Stability of Guanine Adsorbed in a Clay Mineral under Gamma Irradiation at Temperatures (77 and 298 K): Implications for Chemical Evolution Studies
Por:
Melendez-Lopez, A. L., Ramos-Bernal, S., Ramirez-Vazquez, M. L.
Publicada:
1 ene 2014
Categoría:
Physics and Astronomy (miscellaneous)
Resumen:
Chemical evolution is a physical and chemical preamble prior the
appearance of life. In these processes, clay minerals might have played
an important role on the early Earth. The relevance of these solids in
the emergence of life is due to their ancient origin, wide distribution,
and especially, their physico-chemical properties. Clays, therefore, are
considered the most likely inorganic materials to promote organic
reactions in the primitive Earth. John D. Bernal suggested clays as
concentrators of biological precursor molecules, as catalysis and clays
might protect these molecules from high-energy radiation. On the other
hand, nucleic acid bases and their derivatives are important compounds
in biological systems. Their synthesis and stability in environmental
conditions are of paramount importance in chemical evolution.
The aim of this work is to extend the knowledge of the role of clays in
the prebiotic epoch in relation to the behavior of guanine; a nucleic
acid base, adsorbed in a clay mineral. To this end, we studied its
adsorption in clays, its site of binding, and its survival under a high
radiation field and at different temperatures and pH. The results showed
guanine adsorption onto clays increased with the decreasing of the pH.
This result could be explained by electrostatic forces between guanine
positively charged at an acid pH and the negatively charged
interlamellar channel of the clay. X-ray diffractognuns showed that
guanine is adsorbed onto the clay at the interlayer channel To study the
survival of guanine in a high radiation field, the system guanine-clay
was irradiated under different irradiation doses, temperatures; and pH.
The results showed that more than 90% of the guanine survives, and when
the radiolysis is made without clay, the decomposition of this molecule
occurs at low irradiation doses. The radiolysis performed at 77 K showed
very low decomposition; which is important in cometary chemistry. These
results show the protection role of the clay toward ionizing radiation
of an organic compound adsorbed into it.
Filiaciones:
Melendez-Lopez, A. L.:
Univ Nacl Autonoma Mexico, Inst Ciencias Nucl, AP 70-543, Mexico City 04510, DF, Mexico
Ramos-Bernal, S.:
Univ Nacl Autonoma Mexico, Inst Ciencias Nucl, AP 70-543, Mexico City 04510, DF, Mexico
Ramirez-Vazquez, M. L.:
Univ Autonoma Zacatecas, Unidad Acad Estudios Nucleares, Zacatecas 98000, Mexico
|