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41.
Intermolecular Dynamic Kinetic Resolution Cooperatively Catalyzed by an N‐Heterocyclic Carbene and a Lewis Acid 下载免费PDF全文
Zijun Wu Fangyi Li Prof. Dr. Jian Wang 《Angewandte Chemie (International ed. in English)》2015,54(5):1629-1633
The ubiquitous structure of δ‐lactones makes the development of new methods for their enantioselective and stereoselective synthesis an important ongoing challenge. The intermolecular dynamic kinetic resolution (DKR) of β‐halo‐α‐ketoesters cooperatively catalyzed by an N‐heterocyclic carbene and a Lewis acid generates two contiguous stereocenters with remarkable diastereoselectivity through an oxidation/lactonization sequence. 相似文献
42.
A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent‐Induced Increase of the Enantiomerization Barrier in 1‐Aza‐[5]helicene 下载免费PDF全文
Prof. Dr. Tullio Caronna Prof. Dr. Andrea Mele Prof. Dr. Antonino Famulari Dr. Daniele Mendola Prof. Dr. Francesca Fontana Dr. Markus Juza Dr. Matthias Kamuf Dr. Kerstin Zawatzky Prof. Dr. Oliver Trapp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):13919-13924
Helicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors. The properties of these materials are related to the stereodynamics of these helical chiral compounds. However, little is known about features controlling stereodynamics in helicenes; in particular, for heterohelicenes the position of the heteroatom could be relevant in this respect. Herein the complete stereodynamic characterization of monoaza[5]helicenes is shown by enantioselective dynamic HPLC and DFT calculations. At variance with previous theoretical calculations, 1‐aza[5]helicene shows a surprisingly high enantiomerization barrier, which is triggered by specific solvent interactions. 相似文献
43.
Dynamic Covalent Organocatalysts Discovered from Catalytic Systems through Rapid Deconvolution Screening 下载免费PDF全文
Fredrik Schaufelberger Prof. Olof Ramström 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(36):12735-12740
The first example of a bifunctional organocatalyst assembled through dynamic covalent chemistry (DCC) is described. The catalyst is based on reversible imine chemistry and can catalyze the Morita–Baylis–Hillman (MBH) reaction of enones with aldehydes or N‐tosyl imines. Furthermore, these dynamic catalysts were shown to be optimizable through a systemic screening approach, in which large mixtures of catalyst structures were generated, and the optimal catalyst could be directly identified by using dynamic deconvolution. This strategy allowed one‐pot synthesis and in situ evaluation of several potential catalysts without the need to separate, characterize, and purify each individual structure. The systems were furthermore shown to catalyze and re‐equilibrate their own formation through a previously unknown thiourea‐catalyzed transimination process. 相似文献
44.
Cyclotetrabenzoin: Facile Synthesis of a Shape‐Persistent Molecular Square and Its Assembly into Hydrogen‐Bonded Nanotubes 下载免费PDF全文
Qing Ji Ha T. M. Le Dr. Xiqu Wang Dr. Yu‐Sheng Chen Dr. Tatyana Makarenko Prof. Allan J. Jacobson Prof. Ognjen Š. Miljanić 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17205-17209
Cyanide‐catalyzed benzoin condensation of terephthaldehyde produces a cyclic tetramer, which we propose to name cyclotetrabenzoin. Cyclotetrabenzoin is a square‐shaped macrocycle ornamented with four α‐hydroxyketone functionalities pointing away from the central cavity, the dimensions of which are 6.9×6.9 Å. In the solid state, these functional groups extensively hydrogen bond, resulting in a microporous three‐dimensional organic framework with one‐dimensional nanotube channels. This material exhibits permanent—albeit low‐porosity, with a Langmuir surface area of 52 m2 g?1. Cyclotetrabenzoin’s easy and inexpensive synthesis and purification may inspire the creation of other shape‐persistent macrocycles and porous molecular crystals by benzoin condensation. 相似文献
45.
Thomas Heuser Elisabeth Weyandt Dr. Andreas Walther 《Angewandte Chemie (International ed. in English)》2015,54(45):13258-13262
Switchable self‐assemblies respond to external stimuli with a transition between near‐equilibrium states. Although being a key to present‐day advanced materials, these systems respond rather passively, and do not display autonomous dynamics. For autonomous behavior, approaches must be found to orchestrate the time domain of self‐assemblies, which would lead to new generations of dynamic and self‐regulating materials. Herein, we demonstrate catalytic control of the time domain of pH‐responsive peptide hydrogelators in a closed system. We program transient acidic pH states by combining a fast acidic activator with the slow, enzymatic, feedback‐driven generation of a base (dormant deactivator). This transient state can be programmed over orders of magnitude in time. It is coupled to dipeptides to create autonomously self‐regulating, dynamic gels with programmed lifetimes, which are used for fluidic guidance, burst release, and self‐erasing rapid prototyping. 相似文献
46.
Sabyasachi Kar Yu‐Shu Wang Wei‐Qi Li Xiu‐Dong Sun 《International journal of quantum chemistry》2015,115(22):1573-1579
The effect of plasma screening on the dynamic dipole polarizability (DPP) of two‐electron ions Be2+, B3+, and C4+ has been investigated using highly correlated exponential wave functions within the framework of pseudostate summation technique and Debye screening concept. Plasma‐screening effect on the oscillator strengths (OS) of the ultraviolet and visible series has also been investigated for the systems Li+, Be2+, B3+, C4+. The DPP are reported as functions of screening parameters. The OS for S‐P transitions are also reported for various screening parameters. The OS and dynamic polarizability show interesting behavior with increasing screening strength and nuclear charge. © 2015 Wiley Periodicals, Inc. 相似文献
47.
探讨DCE-MRI参数及IFIT1基因对腰椎间盘突出症(LDH)患者椎间盘退变(IDD)程度的评估价值。随机选取确诊的66例LDH患者作为研究对象,根据改良Pfirrmann分级法将患者分为2组:轻中度IDD(Ⅰ~Ⅲ级)组(46例)和重度IDD(Ⅳ~Ⅴ级)组20例。通过DCE-MRI检查考察患者的K-trans值,采用日本骨科学会评分(JOA)评估腰椎功能,采用视觉模拟评分法(VAS)评估腰部疼痛,采用RT-PCR检测外周血单个核细胞(PBMC)中IFIT1的mRNA表达。轻中度IDD组的K-trans值显著低于重度IDD组。轻中度IDD组患者PBMC中的IFIT1 mRNA相对表达量显著低于重度IDD组。K-trans值与PBMC中的IFIT1 mRNA水平和VAS评分正相关,与JOA评分负相关(P<0.05)。PBMC中的IFIT1 mRNA水平与VAS评分正相关,与JOA评分负相关(P<0.05)。K-trans值和PBMC中的IFIT1 mRNA水平联合诊断重度IDD的AUC值、敏感性和特异性分别为0.991、91.3%和100.0%,AUC值和特异性均高于单独诊断。DCE-MRI检查中的K-trans值联合PBMC中的IFIT1 mRNA水平可用于LDH患者IDD程度的诊断。 相似文献
48.
Mattes Holsten Sarah Feierabend Dr. Sven M. Elbert Dr. Frank Rominger Dr. Thomas Oeser Prof. Dr. Michael Mastalerz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9383-9390
One of the most applied reaction types to synthesize shape-persistent organic cage compounds is the imine condensation reaction and it is assumed that the formed cages are thermodynamically controlled products due to the reversibility of the imine condensation. However, most of the synthesized imine cages reported are formed as precipitate from the reaction mixture and therefore rather may be kinetically controlled products. There are even examples in literature, where resulting cages are not soluble at all in common organic solvents to characterize or study their formation by NMR spectroscopy in solution. Here, a triptycene triamine containing three solubilizing n-hexyloxy chains has been used to synthesize soluble congeners of prior insoluble cages. This allowed us to study the formation as well as the reversibility of cage formation in solution by investigating exchange of building blocks between the cages and deuterated derivatives thereof. 相似文献
49.
Donglin He Chengxi Zhao Dr. Linjiang Chen Dr. Marc A. Little Dr. Samantha Y. Chong Rob Clowes Katherine McKie Mark G. Roper Graeme M. Day Dr. Ming Liu Prof. Andrew I. Cooper 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10589-10594
Ethyl acetate is an important chemical raw material and solvent. It is also a key volatile organic compound in the brewing industry and a marker for lung cancer. Materials that are highly selective toward ethyl acetate are needed for its separation and detection. Here, we report a trianglimine macrocycle ( TAMC ) that selectively adsorbs ethyl acetate by forming a solvate. Crystal structure prediction showed this to be the lowest energy solvate structure available. This solvate leaves a metastable, “templated” cavity after solvent removal. Adsorption and breakthrough experiments confirmed that TAMC has adequate adsorption kinetics to separate ethyl acetate from azeotropic mixtures with ethanol, which is a challenging and energy-intensive industrial separation. 相似文献
50.
为了使用单细胞电感耦合等离子体质谱(SC-ICP-MS)方法准确测定单个细胞中的铬(Cr)、锰(Mn)、铁(Fe)、铜(Cu)和锌(Zn)等多种内源性金属元素,该文基于动态反应池(DRC)模式对目标分析物的反应气流量和极杆抑制参数q(RPq)进行了优化,并研究了进样速度、细胞密度、驻留时间等因素对SC-ICP-MS检测的影响。分别采用细胞悬液直接进样、使用超声波探头使细胞悬液中的细胞破碎后进样和使用浓硝酸消解细胞后进样的ICP-MS测定结果对SC-ICP-MS定量结果的准确性进行验证分析。实验结果表明,可采用超声波破碎细胞的ICP-MS测定结果评估SC-ICP-MS测定的单细胞内Zn和Cu含量的准确性,采用酸消解细胞的ICP-MS检测结果验证单细胞内Fe和Cr的含量。缺少细胞标准物质时对SC-ICP-MS方法定量结果进行多角度验证是必要的。研究表明,使用SC-ICP-MS法可以较好地进行单细胞元素相关分析。 相似文献