Photostability of gas- and solid-phase biomolecules within dense molecular clouds due to soft X-rays

TL;DR

This study investigates the stability of key biomolecules like amino acids and nucleobases under soft X-ray irradiation in space-like environments, revealing nucleobases are significantly more resistant than amino acids, with implications for astrobiology.

Contribution

The paper provides experimental data on the photostability of biomolecules in gas and solid phases under soft X-ray conditions relevant to space environments, highlighting differences in their resistance.

Findings

Solid-phase amino acids have half-lives of at least 3E5 to 3E8 years in molecular clouds and disks.

Gas-phase amino acids have longer half-lives than solid-phase, by about an order of magnitude.

Nucleobases are 2-3 orders of magnitude more resistant to radiation than amino acids.

Abstract

An experimental photochemistry study involving gas- and solid-phase amino acids (glycine, DL-valine, DL-proline) and nucleobases (adenine and uracil) under soft X-rays was performed. The aim was to test the molecular stabilities of essential biomolecules against ionizing photon fields inside dense molecular clouds and protostellar disks analogs. In these environments, the main energy sources are the cosmic rays and soft X-rays. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing 150 eV photons. In-situ sample analysis was performed by Time-of-flight mass spectrometer (TOF-MS) and Fourier transform infrared (FTIR) spectrometer, for gas- and solid- phase analysis, respectively. The half-life of solid phase amino acids, assumed to be present at grain mantles, is at least 3E5 years and 3E8 years inside dense molecular clouds and protoplanetary disks, respectively. We estimate that for gas-phase compounds these values increase one order of magnitude since the dissociation cross section of glycine is lower at gas-phase than at solid phase for the same photon energy. The half-life of solid phase nucleobases is about 2-3 orders of magnitude higher than found for amino acids. The results indicate that nucleobases are much more resistant to ionizing radiation than amino acids. We consider these implications for the survival and transfer of biomolecules in space environments.