Implications For An RNA-Clay World:Interaction Of Cytosine With Clay Minerals

The RNA world hypothesis assumes that RNA molecules played a critical role in first step of prebiotic evolution. In this context 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 place severe constraints on the reliability of the RNA world hypothesis. 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 furnished a primordial compartmentalization and a protected environment during Abiotic evolution. In order to clarify the kind of interaction at molecular level between nucleobasis and mineral matrix we report results obtained trough diffractometric (powder X-ray) and spectroscopic (FTIR-DRIFT) techniques on nucleobases-clay (montmorillonite) minerals complexes at high temperature. Results obtained indicated that cytosine intercalated on montmorillonite shows a degradation rate two order of magnitude lower when tightly adsorbed on clay. The implication of the results was analyzed on the light of the RNA-clay-world hypothesis.