Preparation of USY zeolite VOx supported catalysts from V(AcAc)3 and NH4VO3. Catalytic properties for the dehydrogenation of n-butane in oxygen-free atmosphere

The preparation of different samples of vanadia supported on ultrastable zeolite (VO(x)/USY) is discussed. The samples were prepared in order to obtain highly dispersed V-species, avoiding the formation of crystalline vanadia and the destruction of the zeolite framework. Two methods were employed for preparing VO(x)/USY samples: an organic route using V(AcAc)3 and an inorganic route using NH4VO3. The characterization of the samples was performed with XRD, TPR, NH3-TPD, and N2 isotherms. From these results it is concluded that when VO(x) is supported on the surface of USY from acidic aqueous solution of ammonium metavanadate, the destruction of the zeolite framework is accomplished. For higher pH values in the impregnating solution, undesired V2O5 is formed on the USY surface. On the other hand, VO(x)/USY prepared from the organic precursor shows no destruction of the USY structure. In addition, highly dispersed VO(x) are formed, though for relatively high V loadings (6%) an obstruction of the zeolite windows takes place. The samples are tested as catalysts for gas phase dehydrogenation of n-butane to olefins. The catalysts prepared from NH4VO3 are almost inactive for the reaction. On the other hand, both samples prepared from V(AcAc)3 present initial conversion levels in the 8-12% range. However, the selectivity depends on the V loading, the catalysts with 6% loading being the most selective (75%). The catalytic patterns of the samples (activity and selectivity) are in agreement with the physicochemical features of the VO(x)/USY surface.     

Solid solubility of Ge,Si, and Mg in Fe2O3 and photoelectric behavior

Solid solutions of GeO₂ in Fe₂O₃ were prepared by mechanically mixing the solids and firing at 1000°C in air, and from a gel obtained by the addition of an alcohol solution of germanium ethoxide to iron dissolved in HNO₃. The dried gel was then heated at 1000°C. The solubility limit is 5 mole% GeO₂, Fe_1.95Ge_0.05O₃. Similar procedures were used to prepare solid solutions with Si and the solubility limit is greater than 4 mole% SiO₂. Firing of mixtures or gels of Fe₂O₃ containing Mg produces a spinel phase even at the lowest detectable concentrations. The resistivity of pressed pellets of Fe_2?xGe_xO₃ varies from about 10⁶ ohm-cm for x = 0 to about 10^?1 ohm-cm for x = 0.05. The photoassisted electrolysis of water at Ge-doped Fe₂O₃ electrodes is demonstrated. The $\text{Fe}{}_2\text{O}{}_3\text{(Ge)}\text{0.7 M}\text{Fe(CN)}{}^{\mathrm{4?}}{}_6\text{,}\text{0.05 M}\text{Fe(CN)}{}^{\mathrm{3?}}{}_6\text{Pt}$ photoelectrochemical cell showed a 0.29-V open-circuit voltage, 1.2-mA/cm² short-circuit current, 0.31 fill factor, and 0.06% power efficiency.     

Evaluation of recombinant green fluorescent protein, under various culture conditions and purification with HiTrap hydrophobic interaction chromatography resins

To determine the influence of various culture conditions, transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were grown in nine cultures with four variable conditions (storage of inoculated broth at 4°C prior to incubation, agitation speed, isopropyl-β-d-thiogalactopyranoside [IPTG] concentration, and induction time). The pelleted cells were resuspended in extraction buffer and subjected to the three-phase partitioning (TPP) extraction method. To determine the most appropriate purification resin, protein extracts were eluted through one of four types of HiTrap hydrophobic interaction chromatography (HIC) columns prepacked with methyl, butyl, octyl, or phenyl resins and analyzed further on a 12% sodium dodecylsulfatepolyacrylamidegel. With Coomassie staining, a single band between 27 (standard GFPuv) and 29 kDa (molecular weight standard) was visualized for every HIC column sample. TPP extraction with HIC elution provided about 90% of the GFPuv recovered and eight-fold GFPuv enrichment related to the specific mass. Rotary speed and IPTG concentration showed, respectively, greater negative and positive influences on GFPuv expression at the beginning of the logarithmic phase for the set culture conditions (37°C, 24-h incubation).     

Determination of diamine oxidase by a kinetic method with 2,2''-azino-di(3-ethylbenzthiazoline-6-sulfonate)

Hydrogen peroxide, the product of diamine oxidase-catalyzed putrescine or cadaverine oxidation, formed in proportion to the enzyme activity, is measured spectrophotometrically by using the above sulfonate (ABTS) and peroxidase. Only one reagent solution containing 3 mmol of putrescine or 10 mmol of cadaverine, 4 mmol of ABTS and 3000 U of peroxidase per litre of 0.2 mol l^-1 Tris—0.1 mol l^-1 HCl buffer pH 7.5 is needed. Absorbance changes are measured at 410 nm over the first 3 min of the reaction. This initial oxidation rate of the chromogen enables diamine oxidase activity up to 230 U l^-1 to be determined.     

Effect of cholesterol on the properties of phospholipid membranes. 4. Interatomic voids

The properties of the interatomic voids present in fully hydrated dimyristoylphosphatidylcholine (DMPC)-cholesterol mixed membranes of different compositions are analyzed in detail using a generalized variant of the Voronoi-Delaunay method on the basis of computer simulation results. The systems investigated are chosen from both sides of the DMPC-cholesterol miscibility gap; the pure DMPC bilayer has also been included in the analysis as a reference system. The results obtained show that the empty space is organized in a more compact way, forming larger voids in the presence than in the absence of cholesterol. The voids located in the region of the rigid cholesterol rings become, on average, less spherical, oriented more parallel with the membrane normal axis with increasing cholesterol concentration, whereas an opposite effect of cholesterol is observed in the middle of the membrane among the chain terminal methyl groups. In general, the preferential orientation of the voids is found to strongly correlate with that of the molecules in the hydrocarbon phase of the membranes. The membranes are found to contain rather large voids, the volume of which can be an order of magnitude larger than the largest spherical cavities present in the systems. These voids are elongated or branching channels rather than big empty holes. The voids located among the DMPC and cholesterol molecules are lying preferably parallel with the membrane normal axis. The existence of such empty channels can be of great importance in the cross-membrane permeation of small, uncharged penetrants, in particular, of polar molecules.     

The role of complexing ligands in the formation of non-aggregated nanoparticles of zirconia

The hydrolysis and condensation of zirconium n-propoxide in n-propanol have been chemically controlled via the complexation of the zirconium precursor with acetylacetone. The size of the zirconium oxide-based particles is mainly controlled by the complexation ratio x=[acac]/[Zr]. the mean size increases from nanometric to submicronic range when x decreases from 1 to 0.1. Amorphous colloidal particles are obtained at room temperature. They result from a competitive growth/termination mechanism of zirconium-oxo species in the presence of acac surface capping agents. However non-aggregated nanocrystalline particles of tetragonal zirconia, about 2 nm in diameter are formed upon aging at 60°C when hydrolysis is performed in the presence of paratoluene sulfonic acid (PTSA).     

Use of high-molecular-mass polyacrylamides as matrices for microchip electrophoresis of DNA fragments

DNA fragment analysis requires the use of polymer solutions as sieving matrices. Generally, such matrices are constituted of high-molar-weight polymers employed at a concentration higher than their entanglement threshold concentration. These polymer solutions are highly viscous and difficult to use in the narrow channels of a microchip. Ultralarge polyacrylamides synthesized via a nonconventional method, being the low-temperature plasma-induced polymerization (PIP), were used as DNA sieving matrices for microchip electrophoresis. The distinctive features of these polymers (ultralarge molecular mass and linearity) allow their use at a dilute concentration. Dilute PIP polyacrylamides revealed a constant value of resolution in a broad range of DNA fragment sizes (123 bp-1353 bp), thus proving to be effective in common genotyping applications. Moreover, the low viscosity of the dilute solutions enable it to be easier and faster in filling the channel between runs, thus enhancing the throughput of the microchip devices.     

Monitoring of sources of clinical exposure to nickel

Due to the widespread uses of Ni and Ni alloys, patients undergoing medical treatments can experience inadvertent exposure to the metal, present as a contaminant in fluids for intravenous administration or released from surgical implants and other medical devices. Because of the risk of acute allergic reactions in Ni-sensitive subjects, sources of metal exposure within medical care and its concentrations in biological fluids of potentially exposed patients should be periodically monitored, using reliable analytical procedures, which include strict measures of contamination control. The results of a recent survey on the concentrations of Ni and other potentially toxic metals in human albumin solutions are reported.