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Beam-splitting approach opens the door to studying highly diluted liquid samples
Researchers at European XFEL have developed a way to study liquid samples that are too dilute for many existing X-ray experiments. The method is highly sensitive, and in the first experiment a group of international scientists uncovered new details about how vitamin B12 in water changes after absorbing light. The results, published in the Journal of the American Chemical Society, open the possibility to investigate a much wider range of chemical and biological systems than before.
Many important molecules can only be studied with X-rays in very low concentrations, either because they do not dissolve well or because only small amounts are available. That creates a major challenge for experiments in liquids: the surrounding water often produces a much stronger signal than the relatively few molecules of interest, making the measurement extremely difficult.
To overcome this problem, researchers at the SCS (Spectroscopy and Coherent Scattering) instrument at European XFEL developed a special beam-splitting device. It divides each X-ray pulse into three parts: one passes through the sample, while the other two act as references. By comparing all three signals at the same time, the team can correct for fluctuations and isolate changes that would otherwise be too small to detect.
“Normalizing every shot is crucial,” says SCS instrument scientist Benjamin Van Kuiken. “That’s what gives us the sensitivity to work with dilute samples.”
Long-standing question answered
The researchers chose vitamin B12 as a demanding test case. “Vitamin B12 is a tough sample,” says first author Nahid Ghodrati, now a postdoctoral researcher at another European XFEL instrument. “It dissolves only to a limited extent, the water around it creates a strong background signal, and the changes we want to observe happen very quickly.” The researchers used just about 9.5 grams of vitamin B12 per litre of water. Even under these conditions, the team was able to detect extremely small changes triggered by light. A variation of the measured signal as small as 0.005% was visible in the results. The ultrafast changes were captured by X-ray flashes that lasted just 100 quadrillionths of a second.
The experiment did more than demonstrate a new method. It also helped answer a long-standing question about vitamin B12: what exactly happens inside the molecule after it absorbs light? The new measurements indicate that the main change is concentrated around the cobalt atom at the centre of the molecule, rather than involving a larger shift of electrons across the whole structure. “The unique ability of the SCS Instrument to study dilute samples gave us insight into the rapid evolution of the molecule’s electronic structure that we could not get anywhere else,” says James Penner-Hahn, professor at the University of Michigan, USA.
New experiments become possible
This shows that the new approach can provide detailed information even for difficult samples in solution. The researchers expect it to expand the range of experiments possible at European XFEL. “Now that we can study biologically and chemically important molecules that have so far been hard to study in solution and at low concentrations, a lot of new science becomes tangible,” says Andreas Scherz, leading scientist at SCS. University of Michigan professor Roseanne Sension adds: “By allowing access to a new set of biologically and chemically important samples, the SCS instrument has dramatically expanded the range of samples that we hope to study.”
Benjamin Van Kuiken
benjamin.van.kuiken@xfel.eu
+49-40-8998-6545
https://pubs.acs.org/doi/10.1021/jacs.6c01860
https://www.xfel.eu/news_and_events/news/index_eng.html?openDirectAnchor=3015&am...
Artist’s impression of a split beam with vitamin B12 in liquid jet.
Source: European XFEL/Laura Canil
Copyright: European XFEL/Laura Canil
Criteria of this press release:
Journalists
Chemistry, Physics / astronomy
transregional, national
Research results
English
Artist’s impression of a split beam with vitamin B12 in liquid jet.
Source: European XFEL/Laura Canil
Copyright: European XFEL/Laura Canil
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