title: Induction of strand breaks by low-energy electrons (8-68 eV) in a self-assembled monolayer of oligonucleotides: effective cross sections and attenuation lengths.
abstract: Self-assembled monolayers of 5'-32P-labeled 3'-thiolated oligonucleotides chemisorbed on gold were bombarded by low-energy electrons (LEE) of 8-68 eV. Shorter 5'-32P-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 (sigmaeff) and the attenuation length (AL=1b) 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 sigmaeff increases from (3+/-1)x10(-18) to (5.1+/-1.6)x10(-17) cm2 within the same energy range. The energy dependence of sigmaeff shows a resonance peak of (2.8+/-0.9)x10(-17) cm2 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.
authors.affiliation: Group in the Radiation Sciences, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Quebec J1H 5N4, Canada.
authors.forename: Zhongli
authors.initials: Z
authors.lastname: Cai
authors.forename: Marie-Eve
authors.initials: ME
authors.lastname: Dextraze
authors.forename: Pierre
authors.initials: P
authors.lastname: Cloutier
authors.forename: Darel
authors.initials: D
authors.lastname: Hunting
authors.forename: Léon
authors.initials: L
authors.lastname: Sanche