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

TL;DR

This study investigates how amino acids degrade under radiation at very low temperatures relevant to space environments, providing kinetic data and structural insights crucial for astrobiology.

Contribution

It provides new in situ kinetic measurements of amino acid radiolysis at 15-140 K, including structural changes and decay rates relevant to extraterrestrial conditions.

Findings

Amino acids decay via decarboxylation producing CO2 and amines.

Half-lives vary with temperature and water presence.

Amino acids transition from non-zwitterion to zwitterion forms with increasing temperature.

Abstract

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$_2$(R)-COOH at 15 K to the zwitterion structure $^+$NH$_3$-CH$_2$(R)-COO$^-$ at 140 K for each amino acid studied.