Heidelberg 2015 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 3: Femtosecond Spectroscopy 1

MO 3.7: Vortrag

Montag, 23. März 2015, 16:15–16:30, PH/HS1

Ultrafast photophysics of a DNA intercalated psoralen — Sascha Fröbel, •Anna Reiffers, and Peter Gilch — Heinrich-Heine-Universität Düsseldorf, Germany

After we have studied the formation of photolesions within DNA in the past (see e.g. [1]), we have now extended our studies to photolesions induced by intercalated compounds.

A model system for such compounds are psoralens. Psoralens are heterocyclic natural compounds with various applications in the research lab. Apart from this they are primarily known for their use in the treatment of common skin disorders like psoriasis and vitiligo (PUVA (psoralen + UV-A light) therapy). Their function in PUVA therapy is correlated to their intercalation into DNA. Upon photo excitation, intercalated psoralens form [2+2] cycloadducts with thymines and thus damage the host cells. However, the ultrafast photochemical and -physical processes after excitation are still fully unknown.

We have studied the interactions of an intercalated psoralen (4'-aminomethyl-4,5',8-trimethylpsoralen, AMT) with DNA by means of femtosecond transient absorption for the first time. In DNA the fluorescence lifetime is reduced to 4 ps as compared to 1.4 ns for free AMT. This prohibits the population of triplet states. Instead, an unanticipated intermediate with a lifetime of 30 ps is formed, which is assigned to an electron transfer product. Hereby, the DNA acts as an electron donor.

[1]W.J. Schreier et al., Science 2007, 315, 625./G. Ryseck et al., Chem.Phys.Chem. 2011, 12, 1880.