23 research outputs found
Synthesis of l-cystine nanotubes by alkalinization of l-cysteine in the presence of gallium nitride
No full textThe alkaline oxidation of l-cysteine (l-Cys) was conducted in aqueous media forming the insoluble l-cystine dimer as confirmed by X-ray diffraction. In another experiment, a gallium nitride film was added to the l-Cys solution and the l-cystine crystals presented a preferential growth. The transmission electron microscopy images showed the formation of single- and multi-wall l-cystine nanotubes. The infrared and high resolution electron microscopy data suggested that the growth of the tubes resulted from the successive staking of l-cystine dimers onto the (0 0 1) family of planes, which was a consequence of the ionic assembly between l-cystine over a layer of l-Cys molecules previously grafted to the gallium nitride particles. � 2013 Elsevier B.V. All rights reserved
Intercalation studies of zinc hydroxide chloride: Ammonia and amino acids
No full textZinc hydroxide chloride (ZHC) is a layered hydroxide salt with formula Zn 5(OH) 8Cl 2�2H 2O. It was tested as intercalation matrix for the first time and results were compared with intercalation products of the well-known zinc hydroxide nitrate and a Zn/Al layered double hydroxide. Ammonia was intercalated into ZHC, while no significant intercalation occurred in ZHN. Aspartic acid intercalation was only achieved by co-precipitation at pH=10 with ZHC and pH=8 with zinc hydroxide nitrate. Higher pH resistance in ZHC favored total deprotonation of both carboxylic groups of the Asp molecule. ZHC conferred more thermal protection against Asp combustion presenting exothermic peaks even at 452 �C while the exothermic event in ZHN was 366 �C and in the LDH at 276 �C. � 2011 Elsevier Inc. All rights reserved
Immobilization of enzymatic extract from Penicillium camemberti with lipoxygenase activity onto a hybrid layered double hydroxide
No full textA Zn/Al layered double hydroxide was synthesized by alkaline co-precipitation with azelate ions (-OOC(CH2)7COO-). The interlayer space of the layered material is occupied by organic ions as confirmed by X-ray diffraction and FTIR spectroscopy. The resulting hybrid material was tested as support for Penicillium camemberti enzymatic extract, containing lipoxygenase (LOX) activity. The optimal condition for LOX immobilization is done with 0.6 mol L-1 potassium phosphate buffer and pH 6.0. The affinity for the substrate is the same after immobilization, however the specific activity slightly decreases. The immobilization enhanced the thermal stability, which was evident with incubation at 60 °C where the immobilized enzyme retains 68% of specific activity while the free enzyme is inhibited. Recycling assays showed that after eight reaction cycles, the immobilized enzyme retains 60% of the activity. © 2009 Elsevier B.V. All rights reserved
Immunologic parameters evaluations in Nile tilapia (Oreochromis niloticus) exposed to sublethal concentrations of diazinon
No full textA Zn/Al layered double hydroxide was synthesized by alkaline co-precipitation with azelate ions (-OOC(CH2)7COO-). The interlayer space of the layered material is occupied by organic ions as confirmed by X-ray diffraction and FTIR spectroscopy. The resulting hybrid material was tested as support for Penicillium camemberti enzymatic extract, containing lipoxygenase (LOX) activity. The optimal condition for LOX immobilization is done with 0.6 mol L-1 potassium phosphate buffer and pH 6.0. The affinity for the substrate is the same after immobilization, however the specific activity slightly decreases. The immobilization enhanced the thermal stability, which was evident with incubation at 60 °C where the immobilized enzyme retains 68% of specific activity while the free enzyme is inhibited. Recycling assays showed that after eight reaction cycles, the immobilized enzyme retains 60% of the activity. " 2009 Elsevier B.V. All rights reserved.",,,,,,"10.1016/j.bej.2009.08.011",,,"http://hdl.handle.net/20.500.12104/42070","http://www.scopus.com/inward/record.url?eid=2-s2.0-72149096269&partnerID=40&md5=72f4abd7c7a97245bdbc5c6741280b9a",,,,,,"1",,"Biochemical Engineering Journal",,"9
Effect of synthesis conditions on the morphology and crystal structure of biferroic Bi5Ti3FeO15
No full textThe biferroic Aurivillius-phase Bi5Ti3FeO 15 was obtained by molten salt synthesis (MSS) using an equimolar mixture of NaCl/KCl as the ionic solvent. The morphology, size and crystal structure of the material was strongly dependent on the synthesis conditions. Particles with plate-like morphology and high aspect relation were obtained with sizes ranging from 50 nm to 10 ?m. Using conventional X-ray diffraction, it was qualitatively determined that at synthesis temperatures lower than 850 C, the phase has a tetragonal structure, while at temperatures at or above 850 C, the phase presents an orthorhombic structure. Synchrotron X-ray diffraction and Rietveld refinement were used to determine the crystal structure of the best crystallized phase in detail (synthesis temperature: 850 C). The model that best fits the experimental data is the orthorhombic space group A21am. The lattice parameters (�) determined are a=5.47722(6), b=5.44365(6) and c=41.17004(37). The crystalline particles obtained were used to obtain highly textured polycrystalline material with high densities (?>96% of theoretical maximum density). � 2013 Elsevier Ltd and Techna Group S.r.l.All rights reserved
Nocturnalism induced by scheduled feeding in diurnal octodon degus
No full textAn attempt to prepare a metalorganic precursor of gallium with reactivity at low temperature in chemical vapor deposition (CVD) systems was done by reacting N-methylpyrrolidine with metal gallium or gallium nitrate under mild conditions. The precursors were bubbled into a CVD assemblage and then reacted with ammonia at temperatures between 400 and 700 °C. The depositions onto silicon substrates were pyramidal particles of 100 nm width at the base and up to 55 nm in height. The rise in growth temperature increased particle density from 0.9 to 27.1 particles per square micron, but reduced the height from 50 to 10 or 2 nm. XPS spectra showed the presence of gallium and nitrogen. The intensity of the gallium spectrum decreased as the process temperature increased indicating that GaNx particles were deposited rather than the stoichiometric gallium nitride (GaN). An additional N1s band of impurities appeared whose intensity increases with the reaction temperature. The lower impurity content corresponded to the sample prepared with Ga(NO 3)3 at 400 °C. " 2011 Elsevier Ltd. All rights reserved.",,,,,,"10.1016/j.jpcs.2011.10.013",,,"http://hdl.handle.net/20.500.12104/43156","http://www.scopus.com/inward/record.url?eid=2-s2.0-84904785238&partnerID=40&md5=fa66ec2f48a6d7292e90e25c921924e6",,,,,,"2",,"Journal of Physics and Chemistry of Solids",,"33
Open photoacoustic cell technique as a tool for thermal and thermo-mechanical characterization of teeth and their restorative materials
No full textA precursor to produce perovskite-type YCrO 3 was precipitated by bubbling gaseous ammonia into an yttrium/chromium salts solution. X-ray diffraction showed that the as-prepared powders were amorphous. Thermal treatment between 1273 and 1373 K, leads to formation of polycrystalline YCrO 3 with crystal sizes around 20 nm. High resolution X-ray photoelectron spectra showed uniform chemical environment for yttrium and chromium in the amorphous hydroxide and crystalline YCrO 3. Shifts between Y 3d 5/2 and Cr 2p 3/2 binding energy suggest redistribution or charge transfer between yttrium and chromium ions in the YCrO 3 structure. The electrical properties of YCrO 3, whose precursors were precipitated with gaseous ammonia are different than those prepared by combustion synthesis. Electrical conductivity presents a sudden increase at ?473 K, which is associated to the grain size and morphology of the crystallites. The redistribution of charge between Y(III) and Cr(III) is thermally activated by the hopping of small-polarons, which are characterized by the Arrhenius law as the conductive mechanism. " 2012 Elsevier Ltd. All rights reserved.",,,,,,"10.1016/j.materresbull.2012.02.043",,,"http://hdl.handle.net/20.500.12104/42007","http://www.scopus.com/inward/record.url?eid=2-s2.0-84860300742&partnerID=40&md5=43db1070f5641539c7eaa5ec2353b2a7",,,,,,"6",,"Materials Research Bulletin",,"144
Electroencephalographic activity during sexual behavior: A novel approach to the analysis of drug effects on arousal and motivation relevant for sexual dysfunctions
No full textGaN was synthesized onto sapphire substrates by chemical vapor deposition, reacting gallium, ammonium chloride and ammonia. The polycrystalline films were immersed in glycine, aspartic acid and cysteine solutions. Cysteine chemisorbed onto GaN films produced detectable changes in conductivity, mobility and Hall coefficient indicating that GaN is capable of detecting and reacting with thiolate groups, which was confirmed by X-ray photoelectron spectroscopy. The Cys-GaN film solution was adjusted to pH 10, upon which the GaN nanoparticles were transferred to the aqueous phase forming a suspension stable for seven days. The alkaline colloid was then further adjusted down to pH 3 retaining stability for three days. The GaN colloid obtained represents a suitable medium to study GaN properties for biological applications. " 2012 Elsevier B.V.",,,,,,"10.1016/j.colsurfb.2012.04.040",,,"http://hdl.handle.net/20.500.12104/41190","http://www.scopus.com/inward/record.url?eid=2-s2.0-84861548817&partnerID=40&md5=c72ed082231da1ab1c2157fd7fa250c
Hydroxide precursors to produce nanometric YCrO 3: Characterization and conductivity analysis
No full textA precursor to produce perovskite-type YCrO 3 was precipitated by bubbling gaseous ammonia into an yttrium/chromium salts solution. X-ray diffraction showed that the as-prepared powders were amorphous. Thermal treatment between 1273 and 1373 K, leads to formation of polycrystalline YCrO 3 with crystal sizes around 20 nm. High resolution X-ray photoelectron spectra showed uniform chemical environment for yttrium and chromium in the amorphous hydroxide and crystalline YCrO 3. Shifts between Y 3d 5/2 and Cr 2p 3/2 binding energy suggest redistribution or charge transfer between yttrium and chromium ions in the YCrO 3 structure. The electrical properties of YCrO 3, whose precursors were precipitated with gaseous ammonia are different than those prepared by combustion synthesis. Electrical conductivity presents a sudden increase at ∼473 K, which is associated to the grain size and morphology of the crystallites. The redistribution of charge between Y(III) and Cr(III) is thermally activated by the hopping of small-polarons, which are characterized by the Arrhenius law as the conductive mechanism. © 2012 Elsevier Ltd. All rights reserved
Immobilization of laccase on hybrid layered double hydroxide
No full textCrystals of Mg/Al layered double hydroxide were synthesized by alkaline precipitation and treated in an aqueous solution of glutamic acid. The glutamate ions were not intercalated into the interlayer space, but were detected in the material by Fourier transform infrared spectroscopy, suggesting that only the external surfaces of crystals were modified with glutamate ions. The resulting hybrid material was tested as a support for immobilization of the enzyme lacease (Myceliophthora thermophild). The immobilized enzyme preparation was characterized by electronic paramagnetic resonance spectroscopy and by assays of catalytic activity. The activity of the immobilized lacease was 97% of the activity in the free enzyme. Layered double hydroxide is a suitable support for use in remediation of soil studies
