Electron Paramagnetic Resonance, Techniques and Applications

Alger, Raymond S.

doi:10.1119/1.1975893

Cited by 91 publications

(72 citation statements)

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“…Dividing by the linewidth of 1.9 G reported for DPPH [37], this corresponds to a sensitivity of 1.7 · 10 10 and 2.3 · 10 9 spins AE G À1 Hz À1/2 . In the CW EPR experiment with the DPPH samples, the measured sensitivity of the device scaled inversely proportional to the square of the microresonator diameter.…”

Section: Cw Eprmentioning

confidence: 99%

Planar microresonators for EPR experiments

Narkowicz

Suter

Stonies

2005

Journal of Magnetic Resonance

110

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Section: Cw Eprmentioning

confidence: 99%

Planar microresonators for EPR experiments

Narkowicz

Suter

Stonies

2005

Journal of Magnetic Resonance

110

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“…This let us to obtain the highest filling factor and therefore the highest signal-to-noise ratio, in all the EPR spectra [23].…”

Section: -Sample Characterisationmentioning

confidence: 99%

EPR enlightening some aspects of propane ODH over VOx–SiO2 and VOx–Al2O3

Oliva

Cappelli

Rossetti

et al. 2009

Chemical Engineering Journal

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In the oxidative dehydrogenation (ODH) of propane to propylene VOx-based catalysts prepared by flame pyrolysis (FP) showed more selective than those prepared by impregnation. Furthermore, samples prepared by the same method were less active, but more selective when VOx was supported on SiO2 than on Al2O3. In order to assess V local structure, V 4+ ions showed useful labels to characterise these catalysts by EPR spectroscopy. Indeed, the spectrum of a (10 wt%V2O5) FP-prepared VOx/SiO2 catalyst was typical of isolated, tetragonally distorted, paramagnetic complexes of V 4+ forming a monolayer on the sample surface with a strong out-of-plane V 4+ -O bond. In a sample with identical composition, but prepared by impregnation, this bond showed a bit weaker.Furthermore, ferromagnetic domains of clustered V ions formed in the latter sample, hindering at least in part the accessibility to the catalytically active V-based centres. This gives evidence of the higher dispersion of V in the sample bulk provided by the FP preparation method with respect to conventional ones. A by far weaker V 4+ -O bond was revealed by the EPR spectrum of a (10%V2O5) VOx/Al2O3 sample, accounting for its higher oxygen availability, leading to higher activity, but lower selectivity. However, the same catalyst, when prepared by impregnation, showed a ferromagnetic resonance pattern so intense that no EPR spectrum was detectable at all and no information on the V 4+ -O bond strength was available in that case.Such semi-quantitative index of the V-O bond strength can be used as an index of oxygen availability, as a tool to assess catalytic activity and selectivity to the desired olefin.

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“…Charge-transfer complexes can be distinguished from organic free radicals by the different effects of temperature on their ESR spectra (Alger 1968), and such measurements are planned for future research in this project. In any case, the presence of organic free radicals in a liquid raises the possibility of radical-mediated chain polymerizations which may cause the formation of undesirable gums and other sediments in these liquids (Frankenfeld et al 1983).…”

Section: Changes In Chemical Composition Due To Exposurementioning

confidence: 99%

“…The ESR signals from the samples were displayed graphically as first derivatives of the absorption spectra, and the concentrations of radicals giving rise to these signals were measured by double integration of the spectra, using a moment balance (Alger 1968). The system was calibrated with a standard solution of the stable free radical, a, a'-diphenylpicrylhydrazyl (DPPH) in mineral oil.…”

Section: Characterization Of Sample Componentsmentioning

confidence: 99%

Photodegradation of mutagens in solvent-refined coal liquids

Kalkwarf¹,

Stewart²,

Pelroy³

et al. 1984

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SUMMARYThe purpose of this investigation was to evaluate any changes in the chemical composition and microbial mutagenicities of two representative solventrefined coal (SRC) liquids as a function of exposure time to sunlight and air. This information was desired to assess potential health hazards arising from ground spills of these liquids during production, transport and use. Results of microbial mutagenicity assays using Salmonella typhimurium TA98, conducted after exposure, showed that the mutagenicities of both an SRC-II fuel oil blend and an SRC-1 process solvent decreased continuously with exposure time to air and that the decrease was accelerated by simultaneous exposure to simulated sunlight. The liquids were exposed as thin layers supported on surfaces of glass, paper, clay or aluminum; but the type of support had little effect on the results. The contrast between these results and the reported increases of mutagenesis in organisms exposed simultaneously to coal liquids and nearultraviolet light suggested that short-lived mutagenic intermediates, e.g., organic free radicals, were formed in the liquids during exposure to light.The highest activities of microbial mutagenicity in the SRC liquids were found in fractions rich in amino polycyclic aromatic hydrocarbons (amino PAH). After a 36-hour exposure of the fuel oil blend to air in the dark, the mutagenicity of its amine-rich fraction was reduced by 65%; whereas a 36-hour exposure in the light reduced the mutagenicity of this fraction by 92%. Similar rates of reduction in mutagenicity were achieved in exposures of the process solvent. The mutagenicities of other chemical fractions remained low during exposure. Analyses showed that most of the amine components of both liquids contained less than four aromatic rings and that their concentrations generally decreased with exposure time. These results indicate that the microbial mutagenicities of the two SRC liquids may be expected to gradually decrease if they are spilled out of doors, with the rate of decrease dependent on their access to air and sunlight. However, one cannot be sure that all of the potential health hazards of these materials are reduced by such exposures si nee the _i. typhimurium TA98 test system has been reported to be relatively insensitive to potential mutagens in fractions of SRC liquids rich in neutral aromatic compounds.Electron spin resonance (ESR) measurements on the liquids showed free radical concentrations on the order of 5xlo 16 unpaired spins per gram before exposure. In darkness, this concentration decreased continuously during exposure to air, paralleling the decrease in mutagenicities of the samples. In simulated sunlight, the concentration of paramagnetic species rapidly increased within the first few minutes of illumination and then decreased with continued exposure. This behavior suggested that organic free radicals were the major paramagnetic species, although charge-transfer complexes may have also been present. The ESR spectra were not sufficiently resolved to identi...

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Electron Paramagnetic Resonance, Techniques and Applications

Cited by 91 publications

References 0 publications

Planar microresonators for EPR experiments

Planar microresonators for EPR experiments

EPR enlightening some aspects of propane ODH over VOx–SiO2 and VOx–Al2O3

Photodegradation of mutagens in solvent-refined coal liquids

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