Preparation of Silver Nanoparticles‐Based Sensors for the Electrochemical Detection of Thiourea in Leaching Solutions of Waste Electrical and Electronic Equipment

Waste of electrical and electronic equipment is an interesting secondary resource of base and precious metals. Particularly the use of thiourea‐leaching in acidic medium was proposed for noble metals recovery. In this work, a novel and easy‐to‐use electrochemical sensor was developed, aimed to test thiourea from leaching solutions containing significant thiourea and copper amounts. The sensor was constructed using silver nanoparticles (AgNPs) deposited on screen‐printed electrodes. Its performance was studied in a synthetic leaching solution; changes in the overall surface charge of AgNPs resulting in changes in the charge‐transfer resistance for the copper ions were evaluated by electrochemical impedance spectroscopy.     

Human Y‐chromosome SNP characterization by multiplex amplified product‐length polymorphism analysis

We designed an allele‐specific amplification protocol to optimize Y‐chromosome SNP typing, which is an unavoidable step for defining the phylogenetic status of paternal lineages. It allows the simultaneous highly specific definition of up to six mutations in a single reaction by amplification fragment length polymorphism (AFLP) without the need of specialized equipment, at a considerably lower cost than that based on single‐base primer extension (SNaPshot?) technology or PCR‐RFLP systems, requiring as little as 0.5 ng DNA and compatible with the small fragments characteristic of low‐quality DNA. By designation of two primers recognizing the derived and ancestral state for each SNP, which can be differentiated by size by the addition of a noncomplementary nucleotide tail, we could define major Y clades E, F, K, R, Q, and subhaplogroups R1, R1a, R1b, R1b1b, R1b1c, J1, J2, G1, G2, I1, Q1a3, and Q1a3a1 through amplification fragments that ranged between 60 and 158bp.     

Model studies toward the synthesis of kirkine

In model studies towards the synthesis of kirkine, the carbon skeleton was constructed using a radical cascade reaction. Two different approaches towards the synthesis have been examined as well as the regioselectivity of the radical cyclisation.     

A Discussion on Particle Number and Quantum Indistinguishability

The concept of individuality in quantum mechanics shows radical differences from the concept of individuality in classical physics, as E. Schr?dinger pointed out in the early steps of the theory. Regarding this fact, some authors suggested that quantum mechanics does not possess its own language, and therefore, quantum indistinguishability is not incorporated in the theory from the beginning. Nevertheless, it is possible to represent the idea of quantum indistinguishability with a first-order language using quasiset theory (Q). In this work, we show that Q cannot capture one of the most important features of quantum non-individuality, which is the fact that there are quantum systems for which particle number is not well defined. An axiomatic variant of Q, in which quasicardinal is not a primitive concept (for a kind of quasisets called finite quasisets), is also given. This result encourages the searching of theories in which the quasicardinal, being a secondary concept, stands undefined for some quasisets, besides showing explicitly that in a set theory about collections of truly indistinguishable entities, the quasicardinal needs not necessarily be a primitive concept. Graciela Domenech — Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).     

Lead Sensor Using Gold Nanostructured Screen‐Printed Carbon Electrodes as Transducers

Gold nanostructured screen‐printed carbon electrodes are demonstrated to be suitable transducers for the determination of lead using square‐wave voltammetry. Reproducible gold nanostructures have been obtained by direct electrochemical deposition. A calibration plot from 2.5 to 250 μg/L was obtained in acidic solutions of Pb(II) with a reproducibility of 4% (n=10). The detection limit was 0.09 μg/L of lead. The method is then applied to perform a blood lead analysis by adjusting square‐wave parameters in capillary or venous blood with a minimum sample pretreatment and excellent accuracy and reproducibility.     

Support functions and integral formulas in the Lorentzian plane

In the Lorentzian plane, the support function of a closed convex curve is not a periodic one. We redefine this concept and the envelope of a families of lines. Using these, we prove integral formulas in the Crofton's style for convex sets in the Lorentzian plane. Received 10 February 2000.     

Elucidating a particulate matter deposition episode by combining scanning electron microscopy and X-ray fluorescence spectrometry.

Multielemental composition and morphology of particulate matter samples were examined to detect the presence of two potential responsible pollutant emitters at four sites impacted during a pollution episode in the City of Campana, Argentina. Coke and smoke black are the main constituents associated to the industrial plants that were considered, a priori, as responsible pollutant emitters. Wavelength dispersive X-ray fluorescence (WDXRF) was employed for the analysis of metals in samples coming from both, suspected sources and four sites. On the basis of multielemental composition profiles, a screening analysis was undertaken for exploring similarities among sources and sample sites adopting the average concentration profile of the crustal rock as soil surrogate. Particle morphology was studied by scanning electron microscopy (SEM) in source samples and in those environmental samples selected through the screening analysis. Two types of collected samples were analyzed: 1) those with composition profiles closer to the potential sources and 2) those closer to the cluster rock. This strategy was adequate to identify the responsible source of the contamination episode.     

Carbonyl oxides reactions from geraniol-trans-(3,7-dimethylocta-2,6-dien-1-ol), 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis: kinetics and mechanisms

A density functional theory (DFT) study of the mechanisms of carbonyl oxide reactions from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis is presented. The geometries, energies, and harmonic vibrational frequencies of each stationary point were determined by B3LYP/6-31(d,p) and BH&HLYP/cc-pVDZ methods. According to the calculations, the ozonolysis reactions are initiated by the formation of van der Waals (VDW) complexes to yield primary ozonides, which rapidly open to carbonyl oxide compounds. These carbonyl oxide compounds react to form dioxanes and hydroperoxides. The hydroperoxides react by isomerization to form stable products. Glyoxal and methyl-glyoxal have been identified as the final product from geraniol-trans, 6-methyl-5-hepten-2-one, and 6-hydroxy-4-methyl-4-hexenal ozonolysis. Our results are in good agreement with the experimental studies.     

Synthesis and ring-chain-ring tautomerism of bisoxazolidines, thiazolidinyloxazolidines, and spirothiazolidines

The synthesis of fused heterocycles such as thiazolidinyl-oxazolidine 3 is described starting from Tris·HCl. The mercaptomethyl bisoxazolidine 8 was found to convert to the corresponding thiazolidinyloxazolidine 3 and the spiro-heterocycle 4 by a ring-chain-ring tautomerism, depending on the electronic nature of the ring substituents as well as the reaction conditions. This equilibration pathway is absent in the hydroxymethyl bisoxazolidines 2. Computational studies confirm that both kinetic and thermodynamic control features play a role in the product distribution.