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Dresden 2011 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy II

MO 9.5: Vortrag

Dienstag, 15. März 2011, 11:45–12:00, TOE 317

Ultrafast Dynamics of N-H Stretching Excitations of Guanosine-Cytidine Base Pairs in Solution — •Ming Yang1, Łukasz Szyc1, Katharina Röttger2, Henk Fidder1, Erik T. J. Nibbering1, Thomas Elsaesser1, and Friedrich Temps21Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Str. 2A, 12489 Berlin, Germany — 2Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany

In DNA hydrogen bonds (h-bonds) between the nucleobases play a key role. We study the N-H stretching vibrations of h-bonded guanosine-cytidine (GC) base pairs in chloroform solution with linear and ultrafast nonlinear infrared (IR) spectroscopy. We assign the IR-active transitions by combining structural information on the h-bonds in the GC pairs with literature on DFT calculations, and empirical relations connecting frequency shifts and intensities of the IR-active vibrations. We adopt a model of local five N-H stretching vibrations, describing motions of free NH groups of G and C, and h-bonded NH groups between G and C, to interpret the femtosecond two-dimensional (2D) photon echo and pump-probe measurements in terms of couplings and relaxation dynamics. The free N-H stretching vibrations of G and C have a population lifetime of  2.4 ps. Besides a vibrational population lifetime shortening to subpicosecond values observed for the h-bonded N-H stretching vibrations, the 2D spectra reveal vibrational excitation transfer from the 3303 cm−1 G(NH2) to the 3145 cm−1 G(N-H⋯N)and C(NH2) modes on a time scale of 1 ps.

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