Reactions of CH_<b>3</b>SH and CH₃SSCH₃ with Gas-Phase\nHydrated Radical Anions (H₂O)_<i>n</i>^•–, CO₂^•–(H₂O)_<i>n</i>, and O₂^•–(H₂O)_<i>n</i>

Abstract

The chemistry of (H₂O)_<i>n</i>^•–, CO₂^•–(H₂O)_<i>n</i>, and O₂^•–(H₂O)_<i>n</i> with small sulfur-containing molecules was studied in the gas phase\nby Fourier transform ion cyclotron resonance mass spectrometry. With\nhydrated electrons and hydrated carbon dioxide radical anions, two\nreactions with relevance for biological radiation damage were observed,\ncleavage of the disulfide bond of CH₃SSCH₃ and\nactivation of the thiol group of CH₃SH. No reactions were\nobserved with CH₃SCH₃. The hydrated superoxide\nradical anion, usually viewed as major source of oxidative stress,\ndid not react with any of the compounds. Nanocalorimetry and quantum\nchemical calculations give a consistent picture of the reaction mechanism.\nThe results indicate that the conversion of e^– and\nCO₂^•– to O₂^•– deactivates highly reactive species and may actually reduce oxidative\nstress. For reactions of (H₂O)_<i>n</i>^•– with CH₃SH as well as CO₂^•–(H₂O)_<i>n</i> with CH₃SSCH₃, the reaction products\nin the gas phase are different from those reported in the literature\nfrom pulse radiolysis studies. This observation is rationalized with\nthe reduced cage effect in reactions of gas-phase clusters.