Abstract
A carboxylated adenosine analog (C-Ado−) has been synthesized and probed via time-resolved photoelectron spectroscopy in order to induce intra-molecular charge transfer from the carboxylic acid moiety to the nucleobase. Intra-molecular charge transfer can be exploited as starting point to probe low-energy electron (LEE) damage in DNA and its derivatives. Time-dependent density functional theory (TD-DFT) calculations at the B3LYP-6311G level of theory have been performed to verify that the highest occupied molecular orbital (HOMO) was located on carboxylic acid and that the lowest occupied molecular orbital (LUMO) was on the nucleobase. Hence, the carboxylic acid could work as electron source, whilst the nucleobase could serve the purpose of electron acceptor. The dynamics following excitation at 4.66 eV (266 nm) were probed using time-resolved photoelectron spectroscopy using probes at 1.55 eV (800 nm) and 3.10 eV (400 nm). The data show rapid decay of the excited state population and, based on the similarity of the overall dynamics to deoxy-adenosine monophosphate (dAMP–), it appears that the dominant decay mechanism is internal conversion following 1ππ* excitation of the nucleobase, rather than charge-transfer from the carboxylic acid to the nucleobase.
Highlights
DNA is one of the most important biomolecules, as it contains genetic information that is essential to most forms of life
The highest occupied molecular orbitals (MOs) (HOMO), lowest unoccupied MO (LUMO), and relevant π MOs of C-Ado− are shown in Figure 2 along with the relevant energetics
The HOMO, as expected, is predominantly located on the carboxylic acid moiety, with some charge density extending onto the ribose sugar
Summary
DNA is one of the most important biomolecules, as it contains genetic information that is essential to most forms of life. The high-energy radiation ionizes predominantly water to form secondary electrons with a kinetic energy (eKE) between 0 and 20 eV. These so-called low energy electrons (LEEs) are responsible for severe DNA lesions, such as single- and double-strand breakages, which can lead to cell death and disease [6]. LEE attachment can lead to the formation of metastable anionic states known as temporary negative ions or resonances, which are responsible for inducing mutagenesis in living organisms [12,13]. Boudaiffa et al [14] showed that single-strand breaks are caused by core-excited (Feshbach) resonances, which are produced by electron attachment to the π* orbitals of the nucleobases. Computational and experimental evidence [23]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
