LOW-ENERGY ELECTRON DAMAGE IN DNA

Abstract

In this thesis, Photo-Electron Spectroscopy (PES) and Photo-Electron Imaging (PEI) have been exploited to study low-energy electron and photon-driven damage in DNA derivatives. After an introduction on photoelectron spectroscopy and DNA, an instrumental overview, together with a brief explanation of the theoretical methods used, is given.
The results section is divided according to the different chemical systems that have been considered. First, the viability of a dipole-bound state, which are electronic non-valence states that play an important role in electron transfer in DNA, has been studied in a model molecule: despite the presence of an alkyl chain directly poking into it, the dipole-bound state is retained in all cases. Secondly, the possibility of achieving intra-molecular charge transfer as probe for low-energy electron damage has been explored in a carboxylated adenosine analogue. Although no conclusive evidence of charge-transfer from the carboxylic acid to the nucleobase has been observed, this approach has then been applied to different DNA derivatives. The object of the third section of the results chapter is, in fact, the photophysics of the doubly-deprotonated dianion of adenosine-5’-triphosphate, which exhibits electron tunneling through the Repulsive Coulomb Barrier (RCB) upon irradiation at 266 nm; excited states calculation and RCB simulations have been performed to support these findings. Lastly, the photophysics of other doubly-deprotonated di- and tri-phosphorylated purine dianions have been explored in the last section: only one of them, adenosine diphosphate ([ADP–H2]2–), shows evidence of intra-molecular charge transfer, however further research is needed to corroborate this hypothesis.