Product yields and mechanism of penicillamine radiolysis at pH 5

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Abstract
The major products from the radiolysis of penicillamine [similar instructure to the radioprotectorant cysteine] in N2O-saturated solutions at pH 5 are penicillamine disulfide, penicillamine trisulfide and valine with yields of 2.0, 1.2 and 1.5 molecules/100 eV in 10-2 M solutions and 1.8, 0.94 and 0.60 molecules/100 eV in 10-3 M solutions respectively. These yields remain essentially the same when the major attacking radical is changed from .cntdot. OH to .cntdot. CH2OH, .cntdot. Br2- or .cntdot. (CNS)2-, all 4 species produce predominantly penS .cntdot. radicals on attacking penicillamine. The formation of trisulfide and an equivalent amount of valine is attributed to secondary reactions of penS .cntdot. radicals and discussed in the light of recent pulse radiolysis experiments and other work. In deaerated solutions H2 and H2S were observed in significant yields and the valine yield increased. These observations can be accounted for quantitatively by the reactions: .**GRAPHIC**. The yields of minor (G < 0.5 molecules/100 eV) products like NH3 and CH2.dbd.C(CH3)-CH(NH3+)COO- indicated that fragmentation of pen .cntdot. and other secondary radicals from penSH was more important than for cys .cntdot. and other radicals from cysSH.

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