CHAPTER 9: Photochemistry of RNA, RNA Monomers, and Plausible Prebiotic Precursors

Sunlight is the primary source of energy to promote change on Earth. In this context, ultraviolet radiation can be thought as a catalyst of chemical change to refine chemical feedstocks and facilitate their transformations into the building blocks of life. To establish reasonable environmental constraints for the chemical origins of life, it is central to understand how the photochemical reactivity or photochemical resistance of prebiotic molecules might have supported the formation of the RNA monomers on the Earth's surface and particularly in aqueous solution. In this chapter, the photochemistry of the RNA monomers and several conceivably important prebiotic precursors are reviewed. The emphasis is on delineating the primary electronic relaxation or photochemical reaction pathways that may have enabled the accumulation and the selection of the RNA monomers as the building blocks of life during prebiotic times. Finally, the moderately investigated photochemistry of RNA is summarized and contrasted to that of DNA. It is surmised that the enhanced structural rigidity and the increased excitation delocalization length in RNA may have conspired during prebiotic times for RNA oligomers to prosper under the otherwise harsh ultraviolet radiation conditions of early Earth.