Unexpected mechanochemical complexity in the mechanistic scenarios of disulfide bond reduction in alkaline solution

Abstract

The reduction of disulfides has broad importance in chemistry, biochemistry and materials science, in particular upon mechanochemical activation. Here, isotensional simulations disclose that strikingly different mechanisms govern disulfide cleavage depending on external force. Crucial are desolvation and resolvation processes, which directly impact on activation free energies. The preferred pathway up to moderate forces, a bimolecular SN2 attack of OH− at sulfur, competes with unimolecular C-S bond rupture at about 2 nN, while the latter even becomes barrierless beyond. Moreover, our study brings to light a surprisingly rich reactivity scenario that includes the transformation of SN2 pathways into pure bond breaking pathways at forces within the range of 1.2 to 2.2 nN. Given that these forces are easily reached in experiments, these insights will fundamentally change our understanding of mechanochemical activation in general, which is now expected to be considerably more intricate than previously thought.