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排序方式: 共有103条查询结果,搜索用时 31 毫秒
61.
EkaterinaV. Efimtseva GeorgiiV. Bobkov SergeyN. Mikhailov Arthur VanAerschot Guy Schepers Roger Busson Jef Rozenski Piet Herdewijn 《Helvetica chimica acta》2001,84(8):2387-2397
Disaccharide nucleosides with 2′‐O‐(D ‐arabinofuranosyl), 2′‐O‐(L ‐arabinofuranosyl), 2′‐O‐(D ‐ribopyranosyl), 2′‐O‐(D ‐erythrofuranosyl), and 2′‐O‐(5‐azido‐5‐deoxy‐D ‐ribofuranosyl) substituents were synthesized. These modified nucleosides were incorporated into oligonucleotides (see Table). Single substitution resulted in a ΔTm of +0.5 to −1.4° for DNA/RNA and a ΔTm of −0.8 to −4.7° for DNA/DNA duplexes. These disaccharide nucleosides can be well accommodated in RNA/DNA duplexes, and the presence of a NH2−C(5″) group has a beneficial effect on duplex stability. 相似文献
62.
van Houtem MH Benaskar F Fitié CF Martín-Rapún R Vekemans JA Meijer EW 《Organic & biomolecular chemistry》2012,10(30):5898-5908
The synthesis and self-assembly properties of a fluorinated C(3)-symmetrical 3,3'-bis(acylamino)-2,2'-bipyridine discotic (1) in the mesophase and in solution are described. First, 3,4,5-tris-(1H,1H,2H,2H,3H,3H-perfluoroundecyl-1-oxy)benzoyl chloride was coupled to mono-t-BOC protected 2,2'-bipyridine-3,3'-diamine to afford after deprotection the corresponding fluorinated aromatic amine on a multigram scale. Then, three-fold reaction of this amine with trimesyl chloride yielded the target C(3)-symmetrical fluorinated disc. The latter displayed columnar liquid crystallinity over a temperature range of more than 350 K in which helical rectangular and hexagonal columnar mesophases were detected by X-ray diffraction measurements. (1)H-NMR spectroscopy showed a preorganized structure due to strong intramolecular hydrogen bonding between the amide N-H's and bipyridine nitrogen atoms, even in the presence of a large excess of hexafluoroisopropanol. This preorganized structure allows the formation of helical self-assemblies in fluorinated solvents, as was established using UV-Vis spectroscopy. The fluorinated disc and two chiral hydrocarbon analogues (a C(3)-symmetrical and a desymmetrized disc) were mixed in a 1:10 v:v mixture of methoxynonafluorobutane (MNFB) and 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113). Importantly, the C(3)-symmetrical hydrocarbon disc dissolves only in the presence of fluorinated disc in the latter solvent mixture, proving a mutual interaction. CD spectroscopy performed on these mixtures points to a preference for alternating self-assemblies of fluorinated and chiral hydrocarbon discotics. 相似文献
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64.
We report a Pt(II)-catalyzed cyclization of nucleophile-tethered propargylic acetates yielding substituted heterocycles containing multiple heteroatoms including morpholines, dioxanes and sulfamates with high cis-selectivity. 相似文献
65.
Katherine L. Fiedler Jef D. Boeke Cynthia Wolberger Robert J. Cotter 《Journal of mass spectrometry : JMS》2013,48(5):608-615
The core histones, H2A, H2B, H3 and H4, undergo post‐translational modifications (PTMs) including lysine acetylation, methylation and ubiquitylation, arginine methylation and serine phosphorylation. Lysine residues may be mono‐, di‐ and trimethylated, the latter resulting in an addition of mass to the protein that differs from acetylation by only 0.03639 Da, but that can be distinguished either on high‐performance mass spectrometers with sufficient mass accuracy and mass resolution or via retention times. Here we describe the use of chemical derivatization to quantify methylated and acetylated histone isoforms by forming deuteroacetylated histone derivatives prior to tryptic digestion and bottom‐up liquid chromatography‐mass spectrometric analysis. The deuteroacetylation of unmodified or mono‐methylated lysine residues produces a chemically identical set of tryptic peptides when comparing the unmodified and modified versions of a protein, making it possible to directly quantify lysine acetylation. In this work, the deuteroacetylation technique is used to examine a single histone H3 peptide with methyl and acetyl modifications at different lysine residues and to quantify the relative abundance of each modification in different deacetylase and methylase knockout yeast strains. This application demonstrates the use of the deuteroacetylation technique to characterize modification ‘cross‐talk’ by correlating different PTMs on the same histone tail. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Sophie A. Ladoucette Jef L. Teugels 《Methodology and Computing in Applied Probability》2007,9(2):225-242
This paper provides an overview of results pertaining to moment convergence for certain ratios of random variables involving
sums, order statistics and extreme terms in the sense of modulus. Most of the literature on this matter originates from Darling
(1952) who gave a criterion for the convergence in probability to 1 of the ratio of the maximum to the sum in case of nonnegative
random variables.
Sophie A. Ladoucette is supported by the grant BDB-B/04/03 of the Catholic University of Leuven. 相似文献
69.
Multistep deposition of Cu2Si(S,Se)3 and Cu2ZnSiSe4high band gap absorber materials for thin film solar cells
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Hossam ElAnzeery Marie Buffière Khaled Ben Messaoud Souhaib Oueslati Guy Brammertz Ounsi El Daif David Cheyns Rafik Guindi Marc Meuris Jef Poortmans 《固体物理学:研究快报》2015,9(6):338-343
Cu2ZnSi(S,Se)4 and Cu2Si(S,Se)3 are potential materials to obtain cost effective high band gap absorbers for tandem thin film solar cell devices. A method to synthesize Cu2SiS3, Cu2SiSe3and Cu2ZnSiSe4thin film absorbers is proposed. This method is based on a multistep process, using sequential deposition and annealing processes. X‐ray diffraction analysis performed on the final thin films have confirmed the presence of the Cu2Si(S,Se)3 and Cu2ZnSiSe4phases. Scanning electron microscopy images revealed the formation of polycrystalline layers with grains size up to 1 µm. The band gap of the ternary Cu2SiSe3 and Cu2SiS3, and quaternary Cu2ZnSiSe4 based thin films as determined from optical and photoluminescence measurements are found to be close to their theoretical values. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
70.
Harrie J.M. Gijsen Michel J.A. De Cleyn Michel Surkyn Marc G.C. Verdonck Jef Cuypers 《Tetrahedron》2008,64(10):2456-2464
Two diastereoselective, scaleable routes towards trans-3,4-disubstituted piperidines with a 4-hydroxymethyl-3-hydroxy or 4-aminomethyl-3-hydroxy substitution pattern are being described. In the first route, the 3,4-trans configuration was introduced regio- and diastereoselectively via a hydroboration/oxidation sequence starting from 4-hydroxymethylpyridine. In the second route, regioselective epoxide ring opening of N-benzyl-3,4-epoxy-piperidine was achieved with LiCN, in situ generated from acetocyanohydrin and LiNH2. The regioselectivity of both the hydroboration and the epoxide ring opening was positively influenced by the presence of the basic piperidine nitrogen. Both routes have been optimized to be performed at large scale. 相似文献