Urea could have played an important role in the emergence of life on Earth

The team, led by Hans Jakob Wörner from ETH Zurich, built upon their earlier work to develop a new method to observe chemical reactions in liquids with high temporal resolution. This method enables observations of molecular changes within a few femtoseconds or one quadrillionth of a second.

Urea & emergence of life

Urea is one of the simplest molecules containing nitrogen and carbon. This has led to the assumption by many scientists that it played a pivotal role in the emergence of life on Earth. 

This assumption dates back to the 1950s when American chemist Stanley Miller conducted an experiment demonstrating that urea was present on Earth when the planet was very young. 

Miller prepared a mixture of the gases thought to have made up the planet's primordial atmosphere and subjected it to thunderstorm conditions. This resulted in the formation of a sequence of molecules, one of which was urea.

Current theories suggest that urea may have become enriched in the warm primordial soup. Then its exposure to ionizing radiation in the atmosphere produced malonic acid, which may have served as the building blocks for DNA and RNA.

Testing the theory

The new method developed by the research team involves using X-ray spectroscopy to observe chemical reactions in liquids with high temporal resolution. Building on their previous work, the team had to overcome the challenge of the X-rays being absorbed by the liquid. 

They overcame this challenge by developing an apparatus capable of producing a liquid jet with a diameter of less than one micrometer in a vacuum. Using this setup, the researchers were able to investigate the chemical reactions that occurred when concentrated urea was exposed to ionizing radiation. 

They could precisely measure and analyze the changes happening at the atomic and molecular levels in real time. 

When urea molecules are present in a concentrated solution, they tend to group themselves in pairs called dimers. The team found that the hydrogen atom within the urea dimers transferred between the two molecules, resulting in a protonated urea molecule and a urea radical. 

The urea radical is highly reactive and likely to react with other molecules, potentially forming malonic acid. The transfer of the hydrogen atom was rapid, occurring within approximately 150 femtoseconds.

"That's so fast that this reaction preempts all other reactions that might theoretically also take place. This explains why concentrated urea solutions produce urea radicals rather than hosting other reactions that would produce other molecules," said Wörner in a press release. 

The team plans to investigate the subsequent steps leading to the formation of malonic acid to improve our understanding of the origin of life on Earth. 

Talking about other potential applications of their newly developed method, Wörner said, "A whole host of important chemical reactions take place in liquids – not just all biochemical processes in the human body, but also a great many chemical syntheses relevant to the industry. This is why it's so important that we have now expanded the scope of X-ray spectroscopy at high temporal resolution to include reactions in liquids."

The findings of their study are published in the journal Nature Communications.