- Nitroxide radicals as probes for exploring the binding properties of the cucurbit[7]uril host
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EPR spectroscopy was used for the first time to explore the binding properties of cucurbit[7]uril (CB7), a representative member of the cucurbituril family. Evidence for the formation of a complex between nitroxide radicals and the host system in an aqueo
- Mezzina, Elisabetta,Cruciani, Francesca,Pedulli, Gian Franco,Lucarini, Marco
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- An EPR method for measuring the rate of distribution of organic substrates between cyclodextrin, micelles and water
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The combined use of selected nitroxides and EPR spectroscopy has been proved to be suitable for studying the partitioning rate of a given substrate in cyclodextrin-micelle systems. The Royal Society of Chemistry.
- Mileo, Elisabetta,Franchi, Paola,Gotti, Roberto,Bendazzoli, Claudia,Mezzina, Elisabetta,Lucarini, Marco
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- Silylation reactions on nanoporous gold: Via homolytic Si-H activation of silanes
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Si-H bond activation is an important process implicated in many useful synthetic applications including silylation and transfer hydrogenation reactions. Herein we discovered homolytic activation of Si-H bonds on the surface of nanoporous gold (NPG), forming hydrogen radicals and [Au]-[Si] intermediates. By virtue of this new reactivity, we achieved highly selective mono and sequential alcoholysis of dihydrosilane. In addition, the amphiphilic nature of the [Au]-[Si] intermediate allows for a new bis-silylation reaction of cyclic ethers. The present work showcased that the surface reactivity of nanocatalysts may provide exciting opportunity for new reaction discovery.
- Li, Hongbo,Guo, Huifang,Li, Zhiwen,Wu, Cai,Li, Jing,Zhao, Chunliang,Guo, Shuangxi,Ding, Yi,He, Wei,Li, Yadong
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p. 4808 - 4813
(2018/06/07)
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- Spin trapping of Au-H intermediate in the alcohol oxidation by supportedand unsupported gold catalysts
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Electron paramagnetic resonance (EPR) spectroscopy and spin trapping were used to explore the mechanism of alcohol oxidation over gold catalysts. Reaction of secondary alcohols with supported and unsupported gold catalysts (e.g., Au/CeO2, polymer-Incarcerated Au nanoparticles,PPh 3-protected Au nanoparticles) In the presence of spin tr aps led to the formation of a hydrogen spin adduct. Using Isotope labeling, we confirmed that the hydrogen In the spin adduct originates from the cleavage of the C-H bond In the alcohol molecule. The formation of thehydrogen spin adduct most likely results from the abstraction of hydrog en from the Au surface by a spin trap. These results thus strongly suggest Intermediate formation of Au-H species during alcohol oxidation. The role of oxygen In this mechanism Is to restore the catalytic activity rather than oxidize alcohol. This was further confirmed by carrying out gold-catalyzed alcohol oxidation In the absence of oxygen, with nitroxidesas hydrogen abstractors. The support (e.g., metal oxides) can activate oxygen and act as an H abstractor from the gold surface and hence lead t o a faster recovery of the activity. Peroxyl radicals were also observedduring alcohol oxidation, consistent with a free-radical autoxidation m echanism. However, this mechanism Is likely to be a minor side reaction,which does not lead to the formation of an appreciable amount of oxidat ion products.
- Conte, Marco,Miyamura, Hiroyuki,Kobayashi, Shu,Chechik, Victor
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supporting information; experimental part
p. 7189 - 7196
(2009/09/30)
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- Authentic versus alternative mechanisms in spin trapping. Formation of azide spin-adducts in biphasic and non-aqueous systems by the oxidation of azide anion with a variety of hydrazyl radicals
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The formation of azide spin-adducts of a number of spin-traps, including PBN, DMPO, DEPMPO and TBNB, in biphasic and organic media has been studied by EPR spectroscopy. A series of hydrazyl radicals has been employed to oxidise the azide anion to the corresponding short-lived azido radical, which is subsequently trapped. The approach has typically involved the presence of the ether 18-crown-6 in order to facilitate the transport of the azide anion from water into the organic media, with further experiments in non-aqueous systems. The results can largely be rationalised in terms of a "conventional" spin-trapping mechanism, with an efficient that depends on the relevant redox potentials, which are themselves solvent dependent; however, conditions that favour direct oxidation of the trap have also been identified. It is also established that the azide spin-adducts of some nitrones can be transformed, under certain conditions, into secondary spin-adducts by nucleophilic substitution reaction of the first-formed nitroxides.
- Ionita, Petre,Gilbert, Bruce C.,Whitwood, Adrian C.
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p. 2436 - 2440
(2007/10/03)
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- Photoactivated formation of hydrogen spin adduct from phenylsilane. A new example of inverted spin trapping?
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Photodissociation of phenylsilane was studied by EPR spectroscopy using N-benzylidene-tert-butylamine N-oxide (PBN) and bis(benzene)chromium (BBC) as spin trapping systems. Under controlled UV irradiation and in the presence of dioxygen, hydrogen spin add
- Coradin, Thibaud,Le Bideau, Franck,Henique, Josette,Samuel, Edmond,Gourier, Didier
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p. 2465 - 2468
(2007/10/03)
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- EPR Spin-Trapping Study of the Sonolysis of H2O/D2O Mixtures: Probing the Temperatures of Cavitation Regions
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High temperatures and pressures are generated during the violent collapse of acoustic cavitation bubbles produced by ultrasound in liquids.The semiclassical model of the temperature dependence of the kinetic isotope effect for .H and ./su
- Misik, Vladimir,Miyoshi, Norio,Riesz, Peter
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p. 3605 - 3611
(2007/10/02)
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- Applications of EPR to a Study of the Hydrogenation of Ethene and Benzene over a Supported Pd Catalyst: Detection of Free Radicals on a Catalyst Surface
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EPR has not been used extensively in the field of catalysis despite it being the most sensitive technique available for detecting free radicals and paramagnetic metal ions, which are intermediates or participants in many catalytic processes.In this paper,
- Carley, Albert F.,Edwards, Hywel A.,Mile, Brynmor,Roberts, M. Wyn,Rowlands, Christopher C.,et al.
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p. 3341 - 3346
(2007/10/02)
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- 1H NMR of (α-Substituted benzyl-t-butyl)hydroxylamines and EPR of Their Oxidized Forms
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1H NMR study of several (benzyl-t-butyl)hydroxylamine derivatives (BBHA) was performed, which were obtained through the addition of Grignard agents to α-phenyl-N-t-butylnitrone (PBN) or the reduction of PBN.Concominantly, EPR of their oxidized forms (nitr
- Migita, Catherina T.,Nakayama, Masaharu,Takeuchi, Makoto,Ogura, Kotaro
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p. 737 - 740
(2007/10/02)
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- Reactions of Ozonate and Superoxide Radical Anions
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Potassium ozonate has been prepared by reaction of ozone with potassium superoxide dispersed in Freon-12.Orange solutions of potassium ozonate in benzene or toluene containing 18-crown-6 react with nitrone traps to give spin adducts mainly derived from the oxide radical anion, which is a decomposition product of the ozonate radical anion.With 2-methyl-2-nitrosopropane in toluene solution the ozonate gives five nitroxide radicals in whose formation the oxide radical anion is again implicated.With nitrosobenzene electron transfer occurs.Comparable reactions with superoxide are described.
- Forrester, Alexander R.,Purushotham, Vemishetti
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p. 211 - 218
(2007/10/02)
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- N-NITRENES. I. FORMATION OF FREE RADICALS IN THE DISSOCIATION OF DIBENZYLAMINONITRENE
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By ESR with spin traps it was shown that the dissociation of dibenzylaminonitrene to nitrogen and bibenzyl takes place through the formation of benzyl radicals.Various methods of generation of dibenzylaminonitrene in the presence of spin traps (2-methyl-2-nitrosopropane, nitrosodurene, phenyl-N-tert-butyl-nitrone) give spin adducts (nitroxyl radicals) stable at room temperature.The formation of two nitroxyl radicals during the dissociation of dibenzylaminonitrene labeled at one methylene group with deuterium imdicates that one molecule of dibenzylaminonitrene gives two benzyl radicals during dissociation.
- Savin, V. I.,Morozov, V. I.,Kitaev, Yu. P.
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p. 866 - 870
(2007/10/02)
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- Substituent effects in the kinetic analysis of free radical reactions with nitrone spin traps
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The kinetics of reactions of the water radiolysis species with substituted phenyl-N-tert-butyl nitrones (PBN), have been studied directly, in situ, using a pulsed Van de Graaff accelerator and kinetic spectrophotometry.The spin trapping of other secondary radiation-induced electrophilic and nucleophilic free radical species was also studied.The mechanistic aspects of these reactions are discussed in terms of the kinetic data.The effect of structure and substituents on the rate of spin trapping was tested for five para-substituted PBN's.It was found that electron-withdrawing groups increase the rate of nucleophilic reactions involving hydrated electrons, formyl anions, and α-hydroxyalkyl radicals with substituted PBN.Electron-donating substituents produce the opposite effect.These studies confirm that nitrones are effective spin traps because of their high reactivity towards radiation-induced free radicals.Caution must be observed, however, in view of their lack of specificity, in interpreting spin-trapping data in complex steady-state systems involving more than one primary or secondary radical species, or where unstable spin-adducts are formed.
- Greenstock, C. L.,Wiebe, R. H.
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p. 1560 - 1564
(2007/10/02)
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- Spin Trapping of Molecules Adsorbed on Zinc Oxide
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The reactions of the spin trap PBN with hydrogen and propylene adsorbed on ZnO are reported.For hydrogen, evidence is presented that the species trapped are H atoms adsorbed on Zn sites.For propylene, the allyl anion adsorbed on Zn sites reacts with PBN, but the resulting hydroxylamine must be oxidized before a nitroxide radical can be observed.Less than 1percent of adsorbed species are detected by the spin trapping technique.
- Matsuzaki, Tokuo,Uda, Taizo,Kazusaka, Akio,Keulks, George W.,Howe, Russell F.
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p. 7511 - 7513
(2007/10/02)
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