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991.
Paul Chiy Miguel de la Fuente Enrique Barrado Marisol Vega C. Phillips 《Analytical and bioanalytical chemistry》1998,361(4):343-348
The optimum conditions for microwave digestion of herbage and faeces to determine mineral concentrations were obtained by varying sample mass, reagent and heating programme, and it was confirmed that the resulting element concentrations were the same as for certified reference material. The effects of feeding cadmium to sheep at a level that is typical of polluted regions (1 mg/kg) for ten days were investigated, as well as the possible amelioration of cadmium effects by adding 30 mg/kg Zn to the diet. Cadmium in the feed increased the cadmium balance and produced several mineral disturbances, in particular a reduction in sodium balance which is typical of renal tubular disorders. Including zinc in the diet as well as cadmium reduced the cadmium balance to a level similar to that of sheep that did not receive cadmium or zinc, which suggests that the zinc status is critical in determining whether cadmium in feed increases the cadmium balance in sheep. 相似文献
992.
O. A. Scelza S. R. de Miguel G. T. Baronetti A. A. Castro 《Reaction Kinetics and Catalysis Letters》1987,33(1):143-148
Pt–Re/Al2O3 prepared under different impregnating conditions were characterized by TPR and tested in naphtha and n-heptane reforming. Catalysts showed different Pt and Re radial distributions and reduction profiles. When both metals interact, higher dehydrocyclization and conversion are retained after a deactivation step, meanwhile, when Re is segregated from Pt the catalytic performance is negatively affected.
Pt–Re/Al2O3, , -. Pt Re . , , Re Pt .相似文献
993.
Caballero A Tormos R Espinosa A Velasco MD Tárraga A Miranda MA Molina P 《Organic letters》2004,6(24):4599-4602
A new 1-(9-anthryl)-4-ferrocenyl-2-aza-1,3-butadiene showing selective fluorescence enhancement upon binding to lithium cations over other alkaline cations in aqueous environment has been conveniently synthesized and characterized. [structure: see text] 相似文献
994.
The kinetics of piperidine replacement by pyridine at the pentacyano(piperidine)-ferrate(II) complex ion was studied under pseudo-first order conditions in binary aqueous mixtures of methanol, t-butanol, p-dioxane, and glycerol, from a mole fraction of co-solvent from 0 to about 0.15. The observed variations can be explained considering the degree of hydrophobic interaction between released ligand and water molecules which changes according to the structure-forming or struucture-breaking effect of added co-solvent on water. 相似文献
995.
Conejo-García A Campos J Eder C Entrena A Gallo MA Espinosa A 《The Journal of organic chemistry》2005,70(14):5748-5751
[structure: see text] Two-step syntheses of triple-bridged triscationic bicyclophanes are presented. Molecular modeling has been undertaken by means of ab initio calculations (6-31G level) on the triquinolina triscationic bicyclophane. This compound exists as two diastereomeric sets of enantiomers, one with C3 symmetry and the other with C1 symmetry. The C3-symmetrical derivative is 1.94 kcal mol(-1) more stable than its C1-symmetrical one. This energy difference is sufficient to consider the former and its enantiomer the only two conformations existing in solution at room temperature. 相似文献
996.
Ma Prado García-Aparicio Ignacio Ballesteros Alberto González José Miguel Oliva Mercedes Ballesteros Ma José Negro 《Applied biochemistry and biotechnology》2006,129(1-3):278-288
The influence of the liquid fraction (prehydrolysate) generated during steam-explosion pretreatment (210°C, 15 min) of barley
straw on the enzymatic hydrolysis was determined. Prehydrolysate was analyzed for degradation compounds and sugars' content
and used as a medium for enzymatic hydrolysis tests after pH adjusting to 4.8. Our results show that the presence of the compounds
contained in the prehydrolysate strongly affects the hydrolysis step (a 25% decrease in cellulose conversion compared with
control). Sugars are shown to be more potent inhibitors of enzymatic hydrolysis than degradation products. 相似文献
997.
The problem with which analytical laboratories are confronted, after traceability of their results has been demonstrated, is correctly estimating their uncertainty– to which traceability is also to some extent subject. While the general principles for calculating the uncertainty of physical
measurements are applicable to chemical metrology, some refinements are needed, especially careful selection and planning
the level at which uncertainty will be estimated by each laboratory in accordance with its capacity and required demands.
Depending on the particular decision to be made, the mechanism to be used to estimate the uncertainty varies markedly; also,
the rigour of the estimation increases with increasing stringency of the demands. This paper describes the primary sources
of uncertainty in chemical metrology and discusses different approaches to its estimation in relation to the type of analytical
laboratory concerned. The view presented tries to be close to the bench analytical level, in order to be practical and flexible
for laboratories, although it could sometimes be considered slightly heterodox.
Received: 25 March 1997 · Accepted: 20 September 1997 相似文献
998.
Abstract— The catechol oxidase promoted oxidation of catechols produces electronically excited states readily detected by chlorophyll sensitized fluorescence. Both the chemiexcitation step and the transfer step are efficient. The use of chlorophyll has confirmed that the peroxidase catalyzed oxidation of dihydroxyfumarate also generates electronically excited species. It is concluded that efficient enzymatic generation of electronic energy can occur not only through the dioxetane/dioxetanone route, but also via electron transfer processes. 相似文献
999.
The spectrophotometric determination of trace amounts of ambroxol was carried out by liquid-liquid extraction using Bromothymol Blue with a flow-injection system. The determination of ambroxol in the range 8 x 10(-6)-4 x 10(-4) M was possible with a sampling frequency of 40 samples h(-1). The method was satisfactorily applied to the determination of ambroxol in pharmaceutical preparations. 相似文献
1000.
Nuria Merchan Miguel Angel Bañares-Muñoz Miguel Angel Vicente 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(3):219-230
The retention of ethyl 2-oxocyclopentanecarboxylate by a saponite has been studied. Intercalation compounds were prepared by two different methods: 1) in repose at room temperature and 2) heating at 60 °C under reflux. Contact times between 2 and 12 days were considered for each method. The intercalation compounds obtained were characterized by X-ray diffraction, infrared spectroscopy, chemical analyses and thermal analyses. This characterization indicates that the organic compound is retained both in the interlayer region and at the edge of the clay particles. The amount retained outside of the interlayer space is eliminated by careful washing with benzene and cyclohexane. The results obtained when using acid-activated saponite -obtained by treatment of the clay with dilute HCl solutions- in the intercalation experiments were similar to those obtained when using non-activated saponite. 相似文献