Induction of strand breaks by low-energy electrons (8-68 eV) in a self-assembled monolayer of oligonucleotides: Effective cross sections and attenuation lengths

Self-assembled monolayers of 5'-P-32-labeled 3'-thiolated oligonucleotides chemisorbed on gold were bombarded by low-energy electrons (LEE) of 8-68 eV. Shorter 5'-P-32-oligonucleotides produced by LEE-induced strand breaks were separated with denaturing polyacrylamide gel electrophoresis and quantified by phosphor imaging. The yields of short oligonucleotides (y) decrease exponentially with their length (n), following the equation y=ae(-bn), where a and b are constants, which are related to the average effective cross section per nucleotide for DNA strand break (sigma(eff)) and the attenuation length (AL=1/b) of LEE, respectively. The AL decreases with LEE energies from 2.5 +/- 0.6 nm at 8 eV to 0.8 +/- 0.1 nm at 68 eV, whereas sigma(eff) increases from (3 +/- 1)x10(-18) to (5.1 +/- 1.6)x10(-17) cm(2) within the same energy range. The energy dependence of sigma(eff) shows a resonance peak of (2.8 +/- 0.9)x10(-17) cm(2) at 18 eV superimposed on a monotonically rising curve. Transient electron attachment to a sigma(*) anion state of the deoxyribose group, followed by dipolar dissociation into H- and the corresponding positive-ion radical, leading to C-O bond cleavage, is proposed to account for this maximum. (c) 2006 American Institute of Physics.