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排序方式: 共有93条查询结果,搜索用时 187 毫秒
51.
Darius Vrubliauskas Prof. Christopher D. Vanderwal 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6171-6177
A novel CoII-catalyzed polyene cyclization was developed that is uniquely effective when performed in hexafluoroisopropanol as the solvent. The process is presumably initiated by metal-catalyzed hydrogen-atom transfer (MHAT) to 1,1-disubstituted or monosubstituted alkenes, and the reaction is remarkable for its tolerance of internal alkenes bearing either electron-rich methyl or electron-deficient nitrile substituents. Electron-rich aromatic terminators are required in both cases. Terpenoid scaffolds with different substitution patterns are obtained with excellent diastereoselectivities, and the bioactive C20-oxidized abietane diterpenoid carnosaldehyde was made to showcase the utility of the nitrile-bearing products. Also provided are the results of several mechanistic experiments that suggest the process features an MHAT-induced radical bicyclization with late-stage oxidation to regenerate the aromatic terminator. 相似文献
52.
Understanding of the multiple H-bonding arrays of heterocyclic compounds is essential to design effective building blocks of supramolecular polymers. We have carried out a comprehensive computational study on the thermodynamic stabilities of thirty-six H-bonded complexes with all possible H-bonding arrays in the gas phase and chloroform solvent by using M06-2X, SMD calculations and cc-pVDZ basis set. The multiple H-bonding arrays include donor acceptor–acceptor donor (DA–AD), DD–AA for the doubly H-bonded pairs, and DAD–ADA, DDA–AAD and DDD–AAA for the triply H-bonded pairs. The computational results have provided insights into the geometrical, energetic and solvation effects on the stabilities of these H-bonded complexes. The calculated free energies of association for the DD–AA (8–9) and the DDD–AAA (33–35, 36–35) H-bonded complexes are found to be inconsistent with the experimental measurements and observations that these complexes are the most strongly doubly and triply H-bonded pairs in solution, respectively, while the calculated binding free energies for all other H-bonding arrays are in good agreement with experimental values. The computational protocol can be used by practical chemists and undergraduate researchers as an efficient and state-of-the-art tool to study H-bonding interactions in supramolecular chemistry. 相似文献
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54.
We study the effects of correlated molecular transition energy fluctuations in molecular aggregates on the density matrix dynamics, and their signatures in the optical response. Correlated fluctuations do not affect single-exciton dynamics and can be described as a nonlocal contribution to the spectral broadening, which appears as a multiplicative factor in the time-domain response function. Intraband coherences are damped only by uncorrelated transition energy fluctuations. The signal can then be expressed as a spectral convolution of a local contribution of the uncorrelated fluctuations and the nonlocal contribution of the correlated fluctuations. 相似文献
55.
Mechanisms controlling the sensitivity of amperometric biosensors in flow injection analysis systems
Darius Baronas Feliksas Ivanauskas Romas Baronas 《Journal of mathematical chemistry》2011,49(8):1521-1534
This paper numerically investigates the sensitivity of an amperometric biosensor acting in the flow injection mode when the
biosensor contacts an analyte for a short time. The analytical system is modelled by non-stationary reaction-diffusion equations
containing a non-linear term related to the Michaelis-Menten kinetics of an enzymatic reaction. The mathematical model involves
three regions: the enzyme layer where enzymatic reaction as well as the mass transport by diffusion takes place, a diffusion
limiting region where only the diffusion takes place, and a convective region. The biosensor operation is analysed with a
special emphasis to the conditions at which the biosensor sensitivity can be increased and the calibration curve can be prolonged
by changing the injection duration, the permeability of the external diffusion layer, the thickness of the enzyme layer and
the catalytic activity of the enzyme. The apparent Michaelis constant is used as a main characteristic of the sensitivity
and the calibration curve of the biosensor. The numerical simulation was carried out using the finite difference technique. 相似文献
56.
Darius Dobrovolskas Jūras Mickevi?ius Juozas Miškinis Gintautas Tamulaitis Arturs Medvids Chih-Yen Chen C.C. Yang 《Journal of luminescence》2011,131(7):1322-1326
InGaN epilayers exhibiting strong defect-related sub-bandgap emission, which is undesirable in epilayers and quantum well structures designed for light-emitting diodes and laser diodes, have been studied by confocal photoluminescence spectroscopy, Auger electron spectroscopy, and atomic force microscopy. Inhomogeneous spatial distribution of band-edge luminescence intensity and comparatively homogenous distribution of defect-related emission are demonstrated. It is shown that laser annealing at power densities causing the increase of the temperature at the epilayer surface high enough for indium atoms to move to the surface results in suppression of the defect-related emission. 相似文献
57.
Darius Urbonas Martynas Gabalis Raimondas Petruskevicius 《Optical and Quantum Electronics》2014,46(8):1021-1026
Simulation time is one of the bottlenecks of finite-difference-time-domain (FDTD) method. There are several ways of reducing the simulation time, one of which is the usage of graphical processing unit (GPU). Thus in this paper we present comparison between two free FDTD software packages. One is based on central processing unit and other is based on GPU. The 3D test structures we analyzed were metallic rectangular cavity resonator and microring resonator based refractive index sensor. The comparison between two FDTD software packages is made with regard to simulation time and numerical accuracy. It is shown that both packages agree in numerical results and that GPU based FDTD implementation performs same simulation up to 18 times faster. 相似文献
58.
59.
The computation of derivatives via automatic differentiation is a valuable technique in many science and engineering applications. While the implementation of automatic differentiation via source transformation yields the highest efficiency results, particularly for gradient computations, the implementation via operator overloading remains a viable alternative for some application contexts. Examples include the computation of higher order derivatives or cases where C++ as the language of choice still proves to be too complicated for the currently available source transformation tools. In this paper, we utilize a code generator to create libraries that overload intrinsics for derivative computation, and discuss approaches to improve the efficiency of the generated code. We first discuss the use of limited loop unrolling, but the main focus of the paper is multithreaded derivative computation, in particular an asynchronous scheme for C++ and a synchronous scheme for Fortran. We present test results obtained with a proof-of-concept implementation. 相似文献
60.