CHAPTER 7. Nucleobases as Molecular Fossils of Prebiotic Photochemistry: Excited-state Dynamics of C2 and C6 Substituted Purines

Abstract

Many variations of the canonical nucleobases, such as different derivatives and analogues, would likely have been present in a primordial soup. Alternative combinations of molecular building blocks would conceivably have been possible to form self-replicating RNA-like structures. The nucleobases that are involved in replication selectively exhibit short excited-state lifetimes which provide high intrinsic stability against otherwise harmful UV photo-damage. The stark difference in response to UV irradiation between these structures and many of the alternative bases suggests the possibility of a photochemical selection of the molecular building blocks of life long before the advent of biological selection. It is thus conceivable that the molecular photo-properties of nucleobases are molecular fossils of the prebiotic chemistry that occurred 4 billion years ago. This chapter considers the excited-state dynamics of the purine bases by comparing a full set of canonical and alternative nucleobases formed by oxo- and amino- substitutions of purine.