Reactions of CH ₃SH and CH ₃SSCH ₃ with gas-phase hydrated radical anions (H ₂O) _n ^•-, CO ₂ ^•-(H ₂O) _n, and O ₂ ^•-(H ₂O) _n

The chemistry of (H ₂O) _n ^•-, CO ₂ ^•-(H ₂O) _n, and O ₂ ^•-(H ₂O) _n with small sulfur-containing molecules was studied in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. With hydrated electrons and hydrated carbon dioxide radical anions, two reactions with relevance for biological radiation damage were observed, cleavage of the disulfide bond of CH ₃SSCH ₃ and activation of the thiol group of CH ₃SH. No reactions were observed with CH ₃SCH ₃. The hydrated superoxide radical anion, usually viewed as major source of oxidative stress, did not react with any of the compounds. Nanocalorimetry and quantum chemical calculations give a consistent picture of the reaction mechanism. The results indicate that the conversion of e ^- and CO ₂ ^•- to O ₂ ^•- deactivates highly reactive species and may actually reduce oxidative stress. For reactions of (H ₂O) _n ^•- with CH ₃SH as well as CO ₂ ^•-(H ₂O) _n with CH ₃SSCH ₃, the reaction products in the gas phase are different from those reported in the literature from pulse radiolysis studies. This observation is rationalized with the reduced cage effect in reactions of gas-phase clusters.