Reactive molecular dynamics simulations of oxygen species in a liquid water layer of interest for plasma medicine

The application of atmospheric pressure plasmas in medicine is increasingly gaining attention in recent years, although very little is currently known about the plasma-induced processes occurring on the surface of living organisms. It is known that most bio-organisms, including bacteria, are coated by a liquid film surrounding them, and there might be many interactions between plasma species and the liquid layer before the plasma species reach the surface of the bio-organisms. Therefore, it is essential to study the behaviour of the reactive species in a liquid film, in order to determine whether these species can travel through this layer and reach the biomolecules, or whether new species are formed along the way. In this work, we investigate the interaction of reactive oxygen species (i.e. O, OH, HO₂andH_2O2) with water, which is assumed as a simple model system for the liquid layer surrounding biomolecules. Our computational investigations show that OH, HO₂ and H_2O2 can travel deep into the liquid layer and are hence in principle able to reach the bio-organism. Furthermore, O, OH and HO₂ radicals react with water molecules through hydrogen-abstraction reactions, whereas no H-abstraction reaction takes place in the case of H_2O2. This study is important to gain insight into the fundamental operating mechanisms in plasma medicine, in general, and the interaction mechanisms of plasma species with a liquid film, in particular.