We have determined the adsorption of RNA components (adenine, cytosine, uracil, ribose and phosphate) by Mg2+-exchanged montmorillonite. The isotherms for adenine, cytosine and uracil were of the C-type, the amount adsorbed increasing linearly with the equilibrium solute concentration. All three nucleic acid bases were apparently adsorbed by coordination to Mg2+ ions through a water bridge. Very little ribose was adsorbed by Mg-exchanged montmorillonite. The isotherm for phosphate was of the L-type. The plateau value of about 0.012 mmol g–1 indicated that phosphate adsorbed on the edge surface of montmorillonite. At comparable solute concentrations, adsorption decreased in the order adenine > cytosine > uracil. This observation reflects differences in basicity, size, and aqueous solubility among the three compounds.

Amino acids and nucleic acid bases are very important for the living organisms. Thus, their protection from decomposition, selection, pre-concentration and formation of biopolymers are important issues for understanding the origin of life on the Earth. Minerals could have played all of these roles. This paper discusses several aspects involving the adsorption of amino acids and nucleic acid bases onto minerals under conditions that could have been found on the prebiotic Earth; in particular, we recommend the use of minerals, amino acids, nucleic acid bases and seawater ions in prebiotic chemistry experiments. Several experiments involving amino acids, nucleic acid bases, minerals and seawater ions are also suggested, including: (a) using well-characterized minerals and the standardization of the mineral synthesis methods; (b) using primary chondrite minerals (olivine, pyroxene, etc.) and clays modified with metals (Cu, Fe, Ni, Mo, Zn, etc.); (c) determination of the possible products of decomposition due to interactions of amino acids and nucleic acid bases with minerals; (d) using minerals with more organophilic characteristics; (e) using seawaters with different concentrations of ions (i.e. Na+, Ca2+, Mg2+, SO42− and Cl−); (f) using non-protein amino acids (AIB, α-ABA, β-ABA, γ-ABA and β-Ala and g) using nucleic acid bases other than adenine, thymine, uracil and cytosine. These experiments could be useful to clarify the role played by minerals in the origin of life on the Earth.