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41.
42.
Elizabeth Finkelstein Yoav Moriah 《Transactions of the American Mathematical Society》2000,352(2):655-677
In this paper we show that given a knot or link in a -plat projection with and , where is the length of the plat, if the twist coefficients all satisfy then has at least nonisotopic essential meridional planar surfaces. In particular if is a knot then contains closed incompressible surfaces. In this case the closed surfaces remain incompressible after all surgeries except perhaps along a ray of surgery coefficients in .
43.
Jonathan Whitford Manish Shinde Brandon Hunt Sandy Miller Yulia Kostogorova‐Beller 《Journal of Polymer Science.Polymer Physics》2017,55(17):1278-1285
This work reveals influence of electrospinning of polyacrylonitrile–N ,N‐dimethylformamide solution of different concentrations on nanofiber web color parameters, molecular structure, and heat stability. It is found that fiber diameters depend on concentration through the power law relationship; however, the medium concentration‐based web is characterized by a green–yellow hue, representative of the chromophore color; while, the solvent‐rich and solvent‐poor solution‐based webs give rise to Stokes shifts and ultraviolet‐blue emission bands, attributed to fluorescence. The chromophore structure, present in the neat powder, undergoes changes as a result of electrospinning reflected by the enamine‐to‐ketonitrile conversion and the fraction of C?N conjugation. Blue‐shifting of the C?N conjugation is indicative of a reduction of the π‐electron system, which is coincident with the decreased color saturation value but observed only in the nanofibers prepared from the medium concentration solution. A decrease in the glass transition and an increase in cyclization temperatures also support these findings. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1278–1285 相似文献
44.
Nonlinear Dynamics - A nonlinear mathematical model is developed in the time domain to simulate the behaviour of two identical flexibly mounted cylinders in tandem while undergoing vortex-induced... 相似文献
45.
Palladium‐Catalyzed ortho‐Selective CH Deuteration of Arenes: Evidence for Superior Reactivity of Weakly Coordinated Palladacycles 下载免费PDF全文
Dr. Sandy Ma Dr. Giorgio Villa Peter S. Thuy‐Boun Anna Homs Prof. Dr. Jin‐Quan Yu 《Angewandte Chemie (International ed. in English)》2014,53(3):734-737
We disclose a protocol for the palladium‐catalyzed ortho‐selective C? H deuteration of arenes. Phenylacetic acids and benzoic acids are suitable substrates for this reaction. This reaction offers a catalytic route to ortho‐deuterated phenylacetic acids and benzoic acids and demonstrates the sharp difference in reactivity of palladacycle intermediates held together by weak and strong coordination. 相似文献
46.
Selectfluor and NFSI exo‐Glycal Fluorination Strategies Applied to the Enhancement of the Binding Affinity of Galactofuranosyltransferase GlfT2 Inhibitors 下载免费PDF全文
Dr. Lidia Dumitrescu Dr. Guillaume Eppe Abdellatif Tikad Dr. Weidong Pan Sandy El Bkassiny Sudagar S. Gurcha Dr. Ana Ardá Prof. Jesús Jiménez‐Barbero Prof. Gurdyal S. Besra Prof. Stéphane P. Vincent 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):15208-15215
Two complementary methods for the synthesis of fluorinated exo‐glycals have been developed, for which previously no general reaction had been available. First, a Selectfluor‐mediated fluorination was optimized after detailed analysis of all the reaction parameters. A dramatic effect of molecular sieves on the course of the reaction was observed. The reaction was generalized with a set of biologically relevant furanosides and pyranosides. A second direct approach involving carbanionic chemistry and the use of N‐fluorobenzenesulfonimide (NFSI) was performed and this method gave better diastereoselectivities. Assignment of the Z/E configuration of all the fluorinated exo‐glycals was achieved based on the results of HOESY experiments. Furthermore, fluorinated exo‐glycal analogues of UDP‐galactofuranose were prepared and assayed against GlfT2, which is a key enzyme involved in the cell‐wall biosynthesis of major pathogens. The fluorinated exo‐glycals proved to be potent inhibitors as compared with a series of C‐glycosidic analogues of UDP‐Galf, thus demonstrating the double beneficial effect of the exocyclic enol ether functionality and the fluorine atom. 相似文献
47.
Three elementary proofs of the positive definiteness of the A-numerical radius, as defined by Goldberg and Straus, are given and a stronger result concerning exterior powers is conjectured 相似文献
48.
A concise asymmetric synthesis of (-)-halenaquinone is described. The synthesis features a diastereoselective Heck cyclization to set a quaternary center as well as a novel intramolecular inverse-electron-demand Diels-Alder reaction involving a vinyl quinone. The synthesis is highly convergent and features a minimal amount of protecting group manipulations. 相似文献
49.
Dr. Eleonora Grandi Dr. Fatma Feyza Özgen Dr. Sandy Schmidt Prof. Gerrit J. Poelarends 《Angewandte Chemie (International ed. in English)》2023,62(48):e202309012
Biocatalytic cascades are a powerful tool for building complex molecules containing oxygen and nitrogen functionalities. Moreover, the combination of multiple enzymes in one pot offers the possibility to minimize downstream processing and waste production. In this review, we illustrate various recent efforts in the development of multi-step syntheses involving C−O and C−N bond-forming enzymes to produce high value-added compounds, such as pharmaceuticals and polymer precursors. Both in vitro and in vivo examples are discussed, revealing the respective advantages and drawbacks. The use of engineered enzymes to boost the cascades outcome is also addressed and current co-substrate and cofactor recycling strategies are presented, highlighting the importance of atom economy. Finally, tools to overcome current challenges for multi-enzymatic oxy- and amino-functionalization reactions are discussed, including flow systems with immobilized biocatalysts and cascades in confined nanomaterials. 相似文献
50.
Fastner S Predel R Kahnt J Schachtner J Wegener C 《Rapid communications in mass spectrometry : RCM》2007,21(1):23-28
The endocrine system of insects is largely based on peptide hormones. Nevertheless, an unequivocal chemical demonstration of the occurence in the hemolymph (the 'insect blood') is still lacking for most if not all insect peptide hormones, although this is the only way to prove their hormonal status. Focusing on peptides released during ecdysis behavior of the tobacco hornworm Manduca sexta, we developed a purification protocol based on ultrafiltration and a single reversed-phase high-performance liquid chromatography (RP-HPLC) step that for the first time allowed the mass spectrometric and chemical identification of a peptide hormone in the hemolymph of single specimens. Since this method is simple, relatively cheap and fast, it should be useful for routine endocrinological analyses and for monitoring peptide release during different physiological conditions and behaviors in insects. 相似文献