Hydrogen absorption and desorption properties of Mg/MgH2 with nanometric dispersion of small amounts of Nb(V) ethoxide

A study to determine the optimal content of Nb(V) ethoxide required to efficiently catalyze the H₂ sorption kinetics in the Mg/MgH₂ system is reported. The materials were synthesized by hand mixing different amounts of additive (from 0.10 to 1 mol%) to pre-milled MgH₂. Considering kinetics and capacity the best performance corresponds to a 0.25 mol% of Nb ethoxide concentration. With this material, a remarkable kinetic behavior with excellent reversibility is obtained: 5.3 wt% and 5.1 wt% of hydrogen are absorbed and desorbed respectively at 300 °C in 3 min. At 250 °C the material absorbs 5.2 wt% of hydrogen and releases 3.7 wt% in 10 min. Thermal desorption starts at 247 °C and peaks at 268 °C. The H₂ sorption properties of all the materials remain unchanged after 10 cycles of absorption and desorption at 300 °C, and the best material reversibly takes in and releases 5.3 wt% of H₂ during a 10 min combined cycle. The kinetic improvement of the hydrogen desorption and absorption properties is attributed to an enhancement of the kinetic processes that occur on the surface of the material, due to the excellent spreading of the liquid additive at nanometric level, as revealed by SEM/EDS and TEM/EELS.     

Dietary exposure and risk assessment of polychlorinated dibenzo-p-dioxins,polychlorinated dibenzofurans and dioxin-like polychlorinated biphenyls of the population in the Region of Valencia (Spain)

Dietary exposure of the Valencia Region population to polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and PCBs was assessed in the Region of Valencia in 2010–2011. A total of 7700 food samples were collected. Occurrence data were combined with consumption data to estimate dietary exposure in adults (>15 years of age) and young people (6–15 years of age). The estimated intake was calculated by a probabilistic approach. Average intake levels (upper-bound scenario) were 1.58 and 2.76 pg toxic equivalent (TEQ) kg^?1 body weight (bw) day^?1 for adults and young people, respectively. These average intakes are within range of the tolerable daily intake of 1–4 pg WHO-TEQ kg^?1 bw day^?1 recommended by WHO, and slightly above the tolerable weekly intake (TWI) of 14 pg TEQ kg^?1 bw week^?1 and the Provisional tolerable monthly intake of 70 pg TEQ kg^?1 bw month^?1 set by the Scientific Committee on Food and the Joint FAO/WHO Expert Committee on Food, respectively. These results show that the contamination levels in food and therefore the exposure of the general population to PCDD/Fs and PCBs have declined in this region and therefore show the efficiency of the European risk-management measures. In terms of risk characterisation, the results showed that, under the upper-bound scenario, 22% of the adult and 58% of the young people population could exceed the TWI.     

Biochemical characterization of an isoform of chymotrypsin from the viscera of Monterey sardine (Sardinops sagax caerulea), and comparison with bovine chymotrypsin

Chymotrypsin II from the viscera of Monterey sardine was characterized as an isoform of chymotrypsin I previously characterized from the same source and compared with bovine chymotrypsin. Chymotrypsin II had a molecular weight of 25,500 Da, similar to bovine chymotrypsin. The isoform identity as chymotrypsin was established by its catalytic specificity on the specific substrates succinyl-l-ala-ala-pro-l-phenylalanine-p-nitroanilide and benzoyl-l-tyrosine ethyl ester, showing higher specific activity than bovine chymotrypsin. Both enzymes showed maximal activity at pH 8.0, chymotrypsin II being stable at alkaline pH while bovine chymotrypsin was stable at acid and alkaline pH. Optimum temperature was 45 °C for chymotrypsin II and 55 °C for bovine chymotrypsin. Both enzymes were inhibited by phenylmethylsulfonyl-fluoride and soybean trypsin inhibitor, and partially by N-toluenesulfonyl-l-phenylalanine chloromethyl-ketone. This is valid only in specific conditions of this work. K_m and k_cat for chymotrypsin II were 0.048 mM and 4.8 s⁻¹, and 0.09 mM and 1.9 s⁻¹ for bovine chymotrypsin. Catalytic efficiency of chymotrypsin II was 4.8-fold higher than bovine chymotrypsin.     

Studies on diacetylenic vinyl compounds

The copolymerization of maleic anhydride (MAn) with phenyl-4-vinylphenylbutadiyne(PVPB) was carried out using 2, 2-azobisisobutyronitrile as an initiator. Although PVPB does not homopolymerize by free radicals in solution, it copolymerized giving copolymers having average molecular weights up to 12,000, and consisting of slightly more PVPB units. The monomer reactivity ratios were estimated to be r (MAn)=0 and r (PVPB) =0.1–0.2. It was concluded that the copolymerization likely proceeds via a free monomer propagation mechanism rather than through a donor-acceptor complex mechanism.     

Radiation Graft Copolymerization of Acrylic Acid and <Emphasis Type="Italic">N</Emphasis>-Isopropylacrylamide from binary mixtures onto Polytetrafluoroethylene

Summary Acrylic acid and N-isopropylacrylamide were grafted from their binary mixtures in water onto polytetrafluoroethylene films -preirradiated in air. Effects of preirradiation dose as well as temperature of grafting on efficiency of this process were investigated, the optimal values of dose and temperature were 20 kGy and 50 °C, respectively. The calculated monomers reactivity ratios by their graft copolymerization (r₁ and r₂ ) were 0.35 and 0.01, respectively. The grafted copolymers exhibited a temperature-responsive character in the range of 17-30 °C.     

Studies on salts of amine‐containing polymers with benzoic acids. III. Poly(N,N‐dimethylaminoethyl methacrylate‐g‐polyethylene) with benzoic acids

Poly(N,N‐dimethylaminoethyl methacrylate) [poly(DMAEMA)] was grafted onto a commercial polyethylene film by means of γ‐irradiation, and the grafted films were reacted with various liquid‐crystal‐forming benzoic acids. When polymeric salts consisting only of poly(DMAEMA) and the benzoic acids were heated, dissociation of salts was observed, but with poly(DMAEMA) grafted onto polyethylene films, salt dissociation or crystallization of dissociated acids could be avoided, and interesting morphologies, including liquid‐crystal phases, were observed for the systems of benzoic acids–poly(DMAEMA‐g‐polyethylene). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 972–978, 2000     

New Interpenetrating Polymer Networks of N-isopropylacrylamide/ N-acryloxysuccinimide: Synthesis and Characterization

Interpenetrating polymer networks (IPNs) based on poly (N-isopropylacrylamide), PNIPAAm, and poly (N-acryloxysuccinimide), PNAS, were prepared by a sequential method; the PNIPAAm which was polymerized and crosslinked by gamma irradiation, was swelled in a solution of PNAS/polylysine, which function as crosslinking agent for this monomer and as anchoring element of vesicles. The thermosensitivity properties (limit swelling time, lower critical solution temperature (LCST) and water retention), chemical composition (FTIR and elemental analysis), thermal properties (DSC and TGA) and morphology (SEM) were studied to characterize the IPNs.     

Studies on diacetylenic vinyl compounds

Phenyl-4'-vinylphenyl butadiyne was synthesized, and its polymerization under various conditions was quantitatively studied. The polmerization in solution using azobisisobutyronitrile as an initiator was very slow and the yield was low. The polymerization in molten state at 80°C gave mostly an insoluble polymer, but a small part was soluble in chloroform, which was the vinyl polymer. Irradiation with UV light in the crystalline state also gave soluble and insoluble polymers, and the soluble polymer was the vinyl type. The monomer readily polymerized at –78°C in tetrahydrofuran with n-butyl lithium to give poly(p-phenylbutadiynyl styrene).     

Pressurised liquid extraction and capillary electrophoresis–mass spectrometry for the analysis of pesticide residues in fruits from Valencian markets,Spain

A procedure based in capillary electrophoresis–mass spectrometry (CE–MS) for the analysis of seven pesticides (flutolanil, simazine, haloxyfop, acifluorfen, dinoseb, picloram, and ioxynil) in four Mediterranean summer fruits with high water content (peaches, melon, watermelon, and apricot) is developed. Several conditions were studied for the optimisation of both, the separation and the electrospray (ESI) connection. The best results were obtained using 35 mM ammonium formiate (pH 9.7) as separation buffer, 20 °C as capillary temperature and 23 kV as applied voltage in an uncoated fused-silica capillary with 50 cm total length, 25 cm thermostated length, 25 cm at room temperature length, connected to an MS detector by an ESI sprayer kit. The appropriate sheath liquid was ammonium formiate with 10% of formic acid at 5 μL min⁻¹. Separation time for all pesticides was achieved in 12 min. Extraction was carried out by pressurised liquid extraction (PLE) in an ASE® 200 system from Dionex using hot water at 60 °C and 1500 psi, followed by a solid-phase extraction (SPE) clean-up step using StrataX cartridges. Recoveries ranged from 58% to 88% and the relative standard deviations (RSDs) were 9–19%. The limits of detection (LODs) and quantification (LOQs) were in all cases lower than the MRLs, 0.01 and 0.05 mg kg⁻¹, respectively. The potential of the method was demonstrated by analysing summer fruits taken from agricultural Mediterranean zone cooperatives.