Studies on the Flash Vacuum Thermolysis of Thiones of Selected N‐, O‐, and S‐Heterocycles

Thermal decomposition of thiones of selected N‐, O‐ and S‐heterocycles under flash vacuum thermolysis conditions was investigated. In the case of six‐membered 4H‐3,1‐benzoxathiin‐4‐thione 6 , the course of the reaction depended on the substitution pattern at C(2) (Scheme 3). Thus, the 2‐unsubstituted derivative 6a led to the unstable product 2 , which upon treatment with MeOH was converted quantitatively into methyl 2‐mercaptobenzoate ( 7 ). The analogous thermolysis of the 2,2‐dimethyl derivative 6b yielded 2‐methyl‐4H‐1‐benzothiopyran‐4‐thione ( 8 ) as a sole product. In the case of thiophthalide derivatives 15 , a thermal rearrangement in the gas phase leading to the corresponding benzo[c]thiophen‐1(3H)‐ones 16 in high yields was observed (Scheme 6). Unexpectedly, thionation of 1,3‐oxathiolan‐5‐one 17 with Lawesson's reagent under standard conditions led to 1,2‐dithietane derivative 19 , which, after the gas‐phase thermolysis, underwent a ring enlargement to yield 3H‐1,2‐dithiole 20 (Scheme 7). The six‐membered 4H‐1,3‐benzothiazine‐4‐thione 21 was shown to give three products: phenanthro[9,10‐c]‐1,2‐dithiete ( 22 ), 3H‐1,3‐benzodithiole‐3‐thione ( 23 ), and N‐(3H‐1,2‐benzodithiol‐3‐ylidene)prop‐2‐en‐1‐amine ( 24 ) (Scheme 8). The latter is the product of the initial reaction, whereas 22 and 23 are postulated to be formed as secondary products of the conversion of the intermediate 6‐(thioxomethylene)cyclohexa‐2,4‐diene‐1‐thione ( 26 ) (Schemes 9 and 10).     

Oxidation of methanol at the network film of polyoxometallate-linked ruthenium-stabilized platinum nanoparticles

We explore here the ability of ruthenium hydroxo species to undergo spontaneous deposition on Pt nanoparticles and to form colloidal solutions of oxoruthenium-protected (-stabilized) nanoparticles of Pt. These particles can be spontaneously attracted to carbon substrates, and they form ultrathin self-assembled films. Fabrication of the multilayer network films on electrodes has been achieved by linking the positively charged oxoruthenium-covered Pt clusters with heteropolyanions of tungsten. By repeated alternate treatments in a solution of phosphododecatungstate (PW₁₂O₄₀^3–) and in a colloidal suspension of oxoruthenium-protected (-stabilized) Pt nanoparticles, the film thickness can be increased systematically (layer by layer) to form stable three-dimensional assemblies on carbon electrodes. It is apparent from cyclic voltammetric and chronoamperometric measurements (that were performed at 20 and 60 °C) that the resulting hybrid films show attractive properties towards the oxidation of methanol at fairly low potentials (0.25–0.4 V versus the saturated calomel electrode). With approximately the same loading of oxoruthenium-covered Pt nanoparticles and under analogous conditions, linking or derivatizing the nanoparticles with phosphotungstate leads to the systems higher electrocatalytic activity. It is possible that, in addition to ruthenium hydroxo species, PW₁₂O₄₀^3– exhibits an activating effect on dispersed Pt particles. An alternative explanation may involve the possibility of different morphologies of the catalytic films in the presence and absence of phosphotungstate anions.Dedicated to Zbigniew Galus on the occation of his 70th birthday     

The cathodic stripping voltammetric determination of traces of iodide with a hanging copper amalgam drop electrode

A hanging copper amalgam drop electrode (HCADE) is used for the determination of traces of iodide by cathodic stripping voltammetry. The cathodic stripping peak of copper(I) iodide from the HCADE is better defined than that of mercury(I) iodide from a hanging mercury drop electrode. Optimum conditions and interferences are reported. With a 3-min deposition time at ?0.1 V vs. SCE, the calibration plot is linear up to 2 × 10^?6 mol dm^?3 iodide. The detection limit for iodide with the HCADE under voltammetric conditions is 4 × 10^?8 mol dm^?3; this is lowered to 8 × 10^?9 mol dm^?3 by using the differential pulse stripping technique.     

Bounds for the quadratic assignment problem using the bundle method

Semidefinite programming (SDP) has recently turned out to be a very powerful tool for approximating some NP-hard problems. The nature of the quadratic assignment problem (QAP) suggests SDP as a way to derive tractable relaxations. We recall some SDP relaxations of QAP and solve them approximately using a dynamic version of the bundle method. The computational results demonstrate the efficiency of the approach. Our bounds are currently among the strongest ones available for QAP. We investigate their potential for branch and bound settings by looking also at the bounds in the first levels of the branching tree.      

Semianalyticity of isoperimetric profiles

It is shown that, in dimensions <8, isoperimetric profiles of compact real analytic Riemannian manifolds are semianalytic.     

Development of a flow system for the determination of cadmium in fuel alcohol using vermicompost as biosorbent and flame atomic absorption spectrometry

In this study a method for the determination of cadmium in fuel alcohol using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry was developed. The sorbent material used was a vermicompost commonly used as a garden fertilizer. The chemical and flow variables of the on-line preconcentration system were optimized by means of a full factorial design. The selected factors were: sorbent mass, sample pH, buffer concentration and sample flow rate. The optimum extraction conditions were obtained using sample pH in the range of 7.3-8.3 buffered with tris(hydroxymethyl)aminomethane at 50 mmol L⁻¹, a sample flow rate of 4.5 mL min⁻¹ and 160 mg of sorbent mass. With the optimized conditions, the preconcentration factor, limit of detection and sample throughput were estimated as 32 (for preconcentration of 10 mL sample), 1.7 μg L⁻¹ and 20 samples per hour, respectively. The analytical curve was linear from 5 up to at least 50 μg L⁻¹, with a correlation coefficient of 0.998 and a relative standard deviation of 2.4% (35 μg L⁻¹, n = 7). The developed method was successfully applied to spiked fuel alcohol, and accuracy was assessed through recovery tests, with recovery ranging from 94% to 100%.     

Validated HPLC method for the standardization of Phyllanthus niruri (herb and commercial extracts) using corilagin as a phytochemical marker

Phyllanthus niruri L., commonly known in Brazil as ‘quebra‐pedra’, has long been used in the treatment of diverse diseases and especially urolithiasis. The therapeutic effects of P. niruri are attributed to various compounds present in the plant, including the hydrolysable tannin corilagin. In the present study, high‐performance liquid chromatography (HPLC‐/PAD) profiles of leaves and commercial extracts of P. niruri were examined and three compounds, found to be present in all of the samples studied, were isolated by open column chromatography over C₁₈ silica gel followed by preparative HPLC. These compounds were identified by nuclear magnetic resonance as corilagin, rutin and ethyl 3,4,5‐trihydroxybenzoate. Corilagin, which has been proposed as a phytochemical marker for P. niruri, was employed as an external standard in the development and validation of a rapid and efficient qualitative and quantitative HPLC assay for the analyte. The method may be applied in the standardization of herbs and phytomedicines commercialized in Brazil as quebra‐pedra. Copyright © 2009 John Wiley & Sons, Ltd.     

Value distribution of the Lerch zeta-function with algebraic irrational parameter. III

We obtain a limit theorem in the sense of weak convergence of probability measures in the space of analytic functions for the Lerch zeta-function with algebraic irrational parameter. Partially supported by the Lithuanian Studies and Science Foundation.     

Energy forms on conformal C1‐diffeomorphic images of the Sierpinski gasket

The energy form on a conformal C¹‐diffeomorphic image G of the Sierpinski gasket K is constructed by integrating the Lagrangian LG on G, which is given in terms of the pullback of the Lagrangian LK on K and of the differential of the diffeomorphism. The extension of this approach to the class of nested fractals is outlined. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nitrification and denitrification processes for biologic treatment of industrial effluents

Applied Biochemistry and Biotechnology - Nitrification process performance was evaluated using a three-phase fluidized-bed bioreactor. Asynthetic effluent was used for this experiment containing...