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81.
Ben-Ari E Leitus G Shimon LJ Milstein D 《Journal of the American Chemical Society》2006,128(48):15390-15391
Unusual reactions are reported, in which the aromatic PNP ligand (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) acts in concert with the metal in the activation of H2 and benzene, via facile aromatization/dearomatization processes of the ligand. A new, dearomatized electron-rich (PNP*)Ir(I) complex 2 (PNP* = deprotonated PNP) activates benzene to form the aromatic (PNP)Ir(I)Ph 4, which upon treatment with CO undergoes a surprising oxidation process to form (PNP*)Ir(III)(H)CO 6, involving proton migration from the ligand "arm" to the metal, with concomitant dearomatization. 4 undergoes stereoselective activation of H2 to exclusively form the trans-dihydride 7, rather than the expected cis-dihydride complex. Our evidence, including D-labeling, suggests the possibility that the Ir(I)-Ph complex is transformed to the dearomatized Ir(III)(Ph)(H) (independently prepared at low temperature), which may be the actual intermediate undergoing H2 activation. 相似文献
82.
Yuwei Hu Fuan Wang Chun‐Hua Lu Julia Girsh Eyal Golub Prof. Itamar Willner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16203-16209
Mimicking cellular transformations and signal transduction pathways by means of biocatalytic cascades proceeding in organized media is a scientific challenge. We describe two DNA machines that enable the “ON/OFF” switchable activation and deactivation of three‐component biocatalytic cascades. One system consists of a reconfigurable DNA tweezers‐type structure, whereas in the second system the catalytic cascade proceeds on a switchable DNA clamp scaffold. The three‐component catalytic cascades consist of β‐galactosidase (β‐Gal), glucose oxidase (GOx), and the K+‐ion‐stabilized hemin‐G‐quadruplex horseradish peroxidase (HRP)‐mimicking DNAzyme. The hemin‐G‐quadruplex‐bridged closed structure of the tweezers or clamp allows the biocatalytic cascades to operate (switched “ON′′), whereas separation of the hemin‐G‐quadruplex by means of 18‐crown‐6‐ether opens the tweezers/clamp structures, thus blocking the catalytic cascade (switched ”OFF“). This study is complemented by two‐component, switchable biocatalytic cascades composed of GOx and hemin‐G‐quadruplex assembled on hairpin‐bridged DNA tweezers or clamp nanostructures. 相似文献
83.
Cerium(IV) ammonium nitrate (CAN)-catalyzed oxidation of alkyl aromatics with potassium bromate affords aldehydes, ketones acids or alcohols in high yields. 相似文献
84.
Alexander G. Shtukenberg Ran Drori Elena V. Sturm Netta Vidavsky Asaf Haddad Jason Zheng Lara A. Estroff Haim Weissman Sharon G. Wolf Eyal Shimoni Chao Li Noalle Fellah Efi Efrati Bart Kahr 《Angewandte Chemie (International ed. in English)》2020,59(34):14593-14601
The growth of spontaneously twisted crystals is a common but poorly understood phenomenon. An analysis of the formation of twisted crystals of a metastable benzamide polymorph (form II ) crystallizing from highly supersaturated aqueous and ethanol solutions is given here. Benzamide, the first polymorphic molecular crystal reported (1832), would have been the first helicoidal crystal observed had the original authors undertaken an analysis by light microscopy. Polymorphism and twisting frequently concur as they are both associated with high thermodynamic driving forces for crystallization. Optical and electron microscopies as well as electron and powder X‐ray diffraction reveal a complex lamellar structure of benzamide form II needle‐like crystals. The internal stress produced by the overgrowth of lamellae is shown to be able to create a twist moment that is responsible for the observed non‐classical morphologies. 相似文献
85.
Dr. Alexander G. Shtukenberg Prof. Ran Drori Dr. Elena V. Sturm Dr. Netta Vidavsky Asaf Haddad Jason Zheng Prof. Lara A. Estroff Dr. Haim Weissman Dr. Sharon G. Wolf Dr. Eyal Shimoni Chao Li Noalle Fellah Prof. Efi Efrati Prof. Bart Kahr 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14701-14709
The growth of spontaneously twisted crystals is a common but poorly understood phenomenon. An analysis of the formation of twisted crystals of a metastable benzamide polymorph (form II ) crystallizing from highly supersaturated aqueous and ethanol solutions is given here. Benzamide, the first polymorphic molecular crystal reported (1832), would have been the first helicoidal crystal observed had the original authors undertaken an analysis by light microscopy. Polymorphism and twisting frequently concur as they are both associated with high thermodynamic driving forces for crystallization. Optical and electron microscopies as well as electron and powder X-ray diffraction reveal a complex lamellar structure of benzamide form II needle-like crystals. The internal stress produced by the overgrowth of lamellae is shown to be able to create a twist moment that is responsible for the observed non-classical morphologies. 相似文献
86.
Itai Benjamini Simi Haber Michael Krivelevich Eyal Lubetzky 《Random Structures and Algorithms》2008,32(1):101-114
The isoperimetric constant of a graph G on n vertices, i(G), is the minimum of , taken over all nonempty subsets S ⊂ V (G) of size at most n/2, where ∂S denotes the set of edges with precisely one end in S. A random graph process on n vertices, , is a sequence of graphs, where is the edgeless graph on n vertices, and is the result of adding an edge to , uniformly distributed over all the missing edges. The authors show that in almost every graph process equals the minimal degree of as long as the minimal degree is o(log n). Furthermore, it is shown that this result is essentially best possible, by demonstrating that along the period in which the minimum degree is typically Θ(log n), the ratio between the isoperimetric constant and the minimum degree falls from 1 to , its final value. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008 相似文献
87.
We exploit nonlinearity in NbN superconducting stripline resonators, which originates from local thermal instability, for studying stochastic resonance. As the resonators are driven into instability, small amplitude modulation (AM) signals are amplified with the aid of injected white noise. Simulation results based on the equations of motion for the system yield a good agreement with the experimental data both in the frequency and time domains. 相似文献
88.
89.
The degenerate crossing number ${\text{ cr}^{*}}(G)$ of a graph $G$ is the minimum number of crossing points of edges in any drawing of $G$ as a simple topological graph in the plane. This notion was introduced by Pach and Tóth who showed that for a graph $G$ with $n$ vertices and $e \ge 4n$ edges ${\text{ cr}^{*}}(G)=\Omega \big (e^4 / n^4\big )$ . In this paper we completely resolve the main open question about degenerate crossing numbers and show that ${\text{ cr}^{*}}(G)=\Omega \big (e^3 / n^2 \big )$ , provided that $e \ge 4n$ . This bound is best possible (apart for the multiplicative constant) as it matches the tight lower bound for the standard crossing number of a graph. 相似文献
90.
Patrick Martin Gleb Vasilyev Guang Chu Mor Boas Arkadii Arinstein Eyal Zussman 《Journal of Polymer Science.Polymer Physics》2019,57(22):1527-1536
The behavior of a mixture of negatively charged cellulose nanocrystals (CNCs) and positively charged poly(allylamine) (PAAm) is examined in aqueous media. By modulating the pH, the acting Coulomb forces can be varied that can lead not only to adsorption of PAAm chains on the CNC surface but also to the development of a supermolecular structure by bridging of CNC rods by extended PAAm chains. This bridging can result in the formation of CNC clusters, which was demonstrated experimentally. Light scattering and rheological studies showed that these clusters begin to grow and merge, ultimately forming a global percolated network above a critical degree of PAAm ionization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1527–1536 相似文献