Hamburg 2009 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 7: Femtosekundenspektroskopie 1
MO 7.3: Vortrag
Dienstag, 3. März 2009, 11:00–11:15, VMP 6 HS-F
Ultrafast vibrational dynamics of hydrated DNA — •Łukasz Szyc, Jason R. Dwyer, Ming Yang, Erik T. J. Nibbering, and Thomas Elsaesser — Max-Born-Institute, D-12489 Berlin, Germany
Determination of the dynamics and interactions of water molecules with DNA is of utmost importance in understanding the structure and function of DNA. Here we use polarization-sensitive two-colour IR pump-probe spectroscopy to discern the vibrational dynamics of N-H stretching excitations of DNA oligomers containing 23 alternating adenine-thymine base pairs from the O-H stretching excitations of solvation shell water molecules, which are strongly overlapping in the linear absorption spectrum. For a DNA film at 0 % relative humidity (r.h.), where the number of water molecules per base pair is typically two, lifetimes of approximately 0.5 ps are found for N-H and O-H stretching modes. The transient pump-probe anisotropies demonstrate the coupling of different N-H stretching modes. Fully hydrated DNA films show similar N-H stretching bands as at 0 % r.h. and two types of O-H stretching responses. An O-H stretching band with maximum at 3500 cm−1, limited spectral diffusion and population kinetics similar to 0 % r.h. is attributed to water molecules directly interacting with the DNA oligomers. O-H stretching excitations with a 200 fs lifetime, broad absorption and a hot ground state formed by vibrational relaxation are assigned to water molecules weakly interacting with DNA.