Article in ACS Earth and Space Chemistry, 3(1) November 18, 2019
Jihua Hao, Marwane Mokhtari, Ulysse Pedreira Segade, Laurent Michot, and Isabelle Daniel
Chemical evolution of early life requires concentration of monomers to polymerize from the diluted primordial ocean. Transition metals such as Fe, Mn, and Zn, could have reached considerable levels in the early seawater and hydrothermal fluids, but their influences on adsorption of biomolecules have not been clearly addressed yet. In this study, we conducted batch adsorption experiments to explore effects of various metal cations (Li, Mg, Ca, Zn, Ni, and Mn) on the adsorption of selected nucleotides (dGMP, dAMP, and AMP) and adenosine onto nontronite and montmorillonite. We also varied concentration of the cations and pH of the solutions to evaluate their effects. Our results show that Zn and Ni significantly enhance adsorption of nucleotides and adenosine, compared with modern seawater salt environment dominated by Na, Mg, and Ca. This enhancing effect is primarily attributed to the mediating role of transition metals between the clays and nucleotides and adenosine. The enhancing effect depends little on salt concentration, but strongly varies as the pH of the solution changes. Presence of transition metals reverses the declining trend of the adsorption of nucleotide at elevated pH and strongly favors adsorption of nucleotides through precipitation of metal-hydroxides on the clay surface. Enhanced adsorption of biomolecules mediated by transition metals would potentially ease the origin of life in two aspects: concentration of simple organics for polymerization and protection of early biomolecules against UV radiation and heating in early seawater.
ACS Earth and Space Chemistry 2019, 3, 1, 109-119.