Why do free radicals cause such great damage to cells and DNA even though they only exist for a trillionth of a second?

Free radicals are atoms or molecules with unpaired electrons that can wreak havoc on the body, like jilted lovers, wandering around in search of another electron, leaving behind shattered cells, proteins and DNA. Hydroxyl radicals are the most aggressive free radicals in chemistry, with lifetimes of just a trillionth of a second. They form when water, the most abundant molecule in cells, is exposed to radiation, causing it to lose an electron. In previous research, a team of researchers led by Linda Young, a scientist at the Department of Energy's Argonne National Laboratory, observed the ultrafast birth of these free radicals.

The process has important implications in areas such as sunlight-induced biological damage, environmental remediation, nuclear engineering and space travel. Now a team of researchers, including those at the Department of Energy's SLAC National Accelerator Laboratory, has teased out the unique chemical fingerprint of hydroxyl, which will help scientists track the chemical reactions it triggers in complex biological environments. Their findings are published in the journal Physical Review Letters. At SLAC's Linac Coherent Light Source (LCLS) free-electron laser:

Using X-ray pulses that last just a few millionths of a second, scientists have detected incredibly short-lived hydroxyl radicals. The researchers ionized water by shining a thin beam of laser light with X-rays, with energies precisely enough to excite electrons deep inside the free radicals, so they jumped to a specific, higher orbit. When the electrons settle back into their original orbits, a small fraction of them emit X-rays with the free radical's unique signature, or spectrum. The team used new theoretical tools to precisely calculate these X-ray spectra and decipher the information they contain.

To follow up, the team will study what happens in the first moments of water splitting by ionizing radiation with higher time resolution to learn more about the process. Going down this path, the hope is to study similar processes in alkaline environments, which are of both fundamental interest and pressing applications such as nuclear waste remediation, which requires understanding the complex chemistry occurring in tanks experiencing continuous radiation bombardment. Resonant inelastic X-ray scattering (RIXS) provides an excellent opportunity to study ultrafast dynamics in liquids.

Here, researchers used RIXS to study the important hydroxyl radical OH(AQ) in liquid water. Pulse ionization of pure liquid water produced a short-lived OH(Aq) population, which was detected using X-ray free electron laser femtosecond X-rays. The study found that RIXS revealed localized electronic transitions that were masked by strong charge transfer transitions in the UV absorption spectrum, thus providing a method to study the electronic structure and reactivity of hydroxyl radicals in water and multiphase environments. First-principles calculations provided an explanation for the main spectral features.

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Boco Park | Research/From: SLAC National Accelerator Laboratory

Reference journal: Physical Review Letters

DOI: 10.1103/PhysRevLett.124.236001

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