Hydroxyl radicals from isoprene hydroxy hydroperoxide (ISOPOOH) decomposition induced by irons in water

The hydroxyl radical (OH) is an important oxidant in the atmosphere and clouds involving the secondary processing of the majority of organic species. It is also a key member of reactive oxygen species crucial to human health. Yet OH radicals generated by organics are still not well understood. In the present study, isoprene oxidation product isoprene hydroxy hydroperoxide (ISOPOOH) was synthesized in high purity to investigate its potential to form OH radicals in the presence of inorganic iron(II) and iron(III), respectively. Using an electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique, we found that OH and carbon-centered radicals were formed from the aqueous reactions of ISOPOOH with both iron(II) and iron(III) at room temperatures. Kinetic modelling using assembled chemical reaction mechanisms suggests that ISOPOOH can be oxidized by Fe(II) via Fenton-like reactions leading to OH formation. Fe(III) likely reacts with ISOPOOH in a similar mechanism to generate OH radicals directly. The findings from this work allow a better understanding of the role of organics and metals in ROS generation in atmospheric aqueous phase chemistry and human health.