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## Disproportionation of Pu(IV) or a Two Step Mechanism - Redox Behavior of Pu(TV) in Acidic Solutions

WALTHER C.; CHO H.r.; MARQUARDT C.m.; NECK V.; SEIBERT Alice; YUN J.i.; FANGHAENEL THOMAS
Fonte: U.S. Department of Energy Publicador: U.S. Department of Energy
Tipo: Contributions to Conferences Formato: CD-ROM
ENG
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see attachment; JRC.E.6-Actinides research

## Chemistry of indigenous Zn and Cu in the soil-water system : alkaline sodic and acidic soils / by Amir Fotovat.

Fotovat, A.
Tipo: Tese de Doutorado Formato: 708617 bytes; application/pdf
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In this study the soil aqueous phase chemistry of Zn and Cu in alkaline sodic soils are investigated. The chemistry of trace metal ions at indigenous concentrations in alkaline sodic soils are reported. Metal ions at low concentrations are measured by the graphite furnace atomic absorption spectrometry (GFAAS) technique.; Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1998; Copies of author's previously published articles inserted.; Bibliography: leaves 195-230.; xx, 320 leaves : ill. (some col.) ; 30 cm.; Title page, contents and abstract only. The complete thesis in print form is available from the University Library.

## Influencia da temperatura de tres sistemas adesivos na resistencia de união e na interação com esmalte bovino abrasionado; The influence of temperature of three adhesive systems on bonding to ground enamel

Rodrigo Sversut de Alexandre
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Estrutura eletrônica de polímeros conjugados : a influência da desordem

Donizetti Aparecido dos Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
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## Hysteresis and conformational changes in ribosomal ribonucleic acid

Cox, R. A.; Katchalsky, A.
Tipo: Artigo de Revista Científica
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Both rat liver and Escherichia coli rRNA in 0.1m-sodium chloride were titrated with acid or alkali over the range pH3–7 at approx. 0°C. rRNA did not bind acid reversibly and hysteresis was observed, i.e. the plot of acid bound to rRNA against pH had the form of a loop showing that the amount of acid bound at a particular pH depended on the direction of the titration. Although the boundary curves were reproducibly followed on titration from pH7 to 3 and from pH3 to 7, points within the loop were scanned', e.g. by titration from pH7 to a point in the range pH3–4 followed by titration with alkali to pH7. It is inferred that the lag' in the release of certain bound protons is at least 1 pH unit, that at least about 9–15% of the titratable groups (adenine and cytosine residues) that are involved in this process and that the free energy dissipated in completing a cycle is approx. 4.2kJ/mol (1kcal/mol) of nucleotide involved in hysteresis. The interpretation of the scanning' curves was illustrated by means of a cycle of possible changes in the conformation of a hypothetical nucleotide sequence that allows formation of poly(A)·poly(AαH+)-like regions in acidic solutions. It is also inferred that the extent of hysteresis' might depend on the primary nucleotide sequence of rRNA as well as on secondary structure.

## Inactivation of Giardia muris cysts by free chlorine.

Leahy, J G; Rubin, A J; Sproul, O J
Tipo: Artigo de Revista Científica
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The chlorine resistance of cysts of the flagellate protozoan Giardia muris was examined. This organism, which is pathogenic to mice, is being considered as a model for the inactivation of the human pathogen Giardia lamblia. Excystation was used as the criterion for cyst viability. Experiments were performed at pH 5, 7, and 9 at 25 degrees C and pH 7 at 5 degrees C. Survival curves were "stepladder"-shaped, but concentration-time data generally conformed to Watson's Law. Chlorine was most effective at neutral pH and was only slightly less so in acidic solutions. Comparison of inactivation data based on equivalent hypochlorous acid concentrations, which corrects for chlorine ionization, showed that the cysts have a pH-dependent resistance to inactivation. Concentration-time (C X t') products for free chlorine obtained at 25 degrees C ranged from a low of 50 mg min/liter at pH 5 to a high of 218 mg min/liter at pH 9 and were as high as 1,000 mg min/liter at 5 degrees C. It appears that G. muris cysts are somewhat more resistant to inactivation than G. lamblia cysts and rank among the microorganisms that are most resistant to inactivation by free chlorine.

## Activities of 3'-azido-3'-deoxythymidine nucleotide dimers in primary lymphocytes infected with human immunodeficiency virus type 1.

Schinazi, R F; Sommadossi, J P; Saalmann, V; Cannon, D L; Xie, M Y; Hart, G C; Smith, G A; Hahn, E F
Tipo: Artigo de Revista Científica
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The relative antiviral potencies of five nucleotide heterodimers of 3'-azido-3'-deoxythymidine (AZT), 3'-azido-3'-deoxythymidilyl-(5',5')-2'-3'-dideoxy-5'-adenylic acid (AZT-P-ddA), 3'-azido-3'-deoxythymidilyl-(5',5')-2',3'-dideoxy-5'-inosinic acid (AZT-P-ddI), and the corresponding 2-cyanoethyl congeners AZT-P(CyE)-ddA and AZT-P(CyE)-ddI, were determined in primary human peripheral blood mononuclear cells infected with human immunodeficiency virus type 1. The homodimer 3'-azido-3'-deoxythymidilyl-(5',5')-3'-azido-3'-deoxythymidilic acid (AZT-P-AZT) was also included for comparison. The potencies of the compounds were AZT-P-ddA greater than or equal to AZT-P-ddI greater than AZT-P(CyE)-ddA greater than or equal to AZT-P(CyE)-ddI greater than or equal to AZT greater than AZT-P-AZT. Whereas AZT-P-ddA and AZT-P-ddI had in vitro therapeutic indices greater than that of AZT, the homodimer of AZT had a low therapeutic index. AZT-P-ddI exhibited the lowest toxicity in peripheral blood mononuclear, Vero, or CEM cells. Combination studies between AZT and 2',3'-dideoxyinosine (ddI) at nontoxic concentrations indicated a synergistic interaction at a drug ratio of 1:100. At higher ratios (1:500 and 1:1,000), the interactions were synergistic only at concentrations that produced up to 75% virus inhibition. At higher levels of antiviral effects...

## Anaerobic oxidation of ferrous iron by purple bacteria, a new type of phototrophic metabolism.

Ehrenreich, A; Widdel, F
Tipo: Artigo de Revista Científica
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Anoxic iron-rich sediment samples that had been stored in the light showed development of brown, rusty patches. Subcultures in defined mineral media with ferrous iron (10 mmol/liter, mostly precipitated as FeCO3) yielded enrichments of anoxygenic phototrophic bacteria which used ferrous iron as the sole electron donor for photosynthesis. Two different types of purple bacteria, represented by strains L7 and SW2, were isolated which oxidized colorless ferrous iron under anoxic conditions in the light to brown ferric iron. Strain L7 had rod-shaped, nonmotile cells (1.3 by 2 to 3 microns) which frequently formed gas vesicles. In addition to ferrous iron, strain L7 used H2 + CO2, acetate, pyruvate, and glucose as substrate for phototrophic growth. Strain SW2 had small rod-shaped, nonmotile cells (0.5 by 1 to 1.5 microns). Besides ferrous iron, strain SW2 utilized H2 + CO2, monocarboxylic acids, glucose, and fructose. Neither strain utilized free sulfide; however, both strains grew on black ferrous sulfide (FeS) which was converted to ferric iron and sulfate. Strains L7 and SW2 grown photoheterotrophically without ferrous iron were purple to brownish red and yellowish brown, respectively; absorption spectra revealed peaks characteristic of bacteriochlorophyll a. The closest phototrophic relatives of strains L7 and SW2 so far examined on the basis of 16S rRNA sequences were species of the genera Chromatium (gamma subclass of proteobacteria) and Rhodobacter (alpha subclass)...

## Temperature dependence of the speciation of copper and iron in acidic electrolytes

Casas, J. M.; Simpson, J.; Cifuentes, L.
Fonte: INST CHEMICAL ENGINEERS Publicador: INST CHEMICAL ENGINEERS
Tipo: Artículo de revista
EN
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Validated speciation models and revised thermodynamic data have been used to establish the temperature dependence of the concentrations of all the main species in aqueous Cu(II)-H2SO4 and Fe(II)-Fe(III)-H2SO4 solutions in the 25-65 degrees C temperature range. Mathematical relationships have been derived for the temperature dependence of the equilibrium constants for the relevant reactions and also for the species concentrations in a well specified set of conditions. These relationships have been developed in order to use them as components of complex temperature-dependent models in hydrometallurgy, but they are also useful as stand-alone predictors of equilibrium data in the studied systems.

## Interaction of proteins in solution from small angle scattering: a perturbative approach

Spinozzi, Francesco; Gazzillo, Domenico; Giacometti, Achille; Mariani, Paolo; Carsughi, Flavio
Tipo: Artigo de Revista Científica
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In this work, an improved methodology for studying interactions of proteins in solution by small-angle scattering, is presented. Unlike the most common approach, where the protein-protein correlation functions $g_{ij}(r)$ are approximated by their zero-density limit (i.e. the Boltzmann factor), we propose a more accurate representation of $g_{ij}(r)$ which takes into account terms up to the first order in the density expansion of the mean-force potential. This improvement is expected to be particulary effective in the case of strong protein-protein interactions at intermediate concentrations. The method is applied to analyse small angle X-ray scattering data obtained as a function of the ionic strength (from 7 to 507 mM) from acidic solutions of $\beta$-Lactoglobuline at the fixed concentration of 10 $\rm g L^{-1}$. The results are compared with those obtained using the zero-density approximation and show a significant improvement particularly in the more demanding case of low ionic strength.; Comment: 12 pages, 3 figures, to appear in Biophysical Journal (April 2002) Due to an unfortunate name mismatch, the original submission contained an incorrect source

## Effect of encapsulated graphene oxide on alginate-based bead adsorption to remove acridine orange from aqueous solutions

Sun, Ling; Fugetsu, Bunshi
Tipo: Artigo de Revista Científica
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Environmentally-benign high-performance graphene oxide (GO)/alginate-based absorbents were prepared to eliminate acridine orange selected as a typical dye. Characterizations demonstrated GO well encapsulated and its promotion of pore formation on structure. Kinetic studies exhibited that the addition of GO shortened the adsorption equilibrium time, raised the initial rate and the adsorption capacity. Isotherm studies indicated the adsorptive behavior followed Langmuir type, and higher maximum capacity was obtained in the presence of GO. The adsorption positively responded to pH increased from acidic to weakly alkaline. At low pH, GO would contribute dominantly to the adsorption, whereas alginate component was inhibited.

## Oxygen and phosphorus enriched carbons from lignocellulosic material

Puziy, Alexander M.; Poddubnaya, Olga I.; Martínez Alonso, Amelia; Castro Muñiz, Alberto; Suárez García, Fabián; Díez Tascón, Juan Manuel
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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10 pages, 10 figures, 3 tables.-- Printed version published Sep 2007.; Activated carbons were prepared by phosphoric acid activation of fruit stones in air at temperatures 400–1000°C. The surface chemistry was investigated by elemental analysis, cation exchange capacity, infrared spectroscopy and potentiometric titration. The porous structure was analyzed from adsorption isotherms (N2 at 77 K and CO2 at 273 K). It was demonstrated that all carbons show considerable cation exchange capacity, the maximum (2.2 mmol g−1) being attained at 700°C, which coincides with the maximum contents of phosphorus and oxygen. The use of air instead of argon during thermal treatment increased the amount of cation exchangeable surface groups for carbons obtained at 400–700°C. Proton affinity distributions of all carbons show the presence of three types of surface groups with pK 1.8–3.1 (carboxylic and polyphosphates), 4.8–6.3 (second dissociation of carboxylic, weak acid in polyphosphates and enol structures) and 8.1–9.7 (phenols and enol structures). Carbons obtained in air at 400–600°C show enhanced copper adsorption from 0.001 mol L−1 Cu(NO3)2 in acidic solutions as compared to carbons obtained in argon. Carbons obtained in air show well-developed porous structure that is equivalent or higher as compared with carbons obtained in argon; the difference being progressively increased with increasing treatment temperature.; This research was made possible in part by the NATO Collaborative Linkage Grant EST.CLG.979588.; Peer reviewed

## Theoretical study on the reactivity of sulfate species with hydrocarbons

Ma, Qisheng; Ellis, Gregory S.; Amrani, Alon; Zhang, Tongwei
Tipo: Article; PeerReviewed Formato: application/pdf
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The abiotic, thermochemically controlled reduction of sulfate to hydrogen sulfide coupled with the oxidation of hydrocarbons, is termed thermochemical sulfate reduction (TSR), and is an important alteration process that affects petroleum accumulations in nature. Although TSR is commonly observed in high-temperature carbonate reservoirs, it has proven difficult to simulate in the laboratory under conditions resembling nature. The present study was designed to evaluate the relative reactivities of various sulfate species in order to provide greater insight into the mechanism of TSR and potentially to fill the gap between laboratory experimental data and geological observations. Accordingly, quantum mechanics density functional theory (DFT) was used to determine the activation energy required to reach a potential transition state for various aqueous systems involving simple hydrocarbons and different sulfate species. The entire reaction process that results in the reduction of sulfate to sulfide is far too complex to be modeled entirely; therefore, we examined what is believed to be the rate limiting step, namely, the reduction of sulfate S(VI) to sulfite S(IV). The results of the study show that water-solvated sulfate anions View the MathML source are very stable due to their symmetrical molecular structure and spherical electronic distributions. Consequently...

## The Mode of Protonation of Amides

Fraenkel, Gideon; Niemann, Carl
Tipo: Article; PeerReviewed Formato: application/pdf
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The relative basicities of oxygen versus nitrogen in amides is a problem which has not been satisfactorily resolved. However, it might be anticipated from considerations of resonance and structural parameters that in strongly acidic solutions the proton will attach to oxygen rather than to nitrogen, to give [structure] I rather than [structure] II. It is generally recognized that amides are monoprotonated in 100 per cent sulfuric acid. For example, O'Brien and Niemann [1] reported i-factors of 2.0, 2.7, 2.0, 2.9, and 1.9 for benzamide, glycinamide, trichloroacetamide, benzoylglycinamide, and phthalimide, respectively, in this solvent. Similarly, in this study we have found the i-factors of N,N-dimethylformamide, N,N-dimethylacetamide, and acetamide to be 2.1, 2.1, and 2.0, respectively. Thus the problem is to locate the locus of protonation in singly protonated primary, secondary, and tertiary amides.

## Electrocatalytic Hydrogen Evolution in Acidic Water with Molecular Cobalt Tetraazamacrocycles

McCrory, Charles C. L.; Uyeda, Christopher; Peters, Jonas C.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf; chemical/x-cif
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A series of water-soluble molecular cobalt complexes of tetraazamacrocyclic ligands are reported for the electrocatalytic production of H2 from pH 2.2 aqueous solutions. The comparative data reported for this family of complexes shed light on their relative efficiencies for hydrogen evolution in water. Rotating disk electrode voltammetry data are presented for each of the complexes discussed, as are data concerning their respective pH-dependent electrocatalytic activity. In particular, two diimine–dioxime complexes were identified as exhibiting catalytic onset at comparatively low overpotentials relative to other reported homogeneous cobalt and nickel electrocatalysts in aqueous solution. These complexes are stable at pH 2.2 and produce hydrogen with high Faradaic efficiency in bulk electrolysis experiments over time intervals ranging from 2 to 24 h.

## Molecular mechanisms of cobalt-catalyzed hydrogen evolution

Marinescu, Smaranda C.; Winkler, Jay R.; Gray, Harry B.
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
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Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV∕Co. Protonation of Co^I produces a transient Co^(IIII)-H complex that was characterized by nuclear magnetic resonance spectroscopy. The Co^(IIII)-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that Co^(IIII)-H produces hydrogen by two competing pathways: a slower homolytic route involving two Co^(IIII)-H species and a dominant heterolytic channel in which a highly reactive Co^(II)-H transient is generated by Co^I reduction of Co^(IIII)-H.

## Insights into preventive measures for dental erosion

Magalhães, Ana Carolina; Wiegand, Annette; Rios, Daniela; Honório, Heitor Marques; Buzalaf, Marília Afonso Rabelo
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
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Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear...

## Characterization of novel vanadium(III)/acetate clusters formed in aqueous solution

Fry, Fiona; Dougan, Brenda; McCann, Nichola; Zeigler, Christopher; Brasch, Nicola
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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We report the first structures of simple acetate complexes of vanadium(III) formed in aqueous solution. Paramagnetic 1H NMR spectroscopy titration experiments indicate the formation of two major V(III)/acetate complexes in acidic aqueous solution for acetate/V(III) ≤4, pD 3.50. A novel tetranuclear cluster and a trinuclear cluster have been characterized by X-ray diffraction studies. Mass spectrometry measurements show these clusters retain their integrity in solution.

## High-field NMR spectroelectrochemistry of spinning solutions: simultaneous in situ detection of electrogenerated species in a standard probe under potentiostatic control

Prenzler, Paul D; Bramley, Richard; Downing, Stephen; Heath, Graham
Tipo: Artigo de Revista Científica
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This report summarizes the design and performance of the first practicable in situ electrogenerative high-field solution-NMR cell, designed for simultaneous NMR spectroelectrochemistry in a conventional 10- or 16-mm 300 MHz probe. The axially symmetric three-electrode assembly is stationary and self-aligning. It dips into a standard spinning 10-mm sample tube and is adapted for convenient operation in any commercial high-field, multi-nuclear, variable-temperature FT NMR spectrometer. The tubular, rf-transparent working electrode (presently consisting of a gold film, coated on glass) completely spans the detection region; the recommended coating thickness is ≤ 0.01 δ where δ is the rf-absorbing conductor skin depth. With careful shimming, very narrow1H signals (~ 1 Hz) can be obtained. The performance of the in situ NMR-electrochemical cell is illustrated by monitoring the progressive reduction of 'p-quinone' (1,4-benzoquinone) to its dihydro-form by controlled-potential electrolysis in an acidic medium. (C) 2000 Elsevier Science S.A.

Viegas, Yvette