An exploration of the reactivity of singlet oxygen with biomolecular constituents

The thermal reaction between biomolecules and singlet oxygen ((1)O2) is important for rendering the genetic material within toxic cells inactive. Here we present results obtained from state-of-the-art multi-reference computational methods that reveal the mechanistic details of the reaction between (1)O2 and two exemplary biomolecular systems: guanine (Gua) and histidine (His). The results highlight the splitting of the doubly degenerate (1)Δg state of O2 upon complexation and the essentially barrierless potential energy profile of the thermally allowed cycloaddition reaction when the O2 molecule is in its lower energy (1)Δg state.