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991.
Six redox-active cyclophane/crown hybrid molecules (crownophanes) were prepared via cyclization reactions involving N,N′-dimethyl-p-phenylenediamine and tosylated oligoethylene glycols of varying length. These new host molecules differ from other phenylenediamine-containing crown ethers in that the electron-rich π face is designed to be part of the ligating group. Their electrochemical properties were determined by cyclic voltammetry with a correlation found between macrocyclic architecture and ease of oxidation. The affinity of the smaller crownophanes for cations was studied by cyclic voltammetry with the result that these hosts show no electrochemical response to alkali metal cations, but, dependent on macrocycle size, modest selectivity for alkaline earth metal cations. This stands in contrast to previously reported phenylenediamine-containing crown ethers in which the redox centers are linked to guest ions through a macrocyclic amino group. 相似文献
992.
M.H. Dirkse W.K.P. van Loon J.D. Stigter J.W. Post J. Veerman G.P.A. Bot 《Journal of membrane science》2008
The efficiency of chemical reactors can be analysed using the residence time distribution. This research focusses on flat-sheet geometries applied in membrane-based systems. The residence time distribution depends mainly on the 2D velocity field, parallel to the membrane. The velocity average over the transversal direction is calculated using potential flow theory. A combination of real and virtual sources and sinks are used to model the internal inlets and outlets. Furthermore, a novel method is presented to calculate the residence time distribution. By ignoring diffusion and dispersion, every streamline is modelled to have a fixed residence time, which can be calculated with a simple quadrature based on a coordinate transformation. The model predicts the impact of the two-dimensional geometry on the residence time distribution, but it is demonstrated that large zones of nearly stagnant flow have only a limited impact on the residence time distribution. The new model can predict the travelling time from the inlet to each interior location, providing a better tool to analyse spatially distributed chemical reactions. The models agreed highly with pressure measurements (R2 = 0.94–0.98) and they agreed well with tracer experiments for the residence time (R2 = 0.73–0.99). 相似文献
993.
We construct a potential theory for differential forms on compact stratified spaces, and we show that the space of harmonic forms of degree k is isomorphic to the singular cohomology of degree k. This theory applies to any triangulable topological space. 相似文献
994.
A boundary element method for potential flow problem coupled with the dynamics of rigid body was developed to determine numerically the resultant force and moment of force acting on an arbitrarily three-dimensional solid body and its motion in a current of an infinite fluid. An accurate integration method for singular integrands occurring in the boundary integral equations, a computational method for the tangential gradient of a velocity potential on a surface, and a method to properly treat the singularities appearing in the system of the dynamic equations of a rigid body, were proposed to complete the numerical solution of the problem. Several numerical examples were given to show the validity of the method. 相似文献
995.
Yacheng Liu 《Journal of Mathematical Analysis and Applications》2007,331(1):585-607
In this paper we study the initial boundary value problem for fourth order wave equations with nonlinear strain and source terms. First we introduce a family of potential wells and prove the invariance of some sets and vacuum isolating of solutions. Then we obtain a threshold result of global existence and nonexistence. Finally we discuss the global existence of solutions for the problem with critical initial condition I(u0)?0, E(0)=d. So the Esquivel-Avila's results are generalized and improved. 相似文献
996.
Hossein Eshghi Seyed Mohammad Seyedi Reza Sandarooss 《中国化学快报》2007,18(12):1439-1442
The novel macrocyclic dilactams with redox-switched disulfide linkage were synthesized.These compounds were obtained from 2,2'-dithiodibenzoyl chloride in the macrocyclization step by fast addition method in moderate yields. 相似文献
997.
Tomáš Mikysek Ivan Švancara Martin Bartoš Karel Vytřas Pavel Drabina Miloš Sedlák Jiří Klíma Jiří Urban Jiří Ludvík 《Electroanalysis》2007,19(24):2529-2537
Recently designed and synthetized mono‐imidazolinone (I and III) and bisimidazolinone (II and IV) chelating ligands were electrochemically characterized at mercury and carbon paste electrodes. Based on polarographic, voltammetric and coulometric investigations in buffered aqueous media, the general reduction pathway has been suggested. Reduction of the mono‐imidazolinone derivatives proceeds in acidic and neutral media in two two‐electron steps. In the first step, the 2,3‐C?N double bond of the imidazolone ring is reduced yielding a mixture of two diastereoisomers (V and VI). In the second step, the 2,3‐C? N single bond (in protonated form) is further reductively split and as the only final product the compound VII was formed. Both intermediates (V and VI) as well as the final product (VII) were prepared using controlled potential electrolysis on the first and second wave, respectively, isolated and identified by means of NMR. The reduction of bis‐derivatives proceeds most probably in an analogical way: in the first step, both imidazoles are reduced simultaneously at the same potential, whereas the following reduction (ring‐opening) proceeds stepwise. In the case of compound III, the covalent hydration of the parent compound takes place in acidic media, partially preventing its reduction. Finally, voltammetric behaviour of mono‐ and bisimidazolinones at carbon paste electrode is also discussed and, in prospect, possible electroanalytical applications outlined. 相似文献
998.
Giorgia Brancolini Alessandro Venturini Francesco Zerbetto 《Theoretical chemistry accounts》2007,118(1):25-34
The CHARMM force field is used to calculate 36 minima along the potential energy surface of the helix–coil conversion of Ac-A14KG3A14K + 2H+ and to interconnect them through 35 transition states. The energy barriers are used to give the rate constants of interconversion
between the conformers and the relevant kinetic equations are then solved. Fair to good agreement with the data obtained by
drift time spectrometry experiments (D. T. Kaleta, M. F. Jarrold, J. Am. Chem. Soc. 125:7186, 2003) is obtained under a simple
hypothesis of the initial conformer distribution.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
999.
本文报道了以甲基丙烯酸-N,N-甲氨基乙酯(DMAEMA)与过硫酸盐体系以引发的丙烯酰吗啉(AMP)的水溶液聚合,得到下列方程:Rp[K2S2O8]0.46[DMAEMA]0.49[AMP]1.09;Ea=30.21KJ/mol。试用四氯乙烯(TCNE)处理的丙烯酸吗啉聚合物P(AMP)的紫外光谱分析,发现DMAEMA不仅参与引发AMP聚合,而且还进入P(AMP)分子链中。P(AMP)分子量比聚丙烯酰腹P(AAm)的小,而且随AMP(DMAEMA或温度)增加而增加(降低)。P(AMP)及其轻度交联的水凝胶表现出热敏性。 相似文献
1000.
D.U. Matrasulov F.C. Khanna Kh.Yu. Rakhimov Kh.T. Butanov 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):81-86
Doubly heavy baryons, i.e., the baryons containing two heavy quarks are treated in the adiabatic approximation, considering the motion of the light
quark as a relativistic motion. The binding energy and mass spectra of doubly heavy baryons are calculated solving the two-center
Dirac equation the one-centre Schr?dinger equation for Coulomb plus linear potential. The binding energy of the light quark
as a function of the distance between heavy quarks is found.
Received: 16 January 2002 / Accepted: 7 February 2002 相似文献