Search results for " paramagnetic resonance"

showing 10 items of 567 documents

Increased conformational rigidity of humic substances by oxidative biomimetic catalysis

2005

A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed …

conformationMagnetic Resonance SpectroscopySpectrophotometry InfraredPolymers and PlasticsDiffuse reflectance infrared spectroscopy (DRIFT)Biomimetic materialsaromatic compoundgel permeation chromatographyMolecular ConformationPhotochemistryIron compoundslaw.inventionPolymerizationenvironmental managementcovalent bondlawSize exclusion chromatographyBiomimetic catalysisBiomimeticsMaterials ChemistryOrganic chemistryHumic acidElectron paramagnetic resonanceInfrared spectroscopyChromatography High Pressure Liquidchemistry.chemical_classificationSettore CHIM/03 - Chimica Generale e InorganicaCarbon IsotopesChromatographyindustryCatalystsChemistrytetra(2articleelectrophoretic mobilitybiomimetic materialNuclear magnetic resonance spectroscopyunclassified drugConformationsacetic acidpriority journalCovalent bondSpectrophotometrySynthesis (chemical)High Pressure Liquidtechnology6 dichloro 3 sulfonatophenyl)porphyrinic acid derivativeInfraredOxidation-Reductionmolecular stabilityHumic materialsoxidationSettore AGR/13 - Chimica AgrariaSupramolecular chemistryBioengineeringcomplex mixturesCatalysisCatalysisdiffuse reflectance spectroscopyhumic substanceBiomaterialsalkyl etherElectron spin resonance spectroscopycomplex formationParticle SizeNuclear magnetic resonance spectroscopyHumic Substancesfree radicalbiomimetic oxidative humicelectron spin resonanceHigh performance size exclusion chromatography (HPSEC)ferrous chloridemolecular weightsolid statecarbon nuclear magnetic resonancePolymerizationSolubilitychemical structureOxidative coupling of methaneCatalysts; Conformations; Electron spin resonance spectroscopy; Infrared spectroscopy; Iron compounds; Nuclear magnetic resonance spectroscopy; Oxidation; Polymerization; Size exclusion chromatography; Solubility; Synthesis (chemical); Biomimetic catalysis; Diffuse reflectance infrared spectroscopy (DRIFT); High performance size exclusion chromatography (HPSEC); Humic materials; Biomimetic materials; acetic acid; alkyl ether; aromatic compound; biomimetic material; ferrous chloride; free radical; tetra(26 dichloro 3 sulfonatophenyl)porphyrinic acid derivative; unclassified drug; article; carbon nuclear magnetic resonance; catalysis; catalyst; chemical structure; complex formation; conformation; covalent bond; diffuse reflectance spectroscopy; electron spin resonance; electrophoretic mobility; environmental management; gel permeation chromatography; humic substance; industry; molecular stability; molecular weight; oxidation; polymerization; priority journal; solid state; technology; Biomimetics; Carbon Isotopes; Catalysis; Chromatography High Pressure Liquid; Electron Spin Resonance Spectroscopy; Humic Substances; Magnetic Resonance Spectroscopy; Molecular Conformation; Oxidation-Reduction; Particle Size; Spectrophotometry Infraredcatalyst
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Enhancing the luminescence efficiency of silicon-nanocrystals by interaction with H+ions

2018

The emission of silicon nanocrystals (Si-NCs), synthesized by pulsed laser ablation in water, was investigated on varying the pH of the solution. These samples emit μs decaying orange photoluminescence (PL) associated with radiative recombination of quantum-confined excitons. Time-resolved spectra reveal that both the PL intensity and the lifetime increase by a factor of ∼20 when the pH decreases from 10 to 1 thus indicating that the emission quantum efficiency increases by inhibiting nonradiative decay rates. Infrared (IR) absorption and electron paramagnetic resonance (EPR) experiments allow addressing the origin of defects on which the excitons nonradiatively recombine. The linear correl…

defectMaterials sciencePhotoluminescenceExcitonGeneral Physics and Astronomy02 engineering and technology010402 general chemistryPhotochemistry01 natural sciencesIonlaw.inventionlawluminescenceSpontaneous emissionQuantum confinementPhysical and Theoretical ChemistryElectron paramagnetic resonanceSilicon nanocrystalsilicon021001 nanoscience & nanotechnologyphotoluminescence efficiencysilicon nanoparticles luminescence0104 chemical sciencesAmorphous solidlaser ablationQuantum efficiencynanoparticles0210 nano-technologyLuminescence
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EPR investigation on the polyamorphic transformation induced by electron irradiation in SiO2 glass

2013

electron paramagnetic resonance EPR E' center amorphous silicon dioxide sio2 irradiation effects densification
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Modifications of optical absorption band of E'gamma center in silica

2005

We report a study by electron paramagnetic resonance on the E0 point defect in amorphous silicon dioxide (a-SiO2). Our experiments were performed on -ray irradiated oxygen-deficient materials and pointed out that the 29Si hyperfine structure of the E0 consists of a pair of lines split by 49 mT. On the basis of the experimental results, a microscopic model is proposed for the E0 center, consisting of a hole trapped in an oxygen vacancy with the unpaired electron sp3 orbital pointing away from the vacancy in a back-projected configuration and interacting with an extra oxygen atom of the a-SiO2 matrix.

electron paramagnetic resonanceDangling bondParamagnetic resonance
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29Si Hyperfine structure of the E’_alfa center in amorphous silicon dioxide

2006

We report a study by electron paramagnetic resonance on the E0 point defect in amorphous silicon dioxide (a-SiO2). Our experiments were performed on -ray irradiated oxygen-deficient materials and pointed out that the 29Si hyperfine structure of the E0 consists of a pair of lines split by 49 mT. On the basis of the experimental results, a microscopic model is proposed for the E0 center, consisting of a hole trapped in an oxygen vacancy with the unpaired electron sp3 orbital pointing away from the vacancy in a back-projected configuration and interacting with an extra oxygen atom of the a-SiO2 matrix.

electron paramagnetic resonanceDangling bondsParamagnetic resonance
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Characterization of E'delta and triplet point defects in oxygen-deficient amorphous silicon dioxide

2005

We report an experimental study by electron paramagnetic resonance (EPR) of gamma ray irradiation induced point defects in oxygen deficient amorphous SiO2 materials. We have found that three intrinsic (E'gamma, E'delta and triplet) and one extrinsic ([AlO4]0) paramagnetic centers are induced. All the paramagnetic defects but E'gamma center are found to reach a concentration limit value for doses above 10^3 kGy, suggesting a generation process from precursors. Isochronal thermal treatments of a sample irradiated at 10^3 kGy have shown that for T>500 K the concentrations of E'gamma and E'delta centers increase concomitantly to the decrease of [AlO4]0. This occurrence speaks for an hole tra…

electron paramagnetic resonanceFOS: Physical sciencesDisordered Systems and Neural Networks (cond-mat.dis-nn)Condensed Matter - Disordered Systems and Neural NetworksDangling bondsParamagnetic resonance
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Dating of Brazilian shells through electron paramagnetic resonance

2019

In the present work we report dating procedure of these shells by using the electron paramagnetic resonance. The first step of the analysis was the definition of the optimal procedure for sample preparation. At this aim the analysis of the sample composition was carried out by X-ray fluorescence (XRF) measurements and an accurate analysis was study on the effect of the chemical etching with varying typology and concentration of acid to be used for removing the external layer of shells which are affected by alpha particles.

electron paramagnetic resonanceSettore ING-IND/20 - Misure E Strumentazione NucleariSettore FIS/07 - Fisica Applicata(Beni Culturali Ambientali Biol.e Medicin)
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Magnetic transition metal complexes of tetrathiafulvalene (TTF) derivatives

1997

We have prepared and characterized the transition metal complexes of two different TTF derivatives. We have oxidized the different complexes with electrooxidation and chemical oxidation techniques and the results are discussed. The magnetic properties of the complexes have been studied. TTF-carboxylate chelates are not stable enough, but thioether-TTF shows promising charge transfer salts.

endocrine systemMagnetic measurementsTtf derivativesChemistryMechanical EngineeringInorganic chemistryMetals and AlloysCharge (physics)respiratory systemCondensed Matter PhysicsMagnetic susceptibilityElectronic Optical and Magnetic Materialslaw.inventionchemistry.chemical_compoundTransition metalMechanics of MaterialslawMaterials ChemistryPhysical chemistryChelationElectron paramagnetic resonanceTetrathiafulvalene
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Eumelanin Coating of Silica Aerogel by Supercritical Carbon Dioxide Deposition of a 5,6-Dihydroxyindole Thin Film

2018

Eumelanin integration in silica aerogel (SA) was achieved via supercritical adsorption of 5,6-dyhydroxyindole (DHI) from CO2. Notably, after the supercritical treatment, DHI evolved towards spontaneous polymerization, which resulted in uniform pigment development over the SA. The new material was characterized for its morphological and physicochemical properties, disclosing the formation of a eumelanin-like coating, as confirmed by UV&ndash

eumelaninsMaterials science02 engineering and technologyengineering.material010402 general chemistrylcsh:Technology01 natural sciencesArticlesupercritical CO2law.inventionCoatingsupercritical CO<sub>2</sub>lawGeneral Materials ScienceThin filmsilica aerogellcsh:MicroscopyElectron paramagnetic resonancelcsh:QC120-168.85EumelaninSupercritical carbon dioxidelcsh:QH201-278.5lcsh:TAerogel021001 nanoscience & nanotechnologySupercritical fluid0104 chemical sciencesPolymerizationChemical engineeringlcsh:TA1-2040engineeringlcsh:Descriptive and experimental mechanicsMaterials Science (all)lcsh:Electrical engineering. Electronics. Nuclear engineeringSupercritical adsorptionlcsh:Engineering (General). Civil engineering (General)0210 nano-technologylcsh:TK1-9971Materials
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Liposomes modified by mono- and bis-phthalocyanines: A comprehensive EPR study.

2016

The impact of selected metallophthalocyanines, featuring diverse molecular structure, upon the fluidity of liposome membranes was studied using the spin label EPR technique. The “mono”-type MPc’s (M = Zn, Sn; Pc = C32H16N8 is the phthalocyanine ligand) and sandwich LnPc2 complexes (Ln = Nd, Sm, Gd) were explored. Liposomes were obtained in a sonication process, from egg yolk lecithin (EYL) in water. TEMPO and 16-DOXYL spin labels were used to monitor the peripheral and central part of the lipid double layer, respectively, which allowed to localize the phthalocyanine additive within the bilayer, as well as to perform independent measurements of changes in fluidity upon addition thereof. All …

food.ingredientBiophysics02 engineering and technologyLecithinlaw.inventionCyclic N-Oxides03 medical and health scienceschemistry.chemical_compoundSonication0302 clinical medicineNuclear magnetic resonancefoodlawLecithinsOrganometallic CompoundsGeneral Materials ScienceLipid bilayerElectron paramagnetic resonanceSpin labelLiposomeChemistryLiquid crystalsBilayerElectron Spin Resonance SpectroscopySurfaces and InterfacesGeneral Chemistry021001 nanoscience & nanotechnologyCrystallographyMembraneSoft Matter030220 oncology & carcinogenesisLiposomesPhthalocyanine0210 nano-technologyBiotechnologyThe European physical journal. E, Soft matter
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