The formation of peptide-like molecules on interstellar dust grains

Abstract

Molecules with an amide functional group resemble peptide bonds, the\nmolecular bridges that connect amino acids, and may thus be relevant in\nprocesses that lead to the formation of life. In this study, the solid state\nformation of some of the smallest amides is investigated in the laboratory. To\nthis end, CH$_{4}$:HNCO ice mixtures at 20 K are irradiated with far-UV\nphotons, where the radiation is used as a tool to produce the radicals required\nfor the formation of the amides. Products are identified and investigated with\ninfrared spectroscopy and temperature programmed desorption mass spectrometry.\n The laboratory data show that NH$_{2}$CHO, CH$_{3}$NCO, NH$_{2}$C(O)NH$_{2}$,\nCH$_{3}$C(O)NH$_{2}$ and CH$_{3}$NH$_{2}$ can simultaneously be formed. The\nNH$_{2}$CO radical is found to be key in the formation of larger amides. In\nparallel, ALMA observations towards the low-mass protostar IRAS 16293-2422B are\nanalysed in search of CH$_{3}$NHCHO (N-methylformamide) and\nCH$_{3}$C(O)NH$_{2}$ (acetamide). CH$_{3}$C(O)NH$_{2}$ is tentatively detected\ntowards IRAS 16293-2422B at an abundance comparable with those found towards\nhigh-mass sources. The combined laboratory and observational data indicates\nthat NH$_{2}$CHO and CH$_{3}$C(O)NH$_{2}$ are chemically linked and form in the\nice mantles of interstellar dust grains. A solid-state reaction network for the\nformation of these amides is proposed.\n