CM – X-ray laser shows how radiation damage occurs


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December 6, 2021

from German electron synchrotron

With the X-ray laser European XFEL, an international team of researchers has gained new insights into how radiation damage occurs in biological tissue. The study shows in detail how high-energy radiation breaks down water molecules, creating potentially dangerous radicals and electrically charged ions that can trigger harmful reactions in the organism. The team around Maria Novella Piancastelli and Renaud Guillemin from the Sorbonne in Paris, Ludger Inhester from DESY and Till Jahnke from European XFEL present their observations and analyzes in the journal Physical Review X.

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Since water is present in every known living organism, the splitting of the water molecule H2O by radiation, the so-called photolysis of water, is often the starting point for radiation damage. « However, the chain of reactions that can be triggered in the body by high-energy radiation is not yet fully understood, » explains Inhester. « For example, it is very difficult to observe the formation of individual charged ions and reactive radicals in water when high-energy radiation is absorbed. »

To investigate this process, the researchers shot the intense pulses of the X-ray laser at the water vapor. Water molecules normally disintegrate upon the absorption of a single such high-energy X-ray photon. « Thanks to the particularly intense pulses of the X-ray laser, it was even possible to observe how water molecules absorb not just one, but two or more X-ray photons before their fragments fly apart, » reports Inhester. This gives the researchers an insight into what happens inside the molecule after the first absorption of an X-ray photon.

“The movement of the molecule between two absorption events leaves a clear fingerprint, that is, its fragments fly onto very specific ones , characteristic way apart, ”says Piancastelli. “By carefully analyzing this fingerprint and performing detailed simulations, we were able to draw conclusions about the ultrafast dynamics of the water molecule after the first X-ray photon was recorded.” The team measured the directions and speeds of the fragments using a so-called reaction microscope. This enabled the scientists to capture the disintegration of the water molecule, which lasts only a few femtoseconds (billiardths of a second), in a kind of slow-motion film.

It turns out that the disintegration of the water molecule is much more complicated than initially expected. The water molecule (H2O) begins to stretch and expand before finally breaking apart. After just ten femtoseconds, the two hydrogen atoms (H), which are normally bound to the oxygen atom (O) at an angle of 104 degrees, can build up so much momentum that they face each other at an angle of around 180 degrees. As a result, the oxygen atom is actually not thrown away hard when the molecule breaks, since the impulses of the two hydrogen nuclei largely balance each other when flying and the oxygen practically rests in the middle. In an aqueous environment, this free oxygen radical can then easily lead to further potentially harmful chemical reactions.

« In our research, we have for the first time succeeded in investigating the dynamics of a water molecule after it has absorbed high-energy radiation, » says Inhester, who works on the Center for Free-Electron Laser Science (CFEL) works. a cooperation between DESY, the University of Hamburg and the Max Planck Society. “In particular, we were able to characterize the formation of the oxygen radical and the hydrogen ions as well as the timing of this process more precisely. This disintegration of the water molecule is an important first step in the further reaction chain. « Which ultimately lead to radiation damage. »

The analysis contributes to the overall picture of the radiation effects on water. An earlier study in which several members of the same team participated, had investigated the detailed dynamics of the formation of so-called free radicals through less high-energy radiation in water. The processes observed there have a similar dynamic as the currently investigated secondary processes in the absorption of high-energy radiation. The newly gained knowledge addresses elementary questions of reaction dynamics in water, which are The Center for Molecular Water Science (CMWS) currently set up at DESY with international partners are to be further investigated.

The new experiments on individual water molecules were among the first to be carried out with the new COLTRIMS reaction microscope at the SQS experimentation station of the European XFELbecame. « The results show that we can also consider other solvents and molecules with a more complex structure, such as ethanol or cyclic compounds, which are of great interest in chemistry and other disciplines, » says Jahnke.

Researchers from Universities of Frankfurt am Main, Freiburg, Hamburg and Kassel as well as Gothenburg, Lund and Uppsala in Sweden and Turku in Finland, the Fritz Haber Institute of the Max Planck Society and the Max Planck Institute for Nuclear Physics, from the Lawrence Berkeley National Laboratory and the Kansas State University in the USA, the National Research Council and the Technical University of Milan in Italy, the Sorbonne in Paris, European XFEL and DESY.

DESY is one of the world’s leading particle accelerator centers and researches the structure and function of matter – from the interaction of tiny elementary particles to the behavior of novel nanomaterials and vital biomolecules to the large o the mysteries of the universe. The particle accelerators and detectors that DESY develops and builds at its locations in Hamburg and Zeuthen are unique research tools. They generate the strongest X-rays in the world, accelerate particles to absorb energies and open new windows to the universe. DESY is a member of the Helmholtz Association, Germany’s largest scientific association, and is funded by the Federal Ministry of Education and Research (BMBF) (90 percent) and the federal states of Hamburg and Brandenburg (10 percent).

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X-ray laser shows how radiation damage occurs


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