Radiolysis and radioracemization of RNA ribonucleosides: implications for the origins of life.

The RNA nucleosides, namely adenosine, cytidine, guanosine and uridine were γ-radioyzed in solid state and in vacuo at room temperature to a total dose of 3.2 MGy. Through electronic absorption spectroscopy, differential scanning calorimetry and through polarimetry and optical rotatory dispersion spectroscopy, it was found that the purine-based nucleosides (adenosine and guanosine) show a much higher radiolysis resistance than the pyrimidine-based nucleosides (cytidine and uridine). In an astrochemical/astrobiological context, these results may explain why purine nucleobases are found in practically all carbonaceous chondrite meteorites while the pyrimidine nucleobases are absent or below the detection limits of the current analytical techniques. In the hypothesis that both purines and pyrimidines nucleobases were present in certain bodies at the beginning of the solar system 4.6 × 10⁹ years ago, the radiolysis due to radionuclides decay has destroyed more easily and completely the pyrimidine bases due to their much lower radiolysis resistance than the purine bases. [ABSTRACT FROM AUTHOR]