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201.
Dr. Jacek Cieślak Dr. Cristina Ausín Dr. Andrzej Grajkowski Dr. Serge L. Beaucage 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4623-4632
The reaction of 2‐cyano‐2‐methyl propanal with 2′‐O‐aminooxymethylribonucleosides leads to stable and yet reversible 2′‐O‐(2‐cyano‐2,2‐dimethylethanimine‐N‐oxymethyl)ribonucleosides. Following N‐protection of the nucleobases, 5′‐dimethoxytritylation and 3′‐phosphitylation, the resulting 2′‐protected ribonucleoside phosphoramidite monomers are employed in the solid‐phase synthesis of three chimeric RNA sequences, each differing in their ratios of purine/pyrimidine. When the activation of phosphoramidite monomers is performed in the presence of 5‐benzylthio‐1H‐tetrazole, coupling efficiencies averaging 99 % are obtained within 180 s. Upon completion of the RNA‐chain assemblies, removal of the nucleobase and phosphate protecting groups and release of the sequences from the solid support are carried out under standard basic conditions, whereas the cleavage of 2′‐O‐(2‐cyano‐2,2‐dimethylethanimine‐N‐oxymethyl) protective groups is effected (without releasing RNA alkylating side‐products) by treatment with tetra‐n‐butylammonium fluoride (0.5 m) in dry DMSO over a period of 24–48 h at 55 °C. Characterization of the fully deprotected RNA sequences by polyacrylamide gel electrophoresis (PAGE), enzymatic hydrolysis, and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry confirmed the identity and quality of these sequences. Thus, the use of 2′‐O‐aminooxymethylribonucleosides in the design of new 2′‐hydroxyl protecting groups is a powerful approach to the development of a straightforward, efficient, and cost‐effective method for the chemical synthesis of high‐quality RNA sequences in the framework of RNA interference applications. 相似文献
202.
Dr. Ludovic Fournier Dr. Isabelle Aujard Dr. Thomas Le Saux Sylvie Maurin Sandra Beaupierre Prof. Dr. Jean‐Bernard Baudin Prof. Dr. Ludovic Jullien 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(51):17494-17507
The small and synthetically easily accessible coumarinylmethyl backbone has been modified to generate a family of photolabile protecting groups with redshifted absorption. We relied on introducing electron‐donating groups in the 7 position and electron‐withdrawing groups in the 2‐, and 2‐ and 3 positions. In particular, we showed that the diethylamino‐thiocoumarylmethyl and the diethylamino‐coumarylidenemalononitrilemethyl are relevant for uncaging with cyan light. They both exhibit a significant action cross section for uncaging in the 470–500 nm wavelength range and a low light absorption between 350 and 400 nm. These attractive features are favorable to perform chromatic orthogonal photoactivation with UV and blue‐cyan light sources, respectively. 相似文献
203.
Dr. Camino Bartolomé Dr. Fernando Villafañe Dr. Jose M. Martín‐Alvarez Dr. Jesús M. Martínez‐Ilarduya Prof. Dr. Pablo Espinet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(11):3702-3709
The X‐ray structure of the title compound [Pd(Fmes)2(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF3 groups of the Fmes ligand. The 19F NMR spectra in CD2Cl2 at very low temperature (157 K) detect restricted rotation for the two ortho‐CF3 groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol?1) to account for the rotational barrier observed (ΔH≠=26.8 kJ mol?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA. 相似文献
204.
Dr. Matthias Lein Dr. Linbin Jiang Dr. Wanxing Wei Prof. Dr. Jianyi Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14126-14142
The mechanism of CuI‐catalyzed allylic alkylation and the influence of the leaving groups (OPiv, SPiv, Cl, SPO(OiPr)2; Piv: pivavloyl) on the regioselectivity of the reaction have been explored by using density functional theory (DFT). A comprehensive comparison of many possible reaction pathways shows that [(iPr)2Cu]? prefers to bind first oxidatively to the double bond of the allylic substrate at the anti position with respect to the leaving group, and this is followed by dissociation of the leaving group. If the leaving group is not taken into account, the reaction then undergoes an isomerization and a reductive elimination process to give the α‐ or γ‐selective product. If OPiv, SPiv, Cl, or SPO(OiPr)2 groups are present, the optimal route for the formation of both α‐ and γ‐substituted products changes from the stepwise elimination to the direct process, in which the leaving group plays a stabilizing role for the reactant and destabilizes the transition state. The differences to the energy barrier for the α‐ and γ‐substituted products are 2.75 kcal mol?1 with SPO(OiPr)2, 2.44 kcal mol?1 with SPiv, 2.33 kcal mol?1 with OPiv, and 1.98 kcal mol?1 with Cl, respectively; these values show that α regioselectivity in the allylic alkylation follows a SPO(OiPr)2>SPiv>OPiv>Cl trend, which is in satisfactory agreement with the experimental findings. This trend mainly originates in the differences between the attractive electrostatic forces and the repelling steric interactions of the SPO(OiPr)2, SPiv, OPiv, and Cl groups on the Cu group. 相似文献
205.
We consider a nonlinear Neumann problem driven by the p -Laplacian plus an indefinite potential and a Carathéodory reaction which at ±∞ is resonant with respect to any nonprincipal variational eigenvalue of the differential operator. Using critical point theory and Morse theory (critical groups), we show that the problem has at least three nontrivial smooth solutions, two of which have constant sign. In the process we prove some results of independent interest concerning the unique continuation property of eigenfunctions and the critical groups at infinity of a C1-functionals. 相似文献
206.
207.
208.
Huijun Wang Jie Gao Dr. Xiang Xu Dr. Baogen Liu Lingyun Yu Yadong Ren Dr. Rui Shi Prof. Zheng Zeng Prof. Liqing Li 《化学:亚洲杂志》2021,16(9):1118-1129
To investigate the effects of oxygen-containing functional groups on the adsorption of volatile organic compounds (VOCs) with different polarity, oxygen-rich porous carbon materials (OPCs) were synthesized by heat treatment of glucose/potassium oxalate material. The carbon material had a large specific surface area (1697 m2 g−1) and a high oxygen content (18.95 at.%). OPC exhibited high adsorption capacity of toluene (309 mg g−1) and methanol (447 mg g−1). The specific surface area and total pore volume determined the adsorption capacity of toluene and methanol at the high-pressure range, while the oxygen-containing groups became the main factor affecting the methanol adsorption at the low-pressure range due to the hydrogen bond interaction through the density functional theory (DFT) calculations. This study provides an important hint for developing a novel O-doped adsorbent for the VOCs adsorption applications and analyzing the role of oxygen-containing groups in the VOCs adsorption under the low-pressure range. 相似文献
209.
Dongseok Kim Dr. Rosemary L. Calabro Abdullah A. Masud Nadeesha L. Kothalawala Dr. Minsu Gu Dr. Seung-Yeon Kwak Won-Joon Son Dr. Kyu Young Hwang Dr. Hyeonho Choi Prof. Christopher I. Richards Prof. Doo Young Kim Prof. Byeong-Su Kim 《化学:亚洲杂志》2021,16(24):4155-4164
Fluorescent carbon nanodots (CDs) have been highlighted as promising semiconducting materials due to their outstanding chemical and optical properties. However, the intrinsic heterogeneity of CDs has impeded a clear understanding of the mechanisms behind their photophysical properties. In this study, as-prepared CDs are fractionated via chromatography to reduce their structural and chemical heterogeneity and analyzed through ensemble and single-particle spectroscopies. Many single particles reveal fluorescence intensity fluctuations between two or more discrete levels with bi-exponential decays. While the intrinsic τ1 components are uniform among single particles, the τ2 components from molecule-like emissions spans a wider range of lifetimes, reflecting the inhomogeneity of the surface states. Furthermore, it is concluded that the relative population and chemical states of surface functional groups in CDs have a significant impact on emissive states, brightness, blinking, stability, and lifetime distribution of photoluminescence. 相似文献
210.
Michael Eastwood Petr Somberg Vladimír Sou
ek 《Journal of Geometry and Physics》2007,57(12):2539-2546
Using deformation theory, Braverman and Joseph constructed certain primitive ideals in the enveloping algebras of the simple Lie algebras. Except in the case sl(2,C), there is a special value of the deformation parameter giving an ideal of infinite codimension. For the classical Lie algebras, the uniqueness of the special value is equivalent to the existence of tensors with very particular properties. The existence of these tensors was concluded abstractly by Braverman and Joseph but here we present explicit formulae. This allows a rather direct computation of the special value of the deformation parameter. 相似文献