers to Cp′ = Cp and b to Cp′ = Cp*), [Ti(Cp′)2I2] ( 3a / b ) and [Ti(Cp′)2(Me)I] ( 4a / b ), respectively. In contrast to 2a , complex 2b proved to be highly moisture sensitive yielding with cleavage of HCp* [{Ti(Cp*)I}2(μ‐O)] ( 7 ). The corresponding reactions of 1a / b with p‐cresol and thiophenol resulted in the formation of [Ti(Cp′)2{O(p‐Tol)}2] ( 5a / b ) and [Ti(Cp′)2(SPh)2] ( 6a / b ), respectively. Reactions of 1a and 1b with 1,n‐benzenedicarboxylic acids (n = 2–4) resulted in the formation of dinuclear titanium(III) complexes of the type [{Ti(Cp′)2}2{μ‐1,n‐(O2C)2C6H4}] (n = 2, 8a / b ; n = 3, 9a / b ; n = 4, 10a / b ). All complexes were fully characterized analytically and spectroscopically. Furthermore, complexes 7 , 8b , 9a ·THF, 10a / b were also be characterized by single‐crystal X‐ray diffraction analyses. 相似文献
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The internal‐rating‐based Basel II approach increases the need for the development of more realistic default probability models. In this paper, we follow the approach taken in McNeil A and Wendin J 7 (J. Empirical Finance 2007) by constructing generalized linear mixed models for estimating default probabilities from annual data on companies with different credit ratings. The models considered, in contrast to McNeil A and Wendin J 7 (J. Empirical Finance 2007), allow parsimonious parametric models to capture simultaneously dependencies of the default probabilities on time and credit ratings. Macro‐economic variables can also be included. Estimation of all model parameters are facilitated with a Bayesian approach using Markov chain Monte Carlo methods. Special emphasis is given to the investigation of predictive capabilities of the models considered. In particular, predictable model specifications are used. The empirical study using default data from Standard and Poor's gives evidence that the correlation between credit ratings further apart decreases and is higher than the one induced by the autoregressive time dynamics. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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[reaction: see text] A synthesis for oligodeoxynucleotides with a 3'-terminal 2'-N-methyl-2'-acylamido-2'-deoxyuridine residue was developed. Unlike their unmethylated counterparts, these oligodeoxynucleotides can be stably immobilized on aldehyde-displaying glass surfaces to provide DNA microarrays. An anthraquinone carboxamido group as a 2'-substituent doubled the capture efficiency of an immobilized tetradecamer. 相似文献
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Dr. David Schweinfurth Marcella Mazzolini Dr. Dmytro Neshchadin Carolin Hoyer Roman Geier Dr. Karl Gatterer Dr. Nils Trapp Prof. Dr. Georg Gescheidt Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7152-7157
The synthesis of redox‐active p‐ and o‐quinones 2‐phenylamino‐4‐phenylimino[6]helicene‐1‐one 1 , 2‐phenylamino[6]‐helicene‐1,4‐dione 2 , and 4‐phenyl[6]helicene‐1,2‐dione 3 in their enantiopure forms by post‐functionalization of (P)‐ and (M)‐1,2‐dimethoxy[6]helicene is presented. Structural characterization in solution and in the solid state was accomplished by 2D NMR spectroscopy methods and X‐ray diffraction analysis, respectively. Interpretation of electrochemical redox data was accompanied by a detailed orbital picture, derived from DFT calculations. The electronic structures of compounds 1 – 3 were investigated by UV/Vis and electronic circular dichroism (ECD) spectroscopy, complemented by TD‐DFT calculations. Quinones 1 – 3 were chemically reduced to study the EPR signatures of their respective radical anions. DFT methods were used for the atom assignment of the hyperfine coupling constants. The results are discussed within the context of electrochromic chiral switches and molecular recognition. 相似文献
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Reductive Coupling of Diynes at Rhodium Gives Fluorescent Rhodacyclopentadienes or Phosphorescent Rhodium 2,2’‐Biphenyl Complexes
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Carolin Sieck Dr. Meng Guan Tay Dr. Marie‐Hélène Thibault Dr. Robert M. Edkins Dr. Karine Costuas Prof. Dr. Jean‐François Halet Dr. Andrei S. Batsanov Dr. Martin Haehnel Dr. Katharina Edkins Dr. Andreas Lorbach Dr. Andreas Steffen Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10523-10532
Reactions of [Rh(κ2‐O,O‐acac)(PMe3)2] (acac=acetylacetonato) and α,ω‐bis(arylbutadiynyl)alkanes afford two isomeric types of MC4 metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5‐bis(arylethynyl)rhodacyclopentadienes ( A ) are formed, which display intense fluorescence (Φ=0.07–0.54, τ=0.2–2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes ( B ), which show exceptionally long‐lived (hundreds of μs) phosphorescence (Φ=0.01–0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent β‐H‐shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T1 state in the biphenyl complexes B , allowing for more efficient intersystem crossing S1→Tn and T1→S0. Control of the isomer distribution is achieved by modification of the bis‐ (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds. 相似文献