Structural and magnetic characterization of Co67Fe4Ni2Si15B12

 Soft magnetic properties of Co-based amorphous alloy of the composition Co₆₇Fe₄Ni₂Si₁₅B₁₂ have been investigated by isothermal heat treatment up to the conventional crystallization temperature. In the as-cast condition the Curie temperature of the sample is 272 °C and saturation magnetization is 74 emu/g. Magnetic properties undergo variation depending on the heat treatment temperature. For the heat treatment temperatures of around 420 and 490 °C, superior soft magnetic properties are obtained. For both the temperatures initial permeability, μ′ reaches value up to ten times the value of permeability in the as-received samples. Annealing effect on giant magneto-impedance has been observed for the current-driving frequencies of 4.5 and 6 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.     

Ferroelectric and electrical properties of LiNaWO4 compound

The aim of this work is to elaborate the LiNaWO₄ compound, using the solid state method, then to characterize it using an XR study which confirms that it crystallizes in the orthorhombic system with P222 as space group and with the lattice parameters a = 12.82 Å, b = 17.49 Å, c = 7.25 Å and α = β = γ = 90°. The differential scanning calorimetry (DSC) shows two endothermic peaks at T₁ = 388 K and T₂ = 500 K. The first peak is detected by the dielectric study, attributed to a phase transition from a ferroelectric phase to a paraelectric one, while the second peak indicates the presence of a phase transition, confirmed later by the result of the electrical study. All modes pertaining to vibrations of WO₄^2? tetrahedral appear in the Raman spectrum. Moreover, its impedance response is modeled by a single cell formed by a parallel combination of R//C//CPE, i.e. the response of our compound is that of the grain. The variation of the σ_g and σ_dc, as a function of temperature, confirms the phase transition observed in the calorimetric study at T₂. The conduction mechanism in the two phases indicates that the first phase (I) is described by the CBH model and the second phase by the OLPT model.     

Does phenomenological kinetics provide an adequate description of heterogeneous catalytic reactions?

Phenomenological kinetics (PK) is widely used in the study of the reaction rates in heterogeneous catalysis, and it is an important aid in reactor design. PK makes simplifying assumptions: It neglects the role of fluctuations, assumes that there is no correlation between the locations of the reactants on the surface, and considers the reacting mixture to be an ideal solution. In this article we test to what extent these assumptions damage the theory. In practice the PK rate equations are used by adjusting the rate constants to fit the results of the experiments. However, there are numerous examples where a mechanism fitted the data and was shown later to be erroneous or where two mutually exclusive mechanisms fitted well the same set of data. Because of this, we compare the PK equations to "computer experiments" that use kinetic Monte Carlo (kMC) simulations. Unlike in real experiments, in kMC the structure of the surface, the reaction mechanism, and the rate constants are known. Therefore, any discrepancy between PK and kMC must be attributed to an intrinsic failure of PK. We find that the results obtained by solving the PK equations and those obtained from kMC, while using the same rate constants and the same reactions, do not agree. Moreover, when we vary the rate constants in the PK model to fit the turnover frequencies produced by kMC, we find that the fit is not adequate and that the rate constants that give the best fit are very different from the rate constants used in kMC. The discrepancy between PK and kMC for the model of CO oxidation used here is surprising since the kMC model contains no lateral interactions that would make the coverage of the reactants spatially inhomogeneous. Nevertheless, such inhomogeneities are created by the interplay between the rate of adsorption, of desorption, and of vacancy creation by the chemical reactions.     

Expression of Recombinant Human Epidermal Growth Factor in Escherichia coli and Characterization of its Biological Activity

Recombinant human epidermal growth factor (EGF) was successfully expressed as a fusion protein in Escherichia coli system. This system was used OmpA signal sequence to produce soluble protein into the periplasm of E. coli. Human EGF (hEGF) synthesized in bacterial cell was found to be similar in size with the original protein and molecular weight approximately at 6.8 kDa. Cell proliferation assay was conducted to characterize the biological activity of hEGF on human dermal fibroblasts. The synthesized hEGF was found to be functional as compared with authentic hEGF in stimulating cell proliferation and promoting growth of cell. In comparison of biological activity between synthesized and commercial hEGF on cell proliferation, the results showed there was no significant different. This finding indicates the synthesized hEGF in E. coli system is fully bioactive in vitro.     

Alpha-phenyl-N-tert-butylnitrone-type derivatives bound to beta-cyclodextrins: syntheses, thermokinetics of self-inclusion and application to superoxide spin-trapping

alpha-Phenyl-N-tert-butylnitrone (PBN) derivatives bound to beta-cyclodextrin derivatives have been synthesized. Inclusion of the PBN group into the beta-cyclodextrin moiety is host- and temperature-dependent. In the case of the nitrone linked to permethylated cyclodextrin (Me3CD-PBN), the thermokinetic parameters are in favour of a slow chemical exchange between a tight and a loose complex. In contrast, 2,6-di-O-Me-beta-cyclodextrin-grafted PBN (Me2CD-PBN) exists either in a fast exchange or as a strongly self-associated complex. The covalent cyclodextrin-PBN compounds have been used to trap carbon and oxygen-centred free radicals. The self-associated forms of the beta-CD-spin-traps are compatible with effective spin-trapping, affording spin-adducts with enhanced EPR signal intensities relative to noncovalent CD-nitrone systems or the nitrone alone. This kind of cyclodextrin-bound nitrone is the first type of covalent supramolecular spin-trap and should open new possibilities for the study of biological free radicals in vivo.     

Synthesis of novel chitosan resin derivatized with serine diacetic acid moiety and its application to on-line collection/concentration of trace elements and their determination using inductively coupled plasma-atomic emission spectrometry

A novel chelating resin functionalized with serine diacetic acid moiety was synthesized by using chitosan as base material, and applied to the collection/concentration of trace elements in environmental water samples, followed by the determination using inductively coupled plasma-atomic emission spectrometer (ICP-AES). The synthesized resin, crosslinked chitosan serine diacetic acid (CCTS-SDA), showed good adsorption behavior toward trace amounts of Cd, Pb, Cu, Ni, V, Ga, Sc, In, and Th in a wide pH range. Additionally, rare earth elements also can be retained on the resin at neutral pH region. The adsorbed elements can be easily eluted with 1 mol L⁻¹ of nitric acid, and their recoveries were found to be 90-100%. The CCTS-SDA was packed in a mini-column, which was then installed in a computer-controlled auto-pretreatment system (Auto-Pret System) for on-line trace elements collection and determination with ICP-AES. Experimental parameters which related to the improvement of sensitivity and reproducibility were optimized. The limits of detection (LOD) for 13 elements were found to be in sub-ppb level. The proposed method with CCTS-SDA resin was successfully applied to the determination of trace elements in river water samples. The method was validated by determining a certified reference material of river water, SLRS-4.     

Theoretical studies of vibrational spectra of [N(CH3)4]2ZnCl4−yBry compounds with y = 0, 2 and 4

The infrared and Raman spectra of [N(CH₃)₄]₂ZnCl_4?yBr_y, where y = 0, 2 and 4, have been analyzed with ab initio calculations of the vibrational characteristics of constitutive polyhedra, tetramethylammonium [N(CH₃)₄]⁺ and [ZnCl_4?xBr_x]^2? (x = 0, 1, 2, 3 and 4) tetrahedra. The optimized geometries, calculated vibrational frequencies, infrared intensities and Raman activities are calculated using Hartree–Fock and density functional theory B3LYP methods with 3-21G, 6-31G(d) and 6-311G⁺(d,p) basis sets. Calculation of the root mean square difference δ_rms between the observed and calculated frequencies allows to give scaling factors and to deduce that the best agreements are obtained by B3LYP/6-311G⁺(d,p) for [N(CH₃)₄]⁺ and B3LYP/3-21G for [ZnCl_4?xBr_x]^2?. The present study establishes a strongly reliable assignment of the vibrational modes of [ZnCl_4?xBr_x]^2? tetrahedra based on comparison between experimental and ab initio calculations, both of the frequencies and the intensities of the Raman signals.