Low-temperature formation of pyridine and (iso)quinoline via neutral–neutral reactions

Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C₅H₅N), pyridinyl (C₅H₄N·) and (iso)quinoline (C₉H₇N)—the simplest representative mono- and bicyclic aromatic molecules carrying nitrogen—are elusive. Here we afford compelling evidence on the gas-phase formation of methylene amidogen (H₂CN·) and cyanomethyl (H₂CCN·) radicals via molecular beam studies and electronic structure calculations. The modelling of the chemistries of the Taurus molecular cloud (TMC-1) and Titan’s atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl and (iso)quinoline from H₂CN· and H₂CCN· at levels of up to 75%. This study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon-rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy.