Direct evidence for formation of acetimidic acid and acetamide under irradiation of isolated acetonitrile-water complexes at cryogenic temperatures

In this work, we report the first direct evidence for formation of the key simplest molecule with the peptide bond (acetamide) under radiation-induced transformations occurring in the CH3CN center dot center dot center dot H2O complex isolated in an argon matrix at 6 K. The 1:1 CH3CN center dot center dot center dot H2O intermolecular complex was obtained by deposition of CH3CN/H2O/Ar mixtures and characterized by FTIR spectroscopy. The irradiation of the icy matrix with X-rays results first in formation of acetimidic acid, which is transformed to acetamide at higher absorbed doses. In addition, the products of acetonitrile oxidation (hydroxyacetonitrile and acetonitrile N-oxide) have been detected, which probably originate from the reactions of 'hot' radiation-induced oxygen atoms. The formation of acetamide was confirmed by deuterium isotopic substitution in acetonitrile. We believe that the observed transformation may be of basic importance for understanding the radiation-induced synthesis of prebiotic molecules in occurring in cold space media.