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81.
J. M. Campelo A. Garcia D. Luna J. M. Marinas 《Reaction Kinetics and Catalysis Letters》1984,26(1-2):73-77
Electron donor and acceptor properties of AlPO4 and AlPO4–SiO2 (2080 wt. %) supported rhodium catalysts have been studied. It was observed that the effect of metal deposition on both electron acceptor and donor properties depend on the support and precipitation agent. AlPO4 supported rhodium showed better acoeptor than donor properties, while for Rh/AlPO4–SiO2, the acceptor properties were superior. However, the effect of metal on the redox properties is slight.
AlPO4 QlPO4 SiO2 (2080 .%). ]ye . AlPO4 , , Rh/AlPO4–SiO2 . , - .相似文献
82.
Kotel'nikov A. I. Ortega J. M. Medvedev E. S. Psikha B. L. Garcia D. Mathis P. 《Russian Journal of Electrochemistry》2002,38(1):77-87
The electron transfer from the heme of cytochrome c to the bacteriochlorophill dimer in reaction centers of photosynthetic purple bacteria Rps. sulfoviridis is studied by laser flash photolysis at 40–296 K in conditions where one, two, or three cytochrome hemes are chemically reduced. In the model used for the electron transfer kinetics, the protein relaxation is described with a temperature-independent oscillatory coordinate and a temperature-dependent diffusion coordinate, with the protein dielectric relaxation times widely distributed along the diffusion coordinate. It is found that all the protein complexes can be divided into proteins with fast (k
et = 107 to 10–4 s–1) and slow (k
et 100 s–1) electron transfer. These populations presumably differ by the protonation state of the functional group. The contribution of the oscillatory and diffusion coordinates alters, which severely affects k
et. Parameters V
ab, G, , 0, and for these reactions are determined. 相似文献
83.
Herein we report a new preparation of 4-hydroxy-2,5-dimethyl-2,3-dihydrofuran-3-one, the flavor compound strawberry furanone, based on a ‘green’ approach with a minimum number of steps. The first step is an enzymatic dioxygenation of p-xylene to form cyclohexadiene-cis-diol, followed by ring opening via ozonolysis, and ring closure to form the furanone. In efforts to improve the efficiency of the enzymatic step, a directed evolution approach was taken to increase the substrate specificity and selectivity of the toluene dioxygenase enzyme system. 相似文献
84.
Rodríguez-Cea A de la Campa MR Sanz-Medel A 《Analytical and bioanalytical chemistry》2005,381(2):388-393
Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with -naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4±0.1 nmol mL–1 P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE–FPLC, with UV detection, or coupled to ICP–MS with an octapole reaction system, ICP–(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP–(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins. 相似文献
85.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献
86.
Koji Yagi Veronica Garcia Ma. E. Rivas Javier Salas Andres Camargo Takeo Tabata 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):179-184
Some crown ethers were found to show significant antifungal activity against some wood-decay fungi, phytopathogenic fungi and eumycetes,Trichophytons for dermatomycosis. Their toxicity was evaluated by the paper disc method as well as by determining the values of ED50, i.e., the concentration which inhibits the mycelium growth by 50%. The fungi examined areTyromyces palustris, Picnoporous coccineus, Coriolous versicolor, Pyricularia filamentosa, Fusarium sp., Trichophyton rubrum, Trichophyton sp., etc. Among the 26 crown ethers tested, 3,5-di-t-butyl-benzo-15-crown-5 showed relatively high activity, the highest ED50 value of which being 8 M or 3 ppm. Other alkylbenzocrown ethers, dicyclohexyl crown ethers and Kryptofix 22DD also showed considerable activity. On the other hand, unsubstituted crown ethers, benzocrown ethers with a polar substituent, Kryptofix 222B and Kryptofix 221 were inactive. 相似文献
87.
H. -J. Sue E. I. Garcia Meitin D. M. Pickelman C. J. Bott 《Colloid and polymer science》1996,274(4):342-349
The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT
g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed. 相似文献
88.
Creatinine, creatine, and uric acid are three important compounds that are measured in a variety of clinical assays, most notably for renal function. Traditional clinical assays for these compounds have focused on the use of enzymes or chemical reactions. Electrophoretic microchips have the potential to integrate separation power of capillary electrophoresis with devices that are small, portable, and have the speed of conventional sensors. The development of a microchip CE system for the direct detection of creatinine, creatine, and uric acid is presented. The device uses pulsed amperometric detection (PAD) to detect the nitrogen-containing compounds as well as the easily oxidizable uric acid. Baseline separation of creatinine, creatine and uric acid was achieved using 30 mM borate buffer (pH = 9.4) in less than 200 s. Linear calibration curves were obtained with limits of detection of 80 microM, 250 microM and 270 microM for creatinine, creatine and uric acid respectively. An optimization of the separation conditions and a comparison of PAD with other amperometric detection modes is also shown. Finally, analysis of a real urine sample is presented with validation of creatinine concentrations using a clinical assay kit based on the Jaffé reaction. 相似文献
89.
A. Blanco J. M. Campelo A. Garcia D. Luna J. M. Marinas M. S. Moreno 《Reaction Kinetics and Catalysis Letters》1989,38(2):223-228
The effects of surface dehydration on textural properties, crystallinity and the structure of AlPO4–ZrO2 (weight ratio AlPO4/ZrO2=3) systems precipitated with ethylene oxide have been studied by N2 adsorption and XRD measurements. The increase in calcination temperature in the range 773–1273 K decreases the textural parameters as a consequence of AlPO4 crystallization to the tridymite form.
, AlPO4–ZrO2 ( AlPO4/ZrO2=3), , N2 - . 773 1273 , AlPO4 .相似文献
90.
A rapid, precise, accurate, and robust method using capillary electrophoresis (CE) with dynamically coated capillaries for the analysis of the major opium alkaloids in opium is presented. Dynamic coating of the capillary surface is accomplished using a commercially available reagent kit (polycation coating followed by polyanion coating). The addition of dual cyclodextrins (hydroxypropyl-beta-cyclodextrin and dimethyl-beta-cyclodextrin) to the run buffer imparts excellent selectivity for the opium alkaloids. For the determination of morphine, papaverine, codeine, noscapine and thebaine in opium gum and opium latex samples (using tetracaine as an internal standard) good agreement with values obtained by gradient high-performance liquid chromatography is obtained. Compared to the latter technique, CE affords better resolution with significantly faster analysis time (12 min versus 29 min). Dynamically coated capillaries, which give rise to a relatively high and robust electroosmotic flow (EOF) at the background electrolyte pH of 2.5, allow for rapid analysis and excellent migration time and peak area precision (RSDs < or = 0.12% and < or = 1.2%, respectively). Reproducible separations (relative migration times) for over 500 samples have been obtained on a single capillary. The nature of the injection solvent, the injection time and the contents of the waste vials have a profound effect on the pressure injection precision of the relatively hydrophobic solutes. The CE conditions reported in this study are also applicable to the analysis of lysergic acid diethylamide (LSD) exhibits. 相似文献