Ultrafast electronic deactivation of UV-excited adenine and its ribo- and deoxyribonucleosides and -nucleotides: A comparative study

Abstract

The high stability of the DNA bases after UV photoexcitation is generally ascribed to their intrinsic ability to dissipate the supplied electronic energy on ultrafast time scales. The sugar-phosphate backbone of the related nucleosides and nucleotides may modulate the efficiency of these relaxation processes by hydrogen bonding and/or intramolecular energy transfer. To elucidate these effects, we performed a comparative study of the excited-state lifetimes of 9H-adenine, its nucleosides adenosine and deoxyadenosine, and its nucleotides adenosine monophosphate and deoxyadenosine monophosphate by transient electronic absorption spectroscopy under otherwise constant experimental conditions. All five adenine derivatives were found to exhibit virtually identical spectro-temporal behavior with uniform excited-state lifetimes of τ1=0.19±0.03 ps and τ2=0.45±0.05 ps. The results support a common deactivation mechanism within the adenine unit that leaves the DNA sugar-phosphate backbone groups idle.