Effects of genesis and ionizing radiation on the kinetics of reduction of NiO-CeO2 mixed oxides with hydrogen

The reduction of mixed oxides NiO-CeO₂ of various composition with hydrogen was studied at 290–470° by means of thermogravimetry. Some physicochemical properties of the system were also investigated and compared with earlier studied analogous samples of different “origin”. The degree of mutual interaction of the two components, the reduction kinetics and the sensitivity to the different sorts of radiation (gamma-rays, fast neutrons and electrons), applied in different doses, are strongly affected by the “pre-history” and by the composition in both compared series of mixed oxides.     

Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

Stability study of simvastatin under hydrolytic conditions assessed by liquid chromatography

In this work, a liquid chromatography stability-indicating method was developed and applied to study the hydrolytic behavior of simvastatin in different pH values and temperatures. The selected chromatographic conditions were a C18 column; acetonitrile-28 mM phosphate buffer solution, pH 4 (65 + 35) as the mobile phase; 251 degrees C column temperature; and flow rate 1 mL/min. The developed method exhibited an adequate repeatability and reproducibility (coefficient of variation 0.54 and 0.74%, respectively) and a recovery higher than 98%. Furthermore, the detection and quantification limits were 9.1 x 10(-7) and 2.8 x 10(-6) M, respectively. The degradation of simvastatin fitted to pseudo-first order kinetics. The degradation was pH dependent, being much higher at alkaline pH than at acid pH. Activation energy, kinetic rate constants (k) at different temperatures, the half life (t1/2) and the time for 10% degradation to occur (t90) values are also reported.     

Spectroscopic investigation of the adsorption and oxidation of thiourea on polycrystalline Au and Au(111) in acidic media

In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1 M perchloric acid. The combination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed in D2O to clean up the region of the H2O bending around 1600 cm(-1). It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO4(2-) were produced. The second parallel reaction occurs from TU in solution at E > 0.50 VRHE to form (TU)2(2+). All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.     

Determination of formation constants of hydroxo and carbonate complexes of Pr(3+) in 2 M NaCl at 303 K

The hydrolysis of praseodymium III in 2 M sodium chloride at 303 K was studied. Two methods were used: pH titration followed by a computational refinement and solvent extraction in the presence of a competitive ligand. The hydrolysis constants obtained by pH titration were: logbeta(1,H)=-7.68+/-0.07, logbeta(1,2H)=-15.10+/-0.03, and beta(1,3H)=-23.80+/-0.04. The stability constants of praseodymium carbonate complexes were determined by pH titration as well and were: logbeta(1,CO(2-)(3))=5.94+/-0.08 and logbeta(1,2CO(2-)(3))=11.15+/-0.15. Praseodymium carbonate species were taken into consideration for calculating the first hydrolysis constants by the solvent extraction method and the value obtained was: logbeta(1,H)=-7.69+/-0.27. The values for logbeta(1,H) attained by both methods are the same. The species-distribution diagram was obtained from the stability constants of praseodymium carbonate complexes and hydrolysis products in the conditions of the present work.     

Determination of iron at ng/ml level by solid phase spectrophotometry after preconcentration on cation exchange filters

A cationic exchanger paper is used to retain analytes in solution and, after drying, to analyze directly by measuring the UV-Vis absorbance of the paper. The method was applied to determination of iron using its known 1,10-phenanthroline complex. Using 100 ml of sample the applicable concentration range was between 1.0 and 10.0 ng/ml with a detection limit of 0.2 ng/ml and a RSD around 2%. The method was applied to determination of iron total in snow, human serum and wine.     

The Dienone–Phenol Rearrangement of Santonin: A Comprehensive Laboratory Experiment for Advanced Undergraduate Organic Chemistry Students

A comprehensive laboratory experiment suitable for advanced undergraduate organic chemistry students has been designed. The experiment is based on the dienone-phenol rearrangement reaction of the sesquiterpene santonin to give -desmotroposantonin acetate. It challenges students to solve an earlier controversial stereochemical problem. The students carry out the reaction and analyze spectroscopic data to determine the stereochemistry of the starting material and the product. In addition, they perform simple molecular modeling calculations, which enable them to rationalize the stereochemical outcome of the transformation and discuss the mechanism of the dienone-phenol rearrangement and related rearrangements reported in the literature.     

Coordinating ability of the heterocycles 1,3-dithia-2-arsa and stiba-cyclopentanes toward sulfur containing ligands,part I. Dialkyl-dithiocarbamate complexes

Summary The heterocyclic compounds ClMS₂ (CH₂)₂ (M = As, Sb) are tested by first time as source of starting materials in the synthesis of complexes. The preparation and characterization of heterocyclic dithiocarbamatesR ₂NCS₂ MS₂ (CH₂)₂, (M = As, Sb;R =Me,Et,i-Pr) is reported. Spectroscopic and analytical data suggest a bidentate behavior of the dithiocarbamate entity and the presence of aMS₄ core.

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Die Koordinationsfähigkeit der Heterocyclen 1,3-Dithia-2-arsa- und-stiba-cyclopentan gegenüber Schwefel enthaltenden Liganden, I. Dialkyldithiocarbamat-Komplexe

Zusammenfassung Die heterocyclischen Verbindungen ClMS₂ (CH₂)₂ (M = As, Sb) werden erstmals als Quelle für Ausgangsmaterial zur Synthese von Komplexen herangezogen. Es wird über die Herstellung und Charakterisierung der heterocyclischen DithiocarbamateR ₂NCS₂ MS₂ (CH₂)₂ (M = As, Sb;R =Me,Et,i-Pr) berichtet. Spektroskopische und analytische Daten sprechen für ein bidentates Verhalten der Dithiocarbamat-Einheit und der Präsenz einerMS₄-Anordnung im Komplex.

     

Multicommuted flow-through fluorescence optosensor for determination of furosemide and triamterene

Multicommutation implemented with flow-through optosensors is a very promising area of research. This recent approach benefits from the advantages of both methods and results in high sensitivity, selectivity, and speed, and little waste generation. This paper reports the simultaneous determination of furosemide and triamterene, two widely used diuretics, by measurement of their native fluorescence. The system has been proved to be useful for determination of both analytes in pharmaceutical preparations and for determination of triamterene in human urine and serum. A minicolumn filled with Sephadex SPC-25 microbeads was used to achieve separation of both analytes before detection in a flow-through cell filled with the same resin. The sensor is linear in the range 50–1200 and 0.4–8 ng mL⁻¹ with detection limits of 15 and 0.1 ng mL⁻¹ for furosemide and triamterene, respectively.