Deliberate Functionalization And The Consequential Electronic Relaxation Pathways Of The Pyrimidine Chromophore

The nucleic acid bases that we know today are thought to have originated from simple precursors also referred to as proto-biotic RNA. These molecular ancestors of RNA and DNA may have formed from a vast number of organic compounds found on early Earth and/or delivered by meteorite infall. Understanding the evolution of chemical synthesis ranging from those precursors to today’s canonical nucleobases is essential in answering questions to the chemical origins of life. Among other factors, ultraviolet radiation (UVR) from the sun should have played a key role in shaping and selecting the building blocks of life. Whether the carbonyl and/or amino group substituents played any role in regulating the photostability of the canonical pyrimidine nucleobases is currently unknown. The biological relevance of the pyrimidine chromophore and its carbonyl- and amino-substituted derivatives make these molecules excellent candidates for investigating how their interaction with UVR may have enabled the selection of the RNA and DNA pyrimidine nucleobases on early Earth. Time-resolved spectroscopic results, complemented with quantum-chemical calculations, will be presented, which lend support to the idea that functionalization at the C2 and C4 positions of the pyrimidine chromophore has a preponderant role in controlling the inherent electronic relaxation mechanisms and photostability of the DNA and RNA pyrimidine nucleobases and their derivatives. \vspace{5mm}The authors acknowledge the National Science Foundation (Grant No. CHE-1800052) for financial support