Characterization of supramolecular polymer systems composed of prebiotically plausible recognition units

Abstract

Supramolecular polymers have a practical impact on the healthcare field as they can act as scaffolds to repair parts of organs such as the brain or heart. In addition, they can provide insight into theories relating to the origins of life. For instance, the hypothesis that RNA played a more important role in early biology, the RNA World hypothesis, would be strengthened if there were a way to show the spontaneous formation of RNA-like polymers from monomer units. However, the natural nucleobases do not assemble at the monomer level, nor do they form nucleosides readily with ribose, leading some to speculate that the first nucleobases may have been different from the ones used in biology today. This conundrum encouraged us to begin looking for alternative nucleobases that are able to self-assemble into polymers capable of storing information. Our lab has recently demonstrated that a modified 2,4,6-triaminopyrimidine (TAP) will assemble with cyanuric acid (CA) in water through interactions that are analogous to those between complementary nucleobases found in DNA and RNA. When TAP is modified at one of its three faces, it can pair through specific hydrogen bonding with CA on two of its faces, forming rosette structures. These rosettes self-assemble to form extremely long structures through the stacking of tens of thousands of rosettes. In this study we are investigating prebiotically relevant syntheses of TAP nucleosides. Using chromatography techniques and nuclear magnetic resonance we found that the unmodified TAP with D-ribose formed nucleosides in 60% yields with the major product (20%) being a C-nucleoside 5-β-ribofuranosyl-2,4,6-triaminoprymidine or TARC. TARC forms hydrogels with CA, both in the crude reaction and after purification, indicative of the formation of supramolecular polymers out of a complex mixture. The results of this study provide support for the possibility of pre-RNA molecules.