On the capturing of low-energy electrons by DNA

Abstract

Many of the mutagenic or lethal effects of ionization radiation can be attributed to damage caused to the DNA by low-energy electrons. To gain insight on the parameters affecting this process, we measured the low-energy electron (<2 eV) transmission yield through self-assembled monolayers of short DNA oligomers. The electrons that are not transmitted are captured by the layer. Hence, the transmission reflects the capturing efficiency of the electrons by the layer. The dependence of the capturing probability on the base sequence was studied, as was the state of the captured electrons. It is found that the capturing probability scales with the number of G bases in the single-stranded oligomers and depends on their clustering level. Using two-photon photoelectron spectroscopy, we find that, once captured, the electrons do not reside on the bases. Rather, the state of the captured electrons is insensitive to the sequence of the oligomer. Double-stranded DNA does not capture electrons as efficiently as single-stranded oligomers; however, once captured, the electrons are bound more strongly than to the single strands.monolayer ͉ radiation damage ͉ guanine ͉ photoemission M any of the mutagenic or lethal effects of ionization radiation can be attributed to secondary electrons that are created within 10 Ϫ15 sec along radiation tracks and spurs and have kinetic energies Ͻ20 eV (1, 2). Experimental (3) and theoretical (4-6) studies indicate that electrons with subionization energies play an important role in inducing damage in DNA (7). Our goal in the present work is to determine the structural and chemical elements in the DNA that are governing the electron-capturing process by studying electron transmission through organized adsorbed layers of DNA.The detailed mechanism for electron-DNA interaction is difficult to address experimentally in vivo, where many parameters affect the electron-DNA interaction and the electron energy is not well defined. Therefore, we investigated the interaction of electrons possessing well defined energy, with monolayers of single-stranded (ss) and double-stranded (ds) DNA oligomers adsorbed on a gold surface. By methodically varying the bases in the oligomers, the effect of each base on the interaction with electrons could be determined, as could the difference between single and double strands. Furthermore, the binding energy of the captured electrons could be determined.Past findings hint that G bases act as ''DNA protectors.'' For example, G-rich telomeres found at the ends of chromosomes (8) were shown recently to increase the resistance of DNA to ionizing radiation (9). It is also well accepted that G is the most easily oxidized nucleotide (10,11). It has been demonstrated also that positive charges can transport over long distances in DNA through multistep hopping between G bases (12, 13). The putative role of G bases as protectors of the genome from electrons with kinetic energies greater than the ionization energy of the bases seems to result from their ability to easily form cations...

Electron Attachment to Hydrated Oligonucleotide Dimers: Guanylyl‐3′,5′‐Cytidine and Cytidylyl‐3′,5′‐Guanosine

“…[37] However, experiments on the electron-capturing efficiencies of short DNA oligomers provide the only estimate of the relative order of the vertical electron attachment energies (VEAs) for DNA single strands. [4] Theoretical investigations at various levels of sophistication have been complemented with experimental explorations. The coupled cluster level of theory with single, double, and perturbative triple excitations (CCSD(T)) successfully elucidated the tautomeric forms of the covalent bond radical anion of guanine [33,38] and adenine.…”

“…Electron attachment to DNA fragments is one of the most attractive subjects in both radiation biology [1][2][3][4] and functional nanomaterial science. [5][6][7][8] Knowledge of the distribution of excess electron sites for DNA strands is crucial for understanding important biochemical processes, such as anion-related DNA damage and repair, [1,[9][10][11][12][13][14][15][16][17] charge transfer, [5][6][7][18][19][20][21][22][23] and mutations.…”

Comprehensive Analysis of DNA Strand Breaks at the Guanosine Site Induced by Low‐Energy Electron Attachment

“…Ray et al showed experimentally that LEEs are ready to attach to the short single-stranded guanine-rich oligomers. [15] Sanche's group observed significant contributions of guanine in LEE-induced DNA single-strand breaking. [14] Using a reliably high level of theory, Schaefer et al predicted the substantial electron capturing ability of the 2'-deoxyguanosine-3',5'-diphosphate in both gas-phase and aqueous solutions.…”

Probing Biomolecules by Laser‐Induced Acoustic Desorption: Electrons at Near Zero Electron Volts Trigger Sugar–Phosphate Cleavage

“…[6,21] However, the most straightforward mechanism of electroninduced strand breakage would be a direct attachment to the backbone followed by a C À O or P À O bond cleavage. Recent high-resolution electron energy loss spectroscopy (HREELS) measurements on DNA suggested that low-energy electrons mainly interact with the DNA backbone.…”