Hannover 2010 – scientific programme
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MO: Fachverband Molekülphysik
MO 5: Femtosecond Spectroscopy I
MO 5.3: Talk
Tuesday, March 9, 2010, 14:30–14:45, F 102
Ultrafast Two-Dimensional IR Photon Echo Measurements of Hydrated DNA — •Ming Yang, Łukasz Szyc, Erik T.J. Nibbering, and Thomas Elsaesser — Max Born Insitute for Nonlinear Optics and Short Pulse Spectroscopy, Max Born Strasse 2A, D-12489 Berlin, Germany
Biomolecular structure and function are strongly determined by the interactions with the solvent water. The ultrafast dynamical nature of hydration facilitate efficient energy transfer between these biomolecules and the surrounding water shells. We investigate the ultrafast dynamics of NH and OH stretching excitations of an adenine-thymine (A-T) DNA oligomer with two-dimensional infrared photon echo spectroscopy. By controlling the water content of the DNA films we distinguish the contributions of the NH stretching transitions of the DNA bases from the OH stretching vibrations of water. At 0% relative humidity, with only few water molecules present near the phosphate groups, the 2D spectra show diagonal peaks of the NH stretching modes of the A and T bases around 3200 and 3320 cm−1. Off-diagonal peaks indicate vibrational couplings between these modes. At 92% relative humidity, where the DNA oligomer is fully hydrated, we observe the additional water OH stretching contribution, showing spectral diffusion on a time scale of 100 fs. Interestingly, an apparent completion of spectral diffusion for a 500 fs population waiting time suggests the key role of water mediating vibrational energy transfer between the NH stretching modes of DNA and the OH stretching modes of water.