2012 Annual Science Report
Rensselaer Polytechnic Institute Reporting | SEP 2011 – AUG 2012
Project 7: Prebiotic Chemical Catalysis on Early Earth and Mars
The “RNA World” hypothesis is the current paradigm for the origins of terrestrial life. Our research is aimed at testing a key component of this paradigm: the efficiency with which RNA molecules form and grow under realistic conditions. We are studying abiotic production and polymerization of RNA by catalysis on montmorillonite clays. The catalytic efficiency of different montmorillonites are determined and compared, with the goal of determining which properties distinguish good catalysts from poor catalysts. We are also investigating the origin of montmorillonites, to test their probable availability on the early Earth and Mars, and the nature of catalytic activity that could have led to chiral selectivity on Earth.
Our study of the role of montmorillonite catalysis in the formation of RNA oligomers on the early Earth provides insight into the selectivity of this potential prebiotic catalyst. Selected montmorillonite clays are known to catalyze the formation of RNA. Some reactions have shown a preference for homochiral selectivity when racemic mixtures of activated mononucleotides of A with U were reacted with Na+-montmorillonite. An obseved progressive increase in selectivity with an increase in chain length suggests that each homochiral oligomer acts as a chiral auxiliary in the formation of the next higher oligomer (Joshi et al. 2011, 2012). Work is in progress to determine chiral selectivity in the reactions of activated nucleotides of racemic A, U, G and C on Na+- montmorillonite. The extent of catalysis had been found to depend upon the magnitude of the negative charge on the montmorillonite lattice, the number of cations associated with it and the pH at which the reaction is promoted (Aldersley et al. 2012).
We are developing Terahertz (THz) spectroscopy as a novel experimental approach for studying the adsorption and desorption of biomolecules in clay minerals and for studying biomolecular catalysis in the interlayer regions of clay minerals. The dielectric properties of bentonite in the 0.2 – 1.4 THz frequency range have been experimentally determined using time-domain THz spectroscopy: the results indicate that thin layers of bentonite are rather transparent for electromagnetic waves with Thz-frequencies (Wilke et al. 2012, submitted for publication).
A related investigation seeks to determine the environments of formation of catalytic clays. Approximately 130 montmorillonite-rich clays and volcanic ashes were acquired, prepared, and chemically analyzed by X-ray fluorescence, and a subset was analyzed by X-ray diffraction. The results have been used to constrain the natural environments and original volcanic ash compositions that led to the formation of catalytically active montmorillonite. The possible implications of these results for the environments, processes, and materials that may have been present on the Hadean Earth are the subject of a manuscript in preparation.
PROJECT INVESTIGATORS:James Ferris
Project InvestigatorPrakash Joshi
PROJECT MEMBERS:John Delano
RELATED OBJECTIVES:Objective 3.1
Sources of prebiotic materials and catalysts
Origins and evolution of functional biomolecules