Details

Autor(en) / Beteiligte

• Sobolewski, Andrzej L.
• Domcke, Wolfgang
• C. Hättig

Titel

Tautomeric Selectivity of the Excited-State Lifetime of Guanine/Cytosine Base Pairs: The Role of Electron-Driven Proton-Transfer Processes

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2005-12, Vol.102 (50), p.17903-17906

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2005

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• The UV spectra of three different conformers of the guanine/cytosine base pair were recorded recently with UV-IR double-resonance techniques in a supersonic jet [Abo-Riziq, A., Grace, L, Nir, E., Kabelac, M., Hobza, P. & de Vries, M. S. (2005) Proc. Natl. Acad. Sci. USA 102, 20-23]. The spectra provide evidence for a very efficient excited-state deactivation mechanism that is specific for the Watson-Crick structure and may be essential for the photo-stability of DNA. Here we report results of ab initio electronic-structure calculations for the excited electronic states of the three lowest-energy conformers of the guanine/cytosine base pair. The calculations reveal that electron-driven interbase proton-transfer processes play an important role in the photochemistry of these systems. The exceptionally short lifetime of the UV-absorbing states of the Watson-Crick conformer is tentatively explained by the existence of a barrierless reaction path that connects the spectroscopic$^1\pi\pi^*$excited state with the electronic ground state via two electronic curve crossings. For the non-Watson-Crick structures, the photochemically reactive state is located at higher energies, resulting in a barrier for proton transfer and, thus, a longer lifetime of the UV-absorbing$^1\pi\pi^*$state. The computational results support the conjecture that the photochemistry of hydrogen bonds plays a decisive role for the photostability of the molecular encoding of the genetic information in isolated DNA base pairs.