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931.
Extensive catalytic waves of Co(II) are observed in N3?/HN3 buffers, in which hydrogen discharge is not the dominant process, but rather HN3 reduction to NH4+ and N2. Cobalt(I) was shown to be the active intermediate of the catalytic process. The rate-determing step was found to be the Co(I) reduction to the metal. Heterogeneous rate constants were calculated and relationships with average ligand number were derived. 相似文献
932.
8‐Hydroxy‐1,3,6‐pyrene trisulfonic acid, trisodium salt (pyranine), readily reacts with peroxyl radicals generated in the aerobic pyrolysis of 2,2′‐azobis(2‐amidinopropane) (AAPH). The process can be followed by monitoring the decrease in pyranine absorbance (460 nm) or fluorescence (excitation: 460 nm; emission: 510 nm). The reaction follows a nearly zero‐order kinetics in pyranine (0.25–30 μM range), suggesting a very efficient trapping of peroxyl radicals. In agreement with this, the process is order one in AAPH. The bleaching process is totally prevented by Trolox (μM range), and partially prevented by Trp (mM range). The protection afforded by Trp is very little dependent upon the pyranine concentration. This result indicates that the main protective pathway is not a competitive scavenging of the peroxyl radicals. The data suggest protection due to repair of the initially produced pyranyl radicals. These radicals are also very efficient in the destruction of C‐phycocyanin bilin groups. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 525–531, 2003 相似文献
933.
Heriberto Espinoza-Gómez Shui Wai Lin Eduardo Rogel-Hernández 《Heat and Mass Transfer》2005,41(6):503-509
This paper present a method to determine pore diameters and effective transport through membranes using a mixture of oligosaccharides. The results are compared with the Maxwell–Stefan equations. The partition coefficients of the solutes are a function of the pore diameter according to the Ferry equation. Thus, with the pore diameter as the only unknown parameter, rejection is described and the pore diameter is obtained by a Marquardt–Levenberg optimization procedure. 相似文献
934.
Eduardo Gallego 《Differential Geometry and its Applications》2005,22(3):315-325
Using results from integral geometry, we find inequalities involving mean curvature integrals of convex hypersurfaces in hyperbolic space. Such inequalities generalize the Minkowski formulas for euclidean convex sets. 相似文献
935.
Francisco Garcia Sanchez Miguel Hernandez Lopez Eduardo de Gracia Villodres 《Mikrochimica acta》1987,92(4-6):217-224
1,2-Diaminoanthraquinone forms a 11 inclusion complex with-cyclodextrin in aqueous media and at different pH. This can be employed to solubilize the anthraquinone in water for use as a ligand for metal ions. This ligand can be used to determine palladium at trace levels spectrophotometrically. The limit of detection is 11 ng/ml and the R.S.D. is 2.1%. The performance can be improved by using derivative spectrometry. 相似文献
936.
A general method for evaluation of equilibrium geometries and vibronic transition intensities of crystalline excimers is described. The method provides realistic potential surfaces which include, in addition to the α electron surfaces, also the repulsive hard core of the α electrons and the effect of the crystal potential. The method is applied to the study of the potential surfaces of the pyrene excimer, both in the crystal and in the gas phase. The method is also used for a direct evaluation of the vibronic structure of the excimer emission. The calculations reproduce the main experimentally observed properties including the structureless envelope of the emission band and the temperature dependence of its line width. 相似文献
937.
The conditions that ensure that an optimal variational wave function ø under general restricting requirements satisfies the hypervirial theorem are analysed. Application is made to a system where thez -component of angular momentum is a constant of motion and results are discussed in connection with those obtained via symmetry considerations. 相似文献
938.
We consider a class of Hamiltonians for a system of one localized spin-1/2 particle per lattice site with the total spin as
a good quantum number. We introduce a set of conditions in the form of a hypothesis relating the subpartition function, which
is the partition function defined by the subset of energies with a specific value of spin. If the equality in the hypothesis
is satisfied, then the system undergoes a phase transition as a consequence of Yang-Lee theorem. As an application, we estimate
the bounds on the spectrum of the Heisenberg Hamiltonian.
Supported by the National Science Foundation, Washington D.C. and the Robert A. Welch Foundation, Houston, Texas and partly
supported by the United States Atomic Energy Commission, Contract Grant AT (40-1) 3992. 相似文献
939.
940.
Medina RA Goeger DE Hills P Mooberry SL Huang N Romero LI Ortega-Barría E Gerwick WH McPhail KL 《Journal of the American Chemical Society》2008,130(20):6324-6325
Coibamide A (1) is a new, potent antiproliferative depsipeptide which was isolated from a marine Leptolyngbya cyanobacterium collected from the Coiba National Park, Panama. The planar structure of 1 was elucidated by a combination of NMR spectroscopy and mass spectrometry. Exhaustive 1D and 2D NMR spectroscopy included natural abundance 15N and variable temperature experiments; mass spectrometry included TOF-ESI-MSn and FT-MSn experiments. Chemical degradation followed by chiral HPLC- and GC-MS analyses was used to assign the absolute configuration of 1. This highly methylated cyclized depsipeptide exhibited an unprecedented selectivity profile in the NCI 60 cancer cell line panel and appears to act via a novel mechanism. 相似文献