Calculations of the Cd hyperfine field andEFG on Ni surfaces

The hyperfine field andthe electric field gradient on Cd probe atoms at Ni(100) and Ni(111) surfaces are calculated self-consistently within the local density molecular/cluster approach.     

Synthesis of 8-cyano-1,4-dihydro-4-oxopyrrolo[1,2-a]pyrimidine-3-carboxylic acids as potential antimicrobial agents

The preparation of a variety of 8-cyano-1,4-dihydro-7-phenyl-4-oxopyrrolo[1,2-a]pyrimidine-3-carboxylicacids and 8-cyano-1,4-dihydro-7-p-fluorophenyl-4-oxopyrrolo[1,2-a]pyrimidine-3-carboxylic acids is described.     

Use of hexamminecobalt(III)-tricarbonatocobaltate(III) as a redox titrant for the potentiometric estimation of some organic compounds

Hexamminecobalt(III)-tricarbonatocobaltate(III) was prepared, and its bicarbonate solution was standardized against ferrous ammonium sulfate using Ferroin indicator. The Co solution was used as an oxidimetric reagent for the determination of organic systems.Hydroquinone as a reversible system undergoes fast electrochemical reactions, so it can be determined with the Co(III) complex, which acts as an irreversible titrant. Thus it can be determined with both visual and potentiometric methods. Standardized hydroquinone solutions in H₂SO₄ medium gave very similar results when determined potentiometrically against standard Co(III) solution. The acid medium is important for liberating Co(III) ions. Hydrochloric acid behaves similarly but perchloric acid interferes with the reaction. Diluting the hydroquinone solutions had no effect on the determinations. The potentiometric endpoint coincides with the discharge of the color if Ferroin has been present.p-Aminophenol, p-phenylenediamine, and Metol (p-hydroxy-N-methylaniline), which slow or hinder the electrochemical reaction, do not indicate a distinct potential change at the endpoint, so cannot be determined potentiometrically. Their chemical reactions are fast enough to be titrated visually against Co(III) complex using Ferroin indicator. Titration curves representing biamperometric measurements of these solutions fulfill these results.Hydrazine sulfate and isonicotinic acid hydrazide as irreversible systems cannot react with Co(III) and thus cannot be determined either potentiometrically or visually as both electrochemical and chemical reactions are slow to be recognized.     

Polarographic behaviour of uranyl ion in maleic acid and maleate buffer solutions

The polarographic behaviour of uranyl ion in maleic acid solution shows two reduction waves. The half wave potential of the first wave is shifted to more negative values in contrast to that of the second wave, which is shifted to less negative potentials on increase of thepH of the solution. The first wave represents the reduction of the 1:1 uranyl-maleate complex, while the second wave represents the reduction of the 1:2 complex. The presence of 1:1 and 1:2 complexes is supported by spectrophotometric and conductometric methods. The stability constants were also determined and the reduction mechanism is discussed.

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Das polarographische Verhalten von Uranyl-Ionen in Maleinsäure- und Maleat-Puffer-Lösungen

Zusammenfassung Die polarographische Kurve von Uranyl-Ionen in Maleinsäurelösung zeigt zwei Reduktionswellen. Das Halbwellenpotential der ersten Welle verschiebt sich bei ansteigendempH der Lösung zu negativeren Werten, im Gegensatz zur zweiten Welle, die eine positive Verschiebung zeigt. Die erste Welle repräsentiert die Reduktion des 1:1-Uranyl-Maleat-Komplexes, die zweite Welle hingegen die Reduktion des 1:2-Komplexes. Die Präsenz von 1:1- und 1:2-Komplexen wird auch durch spektrophotometrische und konduktometrische Messungen erhärtet. Die Stabilitätskonstanten wurden bestimmt, der Mechanismus der Reduktion wird diskutiert.

     

Determination of trivalent antimony

Summary A method is described for the determination of trivalent antimony. It depends on the oxidation of Sb³⁺ to Sb⁺ with KMnO₄ in sulfuric acid solutions (0.72-3.4N H₂SO₄) in the presence of fluoride ions and at temperatures below 50°. Amounts of antimony ranging from 15.7gmg to 61 mg can be determined accurately.

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Zusammenfassung Eine Methode zur Bestimmung von Sb (III) wurde beschrieben. Sie beruht auf der Oxydation zu Sb(V) mit Permanganat in schwefelsaurer Lösung (0,72-3,4N H₂SO₄) in Gegenwart von Fluorid bei Temperaturen unter 50° C. Mengen zwischen 15,7gmg und 61 mg Antimon lassen sich genau bestimmen.

     

Electroreduction and determination of Pipril (Piperacillin) in both aqueous and biological samples

The electrochemical behavior of the relatively new antibacterial antibiotic Pipril (Piperacillin) at the dropping mercury electrode is investigated using both direct current polarography (DCP) and differential pulse polarography (DPP). At the hanging mercury electrode (HMDE), the reduction mechanism has been elucidated using cyclic voltammetric technique in the pH range from 2 to 10. The effect of some metal ions, e.g. Cu(II) and Pb(II) has been also tested. Determination of the drug using adsorptive stripping analysis was assessed in both aqueous and urine samples. The effect of the different experimental parameters affecting the drug determination, e.g. pH, supporting electrolyte nature, accumulation potential, accumulation time and other operational parameters are also mentioned. Detection limits of 5 × 10⁻⁹ and 1 × 10⁻⁸M Pipril in aqueous and urine samples, respectively, are achieved.     

Temperature Dependence of the Emission Spectrum of Silicon Nanoparticles in Acetone and Isopropanol Solvents

This study investigated the emission spectra of select silicon nanoparticles when subjected to various temperature changes. Two sizes of silicon nanoparticles, dispersed in both isopropanol and acetone solvents, were studied. Photoluminescence responses of the samples were measured in an environmental chamber that allowed exposure to temperatures in the range of ?73 to 65 °C (?100 to 150 °F). These silicon nanoparticles exhibited emission dependence on the temperature of their environment. The emission become brighter as the temperature decreased and less intense as the temperature increased. Thus, the response of these silicon nanoparticles in a harsh environment has been qualified.     

Palladium(II) saccharinate complexes trans-[Pd(sac)2(LH)2] with amino- and acetylamino-pyridine co-ligands: molecular structures of trans-[PdCl2(2-ampyH)2].2dmf (2-ampyH = 2-amino-3-methylpyridine) and trans-[Pd(κ2-2-acmpy)2] (2-acmpyH = 2-acetylamino-3-methylpyridine)

Reaction of Na₂[PdCl₄] with two equivalents of amino- or acetylamino-pyridines (LH) affords trans-[PdCl₂-(LH)₂] {LH = 2-amino-3-methylpyridine (2-ampyH), 3-aminopyridine (3-apyH), 2-acetylamino-3-methylpyridine (2-acmpyH), 3-acetylamino-pyridine (3-acpyH)}. An X-ray crystal structure of trans-[PdCl₂(2-ampyH)₂] shows that the 2-ampy-H ligands are coordinated in a monodentate fashion via the nitrogen atoms of the pyridine rings. Treatment of trans-[PdCl₂(2-acmpyH)₂] with NEt₃ affords the cyclometalated complex, trans-[Pd(κ²-2-acmpy)₂], the X-ray structure of which shows that the 2-acmpy ligand is coordinated to palladium in a bidentate fashion via the nitrogen atom of the pyridine ring and oxygen. Reaction of trans-[PdCl₂(LH)₂] with two equivalents of sodium saccharinate affords the bis(saccharinate) complexes, trans-[Pd(sac)₂(LH)₂], in which the saccharinate anions are coordinated via the amide nitrogen atom.     

Fourier acceleration of iterative processes in disordered systems

Technical details are given on how to use Fourier acceleration with iterative processes such as relaxation and conjugate gradient methods. These methods are often used to solve large linear systems of equations, but become hopelessly slow very rapidly as the size of the set of equations to be solved increases. Fourier acceleration is a method designed to alleviate these problems and result in a very fast algorithm. The method is explained for the Jacobi relaxation and conjugate gradient methods and is applied to two models: the random resistor network and the random central-force network. In the first model, acceleration works very well; in the second, little is gained. We discuss reasons for this. We also include a discussion of stopping criteria.