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Search Results: 1 - 10 of 530332 matches for " Antonio S. C.;Santos "
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Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques  [PDF]
Márcio L. Dos Santos, Heloísa A. Acciari, Carla S. Riccardi, Antonio C. Guastaldi
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.27098
Abstract: The aim of this work was to evaluate the corrosion resistance of AuPdAgIn alloy, submitted to laser beam welding, in 0.9% NaCl solution, using electrochemical techniques. Measures of the open circuit potential (OCP) versus time were applied to electrochemical experiments, as well as potentiodynamic direct scanning (PDS) and electrochemical impedance spectroscopy (EIS) on AuPdAgIn alloy, submitted to laser beam welding in 0.9% NaCl solution. Some differences observed in the microstructure can explain the results obtained for corrosion potential, Ecorr, and corrosion resistance, Rp. EIS spectra have been characterized by distorted capacitive components, presenting linear impedance at low frequencies, including a non-uniform diffusion. The area of the laser weld presented corrosion potential slightly superior when compared to the one of the base metal. The impedance results suggest the best resistant corrosion behavior for laser weld than base metal region. This welding process is a promising alternative to dental prostheses casting.
Synthesis of the Prospective Anticancer Molecule Perillic Acid from Orange Essential Oil by the Yeast Yarrowia lipolytica  [PDF]
Marcelo R. R. Tappin, Felipe M. Knopp, Igor C. Cardoso, Roberta T. Santos, Bruna S. Drummond, Antonio C. Siani, Elba P. S. Bon, Maria Antonieta Ferrara
Green and Sustainable Chemistry (GSC) , 2017, DOI: 10.4236/gsc.2017.72013
Abstract: The bioconversion of the hydrophobic and volatile limonene to perillic acid, a potential anticancer agent, by the yeast Yarrowia lipolytica was studied in two steps. Firstly, experimental design was used for process optimization using high-purity limonene as substrate and secondly orange essential oil containing 89.1% limonene was used as substrate under the previously optimized conditions. Limonene concentration and pH were identified by fractional factorial design as significant factors and were optimized by central composite design. Under optimized process conditions (0.16% (v/v) limonene; pH 6.9), the 24 h biotransformation process resulted in the accumulation of 0.368 g·L-1 of perillic acid corresponding to a molar yield of 23.1%. A subsequent substrate addition under the same reaction conditions doubled perillic acid concentration to 0.793 g·L-1 and a molar yield of 24.2%. The use of orange essential oil under the optimized reaction conditions increased both perillic acid accumulation and yield to 0.872 g·L-1 and 29.7%, respectively. The robustness of Y. lipolytica allowed the efficient biotransformation of a crude by-product of the citrus industry into a valuable fine chemical.
Electrochemical and electrocatalytic studies of toluidine blue immobilized on a silica gel surface coated with niobium oxide
Santos, Antonio S.;Pereira, Arnaldo C.;Kubota, Lauro T.;
Journal of the Brazilian Chemical Society , 2002, DOI: 10.1590/S0103-50532002000400014
Abstract: the electrochemical behavior of toluidine blue (tb) adsorbed on a silica surface modified with niobium oxide (sn) was investigated using a modified carbon paste electrode. the presence of sn gave the electrode high stability, avoiding the leaching out of the mediator from the electrode surface. the formal potential (e0') of the adsorbed tb was ?113 mv vs. sce, indicating a shift of almost 100 mv towards more positive potential values, compared to tb dissolved in aqueous solution or adsorbed on carbon paste. the stability and formal potential remained constant upon changing the solution ph in the range 5 to 8. in these solution ph values the electrocatalytic activity remained almost constant with a sensitivity of 1.2 10-4 a l mol-1 cm-2 and a kmapp of 4.9 10-5 mol l-1. a linear response range for nadh concentration between 2.0 10-4 and 4.0 10-3 mol l-1 at ph 7.0, with a detection limit of 3.4 10-5 mol l-1 was observed for the sensor. a response time of 2 s and a precision of 1.0 %, expressed as relative standard deviation for 10 replicates, were observed for the sensor developed.
Electrochemical and electrocatalytic studies of toluidine blue immobilized on a silica gel surface coated with niobium oxide
Santos Antonio S.,Pereira Arnaldo C.,Kubota Lauro T.
Journal of the Brazilian Chemical Society , 2002,
Abstract: The electrochemical behavior of toluidine blue (TB) adsorbed on a silica surface modified with niobium oxide (SN) was investigated using a modified carbon paste electrode. The presence of SN gave the electrode high stability, avoiding the leaching out of the mediator from the electrode surface. The formal potential (E0') of the adsorbed TB was --113 mV vs. SCE, indicating a shift of almost 100 mV towards more positive potential values, compared to TB dissolved in aqueous solution or adsorbed on carbon paste. The stability and formal potential remained constant upon changing the solution pH in the range 5 to 8. In these solution pH values the electrocatalytic activity remained almost constant with a sensitivity of 1.2 10-4 A L mol-1 cm-2 and a K Mapp of 4.9 10-5 mol L-1. A linear response range for NADH concentration between 2.0 10-4 and 4.0 10-3 mol L-1 at pH 7.0, with a detection limit of 3.4 10-5 mol L-1 was observed for the sensor. A response time of 2 s and a precision of 1.0 %, expressed as relative standard deviation for 10 replicates, were observed for the sensor developed.
Two different modes for copper(II) ion coordination to quinine-type ligands
Rey Nicolás A.,Santos Karina C. dos,Menezes Maria ?. B. C.,Mangrich Antonio S.
Journal of the Brazilian Chemical Society , 2006,
Abstract: Three new copper(II) complexes with the ligands quinuclidine [Cu(C7H13N)2(OH2)Cl]Cl.2H 2O (1), quinine [Cu(C20H23O2N2)(OH 2)2]ClO4 (2), and hydroquinidine [Cu(C20H27O2N2)(OH 2) Cl2]Cl.fraction one-halfH2O (3) have been isolated and characterized. The binding sites were assigned on the basis of vibrational spectroscopy, electron paramagnetic resonance, and thermal analysis results. The possibility of the involvement of the quinuclidinic nitrogen in the coordination was evidenced in complex 1, in which copper(II) is coordinated to two quinuclidine molecules. In the case of quinine-type ligands, if the starting material is deprotonated in both nitrogens, copper(II) coordination occurs through the quinuclidinic nitrogen, as in complex 2. In contrast, if the starting material is protonated in the quinuclidinic nitrogen the binding site is the quinolinic nitrogen, as in complex 3. Therefore, both nitrogens of quinine-type ligands constitute binding sites for copper(II) ions.
Levels of As, Cd, Pb and Hg found in the hair from people living in Altamira, Pará, Brazil: environmental implications in the Belo Monte area
Carvalho, Antonio S. C.;Santos, Alberdan S.;Pereira, Simone F. P.;Alves, Cláudio N.;
Journal of the Brazilian Chemical Society , 2009, DOI: 10.1590/S0103-50532009000600022
Abstract: human hair was used as a bioindicator to evaluate the levels of as, cd, pb and hg in the resident population of the "volta grande" area of the xingu river, in the north of brazil. the concentrations of as and cd are in agreement with the values found in the literature, however, the pb and hg concentration is very different, which can suggest an inter-regional variation. moreover, the high values found for these elements in the residents of the canteiro island can be attributed to environmental exposure of this population in an area with environmental impact from activities of gold mining. the application of these methods showed that the concentrations of the metals studied in this work can correctly classify two different localities in the altamira district. the results reflect the impact of these elements on the health of the inhabitants of this auriferous area.
Biochar & Carbon Sequestration [Biocarv o (Biochar) e Sequestro de Carbono]
Edivaltrys I. P. Rezende,Lilian C. Angelo,Sailer S. dos Santos,Antonio S. Mangrich
Revista Virtual de Química , 2011,
Abstract: The traditional answer to the question of controlling the growth of global warming involves reducing emissions of greenhouse gases like CO2. However, developed and developing countries have difficulty in adopting measures to reduce use of fossil fuels in the short or medium term. The world is currently exceeding the rate of greenhouse gas emissions. Consequently, it is urgently necessary to remove carbon dioxide from the atmosphere. Extensive research efforts in science and technology are underway to develop approaches to capture and sequester carbon. In this work we deal with the different processes proposed, but with great emphasis on the process of biochar production by pyrolysis of biomass which copies the methodology of Terra Preta de índios da Amazonia.
Two different modes for copper(II) ion coordination to quinine-type ligands
Rey, Nicolás A.;Santos, Karina C. dos;Menezes, Maria ?. B. C.;Mangrich, Antonio S.;Pereira-Maia, Elene C.;
Journal of the Brazilian Chemical Society , 2006, DOI: 10.1590/S0103-50532006000300010
Abstract: three new copper(ii) complexes with the ligands quinuclidine [cu(c7h13n)2(oh2)cl]cl·2h 2o (1), quinine [cu(c20h23o2n2)(oh 2)2]clo4 (2), and hydroquinidine [cu(c20h27o2n2)(oh 2) cl2]cl·?h2o (3) have been isolated and characterized. the binding sites were assigned on the basis of vibrational spectroscopy, electron paramagnetic resonance, and thermal analysis results. the possibility of the involvement of the quinuclidinic nitrogen in the coordination was evidenced in complex 1, in which copper(ii) is coordinated to two quinuclidine molecules. in the case of quinine-type ligands, if the starting material is deprotonated in both nitrogens, copper(ii) coordination occurs through the quinuclidinic nitrogen, as in complex 2. in contrast, if the starting material is protonated in the quinuclidinic nitrogen the binding site is the quinolinic nitrogen, as in complex 3. therefore, both nitrogens of quinine-type ligands constitute binding sites for copper(ii) ions.
Caracteriza??o dos estádios ontogenéticos de três espécies de palmeiras: uma proposta de padroniza??o para estudos de dinamica populacional
Portela, Rita de Cássia Quitete;Santos, Flavio Antonio Ma?s dos;
Brazilian Journal of Botany , 2011, DOI: 10.1590/S0100-84042011000400006
Abstract: the objective of this study was to identify, classify and describe the ontogenetic stages and/or size classes of three tropical palm species, astrocaryum aculeatissimum (schott) burret, euterpe edulis mart. and geonoma schottiana mart. the populations were sampled in five fragments of atlantic rain forest in 2005. all individuals had their diameter and height measured, and also the number and kind of leaf recorded in each fragment of nine 30 × 30 m plots. based on these measurements, we assigned each individual to one of five classes. astrocaryum aculeatissimum and e. edulis change their kind of leaf throughout development. geonoma schottiana has a high variation in the kind of leaf, and only the seedlings stage displays only one kind of leaf. the appearance of stem and reproductive events also represents class change. the kind of leaf, the surge of the stem and reproductive events were the main characteristics used for the ontogenetic stage identification. however, for e. edulis and g. schottiana class identification, we also used quantitative characteristic because some stages have wide size variation. studies that characterize and describe species ontogenetic stages are very important for standardization and to allow comparison between studies of population structure and dynamics.
Produ??o e espessura da serapilheira na borda e interior de fragmentos florestais de Mata Atlantica de diferentes tamanhos
Portela, Rita de Cássia Quitete;Santos, Flavio Antonio Ma?s dos;
Brazilian Journal of Botany , 2007, DOI: 10.1590/S0100-84042007000200011
Abstract: nowadays, forests fragmentation is one of the main impacts in the natural communities and can lead to extinction of many species and modifications in many ecological processes. the present work aimed to evaluate the influence of the size and the edge of forest fragments in the production and accumulation of litter and in the canopy openness of four different-size forest fragments of the atlantic forest. the litter production was bigger in the larger fragment (8.90 t ha-1 year-1 in the interior and 8.76 t ha-1 year-1 in the edge) than in the three smaller fragments (7.29 t ha-1 year-1 in the interior and 7.27 t ha-1 year-1 in the edge), however the thickness of the litter layer deposited on the ground and the canopy openness of the forest had no relation with the size of the fragments. no difference was found in the production and accumulation of litter and canopy openness between areas of edge and interior. the dry season had a direct influence in the increase of the litter production. concerning the fragment area, we can infer that the difference between litterfall and accumulation on the ground might be related with the greater decomposition rates in the larger fragment, due to the higher humidity. no relation between litter production and canopy openness was found, probably because of the great spatial heterogeity caused by the frequency of gap formation and structural complexity and deciduousness of the forest.
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