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排序方式: 共有1493条查询结果,搜索用时 31 毫秒
1.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
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3.
We report the addition of M–H bonds (M = Al, Zn, Mg) to a Rh(iii) intermediate generated from the reductive elimination of triethylsilane from [Cp*Rh(H)2(SiEt3)2]. A series of new heterobimetallic complexes possessing Rh–M bonds have been isolated and characterised by a number of spectroscopic (1H, 29Si, 13C, 103Rh NMR, infrared, and X-ray diffraction) and computational techniques (NBO and QTAIM analysis). Experimental and computational data are consistent with cleavage of the M–H bond upon addition to rhodium with formation of new Rh–M and Rh–H bonds. Upon photolysis the Al analogue of this series undergoes a further elimination reaction producing triethylsilane and a highly unusual Rh2Al2H4 containing cluster proposed to contain an Al(i) bridging ligand. 相似文献
4.
We construct analytical solutions for a system composed of a reaction–diffusion equation coupled with a purely diffusive equation. The question is to know if the traveling wave solutions of the reaction–diffusion equation can generate a traveling wave for the diffusion equation. Our motivation comes from the calcic wave, generated after fertilization within the egg cell endoplasmic reticulum, and propagating within the egg cell. We consider both the monostable (Fisher–KPP type) and bistable cases. We use a piecewise linear reaction term so as to build explicit solutions, which leads us to compute exponential tails whose exponents are roots of second-, third-, or fourth-order polynomials. These raise conditions on the coefficients for existence of a traveling wave of the diffusion equation. The question of positivity and monotonicity is only partially answered. 相似文献
5.
Protein Labelling with Versatile Phosphorescent Metal Complexes for Live Cell Luminescence Imaging 下载免费PDF全文
Timothy U. Connell Janine. L. James Prof. Anthony R. White Prof. Paul S. Donnelly 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14146-14155
To take advantage of the luminescent properties of d6 transition metal complexes to label proteins, versatile bifunctional ligands were prepared. Ligands that contain a 1,2,3‐triazole heterocycle were synthesised using CuI catalysed azide–alkyne cycloaddition “click” chemistry and were used to form phosphorescent IrIII and RuII complexes. Their emission properties were readily tuned, by changing either the metal ion or the co‐ligands. The complexes were tethered to the metalloprotein transferrin using several conjugation strategies. The IrIII/RuII–protein conjugates could be visualised in cancer cells using live cell imaging for extended periods without significant photobleaching. These versatile phosphorescent protein‐labelling agents could be widely applied to other proteins and biomolecules and are useful alternatives to conventional organic fluorophores for several applications. 相似文献
6.
Gaseous flow measurements in an internal combustion engine assembly using molecular tagging velocimetry 总被引:1,自引:0,他引:1
A molecular tagging velocimetry (MTV) system was applied for mapping in-cylinder flows in an internal combustion engine. The images were captured inside an optical engine assembly that reproduces operation of a 2.2 L four stroke gasoline engine. A recently developed algorithm to process MTV images is based on a fast-normalized spatial correlation approach implemented using MATLAB software. The code allows accurate detection of the MTV grid nodes displacements. It processes simultaneously velocity vector and circulation fields for individual cycles, and ensemble averages of those over a few hundred sequential cycles to obtain mean and standard deviation values. Then probability density functions are reconstructed to quantify cycle-to-cycle variability of the in-cylinder flow. 相似文献
7.
Harold E. Gascoigne 《Experimental Mechanics》1987,27(3):282-289
A new, room-temperature formulated, epoxy-resin system with superior stress-freezing photoelastic properties is presented.
The ease of producing relatively large, high-quality, precision castings is discussed. Stress-optical, rheological, and mechanical
properties are given.
Cylindrical tubes joined by integrally cast Stub Acme and American Standard rolled thread profiles with typical geometric
parameters are loaded in tension and analyzed using the stressfreezing method. Results are presented for surface axial stress
distributions for the wall surfaces opposite the threaded profiles. Additionally, the fillet stress distribution for the first
engaged thread as a function of the distance along the thread helix from the location of initial contact is presented. Comparison
with a finite-element analysis is given.
Paper was presented at the 1983 SEM Spring Conference on Experimental Mechanics held in Cleveland, OH on May 15–19. 相似文献
8.
We consider context-free grammars of the form G = {f → fb1+b2+1ga1+a2, g → fb1 ga1+1},where ai and bi are integers sub ject to certain positivity conditions. Such a grammar G gives rise to triangular arrays {T(n, k)}0≤k≤n satisfying a three-term recurrence relation. Many combinatorial sequences can be generated in this way. Let Tn (x) =∑nk=0T(n, k)xk. Based on the differential operator with respect to G, we define a sequence of linear operators Pn such that Tn+1(x) = Pn(Tn(x)). Applying the characterization of real stability preserving linear operators on the multivariate polynomials due to Borcea and Br?ndén, we obtain a necessary and sufficient condition for the operator Pn to be real stability preserving for any n. As a consequence, we are led to a sufficient condition for the real-rootedness of the polynomials defined by certain triangular arrays, obtained by Wang and Yeh.Moreover, as special cases we obtain grammars that lead to identities involving the Whitney numbers and the Bessel numbers. 相似文献
9.
S. Kneip B.I. Cho D.R. Symes H.A. Sumeruk G. Dyer I.V. Churina A.V. Belolipetski A. Henig O. Wehrhan E. Frster T.D. Donnelly T. Ditmire 《High Energy Density Physics》2008,4(1-2):41-48
K-shell spectra of targets with microstructured features irradiated by an intense femtosecond laser have been studied. Examination of Kα emission from laser irradiated Si targets coated with micron-scale polystyrene spheres indicates that the emission is enhanced by a factor of 3 over emission from planar solids. Sphere-coated targets also emit K-shell He-like Si radiation indicating the presence of a hot dense plasma beneath the microspheres. Furthermore, Kα from Ti foils coupled to micro-tipped reentrant pyramid and wedge shaped targets has been studied, however, no significant enhancement of the Kα yield is observed for these kinds of targets. These studies illustrate that, with correct tailoring of the target surface, field enhancements can be used to increase X-ray emission from intensely irradiated targets. 相似文献
10.