Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 21: Femtosecond Spectroscopy III

MO 21.6: Talk

Thursday, March 11, 2010, 15:15–15:30, F 102

Ultrafast vibrational energy redistribution through water-phosphate interactions in hydrated DNA — •Łukasz Szyc, Ming Yang, Erik T.J. Nibbering, and Thomas Elsaesser — Max-Born-Institute, Berlin, Germany

The interaction of DNA with water plays a key role for its structural conformation and its local hydrogen bond geometries. The role of hydration shells for the ultrafast energy dissipation and the resulting changes of hydrating structures have been studied in real-time by femtosecond vibrational spectroscopy. By direct excitation of antisymmetric (PO₂)⁻ stretching oscillator we were able to measure its v=1 vibrational lifetime which is around 340 fs and is independent on sample humidity. For the 0% r.h. DNA oligomer, where only a single water molecule interacts with the phosphate group, the recorded time traces show not only an initial fast decay corresponding to v=1 ν_AS(PO₂)⁻ lifetime, but also a slow (≈ 5.5 ps) component, which reflects the time of energy delocalization within the DNA strand. In contrast, in a fully hydrated sample (92% r.h.), the slow relaxation component is completely absent. The excess vibrational energy released by the ν_AS(PO₂)⁻ decay is now mainly transferred to the surrounding water shell. This transfer is faster than the 340 fs decay of ν_AS(PO₂)⁻ and suppresses energy accumulation in the phosphate group.