Work Group Prof. Dr. F. Temps

Isolated DNA & RNA bases

The four main natural DNA bases adenine (Ade), cytosine (Cyt), guanine (Guo) and thymine (Thy), the RNA base uracil (Ura) stand out for extraordinarily high UV-photostabilities owing to ultrafast, highly efficient radiationless electronic deactivation mechanisms, dissipating the dangerous energy of an absorbed UV photon before profound damage of the molecules by a photo-induced chemical reaction can occur. It has been speculated that this high photostability has been a deciding factor in the selection of the major DNA and RNA bases for the genomic code during the evolution of life on Earth at the earliest times before the ozone layer provided efficient UV protection. The underlying basic photophysical mechanisms are now understood to involve conical intersections (CoIns) between the excited and ground electronic states mediating the ultrafast relaxation processes. Much less is known about the fine differences of the dynamics among the many tautomers and isomers of the canonical nucleobases, e.g. 9H-adenine, 7H-adenine, or 2-aminopurine as a highly fluorescent structural isomer of adenine (= 6-aminopurine).   

 DNA bases 
 
Structures of the canonical natural DNA and RNA bases and selected rare RNA bases.

 

To elucidate the fine structural details affecting the photophysical dynamics, we investigate the main bases and their nucleosides and nucleotides in solution in water and other solvents in comparison to selected tautomeric and isomeric structures and the many rare natural DNA and RNA bases. The currrent record holder for the fastest electronic deactivation is inosine. Particular interest is currently paid to the difference between 9H- and 7H-adenine.

Important papers:

  • K. Röttger, R. Siewertsen, F. Temps, "Ultrafast Electronic Deactivation Dynamics of the Rare Nucleobase Hypoxanthine", Chem. Phys. Lett. 536, 140 - 146 (2012). DOI: 10.1016/j.cplett.2012.03.106
  • T. Pancur, N. K. Schwalb, F. Renth, F. Temps, "Femtosecond Fluorescence Up-Conversion Spectroscopy of Adenine and Adenosine: Experimental Evidence for the πσ* State?" Chem. Phys. 313, 199 - 212 (2005).