A chemical known for its danger to humans may have played an unexpected role in the earliest steps toward life on Earth. Hydrogen cyanide, which is highly poisonous, can freeze into crystals at low temperatures. Computer simulations published in ACS Central Science suggest that certain surfaces on these crystals are unusually reactive, allowing chemical processes to occur that normally cannot happen in such cold conditions. According to the researchers, these reactions may have set off a chain of events that produced several of the fundamental building blocks of life.
“We may never know precisely how life began, but understanding how some of its ingredients take shape is within reach. Hydrogen cyanide is likely one source of this chemical complexity, and we show that it can react surprisingly quickly in cold places,” says Martin Rahm, the corresponding author of the study.
Hydrogen Cyanide Beyond Earth and in Early Chemistry
Hydrogen cyanide is not rare in the universe. It has been detected on comets and in the atmospheres of planets and moons (e.g., Saturn’s moon Titan). When hydrogen cyanide interacts with water, it can give rise to polymers, amino acids and nucleobases (components of proteins and DNA strands, respectively). To better understand how reactive this molecule can be, Marco Capelletti, Hilda Sandström and Martin Rahm used computer modeling to study hydrogen cyanide in its frozen state.
In their simulations, the team modeled a stable hydrogen cyanide crystal shaped like a long cylinder about 450 nanometers in length. The structure included a rounded base and a top with multiple flat faces resembling a cut gemstone. This design closely matches earlier observations of crystal formations described as “cobwebs,” which spread outward from a central point where the multifaceted ends meet.
Unexpected Chemistry in Extreme Cold
The calculations showed that these frozen crystals could promote chemical reactions that are usually absent in extremely cold environments. By analyzing the chemical behavior of the crystal surfaces, the researchers identified two reaction pathways that could transform hydrogen cyanide into hydrogen isocyanide, a more reactive compound. Depending on temperature, this conversion could happen within minutes or take several days. The researchers note that having hydrogen isocyanide on the crystal surface increases the likelihood that even more complex prebiotic molecules could form there.
Testing the Predictions in the Lab
The team hopes their findings will inspire laboratory experiments to test these predictions. One proposed approach involves crushing hydrogen cyanide crystals in the presence of substances like water to expose fresh crystal surfaces. Scientists could then observe whether these surfaces promote the formation of complex molecules under extremely cold conditions.
The authors acknowledge funding from the Swedish Research Council and the National Academic Infrastructure for Supercomputing in Sweden.