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Structural study of the interaction of vanadate with the ligand 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmpp) in aqueous solution

Castro, M. M. C. A.; Geraldes, C. F. G. C.; Gameiro, P.; Pereira, E.; Castro, B.; Rangel, M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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The interaction of vanadate with the ligand 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmpp) was studied in aqueous solution using a combination of multinuclear NMR and EPR spectroscopies, as well as potentiometry and cyclic voltammetry. The different species in solution were identified and characterized, and their pKa values and stability constants determined. The vanadium complexes formed in solution are strongly dependent on media composition (ionic strength, presence of buffer), pH and metal-to-ligand ratio (M:L). Two major species -- V(V)/dmpp and V(V)/(dmpp)2 -- are formed in a 140 mM NaCl solution within the pH range 4.5 to 9.0, when M:L=1:2. In the presence of excess ligand (M:L<=1:5), only the 1:2 complex is present, and at pH<4 paramagnetic species are detected by EPR in solution, thus indicating a reducing capacity of the ligand. Cyclic voltammetry shows that redox processes in solution are not just electron transfer, but are accompanied by chemical reactions. The pKa values and stability constants were determined both by 51V NMR spectroscopy and potentiometry. The present results have a particular interest in the understanding of the aqueous solution chemistry in aerobic conditions of bis(1,2-dimethyl-3-hydroxy-4-pyridinonato) oxovanadium(IV) complex...

Aqueous solution and solid state interactions of lanthanide ions with a methacrylic ester polymer bearing pendant 15-crown-5 moieties

Rubio, F.; García, F.; Burrows, H. D.; Pais, A. A. C. C.; Valente, A. J. M.; Tapia, M. J.; García, J. M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica
ENG
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The interaction between trivalent lanthanide ions and poly(1,4,7,10,13-pentaoxacyclopentadecan-2-yl-methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M-1 was obtained for a 1:1 (lanthanide:15-crown-5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)-PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M-1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion-crown interactions comes from ab initio calculations on 15-crown-5/La(III) complex. © 2007 Wiley Periodicals...

An extension of the Pitzer equation for the excess Gibbs energy of aqueous electrolyte systems to aqueous polyelectrolyte solutions

PESSOA FILHO, Pedro de Alcantara; MAURER, Gerd
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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Pitzer`s equation for the excess Gibbs energy of aqueous solutions of low-molecular electrolytes is extended to aqueous solutions of polyelectrolytes. The model retains the original form of Pitzer`s model (combining a long-range term, based on the Debye-Huckel equation, with a short-range term similar to the virial equation where the second osmotic virial coefficient depends on the ionic strength). The extension consists of two parts: at first, it is assumed that a constant fraction of the monomer units of the polyelectrolyte is dissociated, i.e., that fraction does not depend on the concentration of the polyelectrolyte, and at second, a modified expression for the ionic strength (wherein each charged monomer group is taken into account individually) is introduced. This modification is to account for the presence of charged polyelectrolyte chains, which cannot be regarded as punctual charges. The resulting equation was used to correlate osmotic coefficient data of aqueous solutions of a single polyelectrolyte as well as of binary mixtures of a single polyelectrolyte and a salt with low-molecular weight. It was additionally applied to correlate liquid-liquid equilibrium data of some aqueous two-phase systems that might form when a polyelectrolyte and another hydrophilic but neutral polymer are simultaneously dissolved in water. A good agreement between the experimental data and the correlation result is observed for all investigated systems. (c) 2008 Elsevier B.V. All rights reserved.

Estudo da interação entre sistemas luminescentes e alfa e beta-ciclodextrina em solução aquosa ; Study of luminescent materials in aqueous solution by interaction with alfa and beta cyclodextrin

Ribeiro, Anderson Orzari
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 20/12/2004 PT
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O grande interesse no estudo de materiais fotoluminescentes em solução aquosa é devido à possibilidade de aplicação destes sistemas em imunoensaios, na produção de lasers líquidos e como sondas estruturais de biomoléculas. Neste contexto, íons de Terras Raras (TR) e as ciclodextrinas são muito importantes, já que algumas TRs – como o európio e o térbio – apresentam a propriedade da luminescência, enquanto que as ciclodextrinas possuem uma cavidade apolar que pode incorporar moléculas (ou partes delas) em seu interior e protegê-las das moléculas do solvente. Neste projeto desenvolvemos principalmente a síntese de novos complexos luminescentes de európio e térbio com β-dicetonas, e o estudo de seus compostos de inclusão em α-ciclodextrina em solução aquosa. Foram estudados também compostos obtidos através da ligação covalente entre derivados da tetrakis(pentafluorofenil)porfirina e a β-ciclodextrina. Derivados de macrocíclos porfirínicos fotossensíveis vêm sendo empregados com muito sucesso no tratamento do câncer através terapia fotodinâmica. A ligação destes agentes em β-ciclodextrina propicia uma melhor solubilidade no meio fisiológico, característica esta que é um dos requisitos para uma melhor eficiência do tratamento. Todos os materiais obtidos foram caracterizados química e foto-fisicamente...

Estudo da remoção de fenóis de soluções aquosas através da adsorção em quitosana, degradação enzimática por tirosinase e imobilização de tirosinase em matriz de quitosana; Study of the removal of phenols from aqueous solution through adsorpition by quitosan by tyrosinase enzyme degradetion and inmobilization of tyrosinase in chitosan matrix

Chavita, Alexandre Camargo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/04/2010 PT
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476.509%
O presente trabalho apresenta o estudo de processos biotecnológicos para a remoção de fenol de soluções aquosas em regime de batelada em 3 processos distintos (A), (B) e (C) respectivamente. Sendo eles a adsorção de fenóis de soluções aquosas em Quitosana, degradação enzimática de fenóis através da tirosinase em meio aquoso e adsorção/degradação de fenóis de soluções aquosas em Quitosana contendo tirosinase imobilizada. Para isto foram estudadas as influências das variáveis temperatura, pH, concentração da Quitosana e velocidade de agitação no processo (A), temperatura, pH, concentração da tirosinase livre e velocidade de agitação no processo (B) e no processo (C), temperatura, pH, concentração da Quitosana, concentração da tirosinase imobilizada e velocidade de agitação.; This paper presents the study of biotechnology processes for the removal of pHenol from aqueous solution in batch reactor in 3 separate cases (A), (B) and (C) respectively. As they adsorption of pHenols from aqueous solutions on chitosan, enzymatic degradation of pHenols by tyrosinase in aqueous solution and adsorption / degradation of pHenols in aqueous solutions containing chitosan immobilized tyrosinase. For this we examined the influence of varying temperature...

SrBi2Nb2O9 thin films deposited by dip coating using aqueous solution

Zanetti, S. M.; Leite, E. R.; Longo, Elson; Varela, José Arana
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 1409-1412
ENG
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A new approach for SrBi2Nb2O9 (SBN) thin films synthesis using aqueous solution was successfully experienced. The deposition solution was prepared from Sr-Bi-Nb mixed-citrate solution, requiring no special atmosphere and using common reagents. Films were deposited by dip coating onto Pt/Ti/SiO2/Si(100) substrates and hear treated at temperatures ranging from 300 to 700 degrees C. The process of formation and crystallization of SrBi2Nb2O9 thin films, prepared by the aqueous solution method have been studied with particular emphasis on the microstructure of crystallized films. Crystalline phases formation were followed by grazing incident X-ray diffraction (GIXRD), microstructure characterization was evaluated by scanning electron microscopy (SEM) and surface roughness were observed using atomic for ce microscopy (AFM). To reach the desired thickness, substrates were dipped in the deposition solution twice, forming double-layered films. The thickness of each layer ranged from 80 to 100 nm. (C) 1999 Elsevier B.V. Limited. All rights reserved.

Photochemical degradation of pyrazosulfuron-ethyl in aqueous solution

Wang,Yanhui; Du,Liangwei; Bai,Lianyang
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
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This report describes photochemical behaviors of pyrazosulfuron-ethyl in aqueous solution. The photodegradation of pyrazosulfuron-ethyl for the first time was investigated in aqueous solution at two different irradiation wavelengths and pH values ranging from 2.00 to 10.00. Results show that the rate of photodegradation was faster in acidic medium than that in basic medium, when pyrazosulfuron-ethyl was in neutral form. The half-lives of pyrazosulfuron-ethyl under ultra-violet light and simulated sunlight were found to be 27.17 and 153.33 min, respectively. The reactions followed first-order kinetics. The degradation pathways were proposed according to the identification results of photoproducts: carbon-sulfur and nitrogen-sulfur cleavages and photohydrolysis of the sulfonylurea bridge. It was concluded that photodegradation behaviors can occur within the sulfonylurea family, depending on the pH values of aqueous solution and the irradiation wavelengths.

Conduction-band-edge ionization thresholds of DNA components in aqueous solution

Fernando, Harshica; Papadantonakis, George A.; Kim, Nancy S.; LeBreton, Pierre R.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 12/05/1998 EN
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Numerous investigations have focused on DNA damage induced by ionizing radiation; however, photoionization threshold energies of nucleic acid components in aqueous solution are not known. Herein, data from gas-phase photoelectron experiments have been combined with results from self-consistent field and post-self-consistent field molecular orbital calculations and with theoretical Gibbs free energies of hydration to describe aqueous ionization energies of 2′-deoxythymidine 5′-phosphate (5′-dTMP−) and 2′-deoxycytidine 5′-phosphate (5′-dCMP−). For the test molecules, indole and tryptophan, this approach yields aqueous ionization energies (4.46 and 4.58 eV, respectively) in agreement with experimental values (4.35 and 4.45 eV). When uridine and 2′-deoxythymidine ionization energies are evaluated, the results agree with recent data from 193-nm laser measurements indicating that uridine ionization occurs via a one-photon event. For 5′-dCMP− and 5′-dTMP−, a comparison of aqueous ionization energies with gas-phase ionization potentials (IPs) indicates that hydration alters the relative energies of ionization events. In the gas phase, phosphate vertical IPs are ∼1.3 eV smaller than base IPs. In aqueous solution...

Human Lactoferricin Is Partially Folded in Aqueous Solution and Is Better Stabilized in a Membrane Mimetic Solvent

Hunter, Howard N.; Demcoe, A. Ross; Jenssen, Håvard; Gutteberg, Tore J.; Vogel, Hans J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /08/2005 EN
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Lactoferricins are highly basic bioactive peptides that are released in the stomach through proteolytic cleavage of various lactoferrin proteins. Here we have determined the solution structure of human lactoferricin (LfcinH) by conventional two-dimensional nuclear magnetic resonance methods in both aqueous solution and a membrane mimetic solvent. Unlike the 25-residue bovine lactoferricin (LfcinB), which adopts a somewhat distorted antiparallel β sheet, the longer LfcinH peptide shows a helical content from Gln14 to Lys29 in the membrane mimetic solvent but a nonexistent β-sheet character in either the N- or C-terminal regions of the peptide. The helical characteristic of the LfcinH peptide resembles the conformation that this region adopts in the crystal structure of the intact protein. The LfcinH structure determined in aqueous solution displays a nascent helix in the form of a coiled conformation in the region from Gln14 to Lys29. Numerous hydrophobic interactions create the basis for the better-defined overall structure observed in the membrane mimetic solvent. The 49-residue LfcinH peptide isolated for these studies was found to be slightly longer than previously reported peptide preparations and was found to have an intact peptide bond between residues Ala11 and Val12. The distinct solution structures of LfcinH and LfcinB represent a novel difference in the physical properties of these two peptides...

A Comparative Study of DNA Complexation with Mg(II) and Ca(II) in Aqueous Solution: Major and Minor Grooves Bindings

Ahmad, R.; Arakawa, H.; Tajmir-Riahi, H. A.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /04/2003 EN
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Although structural differences for the Mg-DNA and Ca-DNA complexes are provided in the solid state, such comparative study in aqueous solution has been less investigated. The aim of this study was to examine the bindings of Mg and Ca cations with calf thymus DNA in aqueous solution at physiological pH, using constant concentration of DNA (1.25 or 12.5 mM) and various concentrations of metal ions (2 μM–650 μM). Capillary electrophoresis, UV-visible, and Fourier transform infrared spectroscopic methods were used to determine the cation-binding modes, the binding constants, and DNA structural variations in aqueous solution. Direct Ca-PO2 binding was evident by major spectral changes (shifting and splitting) of the backbone PO2 asymmetric stretching at 1222 cm−1 with K = 4.80 × 105 M−1, whereas an indirect Mg-phosphate interaction occurred (due to the lack of shifting and splitting of the phosphate band at 1222 cm−1) with K = 5.6 × 104 M−1. The metal-base bindings were directly for the Mg with K = 3.20 × 105 M−1 and indirectly for the Ca cation with K = 3.0 × 104 M−1. Both major and minor groove bindings were observed with no alteration of the B-DNA conformation.

Quercetin/β-Cyclodextrin Solid Complexes Prepared in Aqueous Solution Followed by Spray-drying or by Physical Mixture

Borghetti, Greice S.; Lula, Ivana S.; Sinisterra, Ruben D.; Bassani, Valquiria L.
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 12/03/2009 EN
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The present study was designed to investigate the influence of operating conditions (temperature, stirring time, and excess amount of quercetin) on the complexation of quercetin with β-cyclodextrin using a 23 factorial design. The highest aqueous solubility of quercetin was reached under the conditions 37°C/24 h/6 mM of quercetin. The stoichiometric ratio (1:1) and the apparent stability constant (Ks = 230 M−1) of the quercetin/β-cyclodextrin complex were determined using phase-solubility diagrams. The semi-industrial production of a 1:1 quercetin/β-cyclodextrin solid complex was carried out in aqueous solution followed by spray-drying. Although the yield of the spray-drying process was adequate (77%), the solid complex presented low concentration of quercetin (0.14%, w/w) and, thus, low complexation efficiency. The enhancement of aqueous solubility of quercetin using this method was limited to 4.6-fold in the presence of 15 mM of β-cyclodextrin. Subsequently, an inclusion complex was prepared via physical mixture of quercetin with β-cyclodextrin (molar ratio of 1:1 and quercetin concentration of 23% (w/w)) and characterized using infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance spectroscopy...

Calculation of the equilibrium pH in a multiple-buffered aqueous solution based on partitioning of proton buffering: a new predictive formula

Nguyen, Minhtri K.; Kao, Liyo; Kurtz, Ira
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
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Upon the addition of protons to an aqueous solution containing multiple buffers, the final H+ concentration ([H+]) at equilibrium is determined by the partitioning of added H+ among the various buffer components. In the analysis of acid-base chemistry, the Henderson-Hasselbalch equation and the Stewart strong ion formulation can only describe (rather than predict) the equilibrium pH following a proton load since these formulas calculate the equilibrium pH only when the reactant concentrations at equilibrium1 1The term “equilibrium” refers to the steady state proton and reactant concentrations when the buffering of excess protons by the various buffers is complete. are already known. In this regard, it is simpler to directly measure the equilibrium pH rather than measure the equilibrium reactant concentrations to calculate the equilibrium pH. As these formulas cannot predict the final equilibrium [H+] following a proton load to a multiple-buffered aqueous solution, we developed a new quantitative approach for predicting the equilibrium [H+] that is based on the preequilibrium22The term “preequilibrium” refers to the initial proton and reactant concentrations immediately upon addition of protons and before the buffering of excess protons by the various buffers. concentrations of all buffers in an aqueous solution. The mathematical model used to derive our equation is based on proton transfer buffer equilibria without requiring the incorporation of electroneutrality considerations. The model consists of a quartic polynomial equation that is derived based solely on the partitioning of H+ among the various buffer components. We tested the accuracy of the model using aqueous solutions with various buffers and measured the equilibrium pH values following the addition of HCl. Our results confirmed the accuracy of our new equation (r2 = 1; measured pH vs. predicted pH)...

Biomimetic Branched Hollow Fibers Templated by Self-assembled Fibrous Polyvinylpyrrolidone (PVP) Structures in Aqueous Solution

Qiu, Penghe; Mao, Chuanbin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 23/03/2010 EN
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Branched hollow fibers are common in nature, but to form artificial fibers with a similar branched hollow structure is still a challenge. We discovered that polyvinylpyrrolidone (PVP) could self-assemble into branched hollow fibers in an aqueous solution after aging the PVP solution for about two weeks. Based on this finding, we demonstrated two approaches by which the self-assembly of PVP into branched hollow fibers could be exploited to template the formation of branched hollow inorganic fibers. First, inorganic material such as silica with high affinity against the PVP could be deposited on the surface of the branched hollow PVP fibers to form branched hollow silica fibers. To extend the application of PVP self-assembly in templating the formation of hollow branched fibers, we then adopted a second approach where the PVP molecules bound to inorganic nanoparticles (using gold nanoparticles as a model) co-self-assemble with the free PVP molecules in an aqueous solution, resulting in the formation of the branched hollow fibers with the nanoparticles embedded in the PVP matrix constituting the walls of the fibers. Heating the resultant fibers above the glass transition temperature of PVP led to the formation of branched hollow gold fibers. Our work suggests that the self-assembly of the PVP molecules in the solution can serve as a general method for directing the formation of branched hollow inorganic fibers. The branched hollow fibers may find potential applications in microfluidics...

Protein Conformation and Supercharging with DMSO from Aqueous Solution

Sterling, Harry J.; Prell, James S.; Cassou, Catherine A.; Williams, Evan R.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
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The efficacy of dimethyl sulfoxide (DMSO) as a supercharging reagent for protein ions formed by electrospray ionization from aqueous solution and the mechanism for supercharging were investigated. Addition of small amounts of DMSO to aqueous solutions containing hen egg white lysozyme or equine myoglobin results in a lowering of charge, whereas a significant increase in charge occurs at higher concentrations. Results from both near-UV circular dichroism spectroscopy and solution-phase hydrogen/deuterium exchange mass spectrometry indicate that DMSO causes a compaction of the native structure of these proteins at low concentration, but significant unfolding occurs at ~63% and ~43% DMSO for lysozyme and myoglobin, respectively. The DMSO concentrations required to denature these two proteins in bulk solution are ~3–5 times higher than the concentrations required for the onset of supercharging, consistent with a significantly increased concentration of this high boiling point supercharging reagent in the ESI droplet as preferential evaporation of water occurs. DMSO is slightly more basic than m-nitrobenzyl alcohol and sulfolane, two other supercharging reagents, based on calculated proton affinity and gas-phase basicity values both at the B3LYP and MP2 levels of theory...

Influence of Formulation and Processing Variables on Properties of Itraconazole Nanoparticles Made by Advanced Evaporative Precipitation into Aqueous Solution

Bosselmann, Stephanie; Nagao, Masao; Chow, Keat T.; Williams, Robert O.
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 30/06/2012 EN
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Nanoparticles, of the poorly water-soluble drug, itraconazole (ITZ), were produced by the Advanced Evaporative Precipitation into Aqueous Solution process (Advanced EPAS). This process combines emulsion templating and EPAS processing to provide improved control over the size distribution of precipitated particles. Specifically, oil-in-water emulsions containing the drug and suitable stabilizers are sprayed into a heated aqueous solution to induce precipitation of the drug in form of nanoparticles. The influence of processing parameters (temperature and volume of the heated aqueous solution; type of nozzle) and formulation aspects (stabilizer concentrations; total solid concentrations) on the size of suspended ITZ particles, as determined by laser diffraction, was investigated. Furthermore, freeze-dried ITZ nanoparticles were evaluated regarding their morphology, crystallinity, redispersibility, and dissolution behavior. Results indicate that a robust precipitation process was developed such that size distribution of dispersed nanoparticles was shown to be largely independent across the different processing and formulation parameters. Freeze-drying of colloidal dispersions resulted in micron-sized agglomerates composed of spherical...

Polyamine Ligand-Mediated Self-Assembly of Gold and Silver Nanoparticles into Chainlike Structures in Aqueous Solution: Towards New Nanostructured Chemosensors

Fernández-Lodeiro, Adrián; Fernández-Lodeiro, Javier; Núñez, Cristina; Bastida, Rufina; Capelo, José Luis; Lodeiro, Carlos
Fonte: WILEY-VCH Verlag Publicador: WILEY-VCH Verlag
Tipo: Artigo de Revista Científica
EN
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Polyamine ligands are very versatile compounds due to their water solubility and flexibility. In the present work, we have exploited the binding ability of a polyamine molecular linker (L2−) bearing different functional groups, which favors the self-assembling of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) into 1D nanochains in aqueous solution. The chainlike assemblies of AuNPs and AgNPs were structurally stable for a long period of time, during which their characteristic optical properties remained unchanged. The mechanism of AuNPs and AgNPs chain assembly associated with the induction of electric dipole–dipole interactions arising from the partial ligand exchange of surface-adsorbed citrate ions by (L2−) was investigated. UV/Vis spectrophotometry and transmission electron microscopy (TEM) were used to determine timedependent structural changes associated with formation of the 1D nanoparticle structures. Finally, the sensing of Hg2+ in aqueous solution using AgNPs@(L)2− and AuNPs@(L)2− assemblies was also carried out in aqueous solution.

Certification of the equivalent spherical diameters of silica nanoparticles in aqueous solution - Certified Reference Material ERM®-FD304

FRANKS Katrin; BRAUN ADELINA; CHAROUD-GOT Jean; COUTEAU Olivier; KESTENS Vikram; LAMBERTY MARIE ANDREE; LINSINGER Thomas; ROEBBEN Gert
Fonte: Publications Office of the European Union Publicador: Publications Office of the European Union
Tipo: EUR - Scientific and Technical Research Reports Formato: Online
ENG
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This report describes the certification of several equivalent spherical diameters of silica nanoparticles in aqueous solution, Certified Reference Material (CRM) ERM®-FD304. The CRM has been certified by the European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, BE. ERM-FD304 consists of silica nanoparticles suspended in aqueous solution. The intended use of this CRM is t o check the performance of instruments and methods that determine the diameter of nanoparticles suspended in liquid medium. The CRM is available in 10 mL pre-scored amber glass ampoules containing approximately 9 mL of suspension. The CRM was prepared from commercially available colloidal silica, Ludox®, grade TM-50 (Grace Davison GmbH, Worms, Germany) Production of the CRM included testing of the homogeneity and stability of the ampouled diltuted raw material, as well as the characterisation using an interlaboratory comparison approach. The CRM has been certified for the scattering intensity based harmonic mean diameter using Dynamic Light Scattering (DLS) and for the extinction intensity based modal Stokes diameter of the silica nanoparticles in aqueous solution using Centrifugal Liquid Sedimentation (CLS) – line start method. An indicative value for size measurements using electron microscopy and information values for pH and zeta-potential were assigned as well. Expanded uncertainties are estimated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) with a coverage factor of k=2...

Effect of Corrosion on the High Cycle Fatigue Strength of Martensitic Stainless Steel X12CrNiMoV12-3

EL MAY, Mohamed; PALIN-LUC, Thierry; SAINTIER, Nicolas; DEVOS, Olivier
Fonte: Elsevier Publicador: Elsevier
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This paper addresses the effects of corrosion on the high cycle fatigue (HCF) strength of a high mechanical strength martensitic stainless steel (X12CrNiMoV12-3) that is used in aeronautic applications. HCF tests (between 105 and 107 cycles) were carried out in two environments: (i) in air and (ii) in an aqueous solution (pH = 6) of 0.1 M NaCl + 0.044 M Na2SO4 at a loading frequency of 120 Hz. Surface crack initiation is observed in air, whereas in solution, the crack initiated at corrosion defects. The decrease observed in the corrosion fatigue strength of specimens at 107 cycles was 33% of that of similar specimens tested in air. The electrochemical behaviour of the passive film was investigated during fatigue testing in a NaCl aqueous solution by monitoring the free potential and through electrochemical impedance spectroscopy (EIS). Based on fractography analysis and the EIS tests results, fatigue crack initiation mechanisms in air and in the NaCl aqueous solution were identified. A scenario for fatigue crack initiation is proposed based on the physical evidence. Local passive film ruptures are the cause of the corrosion fatigue crack initiation. The film is broken by material strain from the applied cyclic stress during fatigue testing...

Oxidation of nitric oxide in aqueous solution to nitrite but not nitrate: comparison with enzymatically formed nitric oxide from L-arginine.

Ignarro, L J; Fukuto, J M; Griscavage, J M; Rogers, N E; Byrns, R E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/09/1993 EN
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Nitric oxide (NO) in oxygen-containing aqueous solution has a short half-life that is often attributed to a rapid oxidation to both NO2- and NO3-. The chemical fate of NO in aqueous solution is often assumed to be the same as that in air, where NO is oxidized to NO2 followed by dimerization to N2O4. Water then reacts with N2O4 to form both NO2- and NO3-. We report here that NO in aqueous solution containing oxygen is oxidized primarily to NO2- with little or no formation of NO3-. In the presence of oxyhemoglobin or oxymyoglobin, however, NO and NO2- were oxidized completely to NO3-. Methemoglobin was inactive in this regard. The unpurified cytosolic fraction from rat cerebellum, which contains constitutive NO synthase activity, catalyzed the conversion of L-arginine primarily to NO3- (NO2-/NO3- ratio = 0.25). After chromatography on DEAE-Sephacel or affinity chromatography using 2',5'-ADP-Sepharose 4B, active fractions containing NO synthase activity catalyzed the conversion of L-arginine primarily to NO2- (NO2-/NO3- ratio = 5.6) or only to NO2-, respectively. Unpurified cytosol from activated rat alveolar macrophages catalyzed the conversion of L-arginine to NO2- without formation of NO3-. Addition of 30 microM oxyhemoglobin to all enzyme reaction mixtures resulted in the formation primarily of NO3- (NO2-/NO3- ratio = 0.09 to 0.20). Cyanide ion...

In vitro susceptibility of oral Candida albicans strains to different pH levels and calcium hydroxide saturated aqueous solution

Weckwerth,Paulo Henrique; Carnietto,Cristiane; Weckwerth,Ana Carolina Villas Boas; Duarte,Marco Antonio Hungaro; Kuga,Milton Carlos; Vivan,Rodrigo Ricci
Fonte: Fundação Odontológica de Ribeirão Preto Publicador: Fundação Odontológica de Ribeirão Preto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 EN
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Candida albicans is present in the oral cavity and in the whole digestive tract of humans and other animals, being frequently related to endodontic treatment failure. The present study determined the incidence of C. albicans in the oral cavity and the susceptibility of isolates to different pH values and saturated calcium hydroxide aqueous solution at pH 12.5. Sixty-five patients attending the Endodontic Clinic at the Sagrado Coração University participated in the study. The collected samples were cultivated in selective media for C. albicans and the isolates were tested in terms of resistance to both alkaline pH and saturated aqueous solution of calcium hydroxide. In relation to time variables, yeast viability was assessed by the Sabouraud's agar culture and fluorescein diacetate and ethidium bromide fluorescent staining method. Results from the different pHs and experimental times, including those from different techniques measuring fungal viability, were compared using the chi-square and Fisher's exact tests (α=0.05). The yeasts became completely inviable after 48 h of contact with the calcium hydroxide solution. On the other hand, when exposed to the alkaline culture broth, the yeasts were found to be viable at pHs 9.5 and 10.5 for up to 7 days. In conclusion...