Product yields and mechanism of penicillamine radiolysis at pH 5

Abstract

Can. J. Chem. 54, 1938 (1976. The major products from the radiolysis of penicillamine in N20-saturated solutions a t p H 5 are penicillamine disulfide, penicillamine trisulfide, and valine with yields of 2.0, 1.2, and 1.5 molecules per 100 eV in lo-' M solutions and 1.8, 0.94, and 0.60 molecules per 100 eV in 10-3 M solutions respectively. These yields remain essentially the same when the major attacking radical is changed from .OH to . C H 2 0 H , .Br2-or .(CNS)?-, and it is concluded that all four species produce predominantly pens. radicals on attacking penicillamine. The formation of trisulfide and an equivalent amount of valine is attributed to secondary reactions of pens. radicals and discussed in the light of recent pulse radiolysis experiments and other work.In deaerated solutions hydrogen and H2S were observed in significant yields and the valine yield increased. These observations can be accounted for quantitatively by the reactions: [To] . The yields of minor (G < 0.5 molecules per 100 eV) products like NH3 and CH2=C(CH3)-CH(NH,+)COO-indicated that fragmentation of p e n and other secondary radicals from penSH was more important than for cys. and other radicals from cysSH.GREESH CHAND GOYAL et DAVID ANTHONY ARMSTRONG. Can. J. Chem. 54, 1938Chem. 54, (1976 Les produits majeurs de la radiolyse de la pinicillamine dans des solutions saturees de NzO 2 un p H de 5 sont le disulfure de ~Cnicillamine, le trisulfure de pCnicillamine et la valine avec des [Traduit par le journal]

The Photolysis of Penicillamine Disulphide in Acidic Aqueous Solution

“…+ PenSPen would require a high degree of selectivity in alignment of the colliding radicals resulting in a very strained molecule. It is noteworthy that Goyal and Armstrong (1976) found no evidence for the monosulphide in the u-radiolysis of penicillamine where Pen. and Pens.…”

The radiation chemistry of 2-mercaptoethanol

“…At pH 4-7 reaction [2] can be neglected and, since the contribution of reaction [S] is small in this pH range, the mechanism then predicts G(H2S) = G(RH) = g,;, (3)(4)(5)(6). While this was observed with the sulphydryl molecules noted above, the values of G(H2S) and G(RH) from 2-mercaptoethanol, although equal, were reported to be only half of g,iq (10 Intuitively this seems to require the existence of a relatively long-lived RSH-ion:…”