Eco-Friendly Adsorption of Adenine on MMT: A Green Chemistry Approach to Prebiotic Surface Processes

Abstract

The adsorption of adenine on montmorillonite (MMT) clay, both in its natural form and exchanged with divalent cations (Ca²⁺, Mg²⁺, Ni²⁺), was investigated under varying pH, temperature, and concentration conditions to gain insights into the role of mineral surfaces in prebiotic molecular organisation. Adsorption isotherms, thermodynamic parameters, and the influence of cations were examined. The presence of divalent cations enhanced adsorption by neutralising the negatively charged clay surface, promoting electrostatic interactions. Thermodynamic analysis revealed that the adsorption process was spontaneous (ΔG°:–2.96 to –3.71 kJ·mol⁻1), driven by weak intermolecular forces, with enthalpy values ranging from 5.46 to 7.09 kJ·mol⁻1 and positive entropy contributions. These findings suggest that montmorillonite (MMT) clay could have acted as an effective adsorbent for concentrating and stabilising biomolecules like adenine under early Earth conditions, potentially facilitating the emergence of complex organic compounds and self-replicating systems. The study highlights the importance of mineral–organic interactions in prebiotic chemistry and provides mechanistic insights into the possible role of clay minerals in the chemical evolution of life.