Spectrophotometric determination of Fe(II) in milligram solid samples

The analytical procedure of determination of Fe(II) in the presence of Fe(III) in milligram samples is proposed. A solid sample is dissolved in hydrochloric acid in argon atmosphere. Subsequently, the pH-value of the solution is fixed and Fe(III) complexed by phosphoric buffer. At the next step Fe(II) is oxidized by -molybdosilicic acid. Finally, the intensity of colouring caused by the reduced form of the acid is measured at the wavelength 770 nm. The proper treatment of the sample during oxidation, and immediately before, is decisive for the accuracy of the analysis. The method was verified by means of the analysis of synthetic magnetite. The theoretical content of Fe(II) was 24.12%, the determined one was 24.02 ± 0.10%. The method was applied to the determination of the homogeneity of an iron catalyst for ammonia synthesis.     

Role of Hydrodynamic Conditions in the Distribution of Anodic Dissolution Rates in Cavity Etching Regions during Electrochemical Micromachining of Partially Insulated Surfaces

Experimental study of the distribution of local rates of electrochemical micromachining in the presence of photoresist masks in various hydrodynamic conditions (macroscopically nonuniform rotating disk electrode, sprayer flow, an electrode placed into a cell with chaotic bulk electrolyte mixing) shows that the maximum etching localization is achieved at the control of the dissolution rate by the mass transport rate (at achieving the anodic limiting current). The localization enhancement as compared to the primary current distribution takes place in the case of a turbulent flow at hydrodynamic conditions where the removal of dissolution products from the undercutting region is hindered. These conditions (electrochemical reaction limited by the ion mass transport rate, high resistance to the mass transport in the undercutting region) are necessary for the localization enhancement using a pulsed anodic–cathodic treatment.     

SYNTHESIS OF CONDUCTIVE POLYANILINE VIA OXIDATION BY MnO2

A unique process of chemical oxidation polymerization of aniline using manganese dioxide (MnO2) as the oxidizing agent in an aqueous medium is described. The reaction between aniline and MnO2 follows a mechanism by which the organic monomer is oxidized while the metal oxide undergoes reductive dissolution. The effects of the amount of oxidizing agent and aniline, pH and temperature of the reactive system, type of acid on the yield and conductivity of polyaniline are discussed. The resulting polyaniline was characterized by [R and UV-Vis spectrometry. Polyaniline with a conductivity of 12.5 S/cm was obtained using 0.033 tool of aniline oxidized by 0.023 tool MnO2 in the presence of 100 mL of 2.7 mol/L HCI at 25℃ for 4 h.     

Immobilization of single-strand specific nuclease (S1 nuclease) fromAspergillus oryzae

S1 nuclease fromAspergillus oryzae (EC 3.1.30.1) was coupled to gelatin-alginate composite matrix using the residual free aldehyde groups on the surface of glutaraldehyde crosslinked matrix. The immobilized enzyme retained approximately 10% activity of the soluble enzyme. When partially purified enzyme was bound to the matrix, the immobilized preparation did not show any detectable enzyme activity. However, the activity could be restored when the coupling was carried out in the presence of a coprotein or substrate. The optimum pH of the immobilized S1 nuclease shifted to 3.8 from 4.3 for the soluble enzyme. Also, optimum temperature increased to 65°C after immobilization. Bound S1 nuclease showed increased pH and temperature stabilities. Immobilization brought about a twofold decrease in the Michaelis-Menton constant (K _m).     

Landau damping of ion-acoustic waves with simultaneous effects of non-extensivity and non-thermality in the presence of hybrid Cairns-Tsallis distributed electrons

The dispersion properties and Landau damping rate of ion-acoustic waves (IAWs) with the hybrid Cairns-Tsallis distributed (CTD) electrons and Maxwellian ions are investigated using the plasma kinetic model based on Vlasov-Poisson's equations. For both super-extensive (q < 1) and sub-extensive (q > 1) plasmas, the dielectric response function, real frequency, and Landau damping rate of IAWs are derived. By taking the effect of θ_{i, e} (ion-to-electron temperature ratio) into account, it is found that with the increase of ion temperature, the real frequency and wave dispersion effects increase as well (for both super-extensive and sub-extensive cases). Exploring the properties of the Landau damping rate of IAWs with the simultaneous presence of non-thermal parameter α and non-extensive parameter q, a comparison of numerical and analytical results is presented. It is found that in different ranges of θ_{e, i} (electron-to-ion temperature ratio), on decreasing the values of the non-extensive parameter and increasing values of the non-thermal parameter, the weak damping rate is observed (vice versa) in super-extensive or super-thermal plasma, although the trend of the damping rate in sub-thermal plasma is similar (as in the case of super-thermal plasma) but is less weak. It is further revealed that the damping rate of IAWs in thermal plasmas (Maxwellian) is stronger than the damping rate of IAWs in the case of non-thermal plasmas (CTD). The current study is applicable to provide deep insight and further allow the exploration of electrostatic plasma modes in different space and laboratory plasma environments where the hybrid CTD plasma exists.     

Interactions in multicomponent systems containing surfactants. System silver iodide — methylene blue and sodium dodecyl sulphate

The precipitation and dissolution of AgI in the presence of methylene blue (MB · Cl) and sodium dodecyl sulphate (NaDS) was followed by X-ray diffraction analysis.At high MB · Cl concentration, the absence of AgI precipitates was observed, which is explained by considering the redox process MB⁺ + 2I^– MB^– + I₂. The decrease in I^– concentration causes dissolution or inhibition of growth of solid AgI which is significant at relatively high MB · Cl concentrations. The addition of NaDS causes the disappearance of these effects, which is explained by the incorporation of MB in NaDS micelles.These explanations are supported by the potentiometric measurements using Ag/Ag₂S and Pt electrodes.     

Immobilization of the restriction endonuclease PstI

PstI has been immobilized in agarose. A solution of low melting agarose containing 1,6-hexamethylenediamine and PstI formed a gel that was effective in the linearization of pBR322 DNA. The gel containing PstI could be treated with 1,5-bis(N-acetylamino-N-succinimidoxy carbonyl)pentane, a crosslinking agent, without affecting the enzyme activity. Polymerization of acrylamide in presence of PstI led to conisderably reduced enzyme activity, although EcoRI under identical conditions showed high activity. It was found that acetylation of amino groups in PstI, by reaction with hydroxysuccinimide acetate, led to total inactivation of the enzyme activity. This reaction showed the presence of reactive amino groups that were essential for the enzyme activity of PstI. Involvement of these amino groups in binding to activated Sepharose 4B, during covalent immobilization, was responsible for inactive enzyme preparations.     

Improved Performance of W／HZSM-5 Catalysts for Dehydroaromatization of Methane

The dehydroaramatization of methane over W-supported ZSM-5 with varying degrees of Li^ ion-exchanged catalysts was studied with and without oxygen at 1073 K and atmospheric pressure.Catalyst activity and stability were found to be influenced by the catalyst acidity related to BrSnsted acid sites and by the presence of oxygen in the feed. The NH3-TPD and FTIR-pyridine results demonstrated that partially exchanged of H^ ions by Li^ into the W/HZSM-5 catalysts could be used to control the amount of strong acid sites on the catalyst surface. Without oxygen, the 3WHLi-Z (5:1) catalyst that has strong acid sites equal to nearly 74% of the original strong acid sites in the parent HZSM-5 exhibited the highest methane conversion and selectivity towards aromatics. However, the catalyst deactivated in a five hour period. In the presence of oxygen, the catalyst activity and stability could be improved further.The results of this study revealed that a suitable amount of strong Bronsted acid sites as well as oxygen addition in the feed increased the catalyst activity and stability. The 3WHLi-Z(5:1) catalyst exhibited improved performance in the dehydroaromatization of methane.     

Dipeptide-catalyzed direct asymmetric aldol reactions in the presence of water

The l-proline-based dipeptide has been discovered and developed as an efficient catalyst for the direct asymmetric aldol reactions of unmodified ketones with various aldehydes including aromatic, aliphatic, heteroaromatic, and unsaturated aldehydes in the presence of water at 0 °C. The resulted methodology and optimal conditions led to the corresponding aldol products with high yields (up to 94%) and good enantioselectivities (up to 97% ee).