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991.
Xingguang Li Xu Ma Zhixun Wang Pei‐Nian Liu Liming Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17340-17344
By using biphenyl‐2‐ylphosphines functionalized with a remote tertiary amino group as a ligand, readily available acetylenic amides are directly converted into 2‐aminofurans devoid of any electron‐withdrawing and hence deactivating/stabilizing substituents. These highly electron‐rich furans have rarely been prepared, let alone applied in synthesis, because of their high reactivities and low stabilities associated with the electron‐rich nature of the furan ring. In this work, these reactive furans smoothly undergo either in situ intermolecular Diels–Alder reactions to deliver highly functionalized/substituted aniline products or intramolecular ones to furnish carbazole‐4‐carboxylates in mostly good to excellent yields. This work offers general and expedient access to this class of little studies electron‐rich furans and should lead to exciting opportunities for their applications. 相似文献
992.
Braulio Aranda Sergio A. Moya Andres Vega Gonzalo Valdebenito Sofia Ramirez‐Lopez Pedro Aguirre 《应用有机金属化学》2019,33(4)
Aminocarbonylation of aryl halides, homogeneously catalysed by palladium, is an efficient method that can be employed for obtaining amides for pharmaceutical and synthetic applications. In this work, palladium (II) complexes containing P^N ligands were studied as catalysts in the aminocarbonylation of iodobenzene in the presence of diethylamine. Two types of systems were used: a palladium (II) complex formed in situ; and one prepared prior to the catalytic reaction. In general, the palladium complexes studied achieved high conversions in an average reaction time of less than 2 hr, which is less than that for the standard system (Pd (II)/PPh3) used. The pre‐synthesized complexes were faster than their in situ counterparts, as the latter require an induction time to form the Pd/P^N species. The structure and electronic properties of the ligand P^N can influence both the activity and the selectivity of the reaction, stabilizing the acyl‐palladium intermediates formed in a better manner. 相似文献
993.
A new dicarboxylic acid modified Mg‐Al LDH (DLDH) containing imide groups was prepared and its effects on the thermal and mechanical properties of the new synthesized aliphatic‐aromatic poly (amide‐imide) (PAI) were investigated via preparation of PAI/nanocomposite films by solution casting method. The results of X‐ray diffraction (XRD), field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) showed a uniform dispersion for LDH layers into the PAI matrix. For comparison, the effects of polyacrylic acid‐co‐poly‐2‐acrylamido‐ 2‐methylpropanesulfonic acid (PAMPS‐co‐PAA) modified Mg‐Al LDH (ALDH) on the PAI properties were also studied. The thermogravimetric analysis (TGA) results exhibited that the temperature at 5 mass% loss (T5) increased from 277 °C to 310 °C for nanocomposite containing 2 mass% of DLDH, while T5 for nanocomposite containing 2 mass% of ALDH increased to 320 °C, along with the more enhancement of char residue compared to the neat PAI. According to the tensile test results, with 5 mass% DLDH loading in the PAI matrix, the tensile strength increased from 51.6 to 70.8 MPa along with an increase in Young's modulus. Also the Young's modulus of PAI nanocomposite containing 5 mass% ALDH reduced from 1.95 to 0.81 GPa. 相似文献
994.
A new Schiff base hydrazone (Z)‐2‐(2‐aminothiazol‐4‐yl)‐N′‐(2‐hydroxy‐3‐methoxybenzylidene) acetohydrazide (H2L) and its chelates [VO (HL)2]·5H2O, [Cu (HL)Cl(H2O)]·2H2O and [Fe(L)Cl(H2O)2]·3H2O have been isolated and characterized using different physico‐chemical methods, for example infrared (IR), electron paramagnetic resonance (EPR), thermogravimetric analysis and DTG in the solid state, and 1H‐NMR, 13C‐NMR and UV in solution. Magnetic and UV–visible measurements proposed that the coordination environments are square pyramidal, tetrahedral and octahedral geometries for oxovanadium (IV), Cu (II) and Fe (III), respectively. The ligand acts as mono‐negative NO towards oxovanadium (IV) and Cu (II) ions, and bi‐negative ONO for Fe (III) ion. The geometries of the ligand and its complexes were performed using Gaussian 9 program with density functional theory. The EPR spectral data of oxovanadium (IV) and Cu (II) chelates confirmed the mentioned geometries. The molecular modeling was done, and illustrated bond lengths, bond angles, molecular electrostatic potential, Mulliken atomic charges and chemical reactivity for the inspected compounds. Theoretical IR and 1H‐NMR of the free ligand were calculated. Furthermore, thermodynamic and kinetic parameters for thermal decomposition steps were studied. Docking study of H2L was applied against the proteins of both bacterial strains Staphylococcus aureus and Escherichia coli, as well as the protein of xanthine oxidase as antioxidant agent by Schrödinger suite program utilizing XP glide protocol. Furthermore, antimicrobial, antioxidant and DNA‐binding activities of the compounds have been carried out. 相似文献
995.
Marwa Chaabene Soumaya Agren Abdul‐Rahman Allouche Mohamed Lahcinie Rafik Ben Chabane Mohamed Hassen V. Baouab 《应用有机金属化学》2019,33(11)
The novel compounds (E)‐2‐(((4‐hydroxyphenyl)imino)methyl)phenol, Tetraphenyl (hydroxyl) imidazole and their corresponding Boron difluoride complexes were synthesized and characterized by spectroscopic techniques. Density functional theory calculations at B3LYP‐D3/6–311++G (d, p) level of theory were performed for the geometric parameters. The MEP surface studies were used to understand the behavior of molecules in terms of charge transfer and to determine how these molecules interact. We used the GIAO and the B3LYP‐D3 with a 6–311++ G (d, p) basis set to simulate the (1H‐NMR and 19F‐NMR) and the IR spectra, respectively. The corresponding calculated results are in good agreement with the experimental data. The stability of the molecule arising from hyperconjugation interaction and charge delocalization were analyzed using NBO analysis. FMOs revealed the occurrence of charge transfer within the molecule. The complexation using BF3.Et2O was also found to have remarkable effects on the electrochemical properties of the studied molecules, where (b) and (d) present lower chemical stability, higher reactivity and higher polarizability than (a) and (c), respectively. Moreover, the energy gap of (a) and (c) decreased after complexation using BF3.Et2O, indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. These values are the factors explaining the possible charge transfer interaction within the molecule. The absorption and emission spectra of the model compound were also simulated and compared to experimental observations in the DMF solvent. The results of DFT calculations supported the structural and spectroscopic data and confirmed the structure modification of frontier molecular orbitals for BF2 complexes as well as tunable potentials and energy levels. 相似文献
996.
997.
Xue‐qin Zhao Sheng Guo Hui Yan You‐yuan Lu Fang Zhang Da‐wei Qian Han‐qing Wang Jin‐ao Duan 《Biomedical chromatography : BMC》2019,33(8)
The leaves of Lycium barbarum (LLB) have been utilized as crude drugs and functional tea for human health in China and Southeast Asia for thousands of years. To control its quality, a rapid and sensitive ultra‐high‐performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry method was established and validated for the first time for simultaneous determination of 10 phenolic acids and flavonoids (including neochlorogenic acid , protocatechuic aldehyde, p‐hydroxybenzoic acid, chlorogenic acid, cryptochlorogenic acid, caffeic acid, p‐coumaric acid, ferulic acid, rutin and kaempferol‐3‐O‐rutinoside) in LLB. The separation was performed on an Acquity UPLC C18 chromatographic column (100 × 2.1 mm internal diameter, 1.7 μm particle size) with 0.1% formic acid in water (A)–acetonitrile (B) as the mobile phase under gradient elution. Multiple reaction monitoring mode was adopted to simultaneously monitor the target components. The developed method was fully validated in terms of linearity (r2 ≥ 0.9860), precision (RSD ≤ 6.58%), repeatability (RSD ≤ 6.60%), stability (RSD ≤ 6.17%), recovery (95.56–108.06%, RSD ≤ 4.64%) and limit of detection (0.021–0.664 ng/mL) and limit of quantitation (0.069–2.210 ng/mL), and then successfully applied to evaluate the quality of 64 batches of LLB collected from 41 producing areas in four different provinces of China. The results showed that the LLB, especially collected from Inner Mongolia regions, were rich in the phenolic acids and flavonoids. Rutin, kaempferol‐3‐O‐rutinoside and chlorogenic acid are the predominant compounds contained in LLB. The above findings will provide helpful information for the effective utilization of LLB. 相似文献
998.
Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO3 (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d33 can be increased up to 324 pC N?1 even from a considerably high value (190 pC N?1) by means of a re‐poling treatment after room‐temperature aging. Such a high d33 value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics. 相似文献
999.
For an adaptive cruise control (ACC) stop‐and‐go system in automotive applications, three radar sensors are needed because two 24 GHz short range radars are used for object detection in an adjacent lane, and one 77 GHz long‐range radar is used for object detection in the center lane. In this letter, we propose a single sensor‐based 24 GHz radar with a detection capability of up to 150 m and ±30° for an ACC stop‐and‐go system. The developed radar is highly integrated with a high gain patch antenna, four channel receivers with GaAs RF ICs, and back‐end processing board with subspace based digital beam forming algorithm. 相似文献
1000.
Kah-Wee Ang Chih-Hang Tung Balasubramanian N. Samudra G.S. Yee-Chia Yeo 《Electron Device Letters, IEEE》2007,28(7):609-612
We report the demonstration of 55 nm gate length strained n-channel field-effect transistors (n-FETs) having an embedded Si1-xGex structure that is beneath the Si channel region and which acts as a strain-transfer structure (STS). The Si1-xGex STS has lattice interactions with both the silicon source and drain regions and with the overlying Si channel region. This effectively results in a transfer of lateral tensile strain to the Si channel region for electron mobility enhancement. The mechanism of strain transfer is explained. Significant drive current Ion enhancement of 18% at a fixed off-state leakage Ioff of 100 nA/mum is achieved, which is attributed to the strain-induced mobility enhancement. Furthermore, continuous downsizing of transistors leads to higher Ion enhancement in the strained n-FETs, which is consistent with the increasing transconductance Gm improvement when the gate length is reduced. 相似文献