Amino acids found in meteorites are the result of reactions between small molecules, such as CO2, CO, CH3OH and NH3 with H2O of ice layers in solid dust particles (silicate grains). Due the action of different energy sources, mainly ultraviolet photons and cosmic rays, they generated radicals able to interact with each other, creating more complex organic molecules. As a result, the organics (i.e amino acids) were incorporated into silicate structures which preserved them from further cosmic rays and ultraviolet photons. On the other hand, the presence of radioactive elements in meteoritic body, principally 40K, 232Th, 235U, 238U and 26Al, can play a role against the preservation of amino acids. In fact the radionuclide decay was the main cause of the amino acids degradation in astrochemical context. According to Urey's works radioactive elements produced a total radiation of ?14 MGy during the life of Solar System (4.6x109 years). It is well known that a chiral molecule submitted to ionizing radiations can experience radioracemization, a transformation process leading to a reduction in optical activity as a consequence of two main events: firstly, the radiolysis of chiral molecules and their degradation into products without asymmetric centre; secondly, the inversion of chiral centre due to the high energy involved during irradiation. We already carried out some studies regarding the amino acids capacity to survive at a dose of gamma radiations equivalent to 1.05x109 years of Solar System life, that is, 3.2 MGy. In the present work we analyze three amino acids (valine, isoleucine and leucine) irradiated in the solid state at 3.2 MGy, either without oxygen or humidity. These three amino acids are considered to be primitive amino acids, in other word amino acids formed at the first stages of Solar System life. The study was conducted to investigate the possibility for the amino acids to retain their initial signature at a such high level of radiation dose, and to examine how the lack of oxygen can influence the amino acids radioracemization. Besides using mass spectrometric techniques, we could identify some interesting degradation pathways carrying out to important products. These could be effectively considered as real precursors of more complex intermediates, very important from a biological point of view. At last, several gamma irradiation experiments were repeated on more complex systems where the selected amino acids were adsorbed into the cavities of a porous material.
REACTIVITY OF SELECTED PRIMITIVE AMINO ACIDS INDUCED BY GAMMA-IRRADIATION IN ASTROCHEMICAL CONTEXT
Giancarlo Angelini;Cristina Cherubini;Ornella Ursini
2015
Abstract
Amino acids found in meteorites are the result of reactions between small molecules, such as CO2, CO, CH3OH and NH3 with H2O of ice layers in solid dust particles (silicate grains). Due the action of different energy sources, mainly ultraviolet photons and cosmic rays, they generated radicals able to interact with each other, creating more complex organic molecules. As a result, the organics (i.e amino acids) were incorporated into silicate structures which preserved them from further cosmic rays and ultraviolet photons. On the other hand, the presence of radioactive elements in meteoritic body, principally 40K, 232Th, 235U, 238U and 26Al, can play a role against the preservation of amino acids. In fact the radionuclide decay was the main cause of the amino acids degradation in astrochemical context. According to Urey's works radioactive elements produced a total radiation of ?14 MGy during the life of Solar System (4.6x109 years). It is well known that a chiral molecule submitted to ionizing radiations can experience radioracemization, a transformation process leading to a reduction in optical activity as a consequence of two main events: firstly, the radiolysis of chiral molecules and their degradation into products without asymmetric centre; secondly, the inversion of chiral centre due to the high energy involved during irradiation. We already carried out some studies regarding the amino acids capacity to survive at a dose of gamma radiations equivalent to 1.05x109 years of Solar System life, that is, 3.2 MGy. In the present work we analyze three amino acids (valine, isoleucine and leucine) irradiated in the solid state at 3.2 MGy, either without oxygen or humidity. These three amino acids are considered to be primitive amino acids, in other word amino acids formed at the first stages of Solar System life. The study was conducted to investigate the possibility for the amino acids to retain their initial signature at a such high level of radiation dose, and to examine how the lack of oxygen can influence the amino acids radioracemization. Besides using mass spectrometric techniques, we could identify some interesting degradation pathways carrying out to important products. These could be effectively considered as real precursors of more complex intermediates, very important from a biological point of view. At last, several gamma irradiation experiments were repeated on more complex systems where the selected amino acids were adsorbed into the cavities of a porous material.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
