排序方式: 共有278条查询结果,搜索用时 15 毫秒
181.
Unexpected Vulnerability of DPEphos to C−O Activation in the Presence of Nucleophilic Metal Hydrides
Dr. Mateusz K. Cybulski Dr. Nicholas A. Beattie Prof. Stuart A. Macgregor Dr. Mary F. Mahon Prof. Michael K. Whittlesey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11141-11145
C−O bond activation of DPEphos occurs upon mild heating in the presence of [Ru(NHC)2(PPh3)2H2] (NHC=N-heterocyclic carbene) to form phosphinophenolate products. When NHC=IEt2Me2, C−O activation is accompanied by C−N activation of an NHC ligand to yield a coordinated N-phosphino-functionalised carbene. DFT calculations define a nucleophilic mechanism in which a hydride ligand attacks the aryl carbon of the DPEphos C−O bond. This is promoted by the strongly donating NHC ligands which render a trans dihydride intermediate featuring highly nucleophilic hydride ligands accessible. C−O bond activation also occurs upon heating cis-[Ru(DPEphos)2H2]. DFT calculations suggest this reaction is promoted by the steric encumbrance associated with two bulky DPEphos ligands. Our observations that facile degradation of the DPEphos ligand via C−O bond activation is possible under relatively mild reaction conditions has potential ramifications for the use of this ligand in high-temperature catalysis. 相似文献
182.
The article reports on utilization of double deposition and stripping steps for increasing sensitivity of Cu(II) determination by anodic stripping voltammetry (ASV) at two lead film working electrodes. A significant preconcentration of copper was achieved thanks to utilization of a simple design of four electrodes system that gives possibility to perform one measurement cycle consisting of two deposition and two stripping steps. Due to the fact that deposition step is doubled, the concentration of Pb(II) needed to lead film electrodes formation was significantly reduced as compared to traditional procedures using three electrodes system. The analytical procedure of Cu(II) determination was optimized. The experimental factors: supporting electrolyte's pH and its concentration, lead ions concentration, potential and time of deposition at both working electrodes were studied. The Cu(II) peak current was linearly dependent on its concentration from 5×10?10 to 2×10?8 mol L?1 (deposition time of 270 and 160 s at the first and the second working electrode, respectively). The obtained detection limit for copper ions determination was 2.1×10?10 mol L?1. The described procedure was validated by analysis of two water certified reference materials. The described procedure was also utilized for real water sample analysis. 相似文献
183.
We have demonstrated the possibility of efficient distributed water ingress sensing by making use of LPGs nanocoated with diamond-like carbon (DLC). Two long-period gratings (LPGs) with different coating thicknesses were tested. A portion of each LPG was soaked and the responses were measured by tracking both the center-wavelength shift and the LPG resonance minimum depth and by simulating a two-detector sensing arrangement in combination with a diffraction grating. The responses exhibit large linear sections and thus allow for a simple distributed sensing over the grating length. 相似文献
184.
M. Fernando Bravo Dr. Kalanidhi Palanichamy Milan A. Shlain Frank Schiro Yasir Naeem Prof. Dr. Mateusz Marianski Prof. Dr. Adam B. Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(51):11782-11795
Synthetic carbohydrate receptors (SCRs) that selectively recognize cell-surface glycans could be used for detection, drug delivery, or as therapeutics. Here we report the synthesis of seven new C2h symmetric tetrapodal SCRs. The structures of these SCRs possess a conserved biaryl core, and they vary in the four heterocyclic binding groups that are linked to the biaryl core via secondary amines. Supramolecular association between these SCRs and five biologically relevant C1-O-octyloxy glycans, α/β-glucoside ( α/β-Glc ), α/β-mannoside ( α/β-Man ), and β-galactoside ( β-Gal ), was studied by mass spectrometry, 1H NMR titrations, and molecular modeling. These studies revealed that selectivity can be achieved in these tetrapodal SCRs by varying the heterocyclic binding group. We found that SCR017 (3-pyrrole), SCR021 (3-pyridine), and SCR022 (2-phenol) bind only to β-Glc. SCR019 (3-indole) binds only to β-Man. SCR020 (2-pyridine) binds β-Man and α-Man with a preference to the latter. SCR018 (2-indole) binds α-Man and β-Gal with a preference to the former. The glycan guests bound within their SCR hosts in one of three supramolecular geometries: center-parallel, center-perpendicular, and off-center. Many host–guest combinations formed higher stoichiometry complexes, 2:1 glycan⋅SCR or 1:2 glycan⋅SCR , where the former are driven by positive allosteric cooperativity induced by glycan–glycan contacts. 相似文献
185.
Mateusz Płoskoń 《Acta Physica Hungarica A》2006,27(2-3):255-258
The study of two-particle azimuthal correlations at high transverse momentum has become an important tool to investigate the interaction of hard partons with the medium formed in high-energy nucleus-nucleus collisions. At SPS energies, pioneering studies by the CERES Collaboration [1] indicated a significant modification of the away-side structure in central collisions. Here we present new results emerging from the analysis of the year 2000 data set recorded with the CERES Time-Projection Chamber, which provides excellent tracking efficiency and significantly improved momentum determination. 相似文献
186.
Atienza-Castellanos C Wielopolski M Guldi DM van der Pol C Bryce MR Filippone S Martín N 《Chemical communications (Cambridge, England)》2007,(48):5164-5166
Fluorene-based bridges exhibit a molecular wire-like behaviour in C(60)-wire-exTTF systems with a very low attenuation factor (beta = 0.09 A(-1)). 相似文献
187.
Accelerating Diffusion‐Ordered NMR Spectroscopy by Joint Sparse Sampling of Diffusion and Time Dimensions 下载免费PDF全文
Mateusz Urbańczyk Prof. Dr. Wiktor Koźmiński Dr. Krzysztof Kazimierczuk 《Angewandte Chemie (International ed. in English)》2014,53(25):6464-6467
Diffusion‐ordered multidimensional NMR spectroscopy is a valuable technique for the analysis of complex chemical mixtures. However, this method is very time‐consuming because of the costly sampling of a multidimensional signal. Various sparse sampling techniques have been proposed to accelerate such measurements, but they have always been limited to frequency dimensions of NMR spectra. It is now revealed how sparse sampling can be extended to diffusion dimensions. 相似文献
188.
Heteroaromatic Belts through Fold‐in Synthesis: Mechanistic Insights into a Macrocycle‐Templated Friedel–Crafts Alkylation 下载免费PDF全文
Mateusz Kondratowicz Damian Myśliwiec Prof. Tadeusz Lis Dr. Marcin Stępień 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):14981-14985
Direct alkylation of 9,9′,9′′‐triethyl[2.2.2](2,7)carbazolophane with dimethoxymethane or paraformaldehyde affords a belt‐like heteroaromatic structure, which forms as a kinetic product in acid‐catalyzed condensations. In a competing, thermodynamically favored process, polymeric structures are formed by a largely regioselective condensation of stereochemically rigid “semi‐belts”. The relationship between these reactivity routes is rationalized in terms of strain release and differential reversibility of consecutive condensation steps. 相似文献
189.
190.
Krzysztof Durka Agnieszka Górska Piotr Jankowski Tomasz Kliś Marcin Kublicki Janusz Serwatowski Mateusz Urban Grzegorz Wesela-Bauman Krzysztof Woźniak 《Tetrahedron letters》2017,58(12):1185-1189
A one-pot protocol was developed for the synthesis of a series of luminescent heteroleptic diaryldiborinic complexes containing the central aryl ring bonded to two boron atoms substituted with pyrazole and complexed with 8-hydroxyquinoline. The luminescent properties of these compounds were measured. In dilute solutions they exhibited an emission at ca. 513 nm with quantum yields of 22–27% which are typical for borinic 8-hydroxyquinoline complexes. The only exception was the complex containing the bithiophene scaffold, for which no fluorescence was observed. The obtained pyrazole-based complexes show improved solubility and thermal stability with respect to their phenyl analogues. The experimental UV–vis absorption and emission data are supported by theoretical calculations of the frontier molecular orbitals, revealing the aromatic linker to quinolinato ligand excitation mechanism. 相似文献