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

Abstract

ABSTRACTIn 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···H2O complex isolated in an argon matrix at 6 K. The 1:1 CH3CN···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.