Scientists from ETH Zurich and the University of Geneva have developed a new technique that enables the observation of chemical reactions taking place in liquids with extremely high time resolution. This innovation allows them to track how molecules change in just a few femtoseconds (in other words, trillionths of a second).
Researchers have developed a new way to observe chemical reactions in liquids, revealing reactions involving molecules such as urea that may have contributed to the emergence of life on Earth. The technique involves a special instrument that creates tiny jets of liquid and X-ray spectroscopy, allowing scientists to study reactions that occur in as little as femtoseconds.
This breakthrough builds on previous research by the same research group led by Hans Jakob Wörner, professor of physical chemistry at ETH Zurich. This work yielded similar results for reactions occurring in gaseous environments.
To extend X-ray spectroscopic observations to liquids, researchers had to design an instrument capable of producing liquid jets less than one micron in diameter in a vacuum. This is crucial because if the jet were wider, it would absorb some of the X-rays used for measurement.
Using this new method, researchers are able to gain insight into the process by which life emerged on Earth. Many scientists believe that urea plays a key role in this. Urea is one of the simplest molecules containing carbon and nitrogen.
More importantly, urea was most likely present when the Earth was very young, as was also shown by a famous experiment in the 1950s: American scientist Stanley Miller prepared a mixture of gases believed to make up the Earth's original atmosphere and exposed it to thunderstorm conditions. This creates a series of molecules, one of which is urea.
According to current theories, urea may have been enriched in warm puddles on the then-lifeless Earth—often called the primordial soup. As the water in the soup evaporates, the concentration of urea increases. Under the influence of ionizing radiation such as cosmic rays, these concentrated ureas may undergo multiple synthesis steps to produce malonic acid. This, in turn, may have produced the building blocks of RNA and DNA.
Using their new method, researchers at ETH Zurich and the University of Geneva studied the first step in this long chain of chemical reactions to find out how concentrated urea solutions behave when exposed to ionizing radiation.
You should know that the urea molecules in concentrated urea solution will form pairs on their own, which are so-called dimers. The researchers have now been able to show that ionizing radiation causes one hydrogen atom in each dimer to move from one urea molecule to the other. In this way, one urea molecule becomes a protonated urea molecule, and the other urea molecule becomes a urea radical. The latter is highly chemically reactive - so reactive, in fact, that it is likely to react with other molecules to form malonic acid.
The researchers also managed to show that this transfer of hydrogen atoms occurs very quickly, taking only about 150 femtoseconds, or 150 quadrillionths of a second. "This reaction is so fast that every other reaction that could theoretically occur is superseded by this reaction," says Wörner. "This explains why a concentrated urea solution produces urea radicals instead of hosting other reactions that would produce other molecules."
Wörner and his colleagues hope to study the next steps leading to the formation of malonate, hoping that this will help them understand the origins of life on Earth.
As for their new method, it can also be used to study the precise sequence of chemical reactions in liquids in general. "A range of important chemical reactions occur in liquids, including not only all biochemical processes in the human body, but also a large number of chemical synthesis relevant to industry," Werner said. "That's why it's so important that we have now expanded the range of high-time-resolution X-ray spectroscopy to also include reactions in liquids."