Detalles de publicación
PP 011016
A detailed analysis of the properties of radiolyzed proteinaceous amino acids
The top down approach in the search of the origins of life
F. Cataldo (&)
has involved the analysis of meteorites and in particular of
Istituto Nazionale di Astrofisica. Osservatorio Astrofisico di
the carbonaceous chondrites (CC). Indeed a plethora of
Catania, Via S. Sofia 78, 95123 Catania, Italy
different classes of molecules have been identified in
e-mail: franco.cataldo@fastwebnet.it
meteorites since long time [1]. The most impressive class
F. Cataldo
of molecules identified yet regards the amino acids which
Lupi Chemical Research, Via Casilina 1626/A,
are the basic molecules used in the current terrestrial bio-
00133 Rome, Italy
chemistry. Not only a considerable number of different
P. Ragni amino acids have been identified in CC [2], but part of
Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300,
them were also detected in enantiomeric excess [3–6]. This
00016 Monterotondo Stazione, Rome, Italy
S. Iglesias-Groth à A. Manchado
Ì
Instituto de Astrofısica de Canarias (IAC), Via Lactea s/n, before the formation of the Solar System [7] but also
38200 La Laguna, Tenerife, Spain
F. Cataldo.
Istituto Nazionale di Astrofisica. Osservatorio Astrofisico diCatania, Via S. Sofia 78, 95123 Catania, Italy
e-mail: franco.cataldo@fastwebnet.it
F. Cataldo
Lupi Chemical Research, Via Casilina 1626/A,
P. Ragni Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300,00016 Monterotondo Stazione, Rome, Italy
S. Iglesias-Groth à A. Manchado
Instituto de Astrofısica de Canarias (IAC), Via Lactea s/n, before the formation of the Solar System [7] but also
38200 La Laguna, Tenerife, Spain
A. Manchado
CSIC, Madrid, Spain
A. Manchado
light on racemic mixtures [8].
CSIC, Madrid, Spain
Abstract The thermal behaviour of 21 proteinaceous L-amino acids either as pristine samples and also as radiolyzed (3.2 MGy) samples was studied with the differential scanning calorimeter. The onset and peak melting point as well as the melting enthalpy of all samples before and after the radiation treatment was measured and reported. The residual amount of each amino acid survived to the radiation dose of 3.2 MGy (Nc) was measured from the melting enthalpies before and after radiolysis and hence the radiation resistance of each amino acid has been determined. The radiolysis causes a systematic reduction of the
melting enthalpy and a shift of the onset and peak melting point to lower values. It is shown that Nc does not correlate with the melting points of the amino acids but shows a correlation with the entity of the shift of the melting point peaks occurred after radiolysis. Such correlation instead does not exist between the Nc parameter and the onset melting points of the amino acids. An explanation of such lack of correlation was given. Furthermore, a general rela-
tionship has been found between the amino acids melting point peak measured on pristine samples and the melting point peaks after solid state radiolysis. Such relationship can be used to predict roughly the expected melting point
after radiolysis at 3.2 MGy of any given amino acid. The last part of the study was dedicated in the attempt to find a correlation between the Nc parameter and the amount of the amino acids survived the radiolysis Rc as measured by
spectropolarimetry (ORD spectroscopy). A general trend was found in the connection between the Nc and Rc parameters but not a very strong correlation.
melting enthalpy and a shift of the onset and peak melting point to lower values. It is shown that Nc does not correlate with the melting points of the amino acids but shows a correlation with the entity of the shift of the melting point peaks occurred after radiolysis. Such correlation instead does not exist between the Nc parameter and the onset melting points of the amino acids. An explanation of such lack of correlation was given. Furthermore, a general rela-
tionship has been found between the amino acids melting point peak measured on pristine samples and the melting point peaks after solid state radiolysis. Such relationship can be used to predict roughly the expected melting point
after radiolysis at 3.2 MGy of any given amino acid. The last part of the study was dedicated in the attempt to find a correlation between the Nc parameter and the amount of the amino acids survived the radiolysis Rc as measured by
spectropolarimetry (ORD spectroscopy). A general trend was found in the connection between the Nc and Rc parameters but not a very strong correlation.