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Estudo da atividade do sistema binário RuO2-Ta2O5 preparado por dois métodos de decomposição térmica na oxidação do Etanol; Study of the activity of the binary RuO2-Ta2O5 system prepared for two methods of thermal decomposition in the oxidation of the Ethanol

Ribeiro, Josimar
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/02/2006 PT
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Neste trabalho investigou-se a influência do método de preparação nas propriedades estruturais e eletrocatalíticas do sistema RuO2/Ta2O5. Durante a investigação sistemática, as propriedades mecânicas e morfológicas dos eletrodos foram determinadas usando ânodos de composição nominal Ti/RuO2-Ta2O5 (Ru:Ta - 10 % - 90 % Ru variando em passos de 10 % atômico) preparados pelo método dos precursores poliméricos (MPP), na qual as soluções precursoras foram preparadas pela dissolução de RuCl3.xH2O - Aldrich e Ta(OC2H5)5 - ACROS em etilenoglicol e ácido cítrico. Ânodos de composição nominal Ti/RuO2-Ta2O5 (Ru:Ta = 30:70; 50:50 e 80:20 % atômico) também foram preparados pelo método tradicional (MT), a partir da mistura das razões molares adequadas dos sais de cloretos precursores (RuCl3.xH2O e TaCl5 ( Aldrich) em isopropanol (Aldrich). Para ambos os métodos, a decomposição térmica foi executada a 450 oC por 1h sob fluxo de 5 dm3 min-1 de O2. Análises da composição e da morfologia da camada de óxidos foram feitas antes e após o teste acelerado de vida (TAV), por meio das técnicas de EDX (Energia dispersiva de raios X) e MEV (Microscopia eletrônica de varredura), respectivamente. A microscopia mostrou estrutura de "barro-rachado" para maioria dos filmes. As análises de EDX evidenciaram uma ligeira redução do conteúdo do Ru após o TAV. Dados de DRX (difração de raios X) mostraram forma rutílica para o RuO2 e ortorrômbica para Ta2O5. Os voltamogramas cíclicos deste sistema em meio ácido (0...

In Vitro Evaluation of Surface Roughness and Microhardness of Restorative Materials Submitted to Erosive Challenges

Briso, A. L. F.; Caruzo, L. P.; Guedes, A. P. A.; Catelan, A.; dos Santos, P. H.
Fonte: Operative Dentistry Inc Publicador: Operative Dentistry Inc
Tipo: Artigo de Revista Científica Formato: 397-402
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 08/54115-5; The aim of this study was to evaluate the effect of different acidic solutions on the microhardness and surface roughness of restorative materials. The 120 specimens of restorative materials (Fuji II LC, Vitremer, Supreme XT, and Supreme XT + Biscover LV) were randomly divided into three groups according to the immersion media: hydrochloric acid, soft drink, or distilled water. Over a period of five weeks, the groups were immersed in the solutions, which were changed weekly. Data were tested using analysis of variance and the Fisher protected least significant difference test (p < 0.05). The results showed that the glass ionomer materials showed the highest surface roughness values (Fuji II LC: 0.111 +/- 0.014 mu m before and 0.139 +/- 0.016 mu m after immersion; Vitremer: 0.177 +/- 0.012 mu m before and 0.084 +/- 0.012 mu m after immersion), whereas the lowest values were found for the resin sealed with Biscover LV before (0.047 +/- 0.011 mu m) and after exposure in distilled water (0.043 +/- 0.007 mu m), soft drink (0.040 +/- 0.005 mu m), and hydrochloric acid (0.045 +/- 0.005 mu m). The Supreme XT showed the highest microhardness values before (44.96 +/- 2.51 KHN) and after the aging process (41.26 +/- 1.22 KHN in water...

Helicobacter pylori requires an acidic environment to survive in the presence of urea.

Clyne, M; Labigne, A; Drumm, B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1995 EN
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The aim of this work was to study the significance of the urease enzyme in promoting Helicobacter pylori survival in various environments. A urease-positive H. pylori isolate, strain N6, and an isogenic urease-negative strain, strain N6(ureB::TnKm), were incubated in phosphate-buffered saline at a pH ranging from 2.2 to 7.2 for 60 min at 37 degrees C in both the presence and the absence of 10 mM urea. The number of CFU per milliliter in each solution, the pH of the bacterial supernatant, and the amounts of ammonia present in the solutions were measured. H. pylori N6 survived well in solutions with pH values ranging from 4.5 to 7.0 in the absence of urea but survived in solutions only with an initial pH below 3.5 in the presence of urea. Neither strain grew after incubation in an alkaline environment. The pH of an acidic solution (i.e., 3.5) rose rapidly to 8.45 in the presence of the wild-type strain and urea. The urease-negative mutant survived in solutions with pH values ranging from 4.5 to 7.2 irrespective of the presence of urea. Ammonia was present in significant amounts when H. pylori N6 was incubated in the presence of urea. Strain N6 survived exposure to concentrations of ammonia as high as 80 mM. The acid environment of the stomach may be crucial for H. pylori survival in the presence of urea. H. pylori does not survive in the normal environment in the presence of urea because of the subsequent rise in pH rather than ammonia toxicity.

Variations in Endogenous Gibberellins in Developing Bean Seeds II. Changes Induced in Acidic and Neutral Fractions by GA1 1

Hashimoto, Tohru; Rappaport, Lawrence
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1966 EN
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Immature (8-mm), medium mature (11-mm), and mature green (16- and 17-mm) bean seeds (Phaseolus vulgaris L. cv. Kentucky Wonder and Bountiful) were incubated in gibberellin A1 solutions for 24 hours at 20°. Extracts from the seeds were separated into nonacidic, acidic ethyl acetate, and acidic butanol fractions. These were chromatographed. The eluates of the chromatograms were tested on Progress No. 9 dwarf peas grown under red light. The level of neutral gibberellin-like substances remained unchanged in immature seed, but they increased markedly in mature green seeds. Coincident with increased levels of the neutral substances, there were significant decreases in acidic ethyl acetate-soluble gibberellin-like substances, including applied GA1, and in 1 acidic butanol-soluble gibberellin-like substance. Seed incubation in GA1 brought about increased activity of substance B-II in immature and medium mature seeds. The level of butanol-soluble gibberellin-like substance B-I in seeds of any size was not affected by incubation in GA1. Considering the marked increases in activity induced in the neutral fraction and the decreases in activity of certain eluates from the chromatograms of the acidic fractions, it was concluded that the neutral fraction may serve as a reserve form of gibberellins in the dry seed. The acidic ethyl acetate substances and substance B-II may be required for normal development of the bean seed.

Mechanism of intestinal fatty acid uptake in the rat: the role of an acidic microclimate.

Shiau, Y F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1990 EN
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1. Micellar solubilization of lipolytic products is an important step in lipid absorption. However, micelles are not absorbed intact; dissociation of lipolytic products from bile salt micelles must occur. The dissociation of micelles has been postulated to occur in an acidic microclimate. 2. The effect of an acidic microclimate on the uptake of micellar fatty acid was examined in the rat intestine. We reported that the presence of a lower pH microclimate is associated with a higher fatty acid uptake, suggesting that a lower pH enhances fatty acid uptakes from the micelles. 3. Fatty acid uptake from solutions containing a constant amount of bile salt (10 mM) and varying amounts of fatty acid (3.3-26.4 mM) revealed a saturation phenomenon which reflects the fatty acid carrying capacity of a 10 mM-taurocholate solution. 4. There was a linear relationship between fatty acid uptake and fatty acid concentration when the micellar solutions contained a constant ratio of fatty acid and taurocholate (1.32). 5. Our results indicate that the fatty acid carrying capacity of the micelle and the number of micelles in the solution are both important determinants for the amount of fatty acids delivered to the microclimate. The amount of fatty acids derived from the dissociation of micelles within the microclimate determines fatty acid uptake by the intestine.

A possible method for characterizing the secondary structure of ribonucleic acids

Cox, R. A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1966 EN
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The E280/E260 ratio was found to be suitable for following the ionization of cytosine residues of polynucleotides on the basis of studies with model compounds such as oligoguanylic acid, oligocytidylic acid, a complex formed between polyadenylic acid and polyuridylic acid, and a copolymer of guanylic acid and cytidylic acid, provided that changes in secondary structure were taken into account. The pK of cytosine residues of a polynucleotide in the amorphous form was found to be 4·70 at 25° in 0·1m-sodium phosphate on the basis of titration at 75–85° and on the assumption that the heat of ionization was the same as the value (5·2kcal./mole) found for CMP. In contrast, the pK of cytosine residues in the double-helical form of DNA was found to be about 3·25. These observations were utilized in estimating the fraction of cytosine residues in helical segments of ribosomal RNA, a copolymer of guanylic acid and cytidylic acid, and a copolymer of adenylic acid, guanylic acid, uridylic acid and cytidylic acid. The ionization of guanine and uracil residues was estimated from changes in the E270/E260 ratio and E230/E260 ratio respectively. In the amorphous form of RNA both residues had the same pK, whereas in the double-helical form ionization was suppressed. The fraction of guanine and uracil residues in amorphous segments may be estimated from the titration curves. The difference in the denaturation spectrum of adenine--uracil and guanine--cytosine base pairs at 280mμ was enhanced in acidic solutions whereas E260 was hardly affected. Hence a comparison of the increments in E280 and E260 obtained on increasing the temperature at constant pH may be used to distinguish the melting ranges of helical domains differing in nucleotide composition. In alkaline solutions comparison of the increments in E260 and E270 yields similar information. In acidic solutions the fraction of cytosine residues involved in helical secondary structure...

Acidic phospholipid bicelles: a versatile model membrane system.

Struppe, J; Whiles, J A; Vold, R R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2000 EN
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With the aim of establishing acidic bicellar solutions as a useful membrane model system, we have used deuterium NMR spectroscopy to investigate the properties of dimyristoyl/dihexanoylphosphatidylcholine (DMPC/DHPC) bicelles containing 25% (w/w in H(2)O) of either dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG). The addition of the acidic lipid component to this lyotropic liquid crystalline system reduces its range of stability because of poor miscibility of the two dimyristoylated phospholipids. Compared to the neutral bicelles, which are stable at pH 4 to pH 7, acidic bicelles are stable only from pH 5.5 to pH 7. Solid-state deuterium NMR analysis of d(54)-DMPC showed similar ordering in neutral and acidic bicelles. Fully deuterated DMPS or DMPG is ordered in a way similar to that of DMPC. Study of the binding of the myristoylated N-terminal 14-residue peptide mu-GSSKSKPKDPSQRR from pp60(nu-src) to both neutral and acidic bicelles shows the utility of these novel membrane mimetics.

Removal of Mercury by Foam Fractionation Using Surfactin, a Biosurfactant

Chen, Hau-Ren; Chen, Chien-Cheng; Reddy, A. Satyanarayana; Chen, Chien-Yen; Li, Wun Rong; Tseng, Min-Jen; Liu, Hung-Tsan; Pan, Wei; Maity, Jyoti Prakash; Atla, Shashi B.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 21/11/2011 EN
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The separation of mercury ions from artificially contaminated water by the foam fractionation process using a biosurfactant (surfactin) and chemical surfactants (SDS and Tween-80) was investigated in this study. Parameters such as surfactant and mercury concentration, pH, foam volume, and digestion time were varied and their effects on the efficiency of mercury removal were investigated. The recovery efficiency of mercury ions was highly sensitive to the concentration of the surfactant. The highest mercury ion recovery by surfactin was obtained using a surfactin concentration of 10 × CMC, while recovery using SDS required < 10 × CMC and Tween-80 >10 × CMC. However, the enrichment of mercury ions in the foam was superior with surfactin, the mercury enrichment value corresponding to the highest metal recovery (10.4%) by surfactin being 1.53. Dilute solutions (2-mg L−1 Hg2+) resulted in better separation (36.4%), while concentrated solutions (100 mg L−1) enabled only a 2.3% recovery using surfactin. An increase in the digestion time of the metal solution with surfactin yielded better separation as compared with a freshly-prepared solution, and an increase in the airflow rate increased bubble production, resulting in higher metal recovery but low enrichment. Basic solutions yielded higher mercury separation as compared with acidic solutions due to the precipitation of surfactin under acidic conditions.

The Effect of Long-Term Storage on the Physiochemical and Bactericidal Properties of Electrochemically Activated Solutions

Robinson, Gareth; Thorn, Robin; Reynolds, Darren
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 24/12/2012 EN
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Electrochemically activated solutions (ECAS) are generated by electrolysis of NaCl solutions, and demonstrate broad spectrum antimicrobial activity and high environmental compatibility. The biocidal efficacy of ECAS at the point of production is widely reported in the literature, as are its credentials as a “green biocide.” Acidic ECAS are considered most effective as biocides at the point of production and ill suited for extended storage. Acidic ECAS samples were stored at 4 °C and 20 °C in glass and polystyrene containers for 398 days, and tested for free chlorine, pH, ORP and bactericidal activity throughout. ORP and free chlorine (mg/L) in stored ECAS declined over time, declining at the fastest rate when stored at 20 °C in polystyrene and at the slowest rate when stored at 4 °C in glass. Bactericidal efficacy was also affected by storage and ECAS failed to produce a 5 log10 reduction on five occasions when stored at 20 °C. pH remained stable throughout the storage period. This study represents the longest storage evaluation of the physiochemical parameters and bactericidal efficacy of acidic ECAS within the published literature and reveals that acidic ECAS retain useful bactericidal activity for in excess of 12 months...

Microrheological Characterization of Collagen Systems: From Molecular Solutions to Fibrillar Gels

Shayegan, Marjan; Forde, Nancy R.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 02/08/2013 EN
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Collagen is the most abundant protein in the extracellular matrix (ECM), where its structural organization conveys mechanical information to cells. Using optical-tweezers-based microrheology, we investigated mechanical properties both of collagen molecules at a range of concentrations in acidic solution where fibrils cannot form and of gels of collagen fibrils formed at neutral pH, as well as the development of microscale mechanical heterogeneity during the self-assembly process. The frequency scaling of the complex shear modulus even at frequencies of ∼10 kHz was not able to resolve the flexibility of collagen molecules in acidic solution. In these solutions, molecular interactions cause significant transient elasticity, as we observed for 5 mg/ml solutions at frequencies above ∼200 Hz. We found the viscoelasticity of solutions of collagen molecules to be spatially homogeneous, in sharp contrast to the heterogeneity of self-assembled fibrillar collagen systems, whose elasticity varied by more than an order of magnitude and in power-law behavior at different locations within the sample. By probing changes in the complex shear modulus over 100-minute timescales as collagen self-assembled into fibrils, we conclude that microscale heterogeneity appears during early phases of fibrillar growth and continues to develop further during this growth phase. Experiments in which growing fibrils dislodge microspheres from an optical trap suggest that fibril growth is a force-generating process. These data contribute to understanding how heterogeneities develop during self-assembly...

Dynamics of pH Modification of an Acidic Protein Bait Used for Tropical Fruit Flies (Diptera: Tephritidae)

Heath, Robert R.; Vazquez, Aime; Schnell, Elena Q.; Villareal, Janett; Kendra, Paul E.; Epsky, Nancy D.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
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Several species of Anastrepha and Bactrocera fruit flies (Diptera: Tephritidae) are captured in traps baited with the protein bait NuLure combined with borax (sodium tetraborate decahydrate) in an aqueous solution, typically 9% NuLure (vol:vol) with 3% borax (wt:vol). NuLure is an acid hydrolysate of corn and has an acidic pH. Addition of borax makes the solution more alkaline, and increase in alkalinity results in increase of ammonia release from the bait solution. This is a very dynamic system, with resultant pH affected by factors such as the amount of borax added, the pH of the water used for preparation, the age of the bait solution, and the development of microbial growth. Problems with borax include amount needed to increase alkalinity of NuLure solutions, which creates difficulties in disposing of spent bait in fruit fly trapping programs. Therefore, research was conducted to evaluate NaOH as an alternative method to increase alkalinity of NuLure solutions. Laboratory experiments compared effect of NaOH versus borax for pH modification on changes in pH and ammonia content of NuLure solutions over time. Although NuLure/NaOH solutions could be adjusted to a more alkaline pH than NuLure/borax solutions, borax plays a critical role in pH stability over time. However...

XAS studies of metal speciation in hydrothermal fluids

Tian, Yuan
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2013
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Knowledge of metal speciation and thermodynamic properties underpins our capability to model metal transport and deposition in natural and engineered systems. Using synchrotronbased X-ray Absorption Spectroscopy and high temperature – high pressure experimental techniques, this project aims to elucidate nickel and manganese speciation in hydrothermal chloride solutions, and obtain the thermodynamic properties for predominant species. Ab initio XANES simulation methods were used in this study to provide independent or complementary information about the nature (stoichiometry and geometry) of aqueous complexes. Application of this technique to the calculation of XANES spectra of Mo(VI) complexes in hydrothermal systems confirmed that [MoO₄]²⁻ is stable in neutral and basic solutions over a wide range of temperature and salinity, and chlorinated Mo complexes (e.g., [MoCl₂O₂(H₂O)₂](aq), [MoOCl₄](aq)) exist in strongly acidic solutions. XANES simulations of Te complexes added additional evidence that [Te(OH)₃] and [TeO₃] species predominate in basic and acidic solutions, respectively, and that the deprotonation process to convert [Te(OH)₃] to [TeO₃] is associated with a distance contraction for the Te-O bond. Ni(II) speciation in hydrothermal brines was investigated over a wide range of temperatures (25-434 °C) and fluid compositions (0-7.68 m Cl⁻) at 400 and 600 bar. Quantitative XAS data interpretation revealed that Ni(II) chloroaqua complexes undergo a structural transition from octahedral at room temperature to distorted tetrahedral at elevated temperatures. Both heating and an increase in salinity promote the stability of tetrahedral complexes relative to octahedral complexes. The NiCl₂(aq) species exists in both octahedral [NiCl₂(H₂O)₄](aq) and tetrahedral [NiCl₂(H₂O)₂](aq) forms...

Study of the diffusion in polymer solutions and hydrogels by NMR spectroscopy and NMR imaging

Wang, Yu Juan
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
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Afin d'étudier la diffusion et la libération de molécules de tailles inférieures dans un gel polymère, les coefficients d'auto-diffusion d'une série de polymères en étoile avec un noyau d'acide cholique et quatre branches de poly(éthylène glycol) (PEG) ont été déterminés par spectroscopie RMN à gradient de champ pulsé dans des solutions aqueuses et des gels de poly(alcool vinylique). Les coefficients de diffusion obtenus ont été comparés avec ceux des PEGs linéaires et dendritiques pour étudier l'effet de l'architecture des polymères. Les polymères en étoile amphiphiles ont des profils de diffusion en fonction de la concentration similaires à leurs homologues linéaires dans le régime dilué. Ils diffusent plus lentement dans le régime semi-dilué en raison de leur noyau hydrophobe. Leurs conformations en solution ont été étudiées par des mesures de temps de relaxation spin-réseau T1 du noyau et des branches. L'imagerie RMN a été utilisée pour étudier le gonflement des comprimés polymères et la diffusion dans la matrice polymère. Les comprimés étaient constitués d'amidon à haute teneur en amylose et chargés avec de l'acétaminophène (de 10 à 40% en poids). Le gonflement des comprimés, ainsi que l'absorption et la diffusion de l'eau...

α-Synuclein structures from fluorescence energy-transfer kinetics: Implications for the role of the protein in Parkinson's disease

Lee, Jennifer C.; Langen, Ralf; Hummel, Patrick A.; Gray, Harry B.; Winkler, Jay R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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26.13%
Parkinson's disease is associated with the deposition and accumulation of α-synuclein fibrils in the brain. A30P and A53T mutations have been linked to the early-onset familial disease state. Time-resolved tryptophan fluorescence energy-transfer measurements have been used to probe the structures of pseudo-wild-type and mutant (A30P) α-synucleins at physiological pH (7.4), in acidic pH (4.4) solutions, and in the presence of SDS micelles, a membrane mimic. Fluorescent donor–energy acceptor (DA) distance distributions for six different tryptophan/3-nitro-tyrosine pairs reveal the presence of compact, intermediate, and extended conformations of the protein. CD spectra indicate that the protein develops substantial helical structure in the presence of SDS micelles. DA distributions show that micelles induce compaction in the N-terminal region and expansion of the acidic C terminus. In acidic solutions, there is an increased population of collapsed structures in the C-terminal region. Energy-transfer measurements demonstrate that the average DA distances for the W4–Y19 and Y19–W39 pairs are longer in one of the two disease-related mutants (A30P).

Sensitivity of the sodium and potassium channels of Myxicola giant axons to changes in external pH

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/02/1976 EN
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Myxicola giant axons were studied using standard voltage-clamp techniques in solutions whose pH values ranged from 3.9 to 10.2. Buffer concentrations of 50 mM or greater were necessary to demonstrate the full effect of pH. In acidic solutions the axon underwent a variable depolarization, and both the sodium and potassium conductances were reversibly depressed with approximate pKa's of 4.8 and 4.4, respectively. The voltage dependence of GNa was only slightly altered by acidic conditions, whereas there occurred large shifts in GK along the voltage axis consistent with a substantial decrease in net negative surface charge in the vicinity of the K+ channels. The sodium and potassium activation rate constants were decreased by acidic conditions, but the results could not be described as a simple translation along the voltage axis.

Isolation and characterization of yeasts: application in controlled processes of volatile acidity bio‐reduction in wines

Moura, Alice Maria Correia Vilela
Fonte: Universidade de Trás-os-Montes e Alto Douro Publicador: Universidade de Trás-os-Montes e Alto Douro
Tipo: Tese de Doutorado
ENG
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26.31%
Tese de doutoramento em Microbiologia; O nível de ácido acético, principal componente da acidez volátil, é fundamental para a qualidade do vinho. Os enólogos têm vindo a utilizar um processo de refermentação, com o objectivo de diminuir a concentração de ácido acético em vinhos com acidez volátil elevada. Este processo consiste em misturar o vinho azedo com mostos frescos ou, alternativamente, na incubação do vinho com o bagaço resultante de uma fermentação alcoólica. Este método, embora de utilização frequente e de baixo custo pode causar efeitos inesperados e, por vezes, negativos, sobre os vinhos refermentados. Assim, um desafio para o desenvolvimento de novas soluções com vista à redução da acidez volátil de vinhos, é a selecção de leveduras com capacidade de refermentação de vinhos azedos, para utilização em processos controlados de desacidificação biológica. Neste trabalho isolamos 135 estirpes de leveduras, ao longo de cinco processos de refermentação, à escala de adega, de vinhos com níveis de acidez volátil indesejáveis. Estes isolados, foram seleccionados num meio diferencial sólido quanto à sua capacidade de consumir ácido acético na presença de glucose. Quatro das estirpes seleccionadas revelaram a capacidade de usar simultaneamente o ácido acético e glucose. A caracterização molecular dessas estirpes...

Tectonic hydrogeological survey of the Rio Tinto Mars analog: Implications for Mars underground water fluxes

Gómez-Ortiz, David; Fernández-Remolar, David; Prieto-Ballesteros, Olga; Gómez-Gómez, Felipe
Fonte: NASA Astrobiology Institute Publicador: NASA Astrobiology Institute
Tipo: Póster Formato: 15731 bytes; application/pdf
ENG
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Poster presented at: Bioastronomy 2007: Molecules, Microbes and Extraterrestrial Life (July 16-20, 2007, San Juan de Puerto Rico).; The Iberian Pyritic Belt (IPB) consists of a 250-km long geological unit in southern Iberian Peninsula, and contains massive sulfide deposits. Interaction between groundwater, sulfide deposits and sulfide-free rocks provides geochemical processes controlling the geochemistry of both surface fluids and groundwater. The resulting waters are characterized by an acidic chemistry and high concentrations of sulfur and iron in solution, which control the formation of analogous mineral associations recognized in Meridiani Planum. To understand the processes that drive the mineral formation of sulfur and iron bearing phases, special attention has been paid to the aquifer of Peña de Hierro (Rio Tinto, IPB). To obtain an accurate design of the fracture pattern present at the area, a tectonic study has been carried out. Three different fault systems (ESE-WNW, NNE-SSW and NNW-SSE) control the drainage pattern, the underground water fluxes, and recharge the aquifer from rainwater. The water level in the Peña de Hierro pit lake and different boreholes in the aquifer indicates that they are closely related by a groundwater flow along N140ºE fractures. These fractures intersect the topographic surface generating artesian springs of acidic water.; This research provides some insights to understand the formation of sulfur bearing compounds observed in Meridiani Planum and other regions of Mars. As observed in the Rio Tinto aquifers...

Durabilidad de los cementos de ceniza volante activados alcalinamente; Durability of Alkali-Activated Fly Ash Cementitious Materials

Palomo, Ángel; Fernández-Jiménez, Ana
Fonte: Consejo Superior de Investigaciones Científicas (España) Publicador: Consejo Superior de Investigaciones Científicas (España)
Tipo: Comunicación de congreso Formato: 241654 bytes; application/pdf
SPA; ENG
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Comunicación presentada en las II Jornadas de Investigación en Construcción: "60 años de Informes de la Construcción", celebradas los pasados 22, 23 y 24 de mayo de 2008 en el Instituto "Eduardo Torroja" de Ciencias de la Construcción (IETCC-CSIC) de Madrid.; [EN] The study described in the present paper addresses the comparative durability behaviour between a new cementitious material made from alkali-activated fly ash (AAFA) with 8M NaOH solution and an ordinary Portland cement (reference system) under different conditions. Cements performance was observed in a number of aggressive environments (deionized water, ASTM seawater, 4.4% sodium sulphate solution and acidic solutions 0.1NHCl); additionally durability respect to alkali-silica reaction and the behaviour at high temperature was also studied. The chief parameters under control were: weight loss, compressive strength, variations in volume, presence of the products of degradation and microstructural changes.; [ES] En este trabajo se realiza un estudio comparativo del comportamiento durable frente a diferentes tipos de agresión de un cemento comercial (sistema de referencia) y un nuevo material cementante elaborado mediante la mezcla de ceniza volante con una disolución de NaOH 8M (sin OPC). En concreto se realizaron estudios para determinar la durabilidad frente a diferentes disoluciones agresivas (agua desionizada...

α-Synuclein structures from fluorescence energy-transfer kinetics: Implications for the role of the protein in Parkinson's disease

Lee, Jennifer C.; Langen, Ralf; Hummel, Patrick A.; Gray, Harry B.; Winkler, Jay R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 23/11/2004
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Parkinson's disease is associated with the deposition and accumulation of alpha-synuclein fibrils in the brain. A30P and A53T mutations have been linked to the early-onset familial disease state. Time-resolved tryptophan fluorescence energy-transfer measurements have been used to probe the structures of pseudo-wild-type and mutant (A30P) alpha-synucleins at physiological pH (7.4), in acidic pH (4.4) solutions, and in the presence of SIDS micelles, a membrane mimic. Fluorescent donor-energy acceptor (DA) distance distributions for six different tryptophan/3-nitro-tyrosine pairs reveal the presence of compact, intermediate, and extended conformations of the protein. CID spectra indicate that the protein develops substantial helical structure in the presence of SIDS micelles. DA distributions show that micelles induce compaction in the N-terminal region and expansion of the acidic C terminus. In acidic solutions, there is an increased population of collapsed structures in the C-terminal region. Energy-transfer measurements demonstrate that the average DA distances for the W4-Y19 and Y19-W39 pairs are longer in one of the two disease-related mutants (A30P).

Glass electrode calibration for use in the voltammetric determination of stability constants under extreme acidic conditions

Billing,Caren; Cukrowski,Ignacy
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 EN
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A glass electrode (GE) can be successfully employed to measure pH in the study of metal-ligand equilibria by voltammetry at extremely low pH (between 0 and 2); two consecutive strong acid-strong base titrations involving different base concentrations (recommended to avoid corrosion of the GE in very basic solutions) are best suited to establish the response parameters of a GE. A novel approach of using a combined linear and binomial GE calibration was developed; this procedure allows measurements between pH 0 and 2 with uncertainty better than ±0.01 pH unit. From an extensive error analysis, it has been established that the uncertainties of about ±0.5 mV in the response slope and ±1.3 mV in E°' might result in an absolute error in pH of about 0.02 which should not generate errors larger than 0.3 % in optimized stability constants (as log K values) determined by voltammetry at extremely low pH. A test of GE suitability for the study of metal complexes by voltammetry is also proposed; it should be implemented only for suspect electrodes that show response parameters outside the limits recommended in this work.