Role of Na+-montmorillonite in the stability of guanine exposed to high-radiation energy in primitive environments: Heterogeneous models

Abstract In the context of chemical evolution, in which the formation of compounds of biological importance was the first step toward the origin of life, the stability of organic molecules is an essential consideration in evaluating plausible scenarios for the primitive Earth. In this framework, the behavior of guanine (a nucleobase) under gamma irradiation in three types of systems was studied: guanine in aqueous solution. guanine adsorbed in sodium montmorillonite (clay); and a suspension containing both sodium montmorillonite and guanine, with a guanine concentration such that the molecule occupied all the clay’s active sites, but excess guanine also existed in the solution. These systems were exposed to a high-gamma radiation field to highlight the clay’s possible role as a protective agent toward ionizing radiation in prebiotic processes. Guanine was analyzed by UV-spectroscopy, and ultra-high-performance liquid chromatography (UHPLC). The clay sample was analyzed by FTIR-ATR spectroscopy and X-ray diffraction (XRD). The obtained results show that the guanine in an aqueous medium decomposed quickly, even at low doses of ionizing radiation. Nonetheless, the molecule is relatively stable when it is adsorbed onto sodium montmorillonite. These results were also evaluated at the molecular level with computer simulation models.