Hannover 2010 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 17: Biomolecules

MO 17.3: Vortrag

Mittwoch, 10. März 2010, 17:00–17:15, F 142

Photostability of DNA building blocks — •Laura Buschhaus¹, Katharina Hunger¹, Sergey A. Kovalenko², and Karl Kleinermanns¹ — ¹Heinrich-Heine-Universität, Düsseldorf, Deutschland — ²Humbold Universität, Berlin, Deutschland

Guanosine monophosphate (GMP) solutions are studied with femtosecond and nanosecond broadband transient absorption spectroscopy. The sample was exited at 265 nm (L_b / L_a exitation) and 187 nm (solely L_a exitation) and probed between 270-1000 nm with a temporal resolution of about 100 fs at different pH. Independent of the pH, the photoinduced evolution involves ultrafast L_b - > L_a conversion (τ < < 100 fs) and exhibits the presence of wide planar plateau on L_a. For neutral GMP a barrierless path connects this region to a conical intersection (CI) with the ground state, giving account of ultrafast decay of this species. For protonated GMPH ⁺ the system decays to a stable minimum characterized by out-of-plane displacement of NH and CH groups, which explains the longer (167 ps) fluorescence lifetime. ¹n₀π* and ¹πσ* states are predicted to play a less relevant role. GC Watson-Crick base pairs are studied with sub-ps to µs time resolution. It is shown that the short-time relaxation of the base pairs is dominated by internal relaxation of the G and C moieties while pair specific contributions like G ->C proton transfer play a less significant role. Instead in GG dimers electron transfer followed by proton transfer seems to take place and the electronic spectrum of the (G-H) radical is tentatively assigned.