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

• Published in: Origins of life and evolution of biospheres 2015-02, Vol.45 (4), p.411-426
• Main Authors: Pandey, Pramod, Pant, Chandra Kala, Gururani, Kavita, Arora, Priyanka, Pandey, Neetu, Bhatt, Preeti, Sharma, Yogesh, Negi, Jagmohan Singh, Mehata, Mohan Singh
• Format: Article
• Language: English
• ISSN: 0169-6149; 1573-0875
• DOI: 10.1007/s11084-015-9437-2

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 super(2+), Ca super(2+) and Cu super(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 super(2+)- exchanged SMT and minimal affinity for Mg super(2+)- exchanged SMT. The vibrational frequency shifts of -NH sub(3) super(+) and -COO super(-) 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 super(2+) complex, M=Mg super(2+), Ca super(2+), Cu super(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 super(2+)(H sub(2)O) sub(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.