Survival of dipeptides under ionizing radiation in astrophysical environments.

Films of linear and cyclic dipeptides as well as alanine amino acid, deposited on ZnSe windows, have been irradiated with a 12C4+ beam of 0.98 MeV u-1 at 10, 80 and 300 K. The effects of irradiation have been studied by measuring in situ the IR absorption spectrum before, during and after the irradiation. The main effect observed is film degradation due to ion-induced fragmentation and sputtering; notably the cyclic species exhibiting higher radioresistance than the linear ones. The measurements at low temperature also provide evidence of the formation of new species of lower masses. Moreover, the similarity between the IR spectra of irradiated alanine and pristine linear alanine-alanine films, suggests ion-induced peptide polymerization and supports the idea that cyclic dipeptides may have survived the harsh conditions of the early universe, contributing to possible radiation-induced pathways leading to larger organic species of potentially prebiotic significance.