Boffins play with the world's most powerful X‑ray gun to shoot molecules

It's all in the name of medicine, they say

A group of scientists has focused the world’s most powerful X‑ray beam on a molecule to test out the Linac Coherent Light Source at the US Department of Energy’s SLAC National Accelerator Laboratory.

The pulse was so intense that within 30 femtoseconds – a millionth of a billionth of a second – more than 50 electrons were stripped away before the molecule blew apart.

A closer inspection reveals almost all the electrons were pulled from the inside out as the molecule was ionized. The molecule then began sucking in electrons further out to fill the empty inner shells, like a “molecular black hole.”

The results have been published Wednesday in Nature. The intensity of the X‑ray laser was cranked up to almost 1020 watts per square centimetre. It’s “about a hundred times more intense than what you would get if you focused all the sunlight that hits the Earth’s surface onto a thumbnail,” said Sebastien Boutet, a co-author of the paper and a staff scientist at the Linac Coherent Light Source at Stanford University in California.

It’s not just a wacky science experiment. The team led by Daniel Rolles and Artem Rudenko, assistant professors in the department of physics at Kansas State University, wanted to push the limits of radiation damage on matter.

“For any type of experiment you do that focuses intense X‑rays on a sample, you want to understand how it reacts to the X‑rays,” Rolles said. “This paper shows that we can understand and model the radiation damage in small molecules, so now we can predict what damage we will get in other systems.”

The Coherent X‑ray Imaging instrument at the laboratory allows researchers to take snapshots of the molecule just before the laser pulse blows it up, so they can work out what happens during the destructive process.

First, a series of mirrors were used to concentrate the power of the X‑ray beam onto a tiny spot measuring just over 100 nanometers in diameter – a thousand times smaller than the width of a human hair. Three different molecules were used: xenon atoms, iodomethane (CH3I) and iodobenzene (C6H5I).

They were chosen because their heavy sizes were a closer match to molecules in biochemical reactions and are sometimes added to enhance contrast for biological imaging.

The iodine atoms in the molecules were particularly prone to radiation damage. As electrons were stripped away from the X‑ray laser, it began stealing electrons from the carbon and hydrogen atoms in iodobenzene.

Those electrons were also eventually kicked from the molecule. The researchers said it was a level of damage that was higher than expected and a reaction not normally observed in nature.

“We think the effect was even more important in the larger molecule than in the smaller one, but we don’t know how to quantify it yet,” Rudenko said. “We estimate that more than 60 electrons were kicked out, but we don’t actually know where it stopped because we could not detect all the fragments that flew off as the molecule fell apart to see how many electrons were missing.”

The researchers hope that this experiment will help scientists achieve images of molecules at higher resolutions, to aid the development of better pharmaceuticals. ®

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