Detalles de publicación
PP 012060
Solid state radiolysis of non-proteinaceus amino acids in vacuum:astrochemical implications
F. Cataldo
Istituto Nazionale di Astrofisica, Osservatorio Astrofisica
di Catania, Via S. Sofia 78, 95123 Catania, CT, Italy
F. Cataldo (&)
Lupi Chemical Research, Via Casilina 1626/A, 00133 Rome,
Italy
e-mail: franco.cataldo@fastwebnet.it
G. Angelini
Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300,
00016 Monterotondo Stazione, Rome, Italy
Y. Hafez
National Center for Astronomy, KACST, P.O. Box 6086,
Riyadh 11442, Saudi Arabia
S. Iglesias-Groth
Instituto de Astrofisica de Canarias, Via Lactea s/n,
38200 La Laguna, Tenerife, Spain
123
Abstract The analysis of the amino acids present in
Murchison meteorite and in other carbonaceous chondrites
has revealed the presence of 66 different amino acids. Only
eight of these 66 amino acids are proteinaceous amino
acids used by the present terrestrial biochemistry in protein
synthesis, the other 58 amino acids are somewhat ‘‘rare’’ or
unusual or even ‘‘unknown’’ for the current terrestrial
biochemistry. For this reason in the present work a series of
‘‘uncommon’’ non-proteinaceous amino acids, namely, L-2-
aminobutyric acid, R(-)-2-aminobutyric acid, 2-aminoisobutyric
acid (or a-aminoisobutyric acid), L-norleucine,
L-norvaline, L-b-leucine, L-b-homoalanine, L-b-homoglutamic
acid, S(-)-a-methylvaline and DL-3-aminoisobutyric
acid were radiolyzed in vacuum at 3.2 MGy a dose
equivalent to that emitted in 1.05 9 109 years from the
radionuclide decay in the bulk of asteroids or comets. The
residual amount of each amino acid under study remained
after radiolysis was determined by differential scanning
calorimetry in comparison to pristine samples. For optically
active amino acids, the residual amount of each
amino acid remained after radiolysis was also determined
by optical rotatory dispersion spectroscopy and by polarimetry.
With these analytical techniques it was possible to
measure also the degree of radioracemization undergone by
each amino acid after radiolysis. It was found that the nonproteinaceous
amino acids in general do not show a higher
radiation and radioracemization resistance in comparison
to the common 20 proteinaceous amino acids studied previously.
The unique exception is represented by a-aminoisobutyric
acid which shows an extraordinary resistance to
radiolysis since 96.6 % is recovered unchanged after
3.2 MGy. Curiously a-aminoisobutyric acid is the most
abundant amino acid found in carbonaceous chondrites.
In Murchison meteorite a-aminoisobutyric acid represents
more than 20 % of the total 66 amino acids found in this
meteorite.
Murchison meteorite and in other carbonaceous chondrites
has revealed the presence of 66 different amino acids. Only
eight of these 66 amino acids are proteinaceous amino
acids used by the present terrestrial biochemistry in protein
synthesis, the other 58 amino acids are somewhat ‘‘rare’’ or
unusual or even ‘‘unknown’’ for the current terrestrial
biochemistry. For this reason in the present work a series of
‘‘uncommon’’ non-proteinaceous amino acids, namely, L-2-
aminobutyric acid, R(-)-2-aminobutyric acid, 2-aminoisobutyric
acid (or a-aminoisobutyric acid), L-norleucine,
L-norvaline, L-b-leucine, L-b-homoalanine, L-b-homoglutamic
acid, S(-)-a-methylvaline and DL-3-aminoisobutyric
acid were radiolyzed in vacuum at 3.2 MGy a dose
equivalent to that emitted in 1.05 9 109 years from the
radionuclide decay in the bulk of asteroids or comets. The
residual amount of each amino acid under study remained
after radiolysis was determined by differential scanning
calorimetry in comparison to pristine samples. For optically
active amino acids, the residual amount of each
amino acid remained after radiolysis was also determined
by optical rotatory dispersion spectroscopy and by polarimetry.
With these analytical techniques it was possible to
measure also the degree of radioracemization undergone by
each amino acid after radiolysis. It was found that the nonproteinaceous
amino acids in general do not show a higher
radiation and radioracemization resistance in comparison
to the common 20 proteinaceous amino acids studied previously.
The unique exception is represented by a-aminoisobutyric
acid which shows an extraordinary resistance to
radiolysis since 96.6 % is recovered unchanged after
3.2 MGy. Curiously a-aminoisobutyric acid is the most
abundant amino acid found in carbonaceous chondrites.
In Murchison meteorite a-aminoisobutyric acid represents
more than 20 % of the total 66 amino acids found in this
meteorite.