Radioactive radiation could damage biological tissue also via a
previously unnoticed mechanism

Date:
December 27, 2021
Source:
Max-Planck-Gesellschaft
Summary:
When cells are exposed to ionizing radiation, more destructive
chain reactions may occur than previously thought. An international
team led by researchers has now observed intermolecular Coulombic
decay in organic molecules. This is triggered by ionizing radiation
such as from radioactivity or from space. The effect damages two
neighboring molecules and ultimately leads to the breaking of bonds
- like the ones in DNA and proteins. The finding not only improves
the understanding of radiation damage but could also help in the
search for more effective substances to support radiation therapy.



FULL STORY ==========================================================================
When cells are exposed to ionizing radiation, more destructive chain
reactions may occur than previously thought. An international team
led by researchers from the Max Planck Institute for Nuclear Physics
in Heidelberg has for the first time observed intermolecular Coulombic
decay in organic molecules. This is triggered by ionizing radiation such
as from radioactivity or from space.

The effect damages two neighbouring molecules and ultimately leads to the breaking of bonds -- like the ones in DNA and proteins. The finding not
only improves the understanding of radiation damage but could also help
in the search for more effective substances to support radiation therapy.


========================================================================== Sometimes radioactive damage cannot be great enough -- especially when it
comes to destroying tumour tissue with ionizing radiation. In radiation therapy, substances that specifically enhance the damage of the radiation
in the tumour tissue are used. "The intermolecular Coulombic decay we
found could help make such sensitizers more effective," says Alexander
Dorn, who heads a research group at the Max Planck Institute for Nuclear Physics and was instrumental in the current study. His team's observations could also improve our understanding of how artificial or natural ionizing radiation damages the genetic material of healthy tissue.

Excess energy leads to a Coulomb explosion The DNA double helix
of the genome resembles a rope ladder with rungs of nucleic base
pairs. "Because experiments with the free nucleic bases are difficult,
we initially studied pairs of benzene molecules as a model system,"
explains Dorn. These hydrocarbon rings are connected in a similar way to
the nucleic bases stacked on top of each other in a strand of DNA. The researchers bombarded the benzene pairs with electrons, thereby imitating radioactive radiation to a certain extent. When an electron hit a benzene molecule, it was ionized and charged with a lot of energy. The team
has now observed that the molecule transferred some of this energy to
its partner molecule. This energy boost was enough to ionize the second molecule as well. Both molecules were thus positively charged. Of course,
that didn't last long. The two molecular ions repelled each other and
flew apart in a Coulomb explosion.

Until now, scientists had assumed that ionizing radiation damages
biomolecules mainly indirectly. The high-energy radiation also ionizes the water of which a cell is largely composed and which surrounds biomolecules
such as DNA. The ionized water molecules -- especially hydroxide ions --
then attack the DNA.

And if an electron of the beta radiation or a gamma quantum does hit
a DNA molecule directly, the excess energy normally is dissipated by
processes in the molecule itself. It thus remains intact. Or at least
that was the assumption up to now. In any case, the weak bonds between different molecules or different parts of the molecule -- as they exist
in DNA and proteins -- should not be affected by this either. However,
in their reaction microscope, the researchers observed that radioactive radiation can indeed break such bonds. This instrument allows them not
only to detect the two separating benzene molecules and measure their
energy but also to characterize the electrons emitted.

Fatal consequences of multiple DNA breaks "It is not yet clear how the intermolecular Coulombic decay affects the DNA strand," says Dorn. If a
single strand in the DNA ladder breaks, the consequences should not be too serious. However, the mechanism observed also releases several electrons
that can "blow up" further pairs of molecules. And if both strands of DNA
are broken in the immediate vicinity, this could have fatal consequences.

In order to better assess the effect of the radiation on the genetic
material, Dorn's team will now also bombard pairs of nucleic acids
with electrons under the reaction microscope. "This is experimentally challenging because we have to heat the nucleic bases in order to
vaporize them," explains Dorn. "But they must not get too hot either --
so that they are not destroyed." Nuclear doctors can also follow the
trail to more effective sensitizers that the Heidelberg team has blazed
with the observation of intermolecular Coulombic decay. The mechanism
could therefore be relevant for both cases of radiation damage: those
that need to be avoided as far as possible and those that should be as
great as possible.

========================================================================== Story Source: Materials provided by Max-Planck-Gesellschaft. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xueguang Ren, Jiaqi Zhou, Enliang Wang, Tao Yang, Zhongfeng Xu,
Nicolas
Sisourat, Thomas Pfeifer, Alexander Dorn. Ultrafast energy
transfer between p-stacked aromatic rings upon inner-valence
ionization. Nature Chemistry, 2021; DOI: 10.1038/s41557-021-00838-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211227154333.htm

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