Reactions of CH3SH and CH3SSCH3 with Gas-Phase Hydrated Radical Anions (H2O)n•-, CO2•-(H2O)n, and O2•-(H2O)n

The chemistry of (H2O)(n)(center dot-), CO2 center dot-(H2O)(n), and O-2(center dot-)(H2O) 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 CH3SSCH3 and activation of the thiol group of CH3SH. No reactions were observed with CH3SCH3. 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 CO2 center dot- to O-2(center dot-) deactivates highly reactive species and may actually reduce oxidative stress. For reactions of (H2O)(n)(center dot-) with CH3SH as well as CO2 center dot-(H2O) with CH3SSCH3, 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.