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排序方式: 共有103条查询结果,搜索用时 15 毫秒
81.
Elena Eremeeva Dr. Michail Abramov Lia Margamuljana Prof. Jef Rozenski Dr. Valerie Pezo Dr. Philippe Marlière Prof. Piet Herdewijn 《Angewandte Chemie (International ed. in English)》2016,55(26):7515-7519
The ability of alternative nucleic acids, in which all four nucleobases are substituted, to replicate in vitro and to serve as genetic templates in vivo was evaluated. A nucleotide triphosphate set of 5‐chloro‐2′‐deoxyuridine, 7‐deaza‐2′‐deoxyadenosine, 5‐fluoro‐2′‐deoxycytidine, and 7‐deaza‐2′deoxyguanosine successfully underwent polymerase chain reaction (PCR) amplification using templates of different lengths (57 or 525mer) and Taq or Vent (exo‐) DNA polymerases as catalysts. Furthermore, a fully morphed gene encoding a dihydrofolate reductase was generated by PCR using these fully substituted nucleotides and was shown to transform and confer trimethoprim resistance to E. coli. These results demonstrated that fully modified templates were accurately read by the bacterial replication machinery and provide the first example of a long fully modified DNA molecule being functional in vivo. 相似文献
82.
Lou X Spiering AJ de Waal BF van Dongen JL Vekemans JA Meijer EW 《Journal of mass spectrometry : JMS》2008,43(8):1110-1122
In the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) analysis of various compounds synthesized in our laboratory, strong [M - H]+ ion peaks were often observed for the molecules with tertiary amino groups. In this work, the MALDI TOF MS behavior of two groups of compounds that incorporate tertiary amino moieties was investigated. One group is bisurea dimethylanilines (BUDMAs) prepared for the study of molecular recognition in thermoplastic elastomers, and the other group is the poly(propylene imine) diaminobutane dendrimers. The results clearly demonstrate the appearance of the [M - H]+ ions. In order to understand the possible mechanisms for the generation of these ions, a series of model compounds, ranging from primary to tertiary amines, were investigated. Unlike the tertiary amines, no [M - H]+ ion peaks were recorded for the primary amines, and only barely detectable ones, if any, for some secondary amines. It appears that the tertiary amino groups play an important role in the formation of these ions. In addition to MALDI TOF MS analysis, these samples were also applied to electrospray ionization (ESI) MS where no [M - H]+ ions were observed. The results indicate that the generation of [M - H]+ ion is due to the unique MALDI conditions and is likely to be formed via dehydrogenation of a protonated tertiary amine resulting in an N=C double bond. The absence of [M - H]+ ion peaks for the primary and secondary amines is probably because upon their formation these ions could easily transfer one proton to the corresponding amines in the MALDI gas-phase plume, yielding neutral imines that cannot be detected by MS. 相似文献
83.
In earlier papers, we have applied multiple-scattering techniques to calculate Casimir forces due to scalar fields between different bodies described by delta function potentials. When the coupling to the potentials became weak, closed-form results were obtained. We simplify this weak-coupling technique and apply it to the case of tenuous dielectric bodies, in which case the method involves the summation of van der Waals (Casimir-Polder) interactions. Once again, exact results for finite bodies can be obtained. We present closed formulas describing the interaction between spheres, between cylinders, and between an infinite plate and a rectangular slab of finite size. For such a slab, we consider the torque acting on it and find that nontrivial equilibrium points can occur. 相似文献
84.
We study a generalization of a ratio of spacings introduced by Galton in 1902. The ratio proves to be an important building block in the construction of a large sample test for the hypothesis that a distribution from an extremal domain of attraction belongs to the domain of attraction of the Gumbel law. 相似文献
85.
Patrick Chaltin Eveline Lescrinier Theo Lescrinier Jef Rozenski Chris Hendrix Helmut Rosemeyer Roger Busson Arthur VanAerschot Piet Herdewijn 《Helvetica chimica acta》2002,85(8):2258-2283
Previously, we developed a methodology for the solid‐phase screening of peptide libraries for interaction with double‐stranded deoxyribonucleic acids (dsDNA). In the search for new and more‐potent DNA ligands, we investigated the strategy of solution‐phase screening of chemical libraries consisting of unnatural oligopeptides. After synthesis of the selected amino acid building blocks, libraries were constructed with the general structure Ac‐Arg‐Ual‐Sar‐X1‐X2‐X3‐Arg‐NH2, where X represents each of twelve unnatural or natural amino acids. Optimization of the sequence of binding peptides was performed with an iterative deconvolution procedure. Selection of interacting peptides was carried out in solution by means of gel‐retardation experiments, starting with libraries of 144 compounds. A 14‐base‐pair double‐stranded DNA fragment was chosen as the target. After several cycles of synthesis and screening of libraries and individual peptides, an oligopeptide was selected with an apparent dissociation constant of 9⋅10−5 M , as determined by gel‐retardation experiments. This peptide was studied by NMR spectroscopy. A certain degree of conformational pre‐organization of the peptides was shown by temperature‐dependent circular‐dichroism experiments. Finally, DNase‐I‐footprinting studies indicated a preferential interaction with a 6‐base‐pair mixed sequence 5′‐CTGCAT‐3′. This study demonstrates that gel‐shift experiments can be used for the solution‐phase screening of library mixtures of peptides against dsDNA. In general, this technique allows the selection of new sequence‐selective dsDNA‐interacting molecules. Furthermore, novel dsDNA‐binding unnatural oligopeptides were developed with affinities in the 0.1 mM range. 相似文献
86.
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88.
Photonic nanostructures for advanced light trapping in silicon solar cells: the impact of etching on the material electronic quality
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Christos Trompoukis Andre Stesmans Eddy Simoen Valérie Depauw Ounsi El Daif Kidong Lee Ivan Gordon Robert Mertens Jef Poortmans 《固体物理学:研究快报》2016,10(2):158-163
Dry plasma etching, commonly used by the Photonics community as the etching technique for the fabrication of photonic nanostructures, could be a source of device performance limitations when used in the frame of silicon photovoltaics. So far, the lack of silicon solar cells with state‐of‐the‐art efficiencies utilizing nanophotonic concepts shows how challenging their integration is, owing to the trade‐off between optical and electrical properties. In this study we show that dry plasma etching results in the degradation of the silicon material quality due to (i) a high density of dangling bonds and (ii) the presence of sub‐surface defects, resulting in high surface recombination velocities and low minority carrier lifetimes. On the contrary, wet chemical anisotropic etching used as an alternative, leads to the formation of inverted nanopyramids that result in low surface recombination velocity and low density of dangling bonds. The proposed inverted nanopyramids could enable high efficiency photonic assisted solar cells by offering the potential to achieve higher short‐circuit current without degrading the open circuit voltage. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
89.
In this letter we describe an efficient synthesis of "psympederin", a hybrid between the novel antitumor natural product psymberin and the blister beetle toxin pederin. Evaluation of antiproliferative activity reveals that the dihydroisocoumarin fragment is important for psymberin toxicity and the cyclic pederate fragment is important for pederin/mycalamide toxicity. On the basis of preliminary results described herein, we speculate that, despite their structural resemblance, psymberin and pederin/mycalamide induce toxicity through different mechanisms. [reaction: see text]. 相似文献
90.
Daniele D'Alonzo Dr. Arthur Van Aerschot Prof. Dr. Annalisa Guaragna Dr. Giovanni Palumbo Prof. Guy Schepers Stefania Capone Dr. Jef Rozenski Prof. Dr. Piet Herdewijn Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10121-10131
Oligonucleotides composed of 1′,5′‐anhydro‐arabino‐hexitol nucleosides belonging to the L series (L ‐HNA) were prepared and preliminarily studied as a novel potential base‐pairing system. Synthesis of enantiopure L ‐hexitol nucleotide monomers equipped with a 2′‐(N6‐benzoyladenin‐9‐yl) or a 2′‐(thymin‐1‐yl) moiety was carried out by a de novo approach based on a domino reaction as key step. The L oligonucleotide analogues were evaluated in duplex formation with natural complements as well as with unnatural sugar‐modified oligonucleotides. In many cases stable homo‐ and heterochiral associations were found. Besides Tm measurements, detection of heterochiral complexes was unambiguously confirmed by LC‐MS studies. Interestingly, circular dichroism measurements of the most stable duplexes suggested that L ‐HNA form left‐handed helices with both D and L oligonucleotides. 相似文献