Enzymatic formation of ions and their detection at a three-phase electrode

An electrochemical method for the detection of enzymatically created anions is described that uses a thin-film electrode with decamethylferrocene as an electroactive redox probe. The enzymatic oxidation of glucose with enzyme glucose oxidase produces gluconic acid as a final product. The oxidation of decamethylferrocene dissolved in the thin-nitrobenzene film, that is spread on the working graphite electrode and submerged in the aqueous solution containing glucose and glucose oxidase, is followed by the up-take of gluconate anions from the aqueous phase to nitrobenzene. The peak currents of the square-wave voltammetric responses of that system are a linear function of the glucose concentration in the milimolar range from 0.1 mmol/L to 0.7 mmol/L (R²=0.994).     

Adsorption of amyloid beta-peptide at polymer surfaces: a neutron reflectivity study.

The adsorption of amyloid beta-peptide at hydrophilic and hydrophobic modified silicon-liquid interfaces was characterized by neutron reflectometry. Distinct polymeric films were used to obtain noncharged (Formvar), negatively (sodium poly(styrene sulfonate)) and positively charged (poly(allylamine hydrochloride)) hydrophilic as well as hydrophobic surfaces (polystyrene and a polysiloxane-dodecanoic acid complex). Amyloid beta-peptide was found to adsorb at positively charged hydrophilic and hydrophobic surfaces, whereas no adsorbed layer was detected on hydrophilic noncharged and negatively charged films. The peptide adsorbed at the positively charged film as patches, which were dispersed on the surface, whereas a uniform layer was observed at hydrophobic surfaces. The thickness of the adsorbed peptide layer was estimated to be approximately 20 A. The peptide formed a tightly packed layer, which did not contain water. These studies provide information about the affinity of the amyloid beta-peptide to different substrates in aqueous solution and suggest that the amyloid fibril formation may be driven by interactions with surfaces.     

Shock wave study on the thermal unimolecular decomposition of allyl radicals

We present the first direct study on the thermal unimolecular decomposition of allyl radicals. Experiments have been performed behind shock waves, and the experimental conditions covered temperatures ranging from 1125 K up to 1570 K and pressures between 0.25 and 4.5 bar. Allyl radicals have been generated by thermal decomposition of allyl iodide, and H-atom resonance absorption spectroscopy has been used to monitor the reaction progress. A marked pressure dependence of the rate constant has been observed which is in agreement with the results from a master equation analysis. However, our experimental results as well as our Rice-Ramsperger-Kassel-Marcus calculations seem to contradict the results of Deyerl et al. (J. Chem. Phys. 1999, 110, 1450) who investigated the unimolecular decomposition of allyl radicals upon photoexcitation and tried to deduce specific rate constants for the unimolecular dissociation in the electronic ground state. At pressures around 1 bar we extracted the following rate equation: k(T) = 5.3 x 10(79)(T/K)(-19.29) exp[(-398.9 kJ/mol)/RT] s(-1). The uncertainty of the rate constant calculated from this equation is estimated to be 30%.     

Effect of Free Trimethylaluminum Content in Methylaluminoxane on Performances of Bis(salicylaldiminate)nickel(II)‐Based Catalysts for Ethylene Polymerization

Summary: The performances of ethylene polymerization catalysts based on III and commercial methylaluminoxane were investigated by reducing the content of free trimethylaluminum in methylaluminoxane by its reaction with 2,6‐di‐tert‐butylphenol. This allowed optimization of the formulation of the catalyst, affording a high‐molecular‐weight linear polyethylene (PE) with a productivity [(1 900 kg of PE/(mol of Ni × h)], ten‐fold higher than that previously achieved for the same system adopting commercial methylaluminoxane not pre‐treated with the above phenol derivative.

     

Optimization of a centrifugation and ultrasound-assisted procedure for the determination of trace and major elements in marine invertebrates by ICP OES

A three factor Doehlert design was applied to optimize the extraction of elements in marine invertebrate samples (oyster, mussel and clam) using centrifugation with diluted acids. The factors were: concentration of acid mixture (HCl + HNO₃ + H₃CCOOH; 1–3 mol L^{− 1}), centrifugation time (10–40 min), and rotation velocity (6000–10,000 rpm). In order to evaluate the ultrasound effect on the extraction of trace metals, a portion of the certified oyster tissue sample (NIST 1556b; 0.250 g) was sonicated for 15 min and then the solution was centrifuged at the optimized conditions. The optimized procedure was then applied to nine marine invertebrate samples (oysters, clams and mussels) collected at Todos os Santos Bay, Bahia, Brazil. The optimized condition of the developed method was: 20 min of centrifugation at 9000 rpm using the acid mixture 1.0 mol L^{− 1}. The effect of sonication prior centrifugation was very variable, but it promoted a significant increase in the extraction (12 to 44%) of some trace elements. Moreover, the combination of the centrifugation with sonication offered other advantages, such as improvement of the precision and accuracy, both demonstrated using the oyster tissue reference sample. The results of major and trace elements in marine invertebrate samples showed that elements such us Cd and Cu in oyster samples and Zn in mussel and clam samples were above recommendations, suggesting that its consumption may impose health risks.     

Production of Enzymes by Paenibacillus chitinolyticus and Paenibacillus ehimensis to Obtain Chitooligosaccharides

Obtaining oligosaccharides from chitosan has been the focus of several studies in the pharmaceutical, chemical, food, and medical areas, due to their functional properties. Here, we evaluated the production potential of biologically functional chitooligosaccharides using enzymes extracts produced by Paenibacillus chitinolyticus and Paenibacillus ehimensis. After 48 h of fermentation, these microorganisms were able to produce chitosanases, which generated oligomers with a degree of polymerization between dimers and hexamers. The maximum conversion of chitosan to oligomers was 99.2 %, achieved after 12 h incubation of chitosan with enzymes produced by P. ehimensis. The chitooligosaccharides generated were capable of scavenging the 2,2-diphenyl-1-picrylhydrazyl radical, reaching a maximum scavenging rate of 61 and 39 % when produced with P. ehimensis and P. chitinolyticus enzymes, respectively. The use of these enzymes in the crude form could facilitate their use in industrial applications.     

Mineral composition of fruit by-products evaluated by neutron activation analysis

Brazil is one of the largest producers of fruits cropping 40 million tons per year. In agro-food processing, approximately 50 % of raw material is discarded generating large amounts of by-products. The lack of information on the nutritional quality of agroindustrial by-products precludes their potential use in the manufacture of food products accessible to all. In this context, the objective of this work was to investigate the nutritional quality of by-products of the industrial processing of fruits. Samples of bagasse, peel and seeds of several fruits (banana, camu camu, coconut, cupuaçu, guava, jackfruit, mango, orange, papaya, pineapple, and soursop) were analysed by neutron activation analysis for the determination of Br, Ca, Co, Cr, Cs, Fe, K, La, Na, Rb, Sc and Zn. In general, higher levels of minerals were found in the by-products rather than in the pulps of fruits. This indicates that the use of the by-products should be encouraged, thereby reducing the economic and environmental impact of waste generated by agroindustrial processing.     

Conformational variability in a new terpenoid-like bischalcone: Structure and theoretical studies

A new terpenoid-like bischalcone (1E,4E)-1-(4-nitrophenyl)-5-(2,6,6-trimethylcyclohex-1-enyl)-penta-1,4-dien-3-one was synthesized from a β-ionone and 4-nitrobenzaldehyde by Claisen-Schmidt condensation reaction and its structure was determined by single crystal X-ray diffraction analysis. Additionally, this compound was featured by powder X-ray diffraction, ¹H, ¹³C NMR and IR spectroscopy techniques. The molecule in the asymmetric unit showed disordered occupancy sites over two positions for the trimethylcyclohexene atoms. These two conformations were related by a rotation of about 180° around the axis of the C-C bond linking the six-membered ring and the olefin carbons. Single-molecule calculations using the DFT method have strengthened this structural finding, since our theoretical approaches also suggest two well-defined conformations of similar energies which resemble the molecular geometries determined by X-ray diffraction. Furthermore, the inspection of the crystal packing revealed that the hydrogen bonding patterns are different for each conformation of the compound reported here.     

Interfacial properties and thermal stability of modified poly(m‐phenylene isophthalamide) thin films

Poly(m‐phenylene isophthalamide) (PMIA) is a resistant to high temperatures and chemically stable engineering material. The application as coatings and membranes, however, is limited by its poor interaction with other materials. In this report, we describe the molecular modification of PMIA through reaction with dimsyl sodium and 2‐iodine‐1‐ethanol. The substitution of 58% of amide hydrogen by ethanol (etOH) groups produces a material (MPMIA) able to develop regularly structured films on silicon substrate. The morphology of the films is dependent on the ionic strength of the precursory solution. MPMIA starts a degradation process by losing the etOH group. MPMIA has a better affinity with poly(p‐cresolformaldehyde) than with a pristine one, increasing the range of composition in which thermal stability and miscibility are observed. Thin films of these blends have different morphologies that vary from nanometric porous to two‐phase microstructured grains, according to the composition. Copyright © 2012 John Wiley & Sons, Ltd.