Extended Data Fig. 8: Alternative mechanism for the formation of glycine in the Miller experiment simulation.

In this pathway, the final step to form glycine involves H-abstraction from H3O, which chemical intuition would label as a cationic species (H3O+). The penultimate species (\({{{{\rm{C}}}}}_{2}{{{{\rm{H}}}}}_{4}{{{{\rm{NO}}}}}_{2}^{-}\)) formed prior to glycine, therefore, cannot be unambiguously labeled as an anion or a radical. The uncertainty regarding the ionic nature of this mechanism illustrates an issue with electron-agnostic MLIPs, like ANI-1xnr. The depiction of bond orders, charges on ions, and radical species is based simply on chemical intuition, since ANI-1xnr does not provide explicit bonding, orbital, or electronic information.