Scientists See How Molecules Defend Themselves Against Radiation

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Light can bring us life, but in its more energetic form, like ultraviolet or X-rays, it can also damage the important molecules that make us. These molecules have a few defense mechanisms in place, and now researchers have taken their closest look yet at one of these.

Sometimes when an ultraviolet photon – a particle of light – hits DNA, the molecule releases a single hydrogen ion to get rid of the excess energy. The goal is to see how this process, known as "excited state proton transfer", works in living organisms, but we are not quite there yet and the team had to look for something analogous.

As discussed in the paper, published in Angewandte Chemie, the researchers looked at this process in a smaller molecule called 2-thiopyridone with the Linac Coherent Light Source (LCLS) at the Department of Energy's SLAC National Accelerator Laboratory.

"Right now, we want to keep it simple," lead author Sebastian Eckert, from the University of Potsdam and Helmholtz-Zentrum Berlin, said in a statement. "It's easier to look at the effects of photoexcitation in 2-thiopyridone because this molecule is small enough to understand and has only one nitrogen atom. We are among the first at LCLS to look at nitrogen at this energy, so it's somewhat of a pilot experiment."

The observations are a significant step forward in understanding biological molecules and were only possible thanks to the incredible capabilities of the LCLS. The nitrogen atom is bonded to the hydrogen atom, and when the excited state proton transfer occurs, the bonding breaks in a few quadrillionths of a second.

Seeing such a short amount of time is not an easy task. The LCLS shoots X-rays in resonance with the nitrogen-hydrogen bond. As long as that stays intact, all is good. But when it breaks, researchers can see this ultrafast change to the system.

"LCLS is the only X-ray light source that can provide enough photons – particles of light," added co-author Munira Khalil, a professor at the University of Washington. "Our detection mechanism is 'photon-hungry' and requires intense pulses of light to capture the effect we want to see."

A very powerful X-ray laser doesn’t really make you think of biology, but the LCLS is becoming an important instrument in understanding the subtlety of living processes, such as photosynthesis.



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