Quantum Chemical Study on Interstellar Synthesis of Cytosine by the Automated Reaction Path Search

Novel reaction pathways with the neutral radical–molecule reaction to form cytosine, a nucleobase of DNA and RNA, which can proceed in the interstellar environment, were discovered by automated reaction pathway calculations based on the transition state theory. We suggested the barrierless and exothermic formation of cytosine in two steps. First, the reaction between the O radical and ethynamine forms a key precursor species, NH 2 CCHO. Then, this radical reacts with CN and HNCH to form cytosine. This study would contribute to elucidating possible reactions on nucleobases under lower temperatures, and further tests are effective by astronomical modeling/observations and laboratory experiments.