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Novel mixed valence states have been obtained by the treatment of cobaltous ferrocyanides (Co+2FeII) and ferricyanides (Co+2FeIII) in an ozone flow. The CN stretching bands occur at 2085 cm–1 for Co+2FeII and at 2160 cm–1 for Co+2FeIII. After the ozonization process of Co+2FeII, an intense band approximately at 2125 cm–1 is detected. This intermediate band must correspond to a mixed valence state of the type: FeII–CN–Co2+–NC–FeIII Mössbauer spectra recorded in situ during the ozonization of Co+2FeII show the presence of two components: a doublet with isomer shift and quadrupole splitting values close to the cobalti ferricyanide and a very broad line for the mixed valence state. From the Mössbauer and infrared spectra of the aged samples of the Co+2FeII after ozonization, a relaxation process to the initial state of the samples is observed but the mixed valence state is stable. 相似文献
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Experimental designs and response surface modeling applied for the optimization of metal-cyanide complexes analysis by capillary electrophoresis 总被引:1,自引:0,他引:1
The development of capillary zone electrophoresis (CZE) methods for the determination of metal cyanide complexes in real samples showed some problems, such as the low detection signal of Au (CN)2- and the low resolution between Ni(II) and Fe(II) cyanides in gold processing solutions, and the lack of separation of Pt(CN)4(2-) and Pd(CN)4(2-) in the leachates from automobile catalytic converters. To optimize some analytical parameters, the present study thus focused on the application of experimental designs and multiregression models. The following factors were examined by a two-level factorial design: applied voltage, injection time, detection wavelength, buffer ion, ionic strength and buffer modifiers. For optimization of the CZE method, subsequent response-surface experiments with the important factors were made with the two kinds of leaching solutions. Optimal analytical conditions were obtained in each case, giving good detection signals and resolution for the components of the studied leachates. 相似文献
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Irene Yarovsky Marie-Isabel Aguilar Milton T. W. Hearn 《Journal of chromatography. A》1994,660(1-2):75-84
The molecular dynamics method has been applied to investigate the conformations of n-butyl ligands immobilised onto an amorphous silica surface analogous to those utilised with silica-based RP-HPLC sorbents. Three systems were constructed which corresponded to ligand densities of 1.64, 2.67 and 3.69 μmol/m2. A number of parameters related to the structure of the sorbent materials were derived in order to characterise the molecular properties of each system. These parameters included the hydrocarbon layer thickness, the frequency of gauche conformations, the distance distribution for carbon atoms and the diffusion coefficients of individual atoms in the n-butyl ligands. From these properties, the positions of chains with respect to the surface as well as their mobility were estimated. It was found that at higher densities, the n-butyl chains are predominantly perpendicular to the surface while at low density they are highly tilted or lying almost parallel to the surface. The degree of ligand flexibility decreased with increasing surface density. Mobility of individual carbon atoms as well as chain disorder increased with distance from the surface for all ligand densities. The simulated properties of n-butyl chains immobilised to a silica surface correlated well with results obtained by Fourier transform IR and 13C-cross polarisation magic angle spinning NMR experimental methods and statistical predictions of the behaviour of immobilised chains. 相似文献
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An extracellular xylanase produced by a Mexican Aspergillus strain was purified and characterized. Aspergillus sp. FP-470 was able to grow and produce extracellular xylanases on birchwood xylan, oat spelt xylan, wheat straw, and corncob, with higher production observed on corncob. The strain also produced enzymes with cellulase, amylase, and pectinase activities on this substrate. A 22-kDa endoxylanase was purified 30-fold. Optimum temperature and pH were 60 degrees C and 5.5, respectively, and isoelectric point was 9.0. The enzyme has good stability from pH 5.0 to 10.0, retaining >80% of its original activity within this range. Half-lives of 150 min at 50 degrees C and 6.5 min at 60 degrees C were found. K(m) and activation energy values were 3.8 mg/mL and 26 kJ/mol, respectively, using birchwood xylan as substrate. The enzyme showed a higher affinity for 4-O-methyl-D-glucuronoxylan with a K(m) of 1.9 mg/mL. The enzyme displayed no activity toward other polysaccharides, including cellulose. Baking trials were conducted using the crude filtrate and purified enzyme. Addition of both preparations improved bread volume. However, addition of purified endoxylanase caused a 30% increase in volume over the crude extract. 相似文献
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van den Brand JF Ent R Anthony PL Arnold RG Arrington J Beise EJ Belz JE Bosted PE Bulten H Chapman MS Coulter KP Dietrich FS Epstein M Filippone BW Gao H Gearhart RA Geesaman DF Hansen J Holt RJ Jackson HE Jones CE Keppel CE Kinney ER Kuhn S Lee K Lorenzon W Lung A Makins NC Margaziotis DJ McKeown RD Milner RG Mueller B Napolitano J Nelson J O'Neill TG Papavassiliou V Petratos GG Potterveld DH Rock SE Spengos M Szalata ZM Tao LH van Bibber K Wasson DA White JL Zeidman B 《Physical review D: Particles and fields》1995,52(9):4868-4871
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Makins NC Ent R Chapman MS Hansen J Lee K Milner RG Nelson J Arnold RG Bosted PE Keppel CE Lung A Rock SE Spengos M Szalata ZM Tao LH White JL Coulter KP Geesaman DF Holt RJ Jackson HE Papavassiliou V Potterveld DH Zeidman B Arrington J Beise EJ Belz E Filippone BW Gao H Lorenzon W Mueller B McKeown RD O'Neill TG Epstein M Margaziotis DJ Napolitano J Kinney E Anthony PL van Bibber K Dietrich FS Gearhart RA Patratos GG Kuhn SE van den Brand JF Bulten H Jones CE 《Physical review letters》1994,72(13):1986-1989
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