Modulation of adenosine 5'-monophosphate adsorption onto aqueous resident pyrite: potential mechanisms for prebiotic reactions

The adsorption of adenosine 5'-monophosphate (5'-AMP) onto pyrite (FeS2) and its modulation by acetate, an organic precursor of complex metabolic pathways, was studied in aqueous media that simulate primitive environments. 5'-AMP adsorption requires divalent cations, indicating that a cationic bridge mediates its attachment to negatively charged sites of the mineral surface. The isotherm of 5'-AMP adsorption exhibits a strong cooperative effect at low nucleotide concentrations in acetate-rich medium, whereas high levels of adsorption were only found at high nucleotide concentrations in a model of primitive seawater (acetate free). The modulating role of acetate is also evidenced in the presence of high dipolar moment molecules: dimethyl sulfoxide (Me2SO) and dimethyl formamide (DMF) strongly inhibit 5'-AMP adsorption in acetate-rich media, whereas no effect of DMF was found in artificial seawater. The observation that exogenous divalent cations are not needed for acetate attachment onto FeS2 reveals that organic acids can interact with the Fe2+ atoms in the mineral surface. All considered, the results show that complex and flexible ironsulfide/biomonomers interactions can be modulated by molecules that accumulate in the interface layer.