Modulation of adenosine 5 '-monophosphate adsorption onto aqueous residentpyrite: Potential mechanisms for prebiotic reactions

The adsorption of adenosine 5'-monophosphate (5'-AMP) onto pyrite (FeS2) an d its modulation by acetate, an organic precursor of complex metabolic path ways, was studied in aqueous media that simulate primitive environments. 5' -AMP adsorption requires divalent cations, indicating that a cationic bridg e mediates its attachment to negatively charged sites of the mineral surfac e. The isotherm of 5'-AMP adsorption exhibits a strong cooperative effect a t 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 al so evidenced in the presence of high dipolar moment molecules: dimethyl sul foxide (Me2SO) and dimethyl formamide (DMF) strongly inhibit 5'-AMP adsorpt ion in acetate-rich media, whereas no effect of DMF was found in artificial seawater. The observation that exogenous divalent cations are not needed f or acetate attachment onto FeS2 reveals that organic acids can interact wit h the Fe2+ atoms in the mineral surface. All considered, the results show t hat complex and flexible iron-sulfide/biomonomers interactions can be modul ated by molecules that accumulate in the interface layer.