Urea is one of the most important industrial emissions in the world and also plays an important role in our body. It is created by the reaction of carbon dioxide and ammonia. Usually, however, either high pressure and high temperatures are required, or suitable catalysts. But now a study shows that urea can also form spontaneously at interfaces between water and air. The knowledge not only opens up potential new synthesis options, but also provides an explanation of how urea could have been involved in the development of life.
In our body, urea is a waste product that arises when the amino acids are reduced and is excreted via the kidney. In industry, on the other hand, the substance is a coveted raw material: urea is the most important nitrogen fertilizer worldwide and also serves as a raw material for the production of synthetic resins and explosives as well as the fuel additive to cleaning car exhaust gases. While the synthesis in our body runs with the help of enzymes, industrial production usually requires high pressure and temperatures above 170 degrees Celsius to ammonia (nh3) and carbon dioxide (CO2) To urea (nh2Conh2) to let.
Reaction room inside of water droplets
“The high energy consumption and the harsh conditions of this process have caused the search for alternative catalytic processes for urea formation,” explains a team around Mercede Mohajer Azizbaig from ETH Zurich in Switzerland. “We have found a previously unknown path of how urea is spontaneous under environmental conditions and without added catalysts: in small NH3-Wassen droplets, in the area of which gaseous CO2 located. “
As the researchers stated, there are very special reaction conditions on the interface of such droplets between water and air. “The surface layer acts like a microscopic flow reactor, with chemical gradients enabling access to unconventional response ways of response,” reports the team. A pH slope between the interior and the outer of the water drops ensures sufficient acidic reaction conditions, so that the ammonia with the CO2 can react from the air. At the same time, there is a concentration gradient that shifts the chemical balance of the reaction in the direction of the urea.
Processes in the early earth
For their tests, the chemists used tiny water droplets with a diameter of a few micrometers, i.e. a very large surface in relation to the volume. In nature, such microtrops can be found, for example, in the sea of sea or fine fog. With the help of spectroscopic recordings, Mohajer Azizbaig and her colleagues demonstrated that urea is actually spontaneous in the droplets. They also underpinned their experimental observations with theoretical calculations that showed that the reaction really does not require any external energy supply.
From the researcher’s point of view, suitable conditions for this reaction could already have been on the young earth. Urine was long considered a possible basic substance from which chemical building blocks of life such as RNA and DNA as well as amino acids could have formed. So far, however, it was unclear to what extent urea could have arisen under the conditions at that time. “In our study we show a way where and how urea could have arisen on the prebiotic earth, namely where water molecules change with atmospheric gases: on the water surface,” says Mohajer Azizbaig’s colleague Ruth Signorell. “Our study shows how apparently banal interfaces become dynamic reaction rooms – an indication that the origin of biological molecules could be more common than suspected for a long time.”
Source: Mercede Mohajer Azizbaig (ETH Zurich, Switzerland) et al., Science, Doi: 10.1126/science.adv2362
