The formation of biomolecules accelerates the formation of furhter biomolecules – even under space conditions

Under environmental conditions typical of interstellar space, the reaction products of peptide formation accelerate the formation of longer and chemically more diverse peptides. This finding emerged from laboratory experiments conducted as part of an international research project initiated by Serge A. Krasnokutski of the University of Jena and carried out in collaboration with Ko-Ju Chuang (Leiden University) and Pauline Poinot (University of Poitiers). Krasnokutski had previously demonstrated that simple starting materials—common in space—are capable of forming peptides (fundamental biomolecules) on dust particles at very low temperatures. Now, together with other researchers from the universities of Jena, Leiden, and Poitiers, he has shown that the organic residues from these reactions significantly promote the formation of additional, more complex peptide chains. The results have been published in the journal “Communications Chemistry”.

Biomolecules that foster new biomolecules

“The crucial question is not whether peptides can form in space,” says Krasnokutski. “Biochemistry offers countless examples of how existing biomolecules contribute to the formation of other biomolecules. We therefore wanted to find out whether the organic molecules we were able to produce under space conditions are also capable of this.” 

Organic residue promotes longer molecular chains

For their experiments, the researchers deposited carbon atoms, carbon monoxide, and ammonia onto a surface cooled to minus 263 degrees Celsius under ultra-high vacuum conditions. This temperature is typical of the molecular clouds from which planetary systems form. “These starting materials first give rise to so-called aminoketene—a highly reactive compound that forms the peptide chains we had previously detected,” the physicist explains. Following the experiment, the researchers removed all volatile chemicals. They then repeated the reaction on the surface already covered by the reaction products from the first experiment.

“To distinguish which substance on the surface originated from the first experiment and which from the second, we used isotope labeled carbon atoms for the second reaction,” Krasnokutski explains. In this way, the team was able to demonstrate that the existing organic residue was not simply incorporated into the new molecules as a starting material; instead, it catalytically promoted the polymerization of new substances.

“However, exactly which components of this complex residue are responsible for this remains unclear,” Krasnokutski notes with a caveat. “Consequently, the results do not yet constitute proof that peptides actually catalyze their own formation under these conditions. Nevertheless, they support the hypothesis of a self-amplifying chemical process leading to biomolecules—occurring in space itself, rather than necessarily on planets.”

Hydrogen increases diversity

The team observed an unexpected effect when they added atomic hydrogen to the reaction. “Atomic hydrogen is the most abundant element in the interstellar medium and is therefore essential for a more realistic simulation of the chemistry occurring on cold cosmic dust particles,” the physicist explains.

Initially, the researchers had expected the hydrogen to inhibit peptide formation. “Atomic hydrogen is highly reactive. We therefore assumed it would cause the intermediate products to be consumed in the reaction with hydrogen before they could proceed to form peptides,” he elaborates. However, the opposite was the case: “The hydrogen did not inhibit the reaction; instead, it actually significantly promoted the formation of longer chains,” says Krasnokutski. “And in the process, additional chemicals were created.”

Possible biochemistry prior to planet formation

“The experiments suggest that a comparatively diverse peptide chemistry can emerge from just a few simple and cosmically abundant starting materials,” the Jena-based scientist says, summarizing the work. He adds: “And this occurs under conditions typical of the early development of star and planetary systems.”

So, did biological life originate in space? “Our results cannot answer that,” Krasnokutski notes with a caveat. “However, we now have a better understanding of the complex biomolecules that can form on dust particles in space.” This raises the question of how complex the chemical processes in space can be. “Asteroids and comets, which are formed from such particles, contain liquid water, which can drive further chemical reactions”, he explains. “Therefore, a particularly interesting area of research will be to investigate such chemical processes and their role in the origin of life on Earth. It will also be very exciting to search specifically for these biomolecules in extraterrestrial samples, such as meteorites and asteroids, now that we know what to look for.”