Earth is the only known planet bestowed with life. Several attempts have been made to explore the pathways of the origin of life on planet Earth. The search for the chemistry which gave rise to life has given answers related to the formation of biomonomers, and their adsorption on solid surfaces has gained much attention for the catalysis and stabilization processes related to the abiotic chemical evolution of the complex molecules of life. In this communication, surface interactions of L-leucine (Leu) on smectite (SMT) group of clay (viz. bentonite and montmorillonite) and their divalent metal ion (Mg(2+), Ca(2+) and Cu(2+)) incorporated on SMT has been studied to find the optimal conditions of time, pH, and concentration at ambient temperature (298 K). The progress of adsorption was followed spectrophotometrically and further characterized by FTIR, SEM/EDS and XRD. Leu, a neutral/non polar amino acid, was found to have more affinity in its zwitterionic form towards Cu(2+)- exchanged SMT and minimal affinity for Mg(2+)- exchanged SMT. The vibrational frequency shifts of -NH3 (+) and -COO(-) favor Van der Waal's forces during the course of surface interaction. Quantum calculations using density functional theory (DFT) have been applied to investigate the absolute value of metal ion affinities of Leu (Leu-M(2+) complex, M = Mg(2+), Ca(2+), Cu(2+)) with the help of their physico-chemical parameters. The hydration effect on the relative stability and geometry of the individual species of Leu-M(2+) × (H2O)n, (n =2 and 4) has also been evaluated within the supermolecule approach. Evidence gathered from investigations of surface interactions, divalent metal ions affinities and hydration effects with biomolecules may be important for better understanding of chemical evolution, the stabilization of biomolecules on solid surfaces and biomolecular-metal interactions. These results may have implications for understanding the origin of life and the preservation of biomarkers.
Explanation of the homochirality of amino acids in the biosphere is one of the most important mysteries in the origin of life. Following the abiotic evolution of life on Earth, possible role of prebiotically available mineral and metal ion have been widely studied. In this communication an effort has been made to investigate the surface interaction of L-alanine (L-ala) and D-alanine (D-ala) on Bentonite (BNT) and its divalent metal ion (M=Ca 2+ , Mg 2+ , Ni 2+ , Cu 2+ and Zn 2+ ) incorporated BNT for the optimal condition of pH, time, concentration and enantiomeric selectivity for D-and L-ala. Cu 2+ , Ni 2+ and Zn 2+ exchanged BNT have higher affinity for both the ala but Mg 2+ exchanged BNT have shown the selective adsorption of L-ala in comparison to the D-ala at pH 4.0±0.1. Further, absolute value of metal ion affinities with ala (ala-M 2+ ) and hydration effect on the relative stability and geometry of the individual species of ala-M 2+ ×(H2O)n, (n =2 and 4) has also been evaluated using DFT calculation. Possible implications for the stability and selectivity of biomolecules in prebiotic era of Earth has been discussed.
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