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排序方式: 共有160条查询结果,搜索用时 15 毫秒
21.
A. S. Buller S. V. Leonov N. R. Litvinova R. V. Litvinov 《Journal of Experimental and Theoretical Physics》2020,130(3):387-396
Frequency-degenerate mixing of forward and backward propagating fast modes is considered in a planar optical waveguide based on a thin left-handed film and a right-handed substrate exhibiting the Kerr effect. Nonlinear coupled-mode equations are solved for the intensities of these modes in the neglect of the contributions of elementary processes that fail to satisfy the phase-matching condition. It is shown that the intramode self-action of four TE modes is accompanied by energy exchange between these modes. The efficiency of energy exchange varies periodically along the propagation direction of modes, thus leading to the inversion of the intensities of forward and backward propagating light fields on the interaction half-period. 相似文献
22.
23.
Dyer HE Huijser S Schwarz AD Wang C Duchateau R Mountford P 《Dalton transactions (Cambridge, England : 2003)》2008,(1):32-35
The reaction of Sm{N(SiMe3)2}3 with the bis(phenol)amines H2O2N(R) (H2O2N(R) = RCH2CH2N(2-HO-3,5-C6H2(t)Bu2)2; R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2N(R))(HO2N(R)). For R = OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of epsilon-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me. 相似文献
24.
Jairo Villalona Peyton M. Higgins Prof. Andrew R. Buller 《Angewandte Chemie (International ed. in English)》2023,62(43):e202311189
Non-canonical amino acids (ncAAs) are useful synthons for the development of new medicines, materials, and probes for bioactivity. Recently, enzyme engineering has been leveraged to produce a suite of highly active enzymes for the synthesis of β-substituted amino acids. However, there are few examples of biocatalytic N-substitution reactions to make α,β-diamino acids. In this study, we used directed evolution to engineer the β-subunit of tryptophan synthase, TrpB, for improved activity with diverse amine nucleophiles. Mechanistic analysis shows that high yields are hindered by product re-entry into the catalytic cycle and subsequent decomposition. Additional equivalents of l -serine can inhibit product reentry through kinetic competition, facilitating preparative scale synthesis. We show β-substitution with a dozen aryl amine nucleophiles, including demonstration on a gram scale. These transformations yield an underexplored class of amino acids that can serve as unique building blocks for chemical biology and medicinal chemistry. 相似文献
25.
Saskia Mioduszewski 《The European Physical Journal C - Particles and Fields》2009,61(4):741-745
Results on high-p
T
probes shown at the Hard Probes 2008 Conference are summarized, with an appreciation of the improvements in precision of
the measurements and experimental techniques since the beginning of RHIC operation. Particular attention is given to the latest
measurements of the nuclear modification factor of identified particles, photon-hadron correlation measurements, and full
jet reconstruction. 相似文献
26.
27.
Biesheuvel PM Lindhoud S de Vries R Cohen Stuart MA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(3):1291-1300
We study the phase behavior of mixtures of oppositely charged nanoparticles, both theoretically and experimentally. As an experimental model system we consider mixtures of lysozyme and lysozyme that has been chemically modified in such a way that its charge is nearly equal in magnitude but opposite in sign to that of unmodified lysozyme. We observe reversible macroscopic phase separation that is sensitive not only to protein concentration and ionic strength, but also to temperature. We introduce a heterogeneous Poisson-Boltzmann cell model that generally applies to mixtures of oppositely charged nanoparticles. To account for the phase behavior of our experimental model system, in addition to steric and electrostatic interactions, we need to include a temperature-dependent short-ranged interaction between the lysozyme molecules, the exact origin of which is unknown. The strength and temperature dependence of the short-ranged attraction is found to be of the same order of magnitude as that between unmodified lysozyme molecules. The presence of a rather strong short-ranged attraction in our model system precludes the formation of colloidal liquid phases (or complex coacervates) such as those typically found in mixtures of globular protein molecules and oppositely charged polyelectrolytes. 相似文献
28.
Speed S Vicente R Aravena D Ruiz E Roubeau O Teat SJ El Fallah MS 《Inorganic chemistry》2012,51(12):6842-6850
The syntheses, structural characterization, and magnetic behavior of two new hexanuclear copper(II) complexes derived from R-phosphonic acids and 1,3-bis(dimethylamino)-2-propanol (Hbdmap) with formulas [Cu(6)(μ-bdmap)(3)(μ(3)-Ph-PO(3))(2)(μ(3)-O···H···μ(3)-O)(ClO(4))(2)(H(2)O)]·5H(2)O (1) and [Cu(6)(μ-bdmap)(3)(μ(3)-t-Bu-PO(3))(2)(μ(3)-O···H···μ(3)-O)(μ(1,3)-dca)(dca)(H(2)O)]·6H(2)O (2) (Ph-H(2)PO(3) = phenylphosphonic acid, t-Bu-H(2)PO(3) = tert-butylphosphonic acid, dca = dicyanamide) are reported. Compounds 1 and 2 are hexanuclear 3.111 R-phosphonate(2-)/1,3-bis(dimethylamino)-2-propanolato(1-) cages including in the center the [μ(3)-O···H···μ(3)-O](3-) unit. The temperature dependence of the magnetic properties of 1 and 2 clearly indicates an overall strong antiferromagnetic coupling confirmed by DFT calculations. 相似文献
29.
Moritz Voss Dr. Sumire Honda Malca Prof. Dr. Rebecca Buller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7336-7345
Freestanding Fe/α-ketoglutarate-dependent halogenases are oxidoreductases that catalyze the installation of halogen atoms into unactivated sp3-hybridized carbon centers with high stereo- and regioselectivity. Since their discovery in 2014, a small number of indole alkaloid and amino acid halogenases have been identified and characterized. First enzyme engineering examples suggest that the accessible substrate range of these enzymes may be expanded through the use of rational enzyme design and directed evolution. Structural investigations of non-heme iron halogenases acting on freestanding as well as tethered substrates are beginning to inform about the principles of the underlying halogenation mechanism. 相似文献
30.
ZnSe nonlinear interference filters, configured as optothermal bistable etalons with absorbed transmission (BEAT) devices, have been operated as all-optical switches using 830 nm diode laser illumination and fibre-optic coupling. Stable switching at powers down to 3 mW have been demonstrated for spot diameters of 10 μm. An observed increase in switch power when using large numerical-aperture illumination is analysed in terms of a reduction in effective cavity finesse. 相似文献