Amino Acid Adsorption to Montmorillonite: Selectivity and Binding Mechanisms

Concentrating simple organic molecules, such as amino acids, in the adsorbed phase could have been an early step in prebiotic evolution towards more complex bio-macromolecules on the early Earth. Smectite clay minerals represent potential selective sorbents for prebiotic molecules because of their negative structural charge and high surface area. This study explored the selective uptake and adsorption mechanisms of amino acids to montmorillonite, a well-characterized smectite. The effects of dissolved salt composition (NaCl vs MgCl₂) and pH (5 vs 7) on the uptake of amino acids to montmorillonite were investigated using adsorption isotherms. Amino acid binding to the clay mineral was determined through analysis of the final fluid composition using high-performance liquid chromatography (HPLC). The adsorption mechanisms of basic amino acids (L-arginine and L-lysine) were characterized using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and powder X-ray diffraction (XRD).