Weak Skyrmions and sphalerons

When the gauged non-linear -model is supplemented by a Skyrme term stable as well as unstable classical solutions exist: weak Skyrmions and sphalerons. Without the Skyrme term there remains only a sequence of sphalerons, which can be continued to finite Higgs masses. Here we investigate a model containing both, a finite Higgs mass and a Skyrme term. Stable weak Skyrmion solutions occur only above critical values of the Higgs mass and the Skyrme coupling constant.     

Synthesis of Carbon Nanohorns by Inductively Coupled Plasma

We demonstrate a new pathway for the synthesis of carbon nanohorns (CNHs) in a reactor by using inductively coupled plasma (ICP) and gaseous precursors. Thermal plasma synthesis allows the formation of different carbon allotropes such as carbon nanoflakes, hybrid forms of flakes and nanotubules, CNHs embryos, seed-like CNHs and onion-like polyhedral graphitic nanocapsules. In this study, pressure has the greatest impact on the selectivity of carbon nanostructures: pressure below 53.3 kPa favors the growth of carbon nanoflakes and higher pressures, 66.7 kPa and above, promotes the formation of CNHs. The ratio between methane and hydrogen as well as the global concentration of CH₄?+?H₂ inside the plasma flame are also crucial to the reaction. CNHs are formed preferentially by injection of a 1:2 ratio of H₂ to CH₄ at 82.7 kPa with a production rate of 20 g/h. The synthesis pathway is easily scalable and could be made continuous, which offers an interesting alternative compared to methods based on laser-, arc- or induction-based vaporization of graphite rods.

Graphical Abstract

     

Optimizing conditions to study seed germination by calorimetry using soybean (Glycine max [L.] Merr.) seeds

To establish the best conditions for germination, calorimetric experiments were conducted with individual soybean seeds (Glycine max [L.] Merr.) under different conditions of imbibition at 24.7 °C. The calorimetric curves were analysed for imbibition and metabolic processes and compared with imbibition curves to establish a general methodology that could be used to evaluate inter- and intra-species physical and physiological variability. Measurements of pH were performed during the determination of the imbibition curves. The best experimental method for calorimetric investigations of seed germination is to insert the seed in 1% agar instead of placing the seed over wetted filter paper disks. Correlation of imbibition experiments and pH results with mass specific enthalpy of imbibition (determined in a KCN solution) or mass specific enthalpy of germination when seeds were germinated in 1% agar allowed determination of the water content needed for soybean seeds of the cultivar studied (A7636 RG) to activate their metabolic machinery (74–80% or 2.5–3 h) and the moment in which they are ready for root protrusion (122% or 9 h). The method presented here should be useful for evaluating soybean coat permeability to water and other factors related to seed damage before and during harvest and storage.     

Use of solid-phase microextraction/gas chromatography-electron capture detection for the determination of energetic chemicals in marine samples

Gas chromatography with electron capture detection (GC-ECD) is a highly explosive-sensitive analytical technique. However, its application to the analysis of sediment extracts is hampered by the presence of numerous endogenous interferences. In the present study, solid-phase microextraction (SPME) was used both as a purification technique for sediment extracts and as an extraction technique for water samples prior to analysis by GC-ECD. SPME/GC-ECD coupling was optimized and applied to the trace analysis of nine explosives including nitroaromatics and RDX in real seawater and marine sediment samples. Addition of a high concentration of salt (30%, w/v) in the aqueous medium and use of a carbowax/divinylbenzene (CW/DVB) coating led to optimal extraction efficiencies. Method detection limits (MDLs) ranged from 0.05 to 0.81 microg/L in water and from 1 to 9 microg/kg in dry sediment. Except for RDX, spike recoveries in seawater were satisfactory (89-147%) when samples were fortified at 2 microg/L of each analyte. Spike recoveries from dry sediment fortified at 10 microg/kg of each analyte gave lower recoveries but these could also be due to degradation in the matrix. With a smaller volume of aqueous sample required compared to solid-phase extraction (SPE), SPME is an attractive method for the analysis of limited volumes of sediment pore-water. Moreover, the use of SPME eliminated interferences present in sediment extracts thus allowing the detection of the target analytes that were otherwise difficult to detect by direct injection.     

Chiral amidophosphane-copper-catalyzed asymmetric conjugate addition of dialkylzinc reagents to nitroalkenes

The copper-amidophosphane-catalyzed asymmetric addition reaction of dialkylzinc reagents with β-aryl and β-alkylnitroalkenes afforded the corresponding nitroalkanes with moderate to good enantioselectivities (54-80% ee). The performance was highly dependent on the reaction procedure where the addition of nitroalkene to the mixture of copper-amidophosphane and dialkylzinc gave higher ee than the addition of dialkylzinc to a mixture of copper-amidophosphane and nitroalkene.     

Genuine heteroleptic complexes of early rare-earth metals: synthesis, X-ray structure, and their use for stereospecific isoprene polymerization catalysis

Genuine heteroleptic neodymium and samarium complexes of formula [Cp*'Ln[(p-tol)NN](BH4)] (Cp*' = C5Me4(nPr), (p-tol)NN = (p-tol)NC(Me)CHC(Me)N(p-tol), Ln = Sm: 1a, Ln = Nd: 1b) have been synthesized for the first time. These unprecedented homologues of early lanthanocenes are prepared by a metathetic reaction between their monocyclopentadienylbisborohydrido precursors with the corresponding potassium diketiminate. Both complexes were obtained in good yields and were characterized by 1H NMR spectroscopy and elemental analysis. Complex 1 a has an non-solvated dimeric structure, as indicated by its crystallographic data. The chloroneodymium analogue [Cp*'Nd[(p-tol)NN](Cl)] (2b) was only obtained as a part of a mixture. Analysis of crystals of 2b by X-ray diffraction revealed a molecular structure very similar to that of 1a. Preliminary isoprene polymerization experiments were carried out with 1 b in the presence of an alkylmagnesium coactivator. The resulting bimetallic Nd/Mg system behaves as an efficient and highly stereospecific catalyst with the synthesis of trans-1,4-polyisoprene with more than 98% regularity. The control of the polymer structure is related to the steric hindrance around the lanthanide atom.     

Size-based characterization of nanometric cationic maghemite particles using capillary zone electrophoresis

Size-sorted maghemite (gamma-Fe(2)O(3)) particle populations of number mean solid diameters ranging from 6 to 10 nm were suspended and directly characterized in their stabilizing acidic, citrated or basic aqueous media using CZE coupled with UV detection. Analytical conditions were optimized in order to ensure reliable mobility measurements of these ferrofluids in their anionic and cationic forms. Particular interest has been paid to the investigation of the positively charged ferrofluids since cationic colloids have received little attention so far. A strategy for capillary wall modification was chosen in order to prevent particle adsorption while preserving high analytical performances. The influence of experimental conditions such as particle volume fraction, injection volume, electric field strength and electrolyte nature on electrophoretic profiles and measured electrophoretic mobilities was evaluated. A size-dependent electrophoretic mobility was demonstrated and discussed in terms of the ratio of the particle radius to Debye length with reference to existing models (Henry, etc.). Although these nanometric particle distributions lie in a very narrow size range, partial separation was obtained with selectivity varying as a function of electrolyte ionic strength.     

Isolation of Functionalized Phenolic Monomers through Selective Oxidation and C?O Bond Cleavage of the β‐O‐4 Linkages in Lignin

Functionalized phenolic monomers have been generated and isolated from an organosolv lignin through a two‐step depolymerization process. Chemoselective catalytic oxidation of β‐O‐4 linkages promoted by the DDQ/tBuONO/O₂ system was achieved in model compounds, including polymeric models and in real lignin. The oxidized β‐O‐4 linkages were then cleaved on reaction with zinc. Compared to many existing methods, this protocol, which can be achieved in one pot, is highly selective, giving rise to a simple mixture of products that can be readily purified to give pure compounds. The functionality present in these products makes them potentially valuable building blocks.