Radioresistance of Adenine to Cosmic Rays

The presence of nucleobases in carbonaceous meteorites on Earth is an indication of the existence of this class of molecules in outer space. However, space is permeated by ionizing radiation, which can have damaging effects on these molecules. Adenine is a purine nucleobase that amalgamates important biomolecules such as DNA, RNA, and ATP. Adenine has a unique importance in biochemistry and therefore life. The aim of this work was to study the effects of cosmic ray analogues on solid adenine and estimate its survival when exposed to corpuscular radiation. Adenine films were irradiated at GANIL (Caen, France) and GSI (Darmstadt, Germany) by 820 MeV Kr³³⁺, 190 MeV Ca¹⁰⁺, 92 MeV Xe²³⁺, and 12 MeV C⁴⁺ ion beams at low temperature. The evolution of adenine molecules under heavy ion irradiation was studied by IR absorption spectroscopy as a function of projectile fluence. It was found that the adenine destruction cross section (σ_d) follows an electronic stopping power (S_e) power law under the form: CS_eⁿ; C is a constant, and the exponential n is a dimensionless quantity. Using the equation above to fit our results, we determined σ_d = 4 × 10^-17 S_e^1.17, with S_e in kiloelectronvolts per micrometer (keV μm^-1). New IR absorption bands arise under irradiation of adenine and can be attributed to HCN, CN^-, C₂H₄N₄, CH₃CN, and (CH₃)₃CNC. These findings may help to understand the stability and chemistry related to complex organic molecules in space. The half-life of solid adenine exposed to the simulated interstellar medium cosmic ray flux was estimated as (10 ± 8) × 10⁶ years. Key Words: Heavy ions-Infrared spectroscopy-Astrochemistry-Cosmic rays-Nucleobases-Adenine. Astrobiology 17, 298-308.