Interaction of nucleobases with clay minerals: implications for an RNA-clay world.

RNA world hypothesis assumes that RNA molecules played a critical role in the first steps of prebiotic evolution. As a consequence the stability of genetic material and nucleobases (adenine, guanine, cytosine, and thymine) is a key aspect of the evolution in primordial environment. It was pointed out that the half-lives for the decomposition of the nucleobases is too short on the geologic time scale to allow an adequate accumulation of these compounds (Levy and Miller, 1998). Moreover it was emphasized that degradation of cytosine (the half-life for deamination at 25°C is 340 yr) is so fast to represent a severe constraint on reliability of RNA world hypothesis (Shapiro 1999). However the presence of specific physical settings could, in principle, improve the stability of nucleobases. In particular it was suggested that clay minerals could have provided a primordial compartimentalization and a protected environment during prebiotic evolution. in order to clarify the interactions at molecular level between nueleobases and mineral matrix (montmorillonite-clay) different possible scenarios were considered. The effects of pH and temperature on the clay-nucieobases complexes were analyzed by using FTIR-DRIFT spectroscopy and X-ray diffractometry Moreover, the relative stability of nucleobases adsorbed on montomorillonite at different temperatures was compared with results obtained in free water solution. The implication of the results obtained were discussed on the light of the RNA-clay¬world hypothesis.