6250
J. Phys. Chem. 1984, 88, 6250-6254
cysteine with N M A and M N P as from cystine. The oxidation of organosulfur compounds by hydroxyl radicals in aqueous solutions has been studied by the pulse radiolysis m e t h ~ d . ~ ' -The ~ ~ principal reactions of .OH with disulfide^,^^ thiols,52 and sulfidess3 are proposed as follows: R S S R t *OH
/
RSSR+.
t OH
'
R S - t RSOH
+ *OH RSR + .OH RSH
-
+ HzO RSR'. + OH-
--+
RS.
From RSR, RS. is not a main product and this is consistent with the negative results of spin trapping study here. It is still puzzling that RS. from RSH was trapped with N M A but not with MNP, though RS- from RSSR was trapped with both NMA and MNP. There is not much difference in the reaction rate of .OH with RSH and RSSR. For examples, rate constants of .OH with CH3SH (51) M. BonifaEiE: and K.-D. Asmus, J. Phys. Chem., 80,2426 (1976). and references cited therein. (52) M. Z. Hoffman and E. Hayon, J . Phys. Chem., 77,990 (1973), and references cited therein. (53) M. BonifaEiC, H.Mkkel, D. Bahnemann, and K.-D. Asmus, J. Chem. SOC.,Perkin Trans. 2, 675 (1975), and references cited therein.
and (CH3S), are 3.3 X 1O'O and 1.7 X 1Olo L mol-' SI, respect i ~ e l y . ~There ' might be some specific reaction between RSH and MNP. We should become cautious not to depend upon only one kind of spin trap in spin trapping experiments. Registry No. MeS., 7175-75-9;-OC(0)CH2S., 58149-58-9;-0C(O)CH(CH,)S., 92525-34-3; EtS., 14836-22-7;HO(CH2)2S*,6857060-5; -OC(O)(CH2)2S*, 92525-35-4; -OC(O)CH2CH(C(O)O-)S., 92525-36-5; (R)--OC(0)CH(NH3t)CH2S.,35772-84-0;PrS-, 4985-58-4; HO(CH2)3S., 67706-92-7; (&)--OC(O)CH(NH3+)(CH2)2S.,92620-15-0; MeSCH2N02-., 92525-37-6; -OC(0)CH2SCH2N0~, 92525-38-7; -OC(O)CH(CHp)SCH2N02-*,92525-39-8;EtSCH,NO
