In a study reported in the journal ACS Central Science, researchers used computer simulations to investigate how frozen hydrogen cyanide behaves at the molecular level. They focused on how electric fields at the surfaces of tiny crystals might concentrate charge and promote reactions, potentially turning a simple toxic molecule into a platform for building more complex compounds.

The team, led by Martin Rahm with coauthors Marco Capelletti and Hilda Sandstrom, modeled a stable hydrogen cyanide crystal as a cylinder around 450 nanometers long. The simulated crystal had a rounded base and a multifaceted top that resembled a cut gemstone, a geometry that matches strange cobweb like structures observed previously when hydrogen cyanide freezes and its crystals branch out from central points.

According to the calculations, some facets at the tips of these crystals are particularly reactive, creating local conditions that can drive chemical transformations in extreme cold. The simulations showed that surfaces on the crystals could support electric fields strong enough to change how molecules are oriented and how easily they exchange atoms and electrons during reactions.

From this analysis, the researchers identified two possible reaction pathways in which hydrogen cyanide on the crystal surface converts into hydrogen isocyanide, a more reactive isomer. These transformations could occur on timescales from minutes to days, depending on the temperature, indicating that significant chemistry is possible even in environments that would ordinarily suppress reaction rates.

Hydrogen cyanide and its derivatives are already known to form polymers, amino acids and nucleobases when mixed with water, linking this molecule to the origin of proteins and DNA. The new work suggests that when hydrogen cyanide freezes, its crystal surfaces could act as reactive hubs that further diversify the set of prebiotic molecules, with hydrogen isocyanide serving as a stepping stone toward more complex precursors of life.

The study also highlights that hydrogen cyanide is widespread in the universe, having been detected on comets and in the atmospheres of planets and moons such as Saturns moon Titan. If frozen hydrogen cyanide crystals can drive fast surface chemistry in these places, then cobweb like networks of crystals could contribute to organic complexity far from Earth as well as on the early planet.

Rahm notes that while the exact path from simple molecules to living systems may never be fully reconstructed, identifying plausible mechanisms for each intermediate step is achievable. The work shows that a molecule best known for its toxicity can, under the right conditions, create environments where new chemistry flourishes in the cold.

The researchers now encourage laboratory experiments to test these predictions under realistic cryogenic conditions. They suggest crushing hydrogen cyanide crystals in the presence of substances such as water and monitoring whether the freshly exposed surfaces indeed generate hydrogen isocyanide and other complex molecules at very low temperatures.

The authors report that their project received funding from the Swedish Research Council and from the National Academic Infrastructure for Supercomputing in Sweden, which provided the computational resources needed for the simulations.

Research Report:Electric Fields Can Assist Prebiotic Reactivity on Hydrogen Cyanide Surfaces

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