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71.
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
72.
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
73.
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
74.
[reaction: see text] The first asymmetric direct Michael addition of aldehydes to vinyl sulfones catalyzed by N-iPr-2,2'-bipyrrolidine is described. 1,4-Adducts are obtained in good yields and enantioselectivities. The determination of absolute configuration allowed us to postulate a Si,Si transition state model, as shown previously for nitroolefins. 相似文献
75.
Thermogravimetric determination of magnesium,potassium and lead by precipitation with dilituric acid
The thermolysis curves of magnesium, potassium, and lead diliturate have established that either the hydrated or anhydrous forms of these precipitates are stable enough for their gravimetric use to be possible. Magnesium and lead were determined by precipitation with dilituric acid while potassium was precipitated with trimethylamine diliturate. 相似文献
76.
The authors compare two different estimators of the crosscorrelation function and show that they give equivalent estimators in the frequency domain. They calculate the first and second order moments of the estimator of the cross-spectral-density (DSPC)due to the statistical errors and the quantification of inputs. From these general formulas, they perform numerical calculations for a particular case and they compare them to practical measurements. They show the interesting fact, that the variance of the statistical errors on the dspc is inferior by estimating its phase than by estimating its module. Furthermore, the quantification of the inputs may influence the variance of the phase of the DSPC estimated. 相似文献
77.
The partial hydrogenation of benzene to cyclohexene by nanoscale ruthenium catalysts in imidazolium ionic liquids 总被引:3,自引:0,他引:3
Silveira ET Umpierre AP Rossi LM Machado G Morais J Soares GV Baumvol IJ Teixeira SR Fichtner PF Dupont J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(15):3734-3740
The controlled decomposition of an Ru(0) organometallic precursor dispersed in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF(6)), tetrafluoroborate (BMI.BF(4)) or trifluoromethane sulfonate (BMI.CF(3)SO(3)) ionic liquids with H(2) represents a simple and efficient method for the generation of Ru(0) nanoparticles. TEM analysis of these nanoparticles shows the formation of superstructures with diameters of approximately 57 nm that contain dispersed Ru(0) nanoparticles with diameters of 2.6+/-0.4 nm. These nanoparticles dispersed in the ionic liquids are efficient multiphase catalysts for the hydrogenation of alkenes and benzene under mild reaction conditions (4 atm, 75 degrees C). The ternary diagram (benzene/cyclohexene/BMI.PF(6)) indicated a maximum of 1 % cyclohexene concentration in BMI.PF(6), which is attained with 4 % benzene in the ionic phase. This solubility difference in the ionic liquid can be used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PF(6). Selectivities of up to 39 % in cyclohexene can be attained at very low benzene conversion. Although the maximum yield of 2 % in cyclohexene is too low for technical applications, it represents a rare example of partial hydrogenation of benzene by soluble transition-metal nanoparticles. 相似文献
78.
Rapp E Jakob A Schefer AB Bayer E Albert K 《Analytical and bioanalytical chemistry》2003,376(7):1053-1061
A mixture of unsaturated fatty acid methyl esters was separated with a new splitless capillary set-up. With the employed apparatus configuration different capillary separation techniques such as capillary high-performance liquid chromatography (cHPLC), capillary electrochromatography (CEC) and pressurized capillary electrochromatography (pCEC) could be applied. The detection and identification of the sample compounds were accomplished by hyphenating these capillary separation techniques with nuclear magnetic resonance (NMR) spectroscopy using a novel configuration of the detection capillary set-up. Using modified electrokinetically driven separation techniques, the electric field was applied solely across the separation column. With this improved interface for capillary liquid chromatography-NMR on-line coupling, the stereochemical assignment of the cis and trans configuration of unsaturated fatty acids could be easily accomplished. Finally, the results of cHPLC-NMR, CEC-NMR and pCEC-NMR coupling experiments were compared.Dedicated to Professor Günter Häfelinger on the occasion of his 65th birthday 相似文献
79.
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
80.
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