DNA Nucleobase Under Ionizing Radiation: Unexpected Proton Transfer by Thymine Cation in Water Nanodroplets

The effects of ionizing radiation on DNA constituents is a widely studied fundamental process using experimental and computational techniques. In particular radiation effects on nucleobases are usually tackled by mass spectrometry in which the nucleobase is embedded in a water nanodroplet. Here we present a multiscale theoretical study revealing the effects and the dynamics of water droplets towards neutral and ionized thymine. In particular, by using both hybrid quantum mechanics/ molecular mechanics and fully ab initio molecular dynamics we reveal an unexpected proton transfer from thymine cation to a nearby water molecule. This leads to the formation of a neutral radical thymine and a Zundel structure, while the hydrated proton localizes at the interface between the deprotonated thymine and the water droplet. This observation opens entirely novel perspective concerning the reactivity and further fragmentation of ionized nucleobases.