Publication costs assisted by the National Research Council of Canada Cysteinyl radicals (CyS•) produced by flash photolysis of dilute aqueous solutions of cysteine at pH >6.5 form the cystine radical anion (CySSCy"). At low concentrations (<6 X 10" 7 M) this transient decays by a first-order reaction (k = 2 x 10" 3 sec"1) independent of pH and cysteine concentration and not involving dissociation to CyS-and CyS". At higher concentrations the transient decays by the well-studied second-order process which is pH and cysteine concentration dependent. The yield of CySSCy" is reduced by the addition of acrylic acid or allyl alcohol but the subsequent first-order decay is little affected. A new reaction between CySSCy" and cystine has been observed (k -3 X 10® M~1 sec"1). Pulse radiolysis studies confirm these results.

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TZU-LIN TUNG and JOHN A. STONE. Can. J. Chem. 53,3 153 (1975). Transient disulfide radical anions have been produced by flash photolysis. Cyclic anions decay only by second order reaction as opposed to the first order decay found for linear ones at low concentration. Linear disulfides, except oxidized penicillamine, increase the rate of decay of the cystine radical anion. The p H dependence of the reaction with cystine suggests that the disulfide radical anion is an electrophile.TZU-LIN TUNG et JOHN A. STONE. Can. J. Chem. 53,3153 (1975).Faisant appel i la photolyse flash, on a produit, i 1'6tat transitoire, les radicaux anions du disulfure. Les anions cycliques ne se decomposent que par une reaction du deuxieme ordre alors que les anions lineaires se dkomposent, i basse concentration, par une reaction du premier ordre. Les disulfures lineaires, i l'exception de la penicillamine oxydk, augmentent le taux de dkomposition du radical anion de la cystine. Le fait que la reaction avec la cystine dkpend du p H indique que le radical anion du disulfure est un electrophile.[Traduit par le journal] Introduction The lifetimes of disulfide radical anions (RSSR-) are increased in the presence of sulfhydryl compounds (1, 2). By studying the flash photolysis and pulse radiolysis of aqueous solutions of cysteine we showed that this increased lifetime was due to a complex mode of decay (3). Our postulated reaction scheme is shown by [I] to [6] in which CyS. represents the cysteinyl group and Cy. the alanyl radical.

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