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排序方式: 共有7294条查询结果,搜索用时 46 毫秒
1.
Dr. Felix Pape Lea T. Brechmann Jun.-Prof. Dr. Johannes F. Teichert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):985-988
Copper(I)–N-heterocyclic-carbene (NHC) complexes enabled the catalytic generation of nucleophilic hydrides from dihydrogen (H2) and their subsequent transfer to allylic chlorides. The highly chemoselective catalyst displayed no concomitant hydrogenation reactivity; in fact, the terminal double bond formed in the hydride transfer remained intact. Switching to deuterium gas (D2) allowed for regioselective monodeuteration with excellent isotope incorporation. 相似文献
2.
Nicholas Favalli Gabriele Bassi Tania Zanetti Jrg Scheuermann Dario Neri 《Helvetica chimica acta》2019,102(4)
The construction of DNA‐encoded chemical libraries (DECLs) crucially relies on the availability of chemical reactions, which are DNA‐compatible and which exhibit high conversion rates for a large number of diverse substrates. In this work, we present our optimization and validation procedures for three copper and palladium‐catalyzed reactions (Suzuki cross‐coupling, Sonogashira cross‐coupling, and copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC)), which have been successfully used by our group for the construction of large encoded libraries. 相似文献
3.
Yu Zhang Dr. Novruz G. Akhmedov Prof. Jeffrey L. Petersen Prof. Carsten Milsmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3042-3052
Luminescent seven-coordinated zirconium and hafnium complexes bearing three mono-anionic 2,2′-pyridylpyrrolide ligands and one chloride were synthesized. Solid-state structures and the dynamic behaviors in solution were probed by X-ray crystallography and variable temperature 1H NMR experiments, respectively. Absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations supported a hybrid of ligand-to-metal charge transfer (LMCT)/ligand-to-ligand charge transfer (LLCT) for the visible light absorption band. The complexes (MePMPMe)3MCl (M=Zr, Hf, MePMPMe=3,5-dimethyl-2-(2-pyridyl)pyrrolide) are emissive in solution at room temperature upon irradiation with visible light due to a combination of phosphorescence and fluorescence characterized by excited state lifetimes in the μs and low to sub-ns timescale, respectively. Electrochemical experiments revealed that the zirconium complex possesses a reversible redox event under highly reducing condition (−2.29 V vs. Fc+/0). 相似文献
4.
Luis Gutiérrez-Arzaluz David Ignacio Ramírez-Palma Lillian G. Ramírez-Palma Prof. Dr. José Enrique Barquera-Lozada Prof. Dr. Jorge Peon Prof. Dr. Fernando Cortés-Guzmán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):775-784
Copper(I) complexes (CICs) are of great interest due to their applications as redox mediators and molecular switches. CICs present drastic geometrical change in their excited states, which interferes with their luminescence properties. The photophysical process has been extensively studied by several time-resolved methods to gain an understanding of the dynamics and mechanism of the torsion, which has been explained in terms of a Jahn–Teller effect. Here, we propose an alternative explanation for the photoinduced structural change of CICs, based on electron density redistribution. After photoexcitation of a CIC (S0→S1), a metal-to-ligand charge transfer stabilizes the ligand and destabilizes the metal. A subsequent electron transfer, through an intersystem crossing process, followed by an internal conversion (S1→T2→T1), intensifies the energetic differences between the metal and ligand within the complex. The energy profile of each state is the result of the balance between metal and ligand energy changes. The loss of electrons originates an increase in the attractive potential energy within the copper basin, which is not compensated by the associated reduction of the repulsive atomic potential. To counterbalance the atomic destabilization, the valence shell of the copper center is polarized (defined by ∇2ρ(r) and ∇2Vne(r)) during the deactivation path. This polarization increases the magnitude of the intra-atomic nuclear–electron interactions within the copper atom and provokes the flattening of the structure to obtain the geometry with the maximum interaction between the charge depletions of the metal and the charge concentrations of the ligand. 相似文献
5.
Dev Raj Chopra Justin Seth Pearson Darius Durant Ritesh Bhakta Anil R. Chourasia 《Surface and interface analysis : SIA》2019,51(2):246-253
The Ti/CuO interface has been studied by the techniques of X-ray photoelectron spectroscopy and atomic force microscopy. Thin films of titanium were deposited on a CuO substrate at room temperature by the e-beam technique. The photoelectron spectra of titanium and copper were found to exhibit significant chemical interaction at the interface. The titanium overlayer was observed to get oxidized to TiO2, while the CuO was observed to get reduced to elemental copper. This chemical interaction was observed to occur until a thickness of 7 nm of the titanium overlayer. For thicknesses greater than this value, the presence of unreacted titanium in the sample was detected. Barrier characteristics at the Ti/CuO interface were also carried out for substrate temperatures of 300°C, 400°C, 500°C, and 600°C as a function of the titanium overlayer thickness. A linear trend in the barrier thickness of the overlayer was observed between 400°C and 600°C substrate temperatures. The atomic force microscopy micrographs of the unannealed samples depicted layer-by-layer growth of elemental titanium on copper. At the Ti/CuO interface in such samples, the micrographs exhibited island formation of TiO2 corresponding to the Volmer-Weber growth model. This formation has been interpreted as the relaxation in the strain energy. The percentage coverage of the underlying substrate by the TiO2 islands showed a linear trend for the thicknesses of the titanium overlayer investigated. The average size of these islands also showed a linear trend as a function of the thickness of the overlayer. 相似文献
6.
Kai Cheng Xiao-Shuai Zhang Jie An Cheng Li Ruo-Yun Zhang Run Ye Prof. Dr. Bang-Jiao Ye Prof. Dr. Bo Liu Prof. Dr. Yuan-Di Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(31):7553-7560
Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag2S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag2S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag2S had more opportunities to react with surrounding O2, which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag2S and PDA-Ag2S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag2S showed distinctly better therapeutic effects than Ag2S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag2S quantum dots, which extended and enhanced the regulatory effect originating from PDA. 相似文献
7.
An efficient and practical route to β‐keto sulfones has been developed through heterogeneous oxidative coupling of oxime acetates with sodium sulfinates by using an MCM‐41‐supported Schiff base‐pyridine bidentate copper (II) complex [MCM‐41‐Sb,Py‐Cu (OAc)2] as the catalyst and oxime acetates as an internal oxidant, followed by hydrolysis. The reaction generates a variety of β‐keto sulfones in good to excellent yields. This new heterogeneous copper (II) catalyst can be easily prepared via a simple procedure from readily available and inexpensive reagents and exhibits the same catalytic activity as Cu (OAc)2. MCM‐41‐Sb,Py‐Cu (OAc)2 is also easy to recover and is recyclable up to eight times with almost consistent activity. 相似文献
8.
Tao He Bin Li Li-Chuan Liu Jing Wang Wen-Peng Ma Guang-Yu Li Prof. Dr. Qing-Wei Zhang Prof. Dr. Wei He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):966-970
A copper-catalyzed trifunctionalization of alkynes that provides rapid access to oxindoles bearing a geminal diboronate side chain, highlighted by the simultaneous formation of one C−C bond and two C−B bonds, is reported. This new reaction features simple reaction conditions (ligand-free catalysis), a general substrate scope, and excellent chemoselectivity. Mechanistic study revealed a reaction sequence constituted by, in the order, borylation, intramolecular cross-coupling, hydroboration, which has been rarely documented. 相似文献
9.
Po‐Yu Lin Dai‐Ying Li Feng‐Hsien Ho Jian‐Hong Liao Subrat Kumar Barik C. W. Liu 《中国化学会会志》2019,66(9):988-995
A structural study of ligand exchange on chalcogen‐passivated copper nanoclusters is far less developed. Herein, we report the synthesis of polyhydrido copper nanoclusters [Cu20H11{Se2P(O iBu)2}9] ( 2 ) passivated by Se‐donor ligands via ligand replacement reaction on [Cu20H11{S2P(O iPr)2}9] ( 1 ) with NH4[Se2P(O iBu)2]. In parallel to the synthesis of 2 , cluster [Cu20H11{S2P(CH2CH2Ph)2}9] ( 4 ) was produced by the ligand exchange reaction on a new derivative of 1 , that is [Cu20H11{S2P(O nPr)2}9] ( 3 ). Solid state structures of both clusters 2 and 4 were unequivocally established by single‐crystal X‐ray diffraction studies and cluster 4 epitomizes exceptional case to preserve both the shape and size of the nanocluster during the course of ligand exchange. Structurally precise cluster 2 is the second example where the copper hydride nanocluster is stabilized by Se‐donor ligands. The anatomy of 2 can be visualized as a twisted cuboctahedral Cu13 core, two triangular faces of which are capped by a Cu6 cupola and a single Cu atom along the C3 rotational axis. 相似文献
10.
The aim of this work is the phytochemical study of the butanolic extract of the aerial parts of Veronica rosea. Four compounds 1–4 have been isolated using different chromatographic methods. The structures of these compounds were determined by NMR spectral analysis and mass spectroscopy. The adsorption and anticorrosion effects of this extract were investigated towards the corrosion of copper in 1 M HNO3 aqueous by the weight loss technique and potentiodynamic polarization. The results showed that the butanolic extract is a good inhibitor and the inhibition efficiency increases with increasing of concentration of the inhibitor. The adsorption of this extract on the copper specimen surface was spontaneous and obeyed the Langmuir’s adsorption isotherm. Large value of adsorption equilibrium Constant (K ads = 35 L g?1) was obtained. The polarization experiments confirmed the data obtained by gravimetric weight-loss. Tafel plot of polarization curves indicates that the extract acts as a mixed type inhibitor. 相似文献