  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.
