Ultra-Low-Energy Electrons Can Break Up Uracil

Ultra-low-energy electrons can break up uracil, a new study shows. How injurious is radiation (alpha, beta, and gamma rays or heavy ions) to living cells? This important question has been addressed in many ways. Much attention has centered on the secondary particles produced in the wake of the intruding primary radiation, especially electrons (about 40,000 electrons are produced for each MeV of energy deposited) with typical energies of tens of electron volts. Many of these secondary particles quickly lose their energy and become attached (solvated) to water molecules in the cell. What is the general effect of electron energies below 20 eV? A report from three years ago (Boudaiffa et al., Science 287, 1658, 2000) showed that electrons in the 3-20 eV range are able to produce substantial genotoxic damage, including breaking single- and double-stranded DNA? What about secondary electrons with even smaller energies?

To look at this energy range for the first time, Tilmann Maerk and his colleagues at the Universitat Innsbruck (Austria) and the University Claude Bernard Lyon (France) scattered a beam of sub-eV electrons from a beam of gaseous uracil molecules. Uracil is one of the base units of RNA molecules, and is thus a crucial component in cells. These scientists found that uracil is efficiently fragmented by electrons with energies as small as milli-electron-volts. It's not the electron's kinetic energy that causes the disruption, but the electron's charge, which changes the uracil's internal potential energy environment. Furthermore, in the process a very mobile atomic hydrogen can be freed, which on its own, as a radical (a free chemical unit by itself), can do damage to biomolecules (see a movie of this process at http://info.uibk.ac.at/ionenphysik/ClusterGroup/Uracil.html; schematic at /png/2003/187.htm). Maerk (43-512-507-6240) says that this low-energy damage seems to be a general result since his group has since performed similar work with thymine (a DNA base) and have seen similar fragmentation. (Hanel et al., Physical Review Letters, 9 May 2003; Innsbruck website)