Iglesias-Groth, S.; Cataldo, Franco; Ursini, Ornella; Manchado, A.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 410, Issue 3, pp. 1447-1453.
Fecha de publicación:
1
2011
Número de citas
29
Número de citas referidas
28
Descripción
Amino acids in Solar system bodies may have played a key role in the
chemistry that led to the origin of life on Earth. We present laboratory
studies testing the stability of amino acids against high energy
radiation. All the 20 chiral amino acids in the levo form found in the
proteins of the current terrestrial biochemistry were irradiated in the
solid state with γ-radiation to a dose of 3.2 MGy, which is the
dose equivalent to that produced by radionuclide decay in comets and
asteroids in 1.05 × 109 yr. For each amino acid the
radiolysis degree and the radioracemization degree were measured by
differential scanning calorimetry and by optical rotatory dispersion
spectroscopy. From these measurements, a radiolysis rate constant
kdsc and a radioracemization rate constant krac
were determined for each amino acid and extrapolated to a dose of 14
MGy, which corresponds to the expected total dose delivered by natural
radionuclide decay to all the organic molecules present in comets and
asteroids in 4.6 × 109 yr, the age of the Solar system.
It is shown that all the amino acids studied can survive a radiation
dose of 14 MGy, although certain fractions of them are lost as a result
of radiolytic processes. Similarly, the radioracemization process
accompanying the radiolysis does not extinguish the initial enantiomeric
enrichment. Knowledge of the radiolysis and radioracemization rate
constants may permit the calculation of the original concentrations of
the amino acids at the time of the formation of the Solar system,
starting from the concentration found today in carbonaceous chondrites.
For some amino acids the concentration in the pre-solar nebula could
have been up to 6 times higher than that currently observed in
meteorites. The preservation of an original enatiomeric excess is also
expected. This study adds experimental support to the suggestion that
amino acids were formed in the interstellar medium and in chiral excess
and then were incorporated into comets and asteroids at the epoch of
Solar system formation.
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