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

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 discs 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 3 × 10 5 and 3 × 10 8 yr inside dense molecular clouds and protoplanetary discs, respectively. We estimate that for gas-phase compounds these values increase 1 order of magnitude since the dissociation cross-section of glycine is lower in gas phase than in solid phase for the same photon energy. The half-life of solid-phase nucleobases is about 2-3 orders of magnitude longer 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.

Radiolysis of amino acids by heavy and energetic cosmic ray analogues in simulated space environments: α-glycine zwitterion form

“…Considering this methodology, the obtained value at 14 K and 300 K were  d = 2.4 10 -12 cm 2 and 3.4 10 -13 cm 2 , respectively. Such methodology was also employed by Pilling et al, 2011c at experiments on the processing of solid glycine by ionizing photons. The error in the determination of specific bond rupture cross section lay in the uncertainty of the area determination in the infrared spectra that was below 10%.…”

The Influence of Crystallinity Degree on the Glycine Decomposition Induced by 1 MeV Proton Bombardment in Space Analog Conditions

“…Experimentally, glycine desorbs only at temperatures around 350-400 K under ultra-high vacuum conditions (e.g. Pilling et al 2011a). If these grains undergo several heating and freezing cycles, such as the ones expected to occur around star-forming regions, the average number density of glycine (or other nonvolatile species) on grain surfaces will increase even more with time.…”

Employing Soft X-Rays in Experimental Astrochemistry

“…A comparison between these two spectra shows that the peak resolution changes with mass/charge ratio, being worst for higher mass/charge values. Figure 6 presents some samples of PEPICO mass spectra of studied molecules of astrophysical interest (Pilling et al 2006;Pilling et al 2011;Ferreira Rodrigues et al 2008). All spectra were obtained with soft x-rays.…”

“…The FTIR spectra of RNA nucleobase uracil after different doses of 150-eV soft X-rays up to 17 h is showed in Figure 22b. Figure 22c shows the integrated absorbance spectra of the solid-phase samples as a function of irradiation time (adapted from Pilling et al 2011). From the variation observed in the integrated area of IR spectrum (3000 to 900 cm-1) along the different radiation doses, photodissociation rates and half-life were determined by employing Eq.…”