Determination of small amounts of lead in uranium

Small amounts of lead in the presence of large amounts of uranium can be determined by complexing the lead with nitrilotriacetic acid in aqueous solution at about pH 6 (adjusted with hexamine)and extracting the uranium into a chloroform solution of diphenylacetic acid. The aqueous phase is then acidified the lead determined polarographically.     

Electrogenerated Chemiluminescence of Cationic Triangulene Dyes: Crucial Influence of the Core Heteroatoms

Trianguleniums are fascinating conjugated hexacyclic cations that exhibit interesting electronic and optical properties. Herein, the electrogenerated chemiluminescence (ECL) emission of this family of fluorescent dyes is reported for the first time. Redox behavior and fluorescence properties of eight cationic triangulene luminophores with different heteroatom patterns in the core structure and various pending substituents were examined to rationalize the ECL. Clearly, the more electron‐rich the carbocation, the more efficient the corresponding ECL; two very distinct classes of triangulenes can be drawn from these studies by using an ECL wall sufficiency formalism.     

Discrimination of Beers by Cyclic Voltammetry Using a Single Carbon Screen-printed Electrode

A fast, simple and costless methodology without sample pre-treatment is proposed for the discrimination of beers. It is based on cyclic voltammetry (CV) using commercial carbon screen-printed electrodes (SPCE) and includes a correction of the signals measured with different SPCE units. Data are submitted to partial least squares discriminant analysis (PLS−DA) and support vector machine discriminant analysis (SVM−DA), which allow a reasonable classification of the beers. Also, CV data from beers can be used to predict their alcoholic degree by partial least squares (PLS) and artificial neural networks (ANN). In general, non-linear methods provide better results than linear ones.     

Addition of mild electrophiles to a Mo[triple bond]N triple bond and nitrile synthesis via metal-mediated N-atom transfer to acid chlorides

The addition of mild electrophiles to the anionic terminal Mo-nitride {[(t)BuOCO]Mo[triple bond]N]Na(DMF)}(2) (1) and the synthesis of nitriles via metal-mediated N-atom transfer is reported. The X-ray structure of a pivaloylimido intermediate indicates the presence of a weakly coordinated DMF molecule. Kinetic studies confirm that cyclometalation and DMF dissociation occur prior to nitrile extrusion.     

Influence of branch content on the microstructure of blends of linear and octene-branched polyethylene: a MD simulation study

Microstructure of linear low-density polyethylene (LLDPE) with linear high-density polyethylene (HDPE) is investigated by molecular dynamics (MD) simulation. The branch content of LLDPE was varied from 10 to 60 branches/1000 C. An equimolar mixture of each of the two polymers is simulated in the NVT ensemble at 500 K and at average experimental densities of the two polymer melts. Initially, chains of LLDPE and HDPE were completely mixed and evolution of conformations with time was monitored. The blends were found to microphase separate when the branch content of LLDPE exceeded 30 branches/1000 C. At 40 branches/1000 C, the two polymers displayed partial microphase separation and complete microphase separation was observed at 60 branches/1000 C. Substantial short-range order and mismatch of molecular conformations is observed in the microphase-separated systems.     

Estimating quantiles in imperfect simulation models using conditional density estimation

In this article, we consider the problem of estimating quantiles related to the outcome of experiments with a technical system given the distribution of the input together with an (imperfect) simulation model of the technical system and (few) data points from the technical system. The distribution of the outcome of the technical system is estimated in a regression model, where the distribution of the residuals is estimated on the basis of a conditional density estimate. It is shown how Monte Carlo can be used to estimate quantiles of the outcome of the technical system on the basis of the above estimates, and the rate of convergence of the quantile estimate is analyzed. Under suitable assumptions, it is shown that this rate of convergence is faster than the rate of convergence of standard estimates which ignore either the (imperfect) simulation model or the data from the technical system; hence, it is crucial to combine both kinds of information. The results are illustrated by applying the estimates to simulated and real data.

     

Synthesis of 1,2,3-triazole-fused heterocycles via Pd-catalyzed cyclization of 5-iodotriazoles

A convenient approach toward polycyclic frameworks containing fused 1,2,3-triazoles is described. The synthesis consists of a Cu-catalyzed cycloaddition and an intramolecular Pd-catalyzed direct arylation or Heck reaction, and affords the products in good to excellent yields.     

High-throughput capillary electrophoretic method for determination of total aminothiols in plasma and urine.

Increased interest in the analysis of aminothiols in body fluids during the last years results in a request for high-throughput analytical methods for their determination. We report here a novel, high-throughput method for the determination of total concentrations of biogenous aminothiols - homocysteine, cysteine, glutathione, cysteinylglycine, gamma-glutamylcysteine, and of penicilamine, mercaptopropionylglycine, and cysteamine, three compounds used to treat disorders of aminothiol metabolism in plasma and urine. Samples were reduced with tris(carboxyethyl)phosphine and labeled with 5-(bromomethyl)fluorescein. Capillary electrophoretic separations were performed in 60 mmol/L borate - 15 mmol/L sodium dodecyl sulfate - 2-amino-2-methyl-1-propanol, pH 10.0, with laser-induced fluorescence detection. Analysis time was less than 2 min. The assay is linear (r > 0.999) up to 500 micromol/L. Reproducibilities of migration times (coefficient of variation, CV) were < 0.5%. Interassay repeatabilities (CV, n = 10) were 5.08% and 6.09% for 5 micromol/L addition of homocysteine and 0.60% and 3.78% for 100 micromol/L addition of cysteine in plasma and urine, respectively. Recovery values were within 94-106% and sensitivity was better than 0.19 micromol/L for all analyzed compounds. Results agreed well with a standard high-performance liquid chromatography (HPLC) method. The diagnostic usefulness of the method has been proven on 79 samples of cystinuric patients and 12 samples of homocystinuric patients. We report here a novel method for the determination of aminothiols in body fluids by capillary electrophoresis (CE). Determination is fast and sensitive enough for diagnostic purposes.     

Palladium catalysed aryl enol ether synthesis from vinyl triflates

Vinyl triflates can be efficiently converted into the corresponding aryl enol ethers by treatment with a phenol, NaO(t)Bu and a catalyst generated from Pd2dba3 and 2-(di-(t)Bu-phosphino)biphenyl.