Abstract
Adsorption of protobiomolecules on primigenial mineral surfaces transacts a very specific and selective role in prebiotic chemical evolution. Cytosine (CYN) is a core constituent of genetic macromolecules i.e., DNA and RNA. A prebiotic simulation experiment following adsorption behaviour of a nucleic acid base CYN, as a function of pH, concentration, time and temperature on the surface of Montmorillonite (MMT), a prominent siliceous clay of smectite group having specific surface area, was studied systematically and methodically using UV, FTIR, SEM and XRD. Biologically significant metal dication [M2+ = Mg2+, Ca2+, Fe2+ and Cu2+] embeded surfaces of MMT (MMT-M2+) were prepared separately by cation-exchange approach. Results observed through UV spectral data reveal a very significant role of metal ions on the quantity of CYN adsorbed on different solid surfaces. The adsorption behaviour fitted well with Langmuir isotherm model and the adsorption isotherm shows monolayer formation of CYN (as adsorbate) on the surface of MMT and MMT-M2+(as adsorbent) showing Langmuir type adsorption. The calculated Langmuir adsorption parameters (KL& Xm) delineate appreciable interaction of CYN on MMT-Fe2+ surface following MMT-Cu2+ as compared to MMT alone and to other metal induced MMTs.In terms of % binding and Xm data, the effectiveness of various adsorbents in adsorption of CYN on MMT/MMT-M2+ at pH 6.6 and temperature 298K was found in the order; MMT-Fe2+> MMT-Cu2+> MMT > MMT-Ca2+> MMT-Mg2+. The results were further confirmed by SEM, XRD and FTIR which also support the outcomes. The present work throws light on the affinity of MMT clay (having multifarious applications in biological systems) with and without biogenic metal diions towards the surface interaction of nucleic acid base mimicking primeval sea shore/sea bed or hydrothermal vent conditions deciphering the phenomena that how biomonomers could have been protected from extreme hazardous conditions of primitive Earth and stabilized during chemical evolution and availed them for consecutive molecular evolution. Results further embark better adsorption capability of transition metal ion incorporated MMTs than the clay without metal ion and exchanged with alkaline Earth dications.
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