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111.
Robert W. Hay Mansour M. Hassan David E. Fenton Brian P. Murphy 《Transition Metal Chemistry》1994,19(5):559-560
Summary The kinetics of the acid dissociation of the copper(II) complex of the 15-membered N3O2 donor macrocycle [prepared by reaction of 2,6-bis(2-aminophenoxymethyl)-pyridine with glyoxal in the presence of a manganese(II) template followed by reduction of the two imine linkages with NaBH4] was studied over an acidity range (0.01–0.5 mol dm-3 [H+]) at 25 °C and I = 1.0 mol dm-3 by stopped-flow methods. A biphasic reaction was observed at 752 nm, the first reaction being complete within 20 ms at 25 °C and too rapid to study in detail. The second reaction shows a good first order dependence on the hydrogen ion concentration over the whole acidity range and k
obs=k0+k
H[H+], where k
0 = 0.52 s-1 and k
H = 40.2 dm3 mol-1 s-1 at 25 °C. The k
0 term represents a small but significant solvolytic reaction. The mechanism of the acid-catalysed dissociation is discussed. 相似文献
112.
Carl B. Ziegler Daniel B. Moran Thomas J. Fenton Yang-I. Lin 《Journal of heterocyclic chemistry》1990,27(3):587-589
A one-pot synthesis of ethyl 8,9-difluoro-6-oxo-6H-benzo[c]quinolizine-5-carboxylate 11 has been developed. The condensation of ethyl 2-pyridylacetate and 2,4,5-trifluorobenzoyl chloride followed by intramolecular nucleophilic aromatic substitution gave the desired ring system. This intermediate was converted to the title compound and its in vitro biological activity is reported. 相似文献
113.
The first structurally characterized Cr(V) dioxo complex, cis-[CrV(O)2(phen)2](BF4) (2, phen=1,10-phenanthroline) has been synthesized by the oxidation of a related Cr(III) complex, cis-[Cr(III)(phen)2(OH2)2](NO3)3.2.5H2O (1, characterized by X-ray crystallography), with NaOCl in aqueous solutions in the presence of excess NaBF4, and its purity has been confirmed by electrospray mass spectrometry (ESMS), EPR spectroscopy, and analytical techniques. Previously reported methods for the generation of Cr(V)-phen complexes, such as the oxidation of 1 with PbO2 or PhIO, have been shown by ESMS to lead to mixtures of Cr(III), Cr(V), Cr(VI), and in some cases Cr(IV) species, 3. Species 3 was assigned as [CrIV(O)(OH)(phen)2]+, based on ESMS and X-ray absorption spectroscopy measurements. A distorted octahedral structure for 2 (CrO, 1.63 A; Cr-N, 2.04 and 2.16 A) was established by multiple-scattering (MS) modeling of XAFS spectra (solid, 10 K). The validity of the model was verified by a good agreement between the results of MS XAFS fitting and X-ray crystallography for 1 (distorted octahedron; Cr-O, 1.95 A; Cr-N, 2.06 A). Unlike for the well-studied Cr(V) 2-hydroxycarboxylato complexes, 2 was equally or more stable in aqueous media (hours at pH=1-13 and 25 degrees C) compared with polar aprotic solvents. A stable Cr(III)-Cr(VI) dimer, [Cr(III)(Cr(VI)O4)(phen)2]+ (detected by ESMS), is formed during the decomposition of 2 in nonaqueous media. Comparative studies of the oxidation of 1 by NaOCl or PbO2 have shown that [Cr(V)(O)2(phen)2]+ was the active species responsible for the previously reported oxidative DNA damage, bacterial mutagenicity, and increased incidence of micronuclei in mammalian cells, caused by the oxidation products of 1 with PbO2. Efficient oxidation of 1 to a genotoxic species, [Cr(V)(O)2(phen)2]+, in neutral aqueous media by a biological oxidant, hypochlorite, supports the hypothesis on a significant role of reoxidation of Cr(III) complexes, formed during the intracellular reduction of Cr(VI), in Cr(VI)-induced carcinogenicity. Similar oxidation reactions may contribute to the reported adverse effects of a popular nutritional supplement, Cr(III) picolinate. 相似文献
114.
115.
Philip J. Thomas Jon C. Fenton Guang Yang Colin E. Gough 《Physica B: Condensed Matter》2000,280(1-4):245-246
We present measurements of the intrinsic quasi-particle conductivity along the c-axis of 2212-BSCCO single-crystal mesa structures in the superconducting and normal states. Direct measurement of the mesa temperature enables corrections to be made for self-heating and permits the acquisition of reliable I–V characteristics over a wide range of temperatures and voltages. Unlike a conventional superconductor, there is no evidence for any change in the quasi-particle conductivity at Tc, consistent with precursor pairing of electrons in the normal state. At low temperatures the initial low-voltage linear conductivity exhibits a T2 dependence, approaching a limiting value at zero temperature. 相似文献
116.
Jumpol Paiboon D.V. Griffiths Jinsong Huang Gordon A. Fenton 《International Journal of Solids and Structures》2013,50(20-21):3233-3241
The purpose of the study is to investigate the influence of porosity and void size on effective elastic geotechnical engineering properties with a 3D model of random fields and finite element. The random field theory is used to generate models of geomaterials containing spatially random voids with controlled porosity and void size. A “tied freedom” analysis is developed to evaluate the effective Young’s modulus and Poisson’s ratio in an ideal block material of finite elements. To deliver a mean and standard deviation of the elastic parameters, this approach uses Monte-Carlo simulations and finite elements, where each simulation leads to an effective value of the property under investigation. The results are extended to investigate an influence of representative volume element (RVE). A comparison of the effective elastic stiffness of 2D and 3D models is also discussed. 相似文献
117.
It has become widely accepted that the most dangerous cardiac arrhythmias are due to reentrant waves, i.e., electrical wave(s) that recirculate repeatedly throughout the tissue at a higher frequency than the waves produced by the heart's natural pacemaker (sinoatrial node). However, the complicated structure of cardiac tissue, as well as the complex ionic currents in the cell, have made it extremely difficult to pinpoint the detailed dynamics of these life-threatening reentrant arrhythmias. A simplified ionic model of the cardiac action potential (AP), which can be fitted to a wide variety of experimentally and numerically obtained mesoscopic characteristics of cardiac tissue such as AP shape and restitution of AP duration and conduction velocity, is used to explain many different mechanisms of spiral wave breakup which in principle can occur in cardiac tissue. Some, but not all, of these mechanisms have been observed before using other models; therefore, the purpose of this paper is to demonstrate them using just one framework model and to explain the different parameter regimes or physiological properties necessary for each mechanism (such as high or low excitability, corresponding to normal or ischemic tissue, spiral tip trajectory types, and tissue structures such as rotational anisotropy and periodic boundary conditions). Each mechanism is compared with data from other ionic models or experiments to illustrate that they are not model-specific phenomena. Movies showing all the breakup mechanisms are available at http://arrhythmia.hofstra.edu/breakup and at ftp://ftp.aip.org/epaps/chaos/E-CHAOEH-12-039203/ INDEX.html. The fact that many different breakup mechanisms exist has important implications for antiarrhythmic drug design and for comparisons of fibrillation experiments using different species, electromechanical uncoupling drugs, and initiation protocols. (c) 2002 American Institute of Physics. 相似文献
118.
A diagnostic ultrasound method is being developed for measuring surface contact areas at the tibio–femoral interface of a total knee replacement in a non-clinical industrial setting as an engineering design tool. As an initial step towards this, a previous study mathematically predicted the effect of ultrasound beam thickness on contact area measurements at a two-body interface. In the current study, a novel metal-on-polymer acoustic test object was constructed to create circular two-body interfaces of known geometry. The object was ultrasonically imaged, contact areas measured, and the results compared with the theoretical model previously developed. 相似文献
119.
Two-dimensional polyacrylamide gel electrophoresis is a valuable tool for studying genetic variation in the human malaria parasite, Plasmodium falciparum. It involves examining the position of protein spots in gel produced from different isolates. Some spots have been seen to vary, while others have had a constant position in all isolates so far examined. These invariant spots provide a reference frame to compare variations in other spots. This paper discusses the usefulness of digital image handling, warping and superimposition in a personal computer environment. Rather than produce a fully automatic interpretation system, we show how the computer may be used as a tool for manipulating gel images, although interpretation of the gels' features remains with the human expert. Autoradiographs are scanned on a desktop scanner, and the images in digital form can be displayed on a monitor attached to a personal computer. The coordinates of the invariant spots on each of several gels are identified by the user. Each of the gels is then warped so that the invariant spots of all the gels coincide as closely as possible. The variable spots are then examined. We have used both affine warping transformations, which match the invariant spots as closely as possible, and thin plate spline transformations, which match them exactly. Colour superimposition proved a useful way of examining the gels. 相似文献
120.