Computational Investigation of the Dissociative Recombination of Adenine, Guanine, Thymine, and Cytosine

Abstract

Dissociative recombination (DR) is a process during which a molecular cation captures an electron and subsequently dissociates into neutral particles. DR is one of the very efficient processes of molecular cation annihilation and of neutral particles production in dilute environment. The DR of small molecules such as H2+ and H3+ were thoroughly investigated during the past three decades. Recently, the cations of interest have been expanded from small inorganic molecules to macromolecules (Phys. Chem. Chem. Phys., 2010,12, 11670-11673). On the other side, DR in dense environment had been neglected, due perhaps to the challenge that its experimental as well as theoretical investigation represent. However, there are so many important applications of DR in non-dilute environment. For example, DNA could lose an electron due to an ionizing radiation, which, at the same time, generated lots of low-energy electrons. The effects of secondary electrons on molecules of biological interests are currently a hot topic. It is now accepted that the attachment of slow electron on a neutral DNA may induce a strand break via dissociative electron attachments (see Radiat. Res.157, 227, 2002). Because these secondary electrons are slow, they could also be easily captured by the DNA+ which dissociative recombination may lead to a single strand and double strand breaks. As a consequence, the DNA chain break would later result in a mutation amongst the nucleotide bases. We studied the DR of temporary DNA+ using the modern electronic structure program ORCA. Given the periodic structure of DNA, we were doing quantum calculations on Guanine, Adenine, Cytosine, and Thymine only. Our results indicate the existence of autoionizing states within the various nucleotide bases and support the possibility of DR to being a channel of DNA strand break.