Bibcode
Cataldo, Franco; Angelini, Giancarlo; Iglesias-Groth, S.; Manchado, A.
Referencia bibliográfica
Radiation Physics and Chemistry, Volume 80, Issue 1, p. 57-65.
Fecha de publicación:
1
2011
Número de citas
17
Número de citas referidas
17
Descripción
The aliphatic amino acids L-alanine and L-leucine and the aromatic amino
acids L-phenylalanine, L-tyrosine and L-tryptophan were irradiated in
the solid state to a dose of 3.2 MGy. The degree of decomposition was
measured by differential scanning calorimetry (DSC). Furthermore the
degree of radioracemization was measured by optical rotatory dispersion
(ORD) spectroscopy. From the DSC measurement a radiolysis rate constant
k and the half life T1/2 for each amino acid have been
determined and extrapolated to a dose of 14 MGy, which corresponds to
the expected total dose delivered by the decay of radionuclides to the
organic molecules present in comets and asteroids in
4.6×109 years, the age of the Solar System. It is shown
that all the amino acids studied can survive a radiation dose of 14 MGy
although they are reduced to 1/4-1/5 of their original value they had at
the beginning of the history of the Solar System. Consequently, the
amount of alanine or leucine found today in the meteorites known as
carbonaceous chondrites is just 1/4-1/5 of the amount originally present
at the epoch of the formation of the Solar System
4.6×109 years ago. Among the amino acids studied,
tyrosine shows the highest radiation resistance while tryptophan does
not combine its relatively high radiation resistance with an elevated
level of radioracemization resistance. Apart from the exception of
tryptophan, it is shown that the radiolysis rate constants k of all the
amino acids studied are in reasonable agreement with the
radioracemization rate constant krac.
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