Stable Valence Anions of Nucleic Acid Bases and DNA Strand Breaks Induced by Low Energy Electrons

Abstract

Abstract:The last decade has witnessed immense advances in our understanding of the effects of ionizing radiation on biological systems. As the genetic information carrier in biological systems, DNA is the most important species which is prone to damage by high energy photons. Ionizing radiations destroy DNA indirectly by forming low energy electrons (LEEs) as secondary products of the interaction between ionizing radiation and water. An understanding of the mechanism that leads to the formation of single and double strand breaks may be important in guiding the further development of anticancer radiation therapy. In this article we demonstrate the likely involvement of stable nucleobases anions in the formation of DNA strand breaks -a concept which the radiation research community has not focused on so far. In Section 21.1 we discuss the current status of studies related to the interaction between DNA and LEEs. The next section is devoted to the description of proton transfer induced by electron attachment to the complexes between nucleobases and various proton donorsa process leading to the strong stabilization of nucleobases anions. Then, we review our results concerning the anionic binary complexes of nucleobases with particular emphasize on the GC and AT systems. Next, the possible consequences of interactions between DNA and proteins in the context of electron attachment are briefly discussed. Further, we focus on existing proposal of single strand break formation in DNA. Ultimately, open questions as well perspectives of studies on electron induced DNA damage are discussed

Valence anions of N-acetylproline in the gas phase: Computational and anion photoelectron spectroscopic studies

“…Due to collisional cooling in the source, one expects to make the most stable anions in these experiments, and thus the measured photoelectron spectra are those of relatively relaxed anion in most cases. 15 Thus, QM calculations meant to interpret these experiments typically focus on the thermodynamically most stable systems. …”

“…20 Further, our own experiments on various complexes between nucleobases and various proton donors as inorganic acids, amino acids, other nucleobases proved that the thermodynamically most stable anions are responsible for the main PES feature. 15 …”

“…Such barrier-free electron attachment induced proton transfer (PT) has been observed many times in the gas phase complexes between nucleobases and various proton donors. 15 Table II presents the thermodynamic characteristics of the studied anions obtained at the B3LYP/6-31++G(d,p) level. The most stable anion, an-endo-t, is characterized by VDE of 1.53 eV that corresponds fairly well to the maximum on the PES spectrum (cf.…”

“…Moreover, the vertical detachment energy (VDE; a maximum EBE value in a given photoelectron feature) can be calculated using appropriate quantum chemical (QM) models. 15 Hence, by combining a PES experiment with QM calculations, one can obtain a clear picture of the structure of the resulting anion and thus elucidate the processes that may have produced that structure.…”

Low‐Energy‐Barrier Proton Transfer Induced by Electron Attachment to the Guanine⋅⋅⋅Cytosine Base Pair

“…[43] Moreover, the positions of the PES maxima in a relatively high range of EBE (a lower intensity feature with the maximum at about 2.0 eV and higher intensity peak with maximum at about 2.6 eV; see Figure 1) demonstrate that, due to electron attachment, proton transfer occurs in the studied base pairs. Indeed, it has been demonstrated in a series of experimental/computational studies [41,42,[44][45][46][47][48][49][50] that VDEs of valence anions of nucleobases involved in complexes with various proton donors (PDs) having deprotonation energies (DPE) sufficiently low to allow for proton transfer between PD and the NB anion fall in the range of 1.6-2.1 eV.…”