Detalles de publicación
PP 010072
Solid State radiolysis of amino acids in an astrochemical perspective
a Istituto Nazionale di Astrofisica—Osservatorio Astrofisica di Catania, Via S. Sofia 78, 95123 Catania, Italy
b Lupi Chemical Research, Via Casilina 1626/A, 00133 Rome, Italy
c Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300, 00016 Monterotondo Stazione, Rome, Italy
d Instituto de Astrofisica de Canarias, Via Lactea s/n, E-38200, La Laguna, Tenerife, Spain
e CSIC, Spain
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
4.6109 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 4.6109 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.
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
4.6109 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 4.6109 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.