Quote from:
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 636 #1, May 7, 2003 by Phil Schewe, James Riordon, and Ben Stein
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)
