EPR Study Of Radicals Research Articles

SET and HAT/PCET acid-mediated oxidation processes in helical shaped fused bis-phenothiazines.

Helical shaped fused bis‐phenothiazines 1–9 have been prepared and their red‐ox behaviour quantitatively studied. Helicene radical cations (Hel.+) can be obtained either by UV‐irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant. The reaction of hydroxy substituted helicenes 5–9 with peroxyl radicals (ROO.) occurs with a ‘classical’ HAT process giving HelO. radicals with kinetics depending upon the substitution pattern of the aromatic rings. In the presence of acetic acid, a fast medium‐promoted proton‐coupled electron transfer (PCET) process takes place with formation of HelO. radicals possibly also via a helicene radical cation intermediate. Remarkably, also helicenes 1–4, lacking phenoxyl groups, in the presence of acetic acid react with peroxyl radicals through a medium‐promoted PCET mechanism with formation of the radical cations Hel.+. Along with the synthesis, EPR studies of radicals and radical cations, BDE of Hel‐OH group (BDEOH), and kinetic constants (kinh ) of the reactions with ROO. species of helicenes 1–9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds.

EPR study of radicals generated from bioactive S‐nitrosothiols and related thiols

AbstractThermal or photolytic reactions of bioactive S‐nitrosothiols and related thiols in the presence of radical generators in deaerated DMSO or aqueous solutions under argon or saturated with nitric oxide (NO) produced nitroxides and an oxyaminyl radical, which were well characterized by EPR spectra. Nitroxides containing a thiyl substituent were obtained. Possible mechanisms are proposed. Bioactive S‐nitrosothiols such as S‐nitrosoglutathione, S‐nitroso‐N‐acetylpenicillamine and related thiols such as glutathione and N‐acetylpenicillamine were used for the investigation. Radical generators utilized as transient radical sources were 2,2′‐azobisisobutyronitrile, 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride, tert‐butyl peroxide and benzoyl peroxide. Copyright © 2002 John Wiley & Sons, Ltd.

ChemInform Abstract: Synthesis and EPR Studies of Radicals and Biradical Anions of C60 Nitroxide Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Synthesis and EPR Studies of Radicals and Biradical Anions of C60 Nitroxide Derivatives

A series of C60 derivatives substituted with the nitroxide group 2,2,6,6-tetramethylpiperidine-1-oxyl have been synthesized. A detailed EPR and ENDOR study of the neutral radicals and of their reduction products is reported. All the neutral species give EPR spectra consisting of a main triplet of lines with ∼15 G splitting by the 14N nucleus, typical of nitroxide radicals. Some of them show additional well-resolved splittings by methyl and methylene protons, which are discussed in relation to the conformation of the nitroxide ring. When the compounds are progressively reduced under vacuum by contact with an alkali metal mirror, new EPR lines are observed; a 1:1:1 triplet with a splitting constant half that of a nitroxide radical and g = 2.0030 is attributed to biradical anions where one electron is located in the fullerene moiety and experiences a strong exchange coupling with the nitroxide unpaired electron. Frozen solution spectra of these species allow the determination of the electron−electron dipolar interaction parameters which are compared with theoretical MO calculations. The experimental values agree with a spin distribution of one unpaired electron mostly in the equatorial plane of the fullerene. Another single line which appears in the spectrum as the reduction proceeds further on (g = 1.9999) is attributed to a new species: possibly a substituted fullerene radical anion in which the nitroxide group is irreversibly reduced.

EPR study of radicals derived from five-carbon alkenenitriles

EPR study of radicals derived from five-carbon alkenenitriles

Epr studies of radicals in conducting solutions, oligomer crystals and conducting polymers

Epr studies of radicals in conducting solutions, oligomer crystals and conducting polymers