Life as we know it relies on a collection of catalytic and informational polymers to perform the functions necessary to its survival. Thus, polymers must have played essential roles in the emergence of the first living cells.On the early Earth, the non-enzymatic synthesis of such polymeric materials did likely occur in an aqueous medium containing monomers at low concentrations. This environment represents a clear hurdle to the synthesis of long polymers as it tends to inhibit polymerization and favors the reverse reaction (hydrolysis). It was therefore surmised that polymerization could have occurred in a distinct structured environment that would permit a local increase in the monomer concentration, reduce water activity and protect monomers/polymers from hydrolysis. Several types of structured environments, among them the eutectic phase in water-ice have been proposed. The eutectic phase might be of particular interest since space exploration has established that water exists on Mars, Europa, Enceladus, and comets, mostly as ice. Ice deposits may also have existed on the early Earth.Metal-ion catalyzed condensation of activated monomers into RNA polymers proceed in the water-ice eutectic phase rather efficiently, delivering RNA analogs with heterogeneous linkages which might inhibit polymer activity or/and the replication of active RNAs. However, we have recently demonstrated the catalytic power of a dipeptide, SerHis, for the formation of phosphodiester bonds in this heterogeneous medium. This dipeptide catalysis delivers significantly higher yield of the 3�-5�linked oligomers. Finally, ribozyme activity has been detected in a water-ice environment and selection for cold-adapted ribozyme seems possible.All these result suggest that the cold conditions and the resulting eutectic phase formation perform a form of quasi-compartmentalization, whose usefulness extends beyond simple reactions, such metal-ion catalyzed reactions. Thus, such heterogenous media could have contributed to the emergence of an RNA world.

Eutectic phases in water-ice: An efficient medium for biopolymerization

243rd National Meeting (2012)

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