Toxic and essential metals determination in commercial seafood: Paracentrotus lividus by ICP-MS

Toxic and essential metals content was determined by inductively coupled plasma mass spectrometry in commercial sea urchins samples from the Mediterranean Sea and Pacific Ocean. Results show that Chilean samples have the highest values of Cd, As, Ni, Cr and V; Spanish samples have the maximum Hg content while Sicilian samples have the lowest content of toxic metals. The toxic metal traces were compared with the limits of European Community (EC) No. 1881/2006 for bivalve molluscs. All samples exceed Pb and Cd limit levels; regarding Hg levels, only Sicilian and Sardinian samples have Hg content below the EC limits. The dietary intake of toxic and essential elements was evaluated for an adult. Furthermore, our study highlights a correlation between the toxic elements content and the marine environmental conditions of the places of origin even though only the generic FAO fishing area is specified.     

Oppenauer oxidation of secondary alcohols with 1,1,1-trifluoroacetone as hydride acceptor

1,1,1-Trifluoroacetone (2a) reacts as a hydride-acceptor in the Oppenauer oxidation of secondary alcohols (1) in the presence of diethylethoxyaluminum. The oxidant allows for selective oxidation of secondary alcohols in the presence of primary alcohols.     

Shear flow effects on polymer melts crystallization: kinetics features

In this work the kinetics of the isothermal crystallization from the melt of isotactic polyolefins in quiescent conditions as well as after the application of a step-shear flow is investigated by means of rheological measurements. It is shown that the kinetics of the crystallization, as measured by the increase of the storage modulus, is not affected by the strain amplitude and the frequency of the oscillation, once they are properly chosen. A strong enhancement of the crystallization kinetics has been obtained when the step-shear flow was applied at the crystallization temperature T_C=92°C for two different molecular weight poly(1-butene) samples (i-PB400 and i-PB200) and at T_C=137°C for a polypropylene (i-PP). In particular, the overall-crystallization rate constants of the i-PB400 increased with increasing the applied shear rate at a constant total strain of 60. At higher shear flow temperatures slower kinetics occurred in all the cases until the effect of the applied shear flow was lost. Moreover, the effect of the molecular weight on the flow induced crystallization phenomenon is investigated on the two i-PB samples and the results have clearly shown that the higher molecular weight i-PB200 polymer is much more sensitive than the i-PB400 to the flow history.     

Biphasic Synthesis of Hydrogen Peroxide from Carbon Monoxide,Water, and Oxygen Catalyzed by Palladium Complexes with Bidentate Nitrogen Ligands

Effective and stable Pd catalysts for the biphasic synthesis of hydrogen peroxide from carbon monoxide, oxygen, and water [Eq. (a)] can be obtained by the right choice of bidentate nitrogen ligand. The best turnover numbers (578) for this reaction have been achieved with palladium complexes with 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ligands.     

Polymer-solvent interactions in thermoreversible gels of isotactic poly(methyl methacrylate) as studied by measurement of 1h NMR relaxation of the solvent

Dynamic structure and polymer-solvent interactions in solutions and gels of isotactic (i) poly(methyl methacrylate) (PMMA) in butyl acetate (BAC) were characterized by measurements of nonselective and selective ¹H NMR spin-lattice relaxation times of the solvent. In thermoreversible gels, the existence of i-PMMA-BAC complex, where the life-time of the bound solvent is − 100 ms or shorter, was confirmed. Although the correlation time of the solvent bound in i-PMMA-BAC complex is 5-10 times longer than for the free solvent, there is still a relative motional freedom for complexed solvent molecules. The same behaviour observed recently for thermoreversible gels of syndiotactic PMMA indicates the same character of polymer-solvent complexes in gels of both stereoregular forms of PMMA.     

Poly(ε-caprolactone) modified by functional groups: Preparation and chemical–physical investigation

Functionalization of polymers is a particular relevant approach in the field of biodegradable polymers, where modifications are often required to allow these materials to replace more conventional, not biodegradable polymers in a wider range of applications. This article will report on functionalization of poly(ε-caprolactone) with unsaturated monomers bearing either anhydride groups (PCL-g-(MA-GMA)) or tertiary amines (PCL-g-DMAEA), obtained through radical grafting in a Brabender mixer. Crystallization kinetics parameters have been determined with several techniques (rheology, optical microscopy and differential scanning calorimetry) and the results obtained are in good agreement. It was observed that the crystallization rate significantly increases in the case of the modified polymers.     

The role of multi-walled carbon nanotubes in shear enhanced crystallization of isotactic poly(1-butene)

The flow-induced crystallization behavior of nanocomposites, containing isotactic poly(1-butene) (PB) and functionalized multi-walled carbon nanotubes (MWNT), was investigated. Three different MWNT concentrations (0.1, 1, 5 wt%) were used to prepare the nanocomposites. Effects of MWNT and shear flow on the crystallization parameters were evaluated separately. Rheological measurements based on oscillatory shear revealed induction time and crystallization half-time at the quiescent state, where both parameters exhibited the nucleating effect of MWNT on PB. Rheological measurements based on steady-state shear flow and short-time shear flow revealed the evolution of molecular orientation, which was studied in both PB and its nanocomposites. A small increase in crystallization kinetic was recorded in PB under shear having moderate values of the Weissenberg (We) number. On the other hand, a dramatic synergistic effect of MWNT and shear was detected under the same shear conditions for nanocomposites. The optical microscopic images exhibited a clear transition from isotropic to row-like morphology in the case of nanocomposites under shear.     

Crystalline graphite from an organometallic solution-phase reaction

We report a chemical method by which graphitic carbon is prepared at reaction temperatures as low as 110 degrees C from readily available molecular reagents. This process requires no forcing conditions such as high pressures, intense light, or electrical discharge but is a simple, catalytic organometallic reaction. The carbon forms in a variety of morphologies including graphene sheets and nanotubes. The mild reaction conditions are similar to those routinely employed in homogeneous catalysis; therefore, they will allow the subtle manipulation of reaction variables to give desired morphologies selectively.     

Specific features of the optical and electrical properties of polycrystalline CdTe films grown by the thermal evaporation method

The results of studying the physical properties of thin CdTe films obtained by the thermal evaporation method have been presented. The optical constants and the band gap of the films under study have been determined (E _g = 1.46 eV). It has been established based on the investigation of optical properties and the Raman spectrum of the films that they possess high structural quality. The activation energy of the electrical conductivity of CdTe films has been determined: E _a = 0.039 eV. The measured spectral dependences of the impedance of CdTe thin films are characteristic of the inhomogeneous medium with two time constants: τ_gb = R _gb C _gb = 1/ω_gb = 1.62 × 10^?3 s and τ_g = R _g C _g = 1/ω_g = 9.1 × 10^?7 s for grain boundaries and grains, respectively.