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141.
Sklute G Amsallem D Shabli A Varghese JP Marek I 《Journal of the American Chemical Society》2003,125(39):11776-11777
The one-pot preparation of chiral homoallylic alcohol and amine derivatives was easily achieved by carbocupration of alkynyl sulfoxides followed by an in situ zinc homologation and reaction with aldehydes or imines. In this process, three new carbon-carbon bonds were created as well as quaternary and tertiary chiral centers with excellent diastereo- and enantioselectivities. 相似文献
142.
Cross-linking and cross-bridging are highly versatile methods of creating composite protein structures with desired mechanical properties such as deformation endurance, elasticity, extensibility, and stability under intensive and repetitive sheering forces. Cross-linking and cross-bridging are distinguished by the bonds that hold the structural components together. Cross-linking implies a covalent association, whereas cross-bridging depends on biological recognition, in which hydrogen bonding, ionic, and hydrophobic interactions predominate. Cross-bridged structures are found in all living systems. Cytoskeletal interaction, cell invasion by pathogens, fertilization, and cellulosomal degradation of cellulose are all examples of biological processes in which cross-bridging proteins play a key role. This article will review the different types of biological cross-bridging proteins that are known and discuss their emerging nano- and biotechnological applications. 相似文献
143.
[reaction: see text] A new tandem reaction was developed for the carbocyclization reaction of propargylic zinc reagents. First, we have shown that zinc salt promotes the Brook rearrangement into the carbanionic species followed by a stereospecific Zn-ene-allene carbocyclization reaction to lead to the corresponding cyclopentylmethylzinc derivatives. A single diastereoisomer is formed, even when a tertiary and a quaternary center are linked in the process. 相似文献
144.
The allylmetalation of functionalised cyclopropenyllithium derivatives leads to the unique formation of 1,1-bismetalated cyclopropyl species that react selectively with different electrophiles. 相似文献
145.
Zhi‐Qi Zhang Meng‐Meng Zheng Xiao‐Song Xue Ilan Marek Fa‐Guang Zhang Jun‐An Ma 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(50):18359-18364
Herein we described an efficient RhII‐catalyzed enantioselective cyclopropenation reaction of internal alkynes with a masked difluorodiazoethane reagent (PhSO2CF2CHN2, Ps‐DFA). This asymmetric transformation offers efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes (40 examples, up to 99 % yield, 97 % ee). The synthetic utility of obtained strained carbocycles is demonstrated by subsequent stereodefined processes, including cross‐couplings, hydrogenation, Diels–Alder reaction, and Pauson–Khand reaction. 相似文献
146.
147.
Ilan Newman Yuri Rabinovich Deepak Rajendraprasad Christian Sohler 《Random Structures and Algorithms》2019,55(2):402-426
A sequence contains a pattern , that is, a permutations of [k], iff there are indices i1 < … < ik, such that f(ix) > f(iy) whenever π(x) > π(y). Otherwise, f is π‐free. We study the property testing problem of distinguishing, for a fixed π, between π‐free sequences and the sequences which differ from any π‐free sequence in more than ? n places. Our main findings are as follows: (1) For monotone patterns, that is, π = (k,k ? 1,…,1) and π = (1,2,…,k), there exists a nonadaptive one‐sided error ?‐test of query complexity. For any other π, any nonadaptive one‐sided error test requires queries. The latter lower‐bound is tight for π = (1,3,2). For specific it can be strengthened to Ω(n1 ? 2/(k + 1)). The general case upper‐bound is O(??1/kn1 ? 1/k). (2) For adaptive testing the situation is quite different. In particular, for any there exists an adaptive ?‐tester of query complexity. 相似文献
148.
Guillermo Salceda-Delgado Alejandro Martinez-Rios Boaz Ilan David Monzon-Hernandez 《Optical and Quantum Electronics》2012,44(14):657-671
The Raman response function and Raman nonlinear index of phosphosilicate fibers are calculated for several P2O5 concentrations. The nonlinear index of phosphosilicate fiber is estimated by using the Boling formula, and it is used to calculate the Raman fraction of the nonlinear index. On the other hand, the Raman response function of the phosphosilicate fibers is fitted to a superposition of six phase-shifted under-damped functions in order to use it in the numerical simulation of ultra-short pulse propagation. We show through numerical simulations that phosphosilicate fibers are a suitable medium to observe a scaling up of the Raman self-frequency shift when compared to silica fibers. 相似文献
149.
150.
Heli Siman-Tov Alexander Gumennik Har’el Ilan Noa Mazursky Aharon J. Agranat 《Applied Physics A: Materials Science & Processing》2011,102(1):45-48
It is shown that the implantation of protons in electrooptical substrates enables the construction of 3D structures with submicron
features that are both conductive and photoconductive embedded in amorphized regions that possess reduced refractive index.
The conductivity and photoconductivity are attributed to the transformation of the material into a degenerate semiconductor
due to the formation of high concentration of OH− complexes that are created by the bonding of the implanted H+ ions to the O−2 ions of the lattice. It is argued that these results extend significantly the capabilities of integrated photonic circuits
and devices fabricated by Refractive Index Engineering by ion implantations. 相似文献