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The alkoxy and peroxy radicals formed in the degradation of hydroperoxides brought about by transition metal ions in acidic media can convert substrates with suitably low oxidation potentials, such as N,N-diethyl-para-phenylendiamine, to the corresponding radical cations. The possibility that these reactions are used in the evaluation of oxidative stress in human beings is discussed.

A number of radicals have been added to 1,3-bis(2,4,6-tri-tert-butylphenyl)diphospha-allene at low temperature in cyclopropane solution. Addition of thiyl and alkoxyl radicals occurs regiospecifically to one of the phosphorus atoms leading to new phosphavinyl radicals, isoelectronic with vinyl radicals, which have been characterised by means of EPR spectroscopy. The results of ab initio calculations are in agreement with the experimentally determined spectral parameters and suggest that these radicals are bent, with a PCP bond angle of ca. 150°. In contrast, silyl and germyl radicals appear to add to the carbon atom of the phosphaallene.

Two conformational isomers have been NMR detected at −30° in 2-substituted pyridones having an isoprophyl group bonded to the Nitrogen atom. Their existence is due to the restricted rotation of the N-isopropyl group influenced by the “gear effect” of the flanking 2-alkyl groups (Me, Et, Pr 1 ). The interconversion barrier for this process (∼15 kcal/mol) was measured by total line shaped analysis and is independent of the size of the flanking alkyl groups. Molecular Mechanics calculations and NOE difference experiments at −70° allow the unambigious identification of the structures corresponding to the gear conformers.

A number of 1-naphthylimines (and some of the corresponding imonium chlorides), having the isopropyl group as a prochiral probe, have been synthesized and their configurations assigned by the combined use of NOE experiments and molecular mechanics calculations. This method also provides reliable information about the conformations adopted in solution. The existence of diastereotopic methyl groups in the isopropyl moiety indicates the presence of conformational enantiomers, due to the rotation about the naphthyl–imino bond in nonplanar conformers. The barriers for the stereomutation of such enantiomeric forms have been determined by line-shape analysis of the temperature-dependent 1H or 13C signals of the prochiral probe. Molecular mechanics calculations have also helped in suggesting which is the preferred stereomutation pathway and in predicting the existence of a derivative having configurationally stable enantiomers. Such a compound has been synthesized and is found to display the predicted property (atropisomerism), in that the two enantiomers can be separated.

International audience; The reaction of carbon disulfide with an excess of sodium dialkylphosphite in an aprotic solvent led to the formation of the carbanion of methylene bisphosphonate and sodium thiophosphate. The mechanistic study of this unexpected reaction, using both 31 P NMR and ESR spectroscopy, suggests the formation of a radical intermediate able to abstract a hydrogen atom from the solvent.

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The direct EPR detection of thioacyl radicals has been reported only once, while thioacyl nitroxides remain an elusive species. We failed to detect the thioacyl radicals from two thioaldehydes and from phosphoryldithioformates but have obtained EPR evidence that thioacyl radicals react with 2-methyl-2-nitrosopropane to give thiocarbonyloxyaminyls rather than thioacyl nitroxides. The results of DFT calculations support this unexpected reactivity of thioacyls, while making questionable their previous EPR identification.

Reliability of the photo-stimulated luminescence (PSL) technique, both as screening and identification methods, has been tested with several kinds of irradiated herbs and spices over a long period of storage. To check the influence of storage modality on the PSL response, the samples were divided into groups kept in environments with different light exposure. The results clearly indicate a marked light-induced bleaching of the PSL signal, which may lead to a false negative classification, in a significant percentage, for spices stored in typical market conditions. To limit the occurrence of wrong classifications, the suggestion reported in the European Committee of Normalization Standard 13751 to draw the necessary amount of product from a light-protected position becomes mandatory. Thermoluminescence measurements, performed for comparison purposes, gave correct results for all the samples tested.

The antimalaric drug artemisinin (QHS) is believed to operate through a mechanism initiated with the cleavage of its endoperoxidic bond induced by transition metal ions. An ESR investigation of the reaction of QHS with human serum in the presence of two spin trapping agents has led to the detection of spin adducts of carbon-centred radicals. Experiments carried out replacing the human serum with iron(II) salts led to the observation of the same spin adducts, thus supporting previous suggestions that also in vivo the drug operates via a radical-based mechanism. UV irradiation of QHS also led to the trapping of transient free radicals.

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1 Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology September 2008, Volume 151, Issue 1, Supplement 1, Page S15 http://dx.doi.org/10.1016/j.cbpa.2008.05.030 © 2008 Published by Elsevier Inc. 25th Congress of the newEuropean Society of Comparative Biochemistry and Physiology, Ravenna, Italy, September 7–11, 2008 New challenges in integrative physiology and biochemistry: From molecular mechanisms to environmental adaptation Archimer Archive Institutionnelle de l’Ifremer http://www.ifremer.fr/docelec/

A number of 1-naphthylimines (and some of the corresponding imonium chlorides), having the isopropyl group as a prochiral probe, have been synthesized and their configurations assigned by the combined use of NOE experiments and molecular mechanics calculations. This method also provides reliable information about the conformations adopted in solution. The existence of diastereotopic methyl groups in the isopropyl moiety indicates the presence of conformational enantiomers, due to the rotation about the naphthyl–imino bond in nonplanar conformers. The barriers for the stereomutation of such enantiomeric forms have been determined by line-shape analysis of the temperature-dependent 1H or 13C signals of the prochiral probe. Molecular mechanics calculations have also helped in suggesting which is the preferred stereomutation pathway and in predicting the existence of a derivative having configurationally stable enantiomers. Such a compound has been synthesized and is found to display the predicted property (atropisomerism), in that the two enantiomers can be separated.

Ethyl (diethoxyphosphoryl)thionformate, ethyl (diethoxythiophosphoryl) thionformate. ethyl (diethoxyphosphoryl)(thiolformate, and ethyl (die thoxythiophosphorl)thiolformate have been allowed to react with a variety of in situ generated free radicals. Spin adducts were observed by EPR with the two thionesters but not with thiolesters even the former compounds, however. exhibited a remarkably lower reactivity than similarly substituted dithioesters.

The variation of 5J in the title compounds with temperature and the size of the substituents has been interpreted as depending on the population of the anti-configuration.

Eight simple amides have been subjected to UV irradiation in the presence of either MNP or NO. In all cases radical species were generated: these were detected by means of EPR spectroscopy in the form of different nitroxides resulting from the trapping of the primary radicals. NO acted as a double spin trap, scavenging a radical to afford a diamagnetic nitroso derivative that in turn acted as trap towards another radical unit. As amido-groups are present in components of skin tissue and may be present in many therapeutic or cosmetic products used as skin sunscreen, and NO is a ubiquitous endogenous reactive species, the nitroxides detected in the present studies might participate in radical processes triggered by sun exposure and resulting in damages, even severe, of biological tissues. (C) 2012 Elsevier Ltd. All rights reserved.

The antioxidant activity of five phenols, i.e. catechol, homovanillyl alcohol, homovanillic acid, gallic acid and syringic acid, present in all olive oils has been investigated. For gallic acid and syringic acid the Bond Dissociation Enthalpy BDE(O–H) has been determined through the EPR (Electron Paramagnetic Resonance spectroscopy) based on radical equilibration technique as 81.0 and 82.1 kcal mol–1, respectively. For both homovanillyl alcohol and homovanillic acid the BDE(O–H) values were assumed to be identical to that of the similar 2-methoxy-4-methylphenol (82.8 kcal mol–1). The inhibition rate constants of the above compounds and of catechol in the autoxidation of cumene (or styrene) were also determined in acetonitrile/chlorobenzene solution and corrected for hydrogen bonding by acetonitrile. The results indicate that in organic solvents gallic acid and catechol are fairly good antioxidants, while homovanillyl alcohol, homovanillic acid and syringic acid, i.e. the three 2-methoxy substituted derivatives, are much less efficient antioxidants.