Adsorption of Ribose Nucleotides on Manganese Oxides with Varied Mn/O Ratio: Implications for Chemical Evolution

Manganese exists in different oxidation states under different environmental conditions with respect to redox potential. Various forms of manganese oxides, namely, Manganosite (MnO), Bixbyite (Mn₂O₃), Hausmannite (Mn₃O₄) and Pyrolusite (MnO₂) were synthesized and their possible role in chemical evolution studied. Adsorption studies of ribose nucleotides (5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP) on these manganese oxides at neutral pH, revealed a higher binding affinity to manganosite (MnO) compared to the other manganese oxides. That manganese oxides having a lower Mn-O ratio show higher binding affinity for the ribonucleotides indirectly implies that such oxides may have provided a surface onto which biomonomers could have been concentrated through selective adsorption. Purine nucleotides were adsorbed to a greater extent compared to the pyrimidine nucleotides. Adsorption data followed Langmuir adsorption isotherms, and X _m and K _L values were calculated. The nature of the interaction and mechanism was elucidated by infrared spectral studies conducted on the metal-oxide and ribonucleotide-metal-oxide adducts.