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Electron Paramagnetic Resonance (electron + paramagnetic_resonance)
Terms modified by Electron Paramagnetic Resonance Selected AbstractsCOLOUR ATTRIBUTES OF MEDIEVAL WINDOW PANES: ELECTRON PARAMAGNETIC RESONANCE AND PROBE MICROANALYSES ON STAINED GLASS WINDOWS FROM PAVIA CARTHUSIAN MONASTERY*ARCHAEOMETRY, Issue 2 2005C. B. AZZONI Stained glass windows from the Carthusian Monastery of Pavia, dating back to the 15th century, were studied by combining two analytical techniques: electron probe micro-analysis (EPMA) and electron paramagnetic resonance (EPR). Chemical compositions and oxidation states of the transition ions, present as minor elements, were investigated by EPMA and EPR, respectively, in order to ascertain the role played by chromophorous ions in the glass coloration. The investigated glass can be defined as K,Ca glass, and the panes with red, green and blue colours were produced using flashing techniques. [source] Book review: Electron Paramagnetic Resonance: Elementary Theory and Practical Applications.CONCEPTS IN MAGNETIC RESONANCE, Issue 4 20082nd edition. No abstract is available for this article. [source] Localization and movement of native interstitials in chlorinated SrCl2:Fe crystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007D. Ghica Abstract The formation of the electron trapped Fe+(IV) centre, produced by X-ray irradiation at 80 K and further annealing at temperatures of up to 700 K in chlorinated SrCl2:Fe crystals, has been investigated by Electron Paramagnetic Resonance. Our studies report the transformation of the monoclinic Fe+(III) centre into the axial Fe+(IV) centre above 450 K. The formation of the Fe+(IV) centre is attributed to the presence and thermally activated movement of neighbouring interstitial chlorine and alkali impurity Na+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electron paramagnetic resonance and electron-nuclear double resonance of nonequivalent Yb3+ centers in stoichiometric lithium niobatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Galina Malovichko Abstract Lithium niobate crystals doped with ytterbium were studied using Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR). The tremendous narrowing of EPR lines in nearly stoichiometric samples, when compared to those in congruent samples, allowed us to distinguish nine non-equivalent centers, as well as line splitting caused by the hyperfine interaction of ytterbium electrons with the nuclear spins of two magnetic isotopes, 171Yb and 173Yb. Eight of the nine centers are described for the first time. It was found that three of the centers have axial C3 symmetry, and all others have the lowest C1 symmetry due to the presence of intrinsic defects and/or charge compensation defects in the near neighborhood of Yb3+. Characteristics of the g -tensor for all of the centers and hyperfine tensors for axial centers were determined. The ENDOR observations of Nb nuclei in the nearest neighborhood of Yb13+ gave direct evidence that the dominated axial Yb1 center has no charge compensator in its nearest surroundings (distant charge compensation mechanism). Both the EPR and ENDOR data for the main axial ytterbium center are explained by a supposition that Yb3+ ions substitute for Li+. Possible models for low-symmetry centers are discussed. The obtained numerous spectroscopic parameters can be used as cornerstones for model calculations of Yb3+ centers in lithium niobate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinelPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007Roberto Paiva Abstract Optical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation-dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V-type centres. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] EPR studies on Na-oleate coated Fe3O4 nanoparticlesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004Y. Köseo Abstract Superparamagnetic iron oxide nanoparticles were prepared by the co-precipitation technique. Then, fine iron oxide nanoparticles were coated by Na-oleate. Magnetic properties of Na-oleate coated and uncoated iron oxide nanoparticles were investigated by Electron Paramagnetic Resonance (EPR) technique. At room temperature, a single, strong and broad EPR signal was observed for both samples with effective g-values of 2,0839 and 2,18838 for coated and uncoated samples, respectively. The intensity, line width and the resonance field for both coated and uncoated samples are strongly temperature dependent. When the sample is coated with Na-oleate, the line width and the resonance field values of the EPR signal increase due to the decrease in the magnetic interaction between the particles. The total effective magnetic moment of such coated particles is found to decrease, which is most likely due to a non-collinear spin structure originated from the pinning of the surface spins and coated surfactant at the interface of nanoparticles. [source] EPR study of Fe3+ centers in ternary layered TlInS2 single crystalPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004F.A. Mikailov Abstract An iron doped TlInS2 single crystal has been studied at room temperature by Electron Paramagnetic Resonance (EPR) technique. The fine structure of EPR spectra of the paramagnetic Fe3+ ions was observed. The spectra were interpreted to correspond to the transitions among the spin multiplets (S=5/2, L=0) of the Fe3+ ion, which is split in the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe3+ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe3+ site and the CF parameters were determined. It was established that the symmetry axis of the axial component in the CF is making an angle of about 48 degree with the (ab) plane of TlInS2 crystal. Experimental results indicate that Fe ions substitute for In ions at the center of the InS4 tetrahedrons, and the rhombic distortion of the CF is caused by Tl ions located in the trigonal cavities between the tetrahedral complexes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ChemInform Abstract: Oxidation of Carbon Monoxide Cocatalyzed by Palladium(0) and the H5PV2Mo10O40 Polyoxometalate Probed by Electron Paramagnetic Resonance and Aerobic Catalysis.CHEMINFORM, Issue 43 2009Hila Goldberg Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The Highest D Value for a MnII Ion: Investigation of a Manganese(II) Polyoxometalate Complex by High-Field Electron Paramagnetic Resonance.CHEMINFORM, Issue 48 2007Celine Pichon Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Cr3+ -doped LiNbO3 crystals grown by the Bridgman methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005Haiping Xia Abstract The growth of LiNbO3 crystals doped with Cr3+ ions in 0.1, 0.2, and 0.5 mol % concentrations by Bridgman method were reported. The Cr3+ ion concentrations in crystals were measured by inductively coupled plasma spectrometry. Electron paramagnetic resonance had been used to investigate the sites occupied by the Cr3+ ions. Two Cr3+ ion centers located at Li+ and Nb5+ sites (CrLi3+ and CrNb3+ centers, respectively) were observed. Optical absorption and temperature-dependence emission spectra of the Cr3+ ions were reported. The crystal-field parameters and Racah parameters of the Cr3+ ion defect sites were reported and compared with those grown by Czochralski technique. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Silicon-Doped LiFePO4 Single Crystals: Growth, Conductivity Behavior, and DiffusivityADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Ruhul Amin Abstract Single crystals of silicon doped LiFePO4 with a silicon content of 1% are grown successfully by the floating zone technique and characterized by single-crystal and powder X-ray diffraction, secondary ion mass spectroscopy, and chemical analysis. Electron paramagnetic resonance demonstrates the presence of only Fe2+; no traces of Fe3+ are found. Impedance spectroscopy as well as step-function polarization/depolarization (DC) measurements are carried out using the cells Ti/LiFe(Si)PO4/Ti and LiAl/LiI/LiFe(Si)PO4/LiI/LiAl. The electronic and ionic conductivities as well as the Li-diffusivity of the sample in the major crystallographic directions ([h00], [0k0], and [00l]) are determined. Within experimental error the transport properties along the b- and c-axes are found to be the same but differ significantly from the a-axis, which exhibits lower values. Compared to undoped LiFePO4, Si-doping leads to an increase of the ionic conductivity while the electronic conductivity decreases, which is in agreement with a donor effect. The activation energies of conductivities and diffusivities are interpreted in terms of defect chemistry and relevant Brouwer diagrams are given. [source] Oxidative Stress Following Traumatic Brain Injury in RatsJOURNAL OF NEUROCHEMISTRY, Issue 5 2000Detection of Free Radical Intermediates, Quantitation of Biomarkers Abstract: Oxidative stress may contribute to many pathophysiologic changes that occur after traumatic brain injury. In the current study, contemporary methods of detecting oxidative stress were used in a rodent model of traumatic brain injury. The level of the stable product derived from peroxidation of arachidonyl residues in phospholipids, 8- epi -prostaglandin F2,, was increased at 6 and 24 h after traumatic brain injury. Furthermore, relative amounts of fluorescent end products of lipid peroxidation in brain extracts were increased at 6 and 24 h after trauma compared with sham-operated controls. The total antioxidant reserves of brain homogenates and water-soluble antioxidant reserves as well as tissue concentrations of ascorbate, GSH, and protein sulfhydryls were reduced after traumatic brain injury. A selective inhibitor of cyclooxygenase-2, SC 58125, prevented depletion of ascorbate and thiols, the two major water-soluble antioxidants in traumatized brain. Electron paramagnetic resonance (EPR) spectroscopy of rat cortex homogenates failed to detect any radical adducts with a spin trap, 5,5-dimethyl-1-pyrroline N -oxide, but did detect ascorbate radical signals. The ascorbate radical EPR signals increased in brain homogenates derived from traumatized brain samples compared with sham-operated controls. These results along with detailed model experiments in vitro indicate that ascorbate is a major antioxidant in brain and that the EPR assay of ascorbate radicals may be used to monitor production of free radicals in brain tissue after traumatic brain injury. [source] ,-Irradiation of ultrahigh-molecular-weight polyethylene: Electron paramagnetic resonance and nuclear magnetic resonance spectroscopy and imaging studies of the mechanism of subsurface oxidationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2004Todd M. Alam Abstract The shelf aging of irradiated ultrahigh-molecular-weight polyethylene (UHMWPE) causes subsurface oxidation, which leads to failure in UHMWPE orthopedic components, yet the mechanisms causing subsurface oxidation remain unclear. The shelf aging of ,-irradiated UHMWPE bars has been studied with electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) imaging and with microtoming and Fourier transform infrared microscopy. The bars initially contained only allyl radicals, and upon air exposure, a surface layer of peroxyl radicals formed through the reaction of allyl radicals with oxygen. Importantly, a band of low radical intensity just beneath the peroxyl layer became apparent. NMR imaging showed a zone of altered proton relaxation in this zone. With increasing time, surface peroxyl radicals persisted in comparison with the interior allyl radicals, although oxygen did not appear to penetrate any more deeply into the bar. The area of maximal oxidation and mechanical disruption, measured after 3 years, was at the interface between the zone of exterior peroxyl radicals and the zone of low radical intensity. We present a mechanism involving the intermediacy of sterically strained reactive dialkyl peroxides at this interface to explain subsurface oxidation. We also demonstrate that EPR and NMR imaging provides information that could potentially be used to identify subsurface oxidized UHMWPE components before failure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5929,5941, 2004 [source] The g -values and hyperfine coupling of amino acid radicals in proteins: comparison of experimental measurements with ab initio calculations,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005Sun Un Abstract Electron paramagnetic resonance (EPR) spectroscopy has been extensively used to identify and characterize protein-based redox active amino acid radicals based on their g -values and hyperfine couplings. To better understand how these parameters depend on the electronic structure and environment of the radical, the theoretical g -values and proton hyperfine tensors of three models corresponding to the tyrosyl, tryptophanyl and glycyl radicals were calculated using Gaussian 03. The g -values were determined using the B3LYP/6,31+G(D,P) combination of density functional and basis set, while the hyperfine tensors were determined using the B3LYP/EPR-III and PBE0/EPR-III combinations. Comparisons are made to measured values. It was found that by appropriately accounting for hydrogen bonds and the dielectric constant of the environment, good agreement could be achieved between the calculated and measured g -values. In all three cases, the g -anisotropy arose from significant spin density on a nitrogen or oxygen atom. The calculated hyperfine tensors for the three radicals did not differ significantly from previous calculations. In the case of the tyrosyl radical, it is shown for the first time that the para -position substituent that is opposite of the CO group can break the symmetry of the phenyl ring, leading to different hyperfine tensors for the two large ortho proton couplings. For the tyrosyl and tryptophanyl models, the calculated hyperfine couplings to hydrogen-bonding protons were in very good agreement with measured values for both the tyrosyl and tryptophanyl models. Copyright © 2005 John Wiley & Sons, Ltd. [source] Electron paramagnetic resonance and electron-nuclear double resonance of nonequivalent Yb3+ centers in stoichiometric lithium niobatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Galina Malovichko Abstract Lithium niobate crystals doped with ytterbium were studied using Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR). The tremendous narrowing of EPR lines in nearly stoichiometric samples, when compared to those in congruent samples, allowed us to distinguish nine non-equivalent centers, as well as line splitting caused by the hyperfine interaction of ytterbium electrons with the nuclear spins of two magnetic isotopes, 171Yb and 173Yb. Eight of the nine centers are described for the first time. It was found that three of the centers have axial C3 symmetry, and all others have the lowest C1 symmetry due to the presence of intrinsic defects and/or charge compensation defects in the near neighborhood of Yb3+. Characteristics of the g -tensor for all of the centers and hyperfine tensors for axial centers were determined. The ENDOR observations of Nb nuclei in the nearest neighborhood of Yb13+ gave direct evidence that the dominated axial Yb1 center has no charge compensator in its nearest surroundings (distant charge compensation mechanism). Both the EPR and ENDOR data for the main axial ytterbium center are explained by a supposition that Yb3+ ions substitute for Li+. Possible models for low-symmetry centers are discussed. The obtained numerous spectroscopic parameters can be used as cornerstones for model calculations of Yb3+ centers in lithium niobate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electron paramagnetic resonance and non-resonant microwave absorption of single wall carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007B. Corzilius Abstract Single wall carbon nanotubes (SWNT) prepared by the "super growth" method exhibit electron paramagnetic resonance (EPR) signals, which originate from temperature activated detrapping of spins. Non-resonant microwave absorption in the temperature range below 20 K is indicative for the opening of a small gap at the Fermi level for tubes of metallic character, which might indicate a transition into a superconducting (SC) state. The expected concurrent microwave field inhomogeneity has been detected by a transient nutation experiment. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] EPR and photoluminescence diagnostics of singlet oxygen generation on porous silicon surfacePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009E. A. Konstantinova Abstract Electron paramagnetic resonance and photoluminescence spectroscopy are used to investigate photosensitized generation of singlet oxygen in the porous silicon layers. The singlet oxygen concentration in the samples was estimated at various oxygen pressures. The time of energy transfer from excitons confined in Si nanocrystals to adsorbed O2 molecules on silicon nanocrystal surface and photosensitization efficiency are found to depend on the porosity of the samples. The singlet oxygen generation efficiency increases strongly for porous silicon with high (>80%) porosity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterisation of Nanohybrids of Porphyrins with Metallic and Semiconducting Carbon Nanotubes by EPR and Optical SpectroscopyCHEMPHYSCHEM, Issue 13 2008Sofie Cambré Abstract Single-walled carbon nanotubes (SWCNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of cobalt(II)OEP, adsorbed on the nanotube walls by ,,,-stacking, demonstrates that the CNTs act as electron acceptors. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Moreover, molecular oxygen is shown to bind selectively to nanohybrids with semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99,% of the porphyrins are interacting with the CNTs. Due to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red-shifted compared to the free porphyrin absorption. In addition a quasi-complete quenching of the porphyrin fluorescence is also observed. [source] The Influence of Solid-State Molecular Organization on the Reaction Paths of Thiyl RadicalsCHEMPHYSCHEM, Issue 6 2005Antonio Faucitano Prof. Abstract Electron paramagnetic resonance (EPR) spectroscopy has been employed to investigate the effect of solid-state molecular organization on the reaction of thiyl radicals with thiols. In an irradiated C18H37SH/thiourea clathrate, the conversion of thiyl to perthiyl radicals is substantial, due to the head-to-head arrangement of the reactants within the channels and the suppression of other possible competing reactions due to hindrance by the clathrate walls. The perthiyl radical was identified using EPR analysis of its molecular dynamics within the clathrate channels. Irradiated polyethylene film containing 30,% C18H37SH afforded a negligible conversion of thiyl to perthiyl radicals because of the random distribution of reactants. These results suggest that in the absence of favorable structure-control effects, the reaction between RS. and RSH is unimportant with respect to other competing reactions. Perthiyl radicals are also the major product in the vacuum solid-state radiolysis of lysozyme. A proposal of the mechanism involved in all cases is based on the equilibrium RS.+RSH,RSS.(H)R, followed by the irreversible conversion of the sulfuranyl radical to the perthiyl radical. As the equilibrium is strongly shifted to the left, the intermediate sulfuranyl radicals were not detected, but the lack of other competing reactions for the thiyl radicals caused the formation of perthiyl radicals to become the major path in the clathrate and in solid lysozyme radiolysis. [source] Thermal and EPR investigations of thallium gallium disulphide single crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2009M. Acikgoz Abstract In this research, the results of the differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) investigations of TlGaS2 single crystal are presented. Specific heat capacity (Cp) anomalies of layered TlGaS2 have been obtained by using a new DSC technique for such crystals. Remarkable heat capacity anomalies have been revealed at the temperatures of 137.7 K, 174.5 K and 238.5 K. It is found that the anomalies appear at maximum with a small deviation (by 3-4%) from the regular values, and Cp discontinuity amounted to approximately 5%. Additionally, EPR spectra of Fe doped TlGaS2 single crystals have been recorded at various temperatures down to 6 K for different orientations of the applied magnetic field. Transformations of present EPR spectra are not sufficient for the confirmation of structural phase transitions, in contrast to the cases in iso structural TlInS2 and TlGaSe2 compounds. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bioaccumulation and ROS generation in liver of freshwater fish, goldfish Carassius auratus under HC Orange No. 1 exposureENVIRONMENTAL TOXICOLOGY, Issue 3 2007Yuanyuan Sun Abstract HC Orange No. 1 (CAS No. 54381-08-7, 2-nitro-4,-hydroxydiphenylamine) is used as a color additive in hair dyes. In this study, laboratory experiment was carried out to determine HC Orange No. 1 bioaccumulation and oxidative stress in the liver of freshwater fish, goldfish Carassius auratus. Fish were exposed to different concentrations (0.05, 0.1, 0.2, 0.5, and 1.0 mg/L) of HC Orange No. 1 for 10 days, with one group assigned as control. The accumulation of HC Orange No. 1 in liver increased with the exposure concentration (R2 = 0.94). A secondary spin trapping technique was used followed by electron paramagnetic resonance (EPR) analysis to study the reactive oxygen species (ROS) production. On the basis of the hyperfine splitting constants and shape of the EPR spectrum, the ROS generated in fish liver after exposure was identified as hydroxyl radical (,OH). There is a good correlation between the exposure concentrations and ,OH generation (R2 = 0.92). The ,OH signal intensity of the EPR spectrum showed a significant increase (P < 0.05) when the HC Orange No. 1 concentration was 1.0 mg/L, compared with that of the control. A good positive relationship (R2 = 0.95) was found between the ,OH formation and accumulation level of HC Orange No. 1 in liver. The changes of the activities of catalase (CAT), superoxide dismutase (SOD), glutathione S -transferase (GST), and contents of reduced glutathione (GSH) were also detected. These observations indicated a possible mechanism of oxidative stress induced by HC Orange No. 1 on fish. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 256,263, 2007. [source] Oxidation of oleuropein studied by EPR and spectrophotometryEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2008Evaggelia D. Tzika Abstract The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4-methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o -semiquinone radicals produced during autoxidation at pH,12 and short-lived o -semiquinone free radicals produced during autoxidation at pH,9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg2+) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV-Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4-methylcatechol was followed by recording spectral changes at 400,nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH,6.5 and a minor one around pH,8. From the data analysis of the initial rate at pH,6.5, the kinetic parameters Km = 0.34,±,0.03,mM and Vmax = 0.029,±,0.002 ,A400,min,1 were determined for oleuropein. [source] Effect of residual vanadyl ions on the spectroscopic analysis of humic acids: a multivariate approachEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2008E. H. Novotny Summary In a study of the vanadyl (VO2+)-humic acids system, the residual vanadyl ion suppressed fluorescence and specific electron paramagnetic resonance (EPR) and NMR signals. In the case of NMR, the proton rotating frame relaxation times (T1,H) indicate that this suppression is due to an inefficient H-C cross polarization, which is a consequence of a shortening of T1,H. Principal components analysis (PCA) facilitated the isolation of the effect of the VO2+ ion and indicated that the organic free radical signal was due to at least two paramagnetic centres and that the VO2+ ion preferentially suppressed the species whose electronic density is delocalized over O atoms (greater g -factor). Additionally, the newly obtained variables (principal components , PC) indicated that, as the result of the more intense tillage a relative increase occurred in the accumulation of: (i) recalcitrant structures; (ii) lignin and long-chain alkyl structures; and (iii) organic free radicals with smaller g -factors. [source] Assignment of the [4Fe-4S] clusters of Ech hydrogenase from Methanosarcina barkeri to individual subunits via the characterization of site-directed mutantsFEBS JOURNAL, Issue 18 2005Lucia Forzi Ech hydrogenase from Methanosarcina barkeri is a member of a distinct group of membrane-bound [NiFe] hydrogenases with sequence similarity to energy-conserving NADH:quinone oxidoreductase (complex I). The sequence of the enzyme predicts the binding of three [4Fe-4S] clusters, one by subunit EchC and two by subunit EchF. Previous studies had shown that two of these clusters could be fully reduced under 105 Pa of H2 at pH 7 giving rise to two distinct S˝ electron paramagnetic resonance (EPR) signals, designated as the g = 1.89 and the g = 1.92 signal. Redox titrations at different pH values demonstrated that these two clusters had a pH-dependent midpoint potential indicating a function in ion pumping. To assign these signals to the subunits of the enzyme a set of M. barkeri mutants was generated in which seven of eight conserved cysteine residues in EchF were individually replaced by serine. EPR spectra recorded from the isolated mutant enzymes revealed a strong reduction or complete loss of the g = 1.92 signal whereas the g = 1.89 signal was still detectable as the major EPR signal in five mutant enzymes. It is concluded that the cluster giving rise to the g = 1.89 signal is the proximal cluster located in EchC and that the g = 1.92 signal results from one of the clusters of subunit EchF. The pH-dependence of these two [4Fe-4S] clusters suggests that they simultaneously mediate electron and proton transfer and thus could be an essential part of the proton-translocating machinery. [source] Defect-Related Emissions and Magnetization Properties of ZnO NanorodsADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Bharati Panigrahy Abstract A clear correlation between defect-related emissions and the magnetization of ZnO nanorods synthesized by a one-step aqueous chemical method is demonstrated. The relative contribution of the emission bands arising from various types of defects is determined and found to be linked with the size of the nanorods and annealing conditions. When the size of the nanorods and the annealing temperature are increased, the magnetization of pure ZnO nanorods decreases with the reduction of a defect-related band originating from singly charged oxygen vacancies (). With a sufficient increase of annealing temperature (at 900,°C), the nanorods show diamagnetic behavior. Combining with the electron paramagnetic resonance results, a direct link between the magnetization and the relative occupancy of the singly charged oxygen vacancies present on the surface of ZnO nanorods is established. [source] Enhanced Light-Harvesting and Photocatalytic Properties in Morph -TiO2 from Green-Leaf BiotemplatesADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Xufan Li Abstract The unique structure of green leaves endows them with an extremely high light-harvesting efficiency. In this work, green leaves are applied as biotemplates to synthesize morph -TiO2. The structural features favorable for light harvesting from the macro- to the nanoscale are replicated in morph -TiO2 through a two-step infiltration process and the N contained in the original leaves is self-doped into the resulting samples. The absorbance intensities within the visible-light range of morph -TiO2 derived from different leaves increase by 103,258% and the band-gap-absorption onsets at the edge of the UV and visible-light range show a red-shift of 25,100,nm compared to those in TiO2 without the template. The photocatalytic activity of morph -TiO2 is also improved, as proven by an electron paramagnetic resonance (EPR) study and degradation of rhodamine dye under irradiation with UV and visible light. The present work, as a new strategy, is of far-reaching significance in learning from nature, driving us to make full use of the most-abundant resources and structure-introduced functions endowed by nature, opening up possibilities for extensive study of the physical and chemical properties of morph -structured oxides and extending their potential for use in applications such as solar cells, photocatalysts, photoelectrical devices, and photoinduced sensors. [source] Two Novel Antioxidative Stilbene Tetramers from Parthenocissus laetevirensHELVETICA CHIMICA ACTA, Issue 7 2009Shan He Abstract Laetevirenols F (1) and G (2), two novel stilbene tetramers with an unprecedented skeleton, were isolated from Parthenocissus laetevirens. Their structures were elucidated by spectroscopic analysis, including 1D- and 2D-NMR experiments, and their possible biogenetic pathway was discussed. In addition, both compounds were determined to be potent singlet-oxygen quenchers by electron paramagnetic resonance (EPR) experiments, which highlights their potential pharmacological applications in singlet oxygen mediated diseases. [source] Radical annihilation of ,-ray-irradiated contact lens blanks made of a 2-hydroxyethyl methacrylate copolymer at elevated temperaturesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Young-Shang Lin Abstract The annihilation of the radicals in irradiated 2-hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main-chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25,45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second-order kinetics; these were different from the kinetics for the color formation and defect-controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Principles of pulse electron paramagnetic resonance.JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2004578 pp., By A Schweiger, G Jeschke, Oxford University Press No abstract is available for this article. [source] Noninvasive in vivo electron paramagnetic resonance study to estimate pulmonary reducing ability in mice exposed to NiO or C60 nanoparticlesJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2009Hidekatsu Yokoyama MD Abstract Purpose To develop new methods that can estimate the influences of manufactured nanomaterials on biological systems, the in vivo pulmonary reducing ability of mice that had received inhalation exposures to NiO or C60 nanoparticles was investigated using a 700 MHz electron paramagnetic resonance (EPR) spectrometer. Materials and Methods NiO or C60 suspensions were atomized and mice in exposure chambers inhaled the resulting aerosol particles for 3 hours. The exposure conditions, number-based geometric average diameters, and the average number concentration were precisely controlled at almost the same levels for both NiO and C60 nanoparticles. Two days or 2 weeks after exposure, an EPR study was conducted noninvasively. Temporal changes in EPR signal intensity at the target area (ie, lung field) were obtained by the region-selected intensity determination (RSID) method. Results NiO nanoparticles significantly suppressed pulmonary reducing ability 2 days and 2 weeks after exposure, but C60 nanoparticles had no such effect. Conclusion This is the first in vivo estimation of the reducing ability in experimental animals exposed to manufactured nanoparticles. J. Magn. Reson. Imaging 2009. © 2009 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||