In-situ measurements of the radiation stability of amino acids at 15-140 K

We present new kinetics data on the radiolytic destruction of amino acids measured in situ with infrared spectroscopy. Samples were irradiated at 15, 100, and 140 K with 0.8-MeV protons, and amino-acid decay was followed at each temperature with and without H${}_2$O present. Observed radiation products included CO${}_2$ and amines, consistent with amino-acid decarboxylation. The half-lives of glycine, alanine, and phenylalanine were estimated for various extraterrestrial environments. Infrared spectral changes demonstrated the conversion from the non-zwitterion structure NH${}_2$-CH${}_2$®-COOH at 15 K to the zwitterion structure ${}^{+}$NH${}_3$-CH${}_2$®-COO${}^{-}$ at 140 K for each amino acid studied.