DNA Lesion Can Facilitate Base Ionization: Vertical Ionization Energies of Aqueous 8-Oxoguanine and its Nucleoside and Nucleotide

Abstract

8-Oxoguanine is one of the key products of indirect radiation damage to DNA by reactive oxygen species. Here, we describe ionization of this damaged nucleobase and the corresponding nucleoside and nucleotide in aqueous phase, modeled by the nonequilibrium polarizable continuum model, establishing their lowest vertical ionization energies of 6.8-7.0 eV. We thus confirm that 8-oxoguanine has even lower ionization energy than the parental guanine, which is the canonical nucleobase with the lowest ionization energy. Therefore, it can act as a trap for the cationic hole formed by ionizing radiation and thus protect DNA from further radiation damage. We also model using time-dependent density functional theory and measure by liquid jet photoelectron spectroscopy the valence photoelectron spectrum of 8-oxoguanine in water. We show that the calculated higher lying ionization states match well the experiment which, however, is not sensitive enough to capture the electron signal corresponding to the lowest ionization process due to the low solubility of 8-oxoguanine in water.

Electron detachment dynamics of the iodide-guanine cluster: does ionization occur from the iodide or from guanine?

“…These experiments were supported by Chatterly and co-workers in two-photon ionization measurements on nucleotides [52], where the guanine-containing nucleotide was the only system where ionization occurred from the base. Indeed, it is well acknowledged that guanine sites within DNA and nucleotides have the greatest propensity to be ionized [25][26][27][28], and a number of studies have revealed that ionizing radiation causes positive hole formation at guanine sites [53][54][55][56][57]. The photophysics and dynamics of these DNA charge-separated states are of key current interest [58,59].…”

“…Guanine is also the hardest of the nucleobases to study via electrospray ionization due to its low solubility. However, it is a key member of the nucleobase series as it is known to exhibit the lowest ionization energy [25][26][27][28], and is renowned for playing a key role in radiation-induced damage of DNA [29,30]. By careful optimization of the electrospray ionization conditions, we have been successful in making I -•G clusters, therefore allowing us to study this complex via laser-induced photodissociation.…”

Clustered DNA Damage: Electronic Properties and Their Influence on Charge Transfer. 7,8-Dihydro-8-Oxo-2′-Deoxyguaosine Versus 5′,8-Cyclo-2′-Deoxyadenosines: A Theoretical Approach

“…Voityuk [34,35] has shown that the hole migration process between stacked base pairs in ds-DNA can take place between triplet excited states [36][37][38]. From this point, the 8,7-dihydro-8-oxo-2 -deoxyguanosie, which shows a lower ionization energy/potential (6.94 eV [22,39]) than its precursor dG, can easily be oxidized and constitutes an endpoint for cation radical migration, which leads to a) protection of the rest of ds-oligo against oxidation, and b) flagging the lesion for glycosylase movements. Of over 80 different types of DNA damage, oxo dG is the most common (600+/− 170 per 10 6 nucleosides) [40].…”

Damage Induced to DNA and Its Constituents by 0–3 eV UV Photoelectrons†

“…Table 2 provides the ionization energies of water ( 33) and known fundamental components of histone proteins and DNA (34)(35)(36)(37)(38)(39)(40)(41)(42)(43), along with the longest UV wavelength capable of ionizing each of these molecules. Ionization of DNA can occur by creation of a cation (hole) or electron photodetachment from a negatively charged group.…”