Reaction Dynamics of Disulfide Bond Cleavage in Hydrated Electron Clusters

Hydrated electron, e⁻_(aq) is a potent reducing agent in organic synthesis and radiation chemistry, with noteworthy biological implications. Since its discovery over 40 years ago, reaction mechanisms involving e⁻_(aq) have been the subject of ongoing debate due to its inherently high structural variability which complicates experimental monitoring. Reaction dynamics of a chemical model comprising a hydrated electron cluster with six water molecules, and a dimethyl disulfide, the prototypical molecule containing a S−S bond, [CH₃SSCH₃(H₂O)₆^•−] at 100K (comparable with temperature in a previous FT-ICR mass spectrometric study) has been examined using density functional theory based molecular dynamics (DFT-MD) simulations performed with the CP2K Quickstep module. Intracluster electron transfer in [CH₃SSCH₃(H₂O)₆^•–] gives [CH₃SSCH₃^•–(H₂O)₆], in which the reduced CH₃SSCH₃^•– anion is greatly stabilized by the water cluster. Although adiabatic electron affinity of dimethyl disulfide is slightly positive (10 kJ mol⁻¹), our DFT-MD simulations show that this process is barrierless and highly exothermic (ΔH = −166 kJ mol^–1) which is comparable with value of −113 ± 13 kJ mol^–1 based on the nanocalorimetry approach. Our results show a considerable degree of solvent reorganization which transforms the cavity solvation (where the hydrated electron originally located) to a solvation network stabilizing the anionic S−S bond.