Production du radical acétyle : étude radiolytique comparée des radicaux libres issus de l’acétaldéhyde et de l’éthylène-glycol

¹ Département de Recherches Biomédicales sur l’Alcoolisme, France.
² Laboratoire de Chimie Physique, CNRS URA 400, Université Paris V, 45, rue des Saint-Pères, 75270 Paris Cedex 06, France.

Résumé

En comparant les résultats obtenus par radiolyse pulsée, sous atmosphère de N₂O, de solutions d’acetaldéhyde tamponnées à pH 7,4 à ceux obtenus dans les mêmes conditions à partir de l’éthylène-glycol, nous montrons que les mêmes espèces radiculaires sont produites, espèces qui peuvent être attribuées aux radicaux acètyle et/ou méthyl-formyle. L’éthylène-glycol, moins toxique que l’acétaldéhyde, peut donc être utilisé comme source du radical acétyle dans le cadre d’études de sa réactivité sur des cibles biologiques. De plus les radicaux issus de l’éthylène-glycol réduisent le ferricytochromc c.

Abstract

Taking into account that acetaldehyde is toxic towards some cellular components (specifically enzymes), it appears of great interest for biologists to produce the acetyl radical from a less toxic precursor in order to distinguish the reactivity of this radical from acetaldehyde toxicity. It was shown previously that acetaldehyde, after reaction with the OH^• radical, produces acetyl and formylmethyl radicals, whereas it was imputed that the radical produced from ethylene-glycol, under the same conditions, is the formylmethyl radical. As the acetyl and formylmethyl radicals can be considered as tautomeric forms, we postulate that it could be possible to obtain, by radiolysis under an atmosphere of N₂O and at neutral pH, the same species from ethylene-glycol than from acetaldehyde.

Thus the optical absorption spectra of the intermediates obtained by pulse radiolysis of N₂O-saturated solutions of acetaldehyde or ethylene-glycol and the kinetics of their decays have been investigated. The primary species obtained by the reaction of the OH^• radical with ethylene-glycol disappears with k = 1.5 × 10⁵ s^-1 and gives another transient which is also observed during pulse radiolysis of acetaldehyde. This latter transient disappears with 2k = 1.5 × 10⁸ mol^-1.l.s^-1. These results suggest that the OH^• radical reactions with acetaldehyde or ethylene-glycol produce acetyl and formylmethyl radicals. Besides, these radicals arc shown to reduce ferricytochrome c (k = 3 × 10⁶ mol^-1.l.s^-1) with G_max (- cyt c-Fc³⁺) ≃ G(OH^•) = 5.6 × 10^-7 mol.J^-1.