The formation of reducing and oxidizing radicals has been investigated in the reaction of hydroxyl radicals with formate, alcohols, and diols in pulse-irradiated aqueous solutions. Reducing radicals (C02~a nd a-alcohol radicals) were identified by their reaction with tetranitromethane, oxidizing alkoxy radicals by their reaction with iodide. The reaction of hydroxyl radicals with formate and ethylene glycol exclusively leads to a radical with reducing properties. The principal reducing radical from methanol, CH2OH, is formed from only 93% of the reacting hydroxyl radicals. The remaining 7% are accounted for by methoxy radicals formed in the reaction OH-+ CH3OH -* H20 + CHsO-. Relative probabilities for hydrogen atom abstraction from the a position, from the OH group, and from other positions of alcohols and diols by OH radicals are derived from the experimental data.

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Publication costs assisted by the Hahn-Meltner-lnstitute GmbH Berlin Dimethyl disulfide is oxidized by hydroxyl radicals to 44% according to CH3SSCH3 + OH--CH3SSCH3+ + OH-. The formation of the positive disulfide ions could be demonstrated by the pulse radiolysis conductivity method; they are relatively long lived. In neutral and slightly acid solution the positive ions decay by a second-order process with 2k = (4:2 ± 0.5) x 109 M_1 sec-1; in slightly basic solution neutralization by OHions is observed. Similar results were obtained with other disulfides (alkyl disulfides, (o-HOOCCeHiSh, (o-H2NC6H4S)2, cystin, cystamin), whose reaction with hydroxyl radicals also leads partially to the formation of positive RSSR+ ions.

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Communications to the Editor 3035 ly difficult to determine the angle with precision. This minimum may therefore "correspond" to the 27 and the 2.27 helices at ^75°, -70°for polyglycine.19 Maigret, et al.,20 found the conformation -80°, =: -40°t o be the most stable conformation in their calculation on '-acetyl-N'-methylalanylamide. The local minimum =* -60°, ^60°of approximately 4 kcal/mol of residue obtained for the tetrapeptide of glycine17 has disappeared in the present calculation and this , pair is now on a 6 kcal/mol of residue contour. There is a suggestion, however, of the formation of a new local minimum at about ^-70°, ^50°, of slightly less than 4 kcal/mol of residue.The local minimum near the fully extended chain conformation of about 5 kcal/mol of residue has shifted from =s! -180°, ce. -180°for the tetrapeptide of glycine17 to ^-180°, ^-165°in the present case. Hence, there is a faint suggestion of pleating21 on substituting the bulkier CH3 group for H in the side chains.The partial charges which are sensibly independent of the rotation angles and are substantially the same as for the tetrapeptide of glycine17 and are given in Table II for some selected conformations.