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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.

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.

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.

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/

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.