Inelastic Interaction of Free Electrons with Molecules of Biological Relevance

Tilmann Märk, Paul Scheier

Institute of Ion Physics Leopold-Franzens University Technikerstr. 25 A-6020 Innsbruck, Austria
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The formation of both positively and negatively charged ions has been investigated in Innsbruck for the collision of highly monochromatized electrons (resolution ~100 meV) with molecules such as DNA and RNA bases, water, organic acids, and sugar including deoxyribose. The aim of these studies is to understand the basic processes that lead finally to the damage of living cells upon exposure to ionizing radiation (a,b,g ions). Sanche and co-workers (B. Boudaiffa, P. Cloutier, D. Hunting, M.A. Hues and L. Sanche, Science 287 (2000) 1658) recently demonstrated that potentially lethal DNA damage (double strand breaks) is not only induced by the primary high energy projectiles. Secondary species of the primary ionizing radiation, like slow electrons with kinetic energies typically below 20 eV, turn out to be even more dangerous leading to substantial cell damage. For all bio-molecules (M) investigated so far we observed that electrons at energies below the threshold for electronic excitation (<3 eV) effectively decompose gas phase molecules generating a mobile hydrogen radical and the corresponding closed shell fragment anion. The reaction is energetically driven by the large electron affinity of the (M-H) radical. This observation has significant consequences for the molecular picture of radiation damage, i.e., genotoxic effects or damage of living cells due to the secondary component of high energy radiation.

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