Thymine Adsorption onto Cation Exchanged Montmorillonite Clay: Role of Biogenic Divalent Metal Cations in Prebiotic Processes of Chemical Evolution.

The adsorption of thymine, a key pyrimidine base of deoxyribonucleic acid (DNA) on montmorillonite clay (Mnt) exchanged with metal ions (Mnt-M2+, M2+ = Fe2+, Co2+, Cu2+, Ca2+, and Mg2+) over a range of concentration (7.0 × 10-5 M to 12.0 × 10-5 M) and pH (4.0 - 9.0) at ambient temperature has been investigated in aqueous environment spectrophotometrically (UV, FTIR, XRD, SEM-EDX). The effectiveness of various adsorbents was determined in terms of percent (%) binding and Langmuir constants (KL and Xm) using Langmuir adsorption isotherm at their respective pH of maximum adsorption. Transition metal ions incorporated Mnt, particularly Fe2+ have shown better adsorption ability than alkaline earth metal ions. The present study reveals the significant role of divalent metal cation exchanged Mnt clay in the chemical evolution of biomolecules of genetic continuity and self-replication which might have occurred through the adsorption of thymine on and between their silicate layers to protect and achieve biocompatibility.

Affinity of Smectite and Divalent Metal Ions (Mg(2+), Ca(2+), Cu(2+)) with L-leucine: An Experimental and Theoretical Approach Relevant to Astrobiology.

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.

Surface interaction of L-alanine on hematite: an astrobiological implication.

In the present work, surface interaction of L-alanine (L-ala) has been investigated on hematite (α-Fe2O3), an abundant mineral on Mars, as a function of time (5 min-48 h), pH (4.0 and 6.20 ± 0.10) and concentration (1 × 10(-3) M-10 × 10(-3) M) with optical absorbance and energy-dispersive spectroscopy (EDS). Adsorption parameters (XM and KL) were calculated from Langmuir adsorption isotherms. L-alanine has maximum affinity (65.31 %) in its zwitterionic form at pH 6.20, while it is only 29.86 % adsorbed at pH 4.0. Possible astrobiological implications are discussed.