Poly(2,5-bibenzimidazole) Membranes: Physico-Chemical Characterization Focused on Fuel Cell Applications

Membranes of Poly(2,5-benzimidazole) (ABPBI), prepared by polycondensation in polyphosphoric acid, were characterized from the fuel cell application point of view: mechanical properties of the membranes for different acid doping levels, thermal stability, permeability for the different gases/vapors susceptible of use in the cell (hydrogen, oxygen, methanol and ethanol), electro-osmotic water drag coefficient, oxidation stability to hydroxyl radicals, phosphoric acid leaching rate and, finally, in-plane membrane conductivity. ABPBI membranes presented an excellent thermal stability, above 500 degrees C in oxygen, suitable mechanical properties for high phosphoric acid doping levels, a low methanol and ethanol limiting permeation currents, and oxygen permeability compared to Nafion membranes, and a low phosphoric acid leaching rate when exposed to water vapor. On the contrary, hydrogen permeation current was higher than that of Nafion, and the chemical stability was very limited. Membrane conductivity achieved 0.07 S cm(-1) after equilibration with a humid environment. Fuel cell tests showed reasonable good performances, with a maximum power peak of 170 mW cm(-2) for H-2/air at 170 degrees C operating under a humidified hydrogen stream, 39.9 mW cm(-2) for CH3OH/O-2 at 200 degrees C for a methanol/water weight ratio of 1: 2, and 31.5 mW cm(-2) for CH3CH2OH/O-2 at the same conditions than for methanol. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.014207jes] All rights reserved.

Improvement of fungal arabinofuranosidase thermal stability by reversible immobilization

A gene encoding a-L-arabinofuranosidase (abfA) from Aspergillus niveus was identified, cloned, and successfully expressed in Aspergillus nidulans. Based on amino acid sequence comparison, the 88.6 kDa enzyme could be assigned to the GH family 51. The characterization of the purified recombinant AbfA revealed that the enzyme was active at a limited pH range (pH 4.0-5.0) and an optimum temperature of 70 degrees C. The AbfA was able to hydrolyze arabinoxylan, xylan from birchwood, debranched arabinan, and 4-nitrophenyl arabinofuranoside. Synergistic reactions using both AbfA and endoxylanase were also assessed. The highest degree of synergy was obtained after the sequential treatment of the substrate with endoxylanase, followed by AbfA, which was observed to release noticeably more reducing sugars than that of either enzyme acting individually. The immobilization of AbfA was performed via ionic adsorption onto various supports: agarose activated by polyethyleneimine polymers, cyanogen bromide activated Sepharose, DEAE-Sepharose, and Sepharose-Q The Sepharose-Q derivative remained fully active at pH 5 after 360 min at 60 degrees C, whereas the free AbfA was inactivated after 60 min. A synergistic effect of arabinoxylan hydrolysis by AbfA immobilized in Sepharose-Q and endoxylanase immobilized in glyoxyl agarose was also observed. The stabilization of arabinofuranosidases using immobilization tools is a novel and interesting topic. (C) 2012 Elsevier Ltd. All rights reserved.

Bioclimatic characterization of outdoor and confined systems for pregnant sows

Pregnant sows confinement systems were created in order to maximize the productivity, however there are problems concerning the animal welfare. The aim of this research was to evaluate pregnant sows in outdoors and in confinement systems in relation to the thermal environment and physiological animal responses. The experiment was conducted in a commercial farm in Monte Mor city, Sao Paulo, Brazil. The physiological evaluation was performed by recording physiological variables, such as respiratory frequency and skin temperature. Furthermore, variables like dry bulb temperature, wet bulb temperature, and black globe temperature were also evaluated to characterize the ambient by means of enthalpy and black globe humidity index. In each treatment six animals were evaluated. The experimental design was completely randomized in a split-plot version whose averages were compared by the Tukey test. The findings of the experiment revealed higher values for all the bioclimatic variables in the confined treatment. Hence, the outdoor system provided better thermal conditioning for pigs, resulting in a lower heat stress.

The migration of Mn2+ ions in Cd1-xMnxS nanocrystals: Thermal annealing control

This work reports evidence of the induced migration of Mn2+ ions in Cd(1-x)MnxS nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn2+ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions. (C) 2011 Elsevier Ltd. All rights reserved.

DETERMINATION OF DICLOFENAC SODIUM IN RABBIT PLASMA BY HPLC/UV: EVALUATION AND CHARACTERIZATION OF ITS CRYSTALLINE FORMS, ANHYDROUS AND HYDRATE, ON THE ANTIPYRETIC EFFECT

Diclofenac sodium (DS) is a non-steroidal anti-inflammatory drug that is widely prescribed for the treatment of rheumatoid arthritis and post-surgery analgesia. The active pharmaceutical ingredient is the anhydrous form; however, it can also exist in hydrate form. In this context, knowing the properties of the solid state is important and relevant in the pharmaceutical area because they have a significant impact on the solubility, bioavailability, and chemical stability of the drugs. In the present study, data from XRPD, FTIR spectroscopy, and thermal analysis were used for the identification and characterization of DS forms (anhydrous and hydrate). An HPLC method was optimized to evaluate the plasma concentration of DS in rabbits. The optimized method exhibited good linearity over the range 0.1-60 mu g/mL with correlation coefficients of >0.9991. The mean recovery was 100%. Precision and accuracy were determined within acceptable limits. Finally, to compare the pharmacological properties of anhydrous and hydrate DS forms, we investigated their effects in the febrile response induced by lipopolysaccharide from E. coli in rabbits. The results show that the antipyretic effect of anhydrous and hydrate DS forms are similar.

Electrical characterization of poly(amide-imide) for application in organic field effect devices

The admittance spectra and current-voltage (I-V) characteristics are reported of metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors employing cross-linked poly(amide-imide) (c-PAI) as the insulator and poly(3-hexylthiophene) (P3HT) as the active semiconductor. The capacitance of the MIM devices are constant in the frequency range from 10 Hz to 100 kHz, with tan delta values as low as 7 x 10(-3) over most of the range. Except at the lowest voltages, the I-V characteristics are well-described by the Schottky equation for thermal emission of electrons from the electrodes into the insulator. The admittance spectra of the MIS devices displayed a classic Maxwell-Wagner frequency response from which the transverse bulk hole mobility was estimated to be similar to 2 x 10(-5) cm(2) V(-1)s(-1) or similar to 5 x 10(-8) cm(2) V(-1)s(-1) depending on whether or not the surface of the insulator had been treated with hexamethyldisilazane (HMDS) prior to deposition of the P3HT. From the maximum loss observed in admittance-voltage plots, the interface trap density was estimated to be similar to 5 x 10(10) cm(-2) eV(-1) or similar to 9 x 10(10) cm(-2) eV(-1) again depending whether or not the insulator was treated with HMDS. We conclude, therefore, that HMDS plays a useful role in promoting order in the P3HT film as well as reducing the density of interface trap states. Although interposing the P3HT layer between the insulator and the gold electrode degrades the insulating properties of the c-PAI, nevertheless, they remain sufficiently good for use in organic electronic devices. (c) 2012 Elsevier B.V. All rights reserved.

Elaboration and Characterization of Nano-Biocomposites Based on Plasticized Poly(Hydroxybutyrate-Co-Hydroxyvalerate) with Organo-Modified Montmorillonite

Nano-biocomposites based on a biodegradable bacterial copolyester, poly(hydroxybutyrate-co-hydroxyvalerate), have been elaborated with an organo-modified montmorillonite (OMMT) clay as nanofiller, and acetyl tributyl citrate as plasticizer. The corresponding (nano)structures, thermal and mechanical properties, permeability, and biodegradability have been determined. Polyhydroxyalkanoates are very thermal sensitive then to follow the degradation the corresponding matrices have been analyzed by size exclusion chromatography. The results indicate that the addition of the plasticizer decreases the thermo-mechanical degradation, during the extrusion. These nano-biocomposites show an intercalated/exfoliated structure with good mechanical and barrier properties, and an appropriated biodegradation kinetic. Intending to understand the changes in the thermal properties, the nano-biocomposites were characterized by thermal gravimetric analysis and differential scanning calorimetry. The presence of the OMMT clay did not influence significantly the transition temperatures. However, the filler not only acted as a nucleating agent which enhanced the crystallization, but also as a thermal barrier, improving the thermal stability of the biopolymer. The results indicated that the addition of the plasticizer reduces the glass transition temperature and the crystalline melting temperature. The plasticizer acts as a processing aid and increases the processing temperature range (lower melting temperature).

Synthesis and characterization of CeO2-graphene composite

The synthesis and characterization of graphite oxide (GO), graphene (GS), and the composites: GS-CeO2 and GO-CeO2 are reported. This synthesis was carried out by mixing aqueous solutions of CeCl3 center dot 7H(2)O and GO, which yields the oxidized composite GO-CeO2. GO-CeO2 was hydrothermally reduced with ethylene glycol, at 120 A degrees C, yielding the reduced composite GS-CeO2. GO, GS ,and the composites with CeO2 were characterized by CHN, TG/DTG, BET, XRD, SEM microscopy, FTIR, and Raman spectroscopy. The estimation of crystallite size of CeO2 anchored on GO and on GS by Raman, XRD, and SEM agreed very well showing diameters about 5 nm. The role of particles of CeO2 coating carbon sheets of GO and GS was discussed.

Strontium zirconate heterogeneous catalyst for biodiesel production: Synthesis, characterization and catalytic activity evaluation

Strontium zirconate oxide was synthesized by co-precipitation and the citrate route and was evaluated as a heterogeneous catalyst for biodiesel production. The catalyst samples were characterized by XRD, FTIR, and TG, and catalytic activity was measured based on the ester content of the biodiesel produced that was quantified by GC. The co-precipitate samples were obtained in alkaline pH and had a mixture of the perovskite and pure strontium and zirconium oxide phases. Ester conversion using these samples was approximately 1.6%, indicating no catalytic activity. The citrate route was more efficient in producing perovskite when carried out at pH 7-8; excess SrCO3 was found on the catalyst surface due to CO2 adsorption, thus demonstrating no catalytic activity. The same synthesis carried out at pH 2 resulted in free OH- groups, with a small amount of the carbonate species that produced ester yield values of 98%. Therefore, matrices based on strontium zirconate produced via the citrate route in acidic media are potential heterogeneous catalysts for transesterification. (C) 2012 Elsevier B.V. All rights reserved.

Dinuclear copper(II) complexes with valsartan. Synthesis, characterization and cytotoxicity

Two novel dinuclear complexes involving the antihypertensive drug valsartan and copper(II) ion have been prepared in water and DMSO. The complex compositions were determined as: [Cu(vals)(H(2)O)(3)](2)center dot 6H(2)O and [Cu(vals)(H(2)O)(2)DMSO](2)center dot 2H(2)O. They were thoroughly characterized by elemental and thermal analysis, spectrophotometric titrations and UV-visible, diffuse reflectance, FTIR, Raman and EPR spectroscopies. No effect of the ligand on two tested osteoblastic cell lines in culture (one normal MOT3E1 and one tumoral UMR106) was observed in concentrations up to 100 mu M. Higher concentrations of Valsartan are required to induce cytotoxicity in both cell lines. The antiproliferative effect of the tested complex ([Cu(vals) (H(2)O)(3)](2)center dot 6H(2)O) in a dose-response manner, was higher in the UMR106 osteoblastic cell line than that of the MC3T3E1 normal line at concentrations >= 100 mu M. Morphological alterations are in accordance with proliferative observations. (C) 2011 Elsevier Inc. All rights reserved.

Comparative study and characterization of starches isolated from unconventional tuber sources

Some properties of canna (Canna indica L.) and bore (Alocasia macrorrhiza) starches were evaluated and compared using cassava starch (Manihot esculenta Crantz) as a reference. Proximate analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and viscosity measurements were performed. Canna and bore starches showed a similar degree of purity as that of the cassava starch. Canna starch exhibited higher thermal stability and viscosity of solution values than those of bore and cassava starches. XRD spectra showed that canna starch crystallizes as a B-type structure; however, bore and cassava starches crystallize as an A-type structure. Results proved that canna and bore starches are promising bio(materials), obtained from unconventional sources, to be used for industrial applications, as their physicochemical properties are similar to those of cassava starch, which it is known has potential applications in this area.

Functional characterization and oligomerization of a recombinant xyloglucan-specific endo-beta-1,4-glucanase (GH12) from Aspergillus niveus

Xyloglucan is a major structural polysaccharide of the primary (growing) cell wall of higher plants. It consists of a cellulosic backbone (beta-1,4-linked glucosyl residues) that is frequently substituted with side chains. This report describes Aspergillus nidulans strain A773 recombinant secretion of a dimeric xyloglucan-specific endo-beta-1,4-glucanohydrolase (XegA) cloned from Aspergillus niveus. The ORF of the A. niveus xegA gene is comprised of 714 nucleotides, and encodes a 238 amino acid protein with a calculated molecular weight of 23.5 kDa and isoelectric point of 4.38. The optimal pH and temperature were 6.0 and 60 degrees C, respectively. XegA generated a xyloglucan-oligosaccharides (XGOs) pattern similar to that observed for cellulases from family GH12, i.e., demonstrating that its mode of action includes hydrolysis of the glycosidic linkages between glucosyl residues that are not branched with xylose. In contrast to commercial lichenase, mixed linkage beta-glucan (lichenan) was not digested by XegA, indicating that the enzyme did not cleave glucan beta-1,3 or beta-1,6 bonds. The far-UV CD spectrum of the purified enzyme indicated a protein rich in beta-sheet structures as expected for GH12 xyloglucanases. Thermal unfolding studies displayed two transitions with mid-point temperatures of 51.3 degrees C and 81.3 degrees C respectively, and dynamic light scattering studies indicated that the first transition involves a change in oligomeric state from a dimeric to a monomeric form. Since the enzyme is a predominantly a monomer at 60 degrees C. the enzymatic assays demonstrated that XegA is more active in its monomeric state. (c) 2012 Elsevier B.V. All rights reserved.

Physical-chemical, thermal, and functional properties of achira (Canna indica L.) flour and starch from different geographical origin

Achira (Canna indica L.) is a plant native to the Andes in South America, a starchy source, and its cultivation has expanded to different tropical countries, like Brazil. In order to evaluate the potential of this species, starch and flours with different particle size were obtained from Brazilian achira rhizomes. Proximal analyses, size distribution, SEM, swelling power, solubility, DSC, XRD analysis, and FTIR were performed for characterization of these materials. Flours showed high dietary fiber content (16.532.2% db) and high concentration of starch in the case of the smaller particle size fraction. Significant differences in protein and starch content, swelling power, solubility, and thermal properties were observed between the Brazilian and the Colombian starch. All the studied materials displayed the B-type XRD pattern with relative crystallinity of 20.1% for the flour and between 27.0 and 28.0% for the starches. Results showed that the starch and flour produced from achira rhizomes have great technological potential for use as functional ingredient in the food industry.

Synthesis and characterization of implants for bone substitutions made of biomedical apatites containing silicon

In the last decades the development of bone substitutes characterized by a superior biomimetism has become of particular interest, owing to the increasing economic and societal impact of the bone diseases. In the present work of research the development of bone substitutes characterized by improved biomimetism, has been faced in a chemical, structural and morphological perspective. From a chemical point of view, it has been developed the synthesis of hydroxyapatite powders, exhibiting multiple ionic substitutions in both cationic and anionic sites, so to simulate the chemical composition of the natural bone. Particular emphasis has been given to the effect of silicon on the chemical-physical and solubility properties of the obtained hydroxyapatites. From a structural point of view, it has been developed the synthesis of ceramic composite materials, based on hydroxyapatite and calcium silicates, employed both as a reinforcing phase, to raise the mechanical strength of the composite compared to hydroxyapatite, and as a bioactive phase, able to increase the bioactivity properties of the whole ceramic. Finally the unique morphological features of the bone were mimicked by taking inspiration by Nature, so that native wood structures were treated in chemical and thermal way to obtain hydroxyapatite porous materials characterized by the same morphology as the native wood. The results obtained in the present work were positive in all the three different areas of investigation, so to cover the three different aspects of biomimetism, chemical, structural and morphological. Anyway, only at the convergence of the three different fields it is possible to find out the best solutions to develop the ideal bone-like scaffold. Thus, the future activity should be devoted to solve the problems at the borderline between the different research lines, which hamper this convergence and in consequence, the achievement of a bone scaffold able to mimic the various aspects exhibited by the bone tissue

Synthesis and characterization of novel poly(imino ketone)s via palladium-catalyzed aryl amination

The challenge of the present work was to synthesize and to characterize new classes of N-containing polymers via palladium-catalyzed aryl amination. This work was inspired by a desire to combine the properties of high-performance polymers such as PEKs with those of N-containing conductive polymers such as polyaniline (PANI), poly(aromatic amides) (PAAs), and the ready synthesis of N-containing simple aromatic compound by the Buchwald-Hartwig reaction. Careful investigation of a model reaction was carried out to provide insights into the formation of side products which will have a negative effect upon the molecular weight or upon the materials properties of the desired polymers in the polycondensation reaction. In this thesis, five new different polymer classes namely, poly(imino ketone)s (PIKs), poly(imino acridine)s (PIAcs), poly(imino azobenzene)s (PIAzos), poly(imino fluorenone)s (PIFOs), and poly(imino carbazole)s (PICs) were synthesized and fully characterized by means of 1H-NMR, elemental analysis, UV, FT-IR, X-ray, GPC, TGA, DSC, DMA, and dielectric spectroscopy. To optimize the polycondensation process, the influence of the concentration, temperature, ligands and the reactivity of the halogen containing monomers were investigated. A temperature of 100-165 °C and a concentration of 30-36 % were found to be optimal for the palladium-catalyzed polycondensation to produce polymer with high molecular weight (Mn = 85 900, Mw = 474 500, DP = 126). Four different ligands were used successfully in the Pd-catalyzed process, of which the Pd/BINAP system was found to be the most effective catalyst, producing the highest yield and highest molecular weight polymers. It was found that the reactivity decreases strongly with increasing electronegativity of the halogen atoms, for example better yields, and higher molecular weights were obtained by using dibromo compounds than dichloro compounds while difluoro compounds were totally unreactive. Polymer analogous transformations, such as the protonation reaction of the ring nitrogens in PIAcs, or of the azobenzene groups of PIAzos, the photo and thermal cis-trans-isomerization of PIAzos, and of poly(imino alcohol)s were also studied. The values of the dielectric constants of PIKs at 1 MHz were in the range 2.71-3.08. These low values of the dielectric constant are lower than that of "H Film", a polyimide Kapton film which is one of the most preferred high-performance dielectrics in microelectronic applications having a dielectric constant of 3.5. In addition to the low values of the dielectric constants, PIKs have lower and glass transition temperatures (Tgs) than arimides such as Kapton which may make them more easily processable. Cyclic voltammetry showed that PICs exhibited low oxidation and reduction potentials and their values were shifted to low values with increasing degree of polymerization i.e. with increasing of the carbazole content in backbone of PICs (PIC-7, 0.44, 0.33 V, DP= 37, PIC-5, 0.63, 0.46, DP= 16, respectively).