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2-Mercaptobenzothiazole clay as matrix for sorption and preconcentration of some heavy metals from aqueous solution

Dias Filho, Newton L.; Gushikem, Yoshitaka; Polito, Wagner L.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 167-172
ENG
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2-Mercaptobenzothiazole loaded on previously polystyrene treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II) Pb(II), Zn(II) and Cd(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorptiou isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II) and some transition metal ions were also present.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion

Ishihata,Hiroshi; Finger,Werner J; Kanehira,Masafumi; Shimauchi,Hidetoshi; Komatsu,Masashi
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 EN
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OBJECTIVES: To assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test. MATERIAL AND METHODS: Twenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants. RESULTS: Comparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values refected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were signifcantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not signifcantly different. Treated specimens showed no surface remnants after rinsing. CONCLUSIONS: The experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.

The thermodynamically stable state of myelin basic protein in aqueous solution is a flexible coil.

Gow, A; Smith, R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/01/1989 EN
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Conformational studies of myelin basic protein (MBP) in solution generally have used protein purified in organic solvents and acid. The use of such conditions raises the possibility that the secondary structure reported for the basic protein represents a denatured state. Therefore we have purified this protein by using a procedure that avoids denaturants. Bovine myelin was extracted with 0.2 M-CaCl2 and the protein was purified from the supernatant by chromatography on Sephadex G-75. The conformation of the basic protein was characterized by using c.d. and 1H-n.m.r. spectroscopy. In solution, it appeared to be predominantly randomly coiled, with only small segments of persistent structure. However, in the presence of myristoyl lysophosphatidylcholine the secondary structure of MBP became more ordered, and sedimentation-velocity experiments showed that MBP aggregated. Comparison of our results with published data indicates that Ca2+-extracted basic protein behaves similarly to the protein purified by traditional methods with respect to its ordered conformation in solution in the absence and in the presence of lipid and with respect to its self-association. Thus its thermodynamically stable structure in aqueous solution appears to be a highly flexible coil.

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.

Efficacy of nano-hydroxyapatite prepared by an aqueous solution combustion technique in healing bone defects of goat

Nandi, Samit Kumar; Kundu, Biswanath; Ghosh, Samir Kumar; De, Dipak Kumar; Basu, Debabrata
Fonte: The Korean Society of Veterinary Science Publicador: The Korean Society of Veterinary Science
Tipo: Artigo de Revista Científica
EN
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The present study was undertaken to evaluate porous hydroxyapatite (HAp), the powder of which was prepared by a novel aqueous solution combustion technique, as a bone substitute in healing bone defects in vivo, as assessed by radiologic and histopathologic methods, oxytetracycline labeling, and angiogenic features in Bengal goat. Bone defects were created in the diaphysis of the radius and either not filled (group I) or filled with a HAp strut (group II). The radiologic study in group II showed the presence of unabsorbed implants which acted as a scaffold for new bone growth across the defect, and the quality of healing of the bone defect was almost indistinguishable from the control group, in which the defect was more or less similar, although the newly formed bony tissue was more organized when HAp was used. Histologic methods showed complete normal ossification with development of Haversian canals and well-defined osteoblasts at the periphery in group II, whereas the control group had moderate fibro-collagenization and an adequate amount of marrow material, fat cells, and blood vessels. An oxytetracycline labeling study showed moderate activity of new bone formation with crossing-over of new bone trabeculae along with the presence of resorption cavities in group II...

The XAS Model of the Copper(II)-Imidazole Complex Ion in Liquid Aqueous Solution: A Strongly Solvated Square Pyramid

Frank, Patrick; Benfatto, Maurizio; Hedman, Britt; Hodgson, Keith O.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Copper K-edge EXAFS and MXAN analyses were combined to evaluate the structure of the copper(II)-imidazole complex ion in liquid aqueous solution. Both methods converged to the same square pyramidal inner coordination sphere [Cu(Im)4Lax]2+, (Lax indeterminate) with four equatorial nitrogens at: EXAFS, 2.02±0.01 Å, and; MXAN, 1.99±0.03 Å. A short axial N/O scatterer, (Lax), was found at 2.12±0.02 (EXAFS) or 2.14±0.06 Å (MXAN). A second but very weak axial Cu-N/O interaction was found at 2.9±0.1 Å (EXAFS) or 3.0±0.1 Å (MXAN). In the MXAN fits, only a square pyramidal structural model successfully reproduced the doubled maximum of the rising K-edge XAS, specifically excluding an octahedral model. Both EXAFS and MXAN also found eight outlying oxygen scatterers at 4.2±0.3 Å that contributed significant intensity over the entire XAS energy range. Two prominent rising K-edge shoulders at 8987.1 eV and 8990.5 eV were found to reflect multiple scattering from the 3.0 Å axial scatterer and the imidazole rings, respectively. In the MXAN fits, the imidazole rings took in-plane rotationally staggered positions about copper. The combined (EXAFS and MXAN) model for the unconstrained cupric-imidazole complex ion in liquid aqueous solution is an axially elongated square pyramidal core...

A Long-Wavelength Fluorescent Squarylium Cyanine Dye Possessing Boronic Acid for Sensing Monosaccharides and Glycoproteins with High Enhancement in Aqueous Solution

Saito, Shingo; Massie, Tara L.; Maeda, Takeshi; Nakazumi, Hiroyuki; Colyer, Christa L.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 27/04/2012 EN
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Fluorescence sensing of saccharides and glycoproteins using a boronic acid functionalized squarylium cyanine dye (“SQ-BA”) is characterized in terms of synthetic, fluorometric, thermodynamic and kinetic parameters. In our previous work, this newly synthesized dye was successfully applied to the separation and quantification of Gram-positive bacteria by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF); however, the fundamental properties of the dye and its saccharide complexes still required elucidation, as presented in this paper. The dye itself forms nonemissive, soluble aggregates in aqueous solution. With the addition of a monosaccharide, the dye aggregate dissociates to form an emissive monomer accompanied by the formation of a cyclic cis-diol ester with long-wavelength emission (λex = 630 nm, λem = 660 nm). A very large fluorescence enhancement factor of 18× was observed for the sensing dye as a fructose complex at pH 10, yielding a limit of detection of 10 μM fructose. The relative order of fluorescence enhancement of SQ-BA with other monosaccharides was found to be: fructose > ribose > arabinose ≈ galactose > xylose > mannose > rhamnose > fucose ≈ glucose; and apparent affinity constants of 102.80...

Geometric consequences of electron delocalization for adenine tautomers in aqueous solution

Raczyńska, Ewa D.; Makowski, Mariusz
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
EN
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Geometric consequences of electron delocalization were studied for all possible adenine tautomers in aqueous solution by means of ab initio methods {PCM(water)//DFT(B3LYP)/6-311+G(d,p)} and compared to those in the gas phase {DFT(B3LYP)/6-311+G(d,p)}. To measure the consequences of any type of resonance conjugation (π-π, n-π, and σ-π), the geometry-based harmonic oscillator model of electron delocalization (HOMED) index, recently extended to the isolated (DFT) and hydrated (PCM//DFT) molecules, was applied to the molecular fragments (imidazole, pyrimidine, 4-aminopyrimidine, and purine) and also to the whole tautomeric system. For individual tautomers, the resonance conjugations and consequently the bond lengths strongly depend on the position of the labile protons. The HOMED indices are larger for tautomers (or their fragments) possessing the labile proton(s) at the N rather than C atom. Solvent interactions with adenine tautomers slightly increase the resonance conjugations. Consequently, they slightly shorten the single bonds and lengthen the double bonds. When going from the gas phase to water solution, the HOMED indices increase (by less than 0.15 units). There is a good relation between the HOMED indices estimated in water solution and those in the gas phase for the neutral and ionized forms of adenine. Subtle effects...

Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method

Quang, Hong Le; Chua, Soo-Jin; Loh, Kian Ping; Chen, Zhen; Thompson, Carl V.; Fitzgerald, Eugene A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 69588 bytes; application/pdf
EN
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Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application.; Singapore-MIT Alliance (SMA)

Growth of ZnO Nanorods on GaN Using Aqueous Solution Method

Quang, Hong Le; Chua, Soo-Jin; Loh, Kian Ping; Chen, Zhen; Thompson, Carl V.; Fitzgerald, Eugene A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 553272 bytes; application/pdf
EN
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Uniformly distributed ZnO nanorods with diameter 80-120 nm and 1-2µm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip with high aspect ratio to flat tip with smaller aspect ratio. These kinds of structure are useful in laser and field emission application.; Singapore-MIT Alliance (SMA)

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...

Layered LiNi0.5Co0.5O2 cathode materials grown by soft-chemistry via various solution methods

Julien, C.; Letranchant, C.; Rangan, S.; Lemal, M.; Ziolkiewicz, S.; Castro García, Socorro; El-Farh, L.; Benkaddour, M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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The lithiated nickel–cobalt oxide LiNi0.5Co0.5O2 used as cathode material was grown at low-temperature using different aqueous solution methods. The wet chemistry involved the mixture of metal salts (acetates or nitrates) with various carboxylic acid-based aqueous solutions. Physicochemical and electrochemical properties of LiNi0.5Co0.5O2 products calcined at 400–600°C were extensively investigated. The four methods used involved complexing agents such as either citric, oxalic, aminoacetic (glycine), or succinic acid in aqueous medium which functioned as a fuel, decomposed the metal complexes at low temperature, and yielded the free impurity LiNi0.5Co0.5O2 compounds. Thermal (TG–DTA) analyses and XRD data show that powders grown with a layered structure ( space group) have been obtained at temperatures below 400°C by the acidification reaction of the aqueous solutions. The local structure of synthesized products was characterized by Fourier transform infrared (FTIR) spectroscopy. The electrochemical properties of the synthesized products were evaluated in rechargeable Li cells using a non-aqueous organic electrolyte (1 M LiClO4 in propylene carbonate, PC). The LiNi0.5Co0.5O2 positive electrodes fired at 600°C exhibited good cycling behavior.

Self-assembly of triblock copolymers in aqueous solution

Urbano, Bruno; Silva, Patricio; Olea, Andrés F.; Fuentes, Irma; Martínez, Francisco
Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
EN
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Indexación: Scielo; The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.

Self-assembly of triblock copolymers in aqueous solution; Self-assembly of triblock copolymers in aqueous solution

Fonte: Sociedad Chilena de Química Publicador: Sociedad Chilena de Química
Tipo: Artículo de revista
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Resumen: The aggregation of PE4VP-b-PS-b-PE4VP block copolymers was studied in aqueous solution. Triblock copolymers P4VP-b-PS-b-P4VP were synthesized by sequential anionic polymerization of poly(styrene) and poly(4-vinylpirydine) using sodium naphthalene as a bifunctional initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PE4VP-b-PS-b-PE4VP block copolymers. Both star and crew-cut micelles were formed. The concentrations at which micelles are formed cmc were determined, by steady-state and time-resolved fluorescence probing methods, as a function of quatemization degree. The results indicate that cmc of crew-cut micelles increases with increasing charge density of the PE4VP blocks. For star micelles there is not a clear dependency of cmc with the percentage of quatemization. The lifetime of pyrene fluorescence and the ratio I1/I3 were determined at concentrations of copolymers well above the cmc, and the results show that the location of pyrene into the micelle changes with the charge density of the micelle corona. The micropolarity sensed by pyrene decreases with increasing quatemization degree. The presence of aggregates was confirmed by transmission electronic microscopy.

Synthesis, thermal behavior, and aggregation in aqueous solution of poly(methyl methacrylate)-b-poly(2-hydroxyethyl methacrylate)

ACEVEDO, B.; MARTINEZ, F.; OLEA, A. F.
Fonte: 2014 Sociedad Chilena de Química Publicador: 2014 Sociedad Chilena de Química
Tipo: Artigo de Revista Científica
EN
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Indexación: Scielo; ABSTRACT Amphiphilic block copolymers of poly(methyl methacrylate) PMMA and poly(2-hidroxyethyl methacrylate) PHEMA were synthesized by a two-step atom transfer radical polymerization (ATRP). Copolymers with various degrees of polymerization and different relative block sizes were obtained. The structure of the resulting polymers have been characterized and verified by FT-IR and 1H-NMR, molecular weight were determined by size exclusion chromatography analyses. The thermal properties of these polymers were investigated by differential scanning calorimetry DSC and thermogravimetric analysis TGA. The glass transition temperature of mono halogenated PMMA increases from 116 °C to 123 °C with increasing molecular weight, whereas the glass transition temperature of block copolymers depends slightly on polymer structure. The derivatives of TGA curves indicate that thermal degradation occurs in one stage. The self-assembly of PMMA-b-PHEMA in aqueous solution have been investigated by fluorescence probing methods. The critical micelle concentrations are in the range 10-6 - 10-7 M. The micropolarity sensed by pyrene is higher than in aggregates formed by block copolymers based on polystyrene. Keywords: Block copolymers...

Certification Report - The certification of equivalent diameters of a mixture of silica nanoparticles in aqueous solution: ERM®-FD102

KESTENS Vikram; 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 production of ERM®-FD102, silica nanoparticles in an aqueous solution certified for different equivalent diameters. The material was produced following ISO Guide 34:2009. The certified reference material (CRM), which has been produced by the Institute for Reference Materials and Measurements (IRMM) of the European Commission's Joint Research Centre (JRC), is a mixture of two monomodal populations of silica nanoparticles with distinct nominal particle sizes of 20 nm and 80 nm. These nominally 20 nm and 80 nm particle populations are further referred to as size class A and size class B, respectively. The CRM was prepared from two commercially available silica sols, moderately diluted in an aqueous solution and bottled in 10 mL pre-scored amber glass ampoules. Between unit-homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006. The minimum sample intake for the different methods was determined from the results and information provided by the laboratories that participated in the interlaboratory comparison (ILC) exercises of the characterisation study. The material was characterised, for size classes A and B, by an intercomparison amongst laboratories of demonstrated competence and adhering to ISO/IEC 17025. Technically invalid results were removed but no outlier was eliminated on statistical grounds only. Uncertainties of the certified values were calculated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) and include uncertainty contributions related to possible inhomogeneity and instability and to characterisation. The material is intended for quality control and assessment of method performance. As any reference material...

Detecting Ni(II) in aqueous solution by3-(2-pyridyl)-[1,2,3]triazolo[1,5-a]pyridine anddimethyl- -cyclodextrin

Gomez Machuca, Horacio; Rojas Aranguiz, Max; Fernández Sandoval, Samuel; Jullian Matthaei, Carolina María
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo de revista
EN
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Artículo de publicación ISI; A new supramolecular sensitizer for nickel(II) ion in aqueous solution based on a pyridyltriazolopyridine-cyclodextrin inclusion complex is proposed. The inclusion complexation behavior, characterization andbinding ability of pyridyltriazolopyridine (PTP) with dimethyl- -cyclodextrin (DM CD) has been inves-tigated both in solution and solid state by means of absorption, fluorescence,1H NMR, DSC, and molecularmodeling methods. The stoichiometry of the inclusion complex is 1:1, and the thermodynamic studiesindicate that the inclusion of PTP is mainly an entropic driven process. The 2D NMR studies revealed thatthe pyridyl-triazolopyridine is included by both sides of cyclodextrin which are in good agreement withthe docking results. The fluorescence changes upon addition of divalent cations to the inclusion complexindicate a high selectivity and sensitivity for Ni2+by fluorescence quenching in neutral aqueous solution.; Fondecyt 1120142 and to CEPEDEQ from theChemical and Pharmaceutical Science Faculty of the University ofChile for the use of NMR. Ministerio de Ciencia e Innovación (Spain) (Project Consolider-Ingenio Supramed CSD 2010-00065) and to Generalitat Valenciana (Valencia, Spain)(Project PROMETEO 2011/008).

Mechanism for the Phase Transition of a Genetically Engineered Elastin Model Peptide (VPGIG)_(40) in Aqueous Solution

Yamaoka, Tetsuji; Tamura, Takumi; Seto, Yuuki; Tada, Tomoko; Kunugi, Shigeru; Tirrell, David A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 10/11/2003
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The concentration dependence of the pressure- and temperature-induced cloud point transition (P_c and T_c, respectively) of aqueous solutions of an elastin-like polypeptide with a repeating pentapeptide Val−Pro−Gly−Ile−Gly sequence (MGLDGSMG(VPGIG)_(40)VPLE) was investigated by using apparent light scattering, differential scanning calorimetry, and circular dichroism methods. In addition, the effects of salts and surfactants on these properties were investigated. The P_c and T_c of the present peptide in aqueous solution were strongly concentration dependent. The calorimetric measurements showed that the enthalpy of transitions was 300−400 kJ/mol, i.e., 7−10 kJ/mol per VPGIG pentamer. The T_c of the (VPGIG)_(40) solution was highly affected by the addition of inert salts or SDS. The effects of salts were consistent with those observed in the lyotropic series or Hoffmeister series. The CD spectrum at low peptide concentrations indicated that the present peptide forms type II β-turn-like structure(s) at higher temperatures, but the temperature dependence of random coil diminishment (195 nm) and β-turn formation (210 nm) were not exactly coincident. A hypothetical mechanism of the (VPGIG)_(40) phase transition that could account for these observations was postulated. Observations suggest that the temperature-responsive properties of the elastin model peptides occur via a mechanism involving conformational change−association−aggregation and that the first two are strongly interactive.

In vitro dentin permeability after application of Gluma® desensitizer as aqueous solution or aqueous fumed silica dispersion

Ishihata, Hiroshi; Finger, Werner J; Kanehira, Masafumi; Shimauchi, Hidetoshi; Komatsu, Masashi
Fonte: Universidade de São Paulo. Faculdade de Odontologia de Bauru Publicador: Universidade de São Paulo. Faculdade de Odontologia de Bauru
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 01/04/2011 ENG
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OBJECTIVES: To assess and to compare the effects of Gluma® Desensitizer (GDL) with an experimental glutaraldehyde and HEMA containing fumed silica dispersion (GDG) on dentin permeability using a chemiluminous tracer penetration test. MATERIAL AND METHODS: Twenty disc-shaped dentin specimens were dissected from extracted human third molars. The dentin specimens were mounted in a split chamber device for determination of permeability under liquid pressure using a photochemical method. Ten specimens were randomly selected and allocated to the evaluation groups Gluma® Desensitizer as aqueous solution and glutaraldehyde/HEMA as fumed silica dispersion, respectively. Dentin disc permeability was determined at two pressure levels after removal of smear with EDTA, after albumin soaking, and after application of the desensitizing agents. Two desensitizer-treated and rinsed specimens of each group were examined by scanning electron microscopy (SEM) for surface remnants. RESULTS: Comparatively large standard deviations of the mean EDTA reference and albumin soaked samples permeability values refected the differences of the dentin substrates. The mean chemiluminescence values of specimen treated with GDL and GDG, respectively, were signifcantly reduced after topical application of the desensitizing agents on albumin-soaked dentin. The effects of GDL and GDG on permeability were not signifcantly different. Treated specimens showed no surface remnants after rinsing. CONCLUSIONS: The experimental desensitizer gel formulation reduced dentin permeability as effectively as the original Gluma® Desensitizer solution.