DNA in an aqueous environment is characterized by both well-defined hydrogen-bonded structures of base pairs and a water shell undergoing structural fluctuations on ultrafast time scales. Two-dimensional (2D) nonlinear infrared spectroscopy is applied to discern vibrational excitations of DNA and its water shell and to map their dynamics. NH and OH stretching excitations of hydrated double-stranded DNA oligomers which contain 23 alternating adenine-thymine (A-T) base pairs are separated in measurements at different hydration levels. Pronounced vibrational couplings and energy transfer occur between the different NH modes while their lineshapes are rather insensitive to the presence of a water shell. An analysis of spectral diffusion of OH stretching excitations in the water shell demonstrates a moderate slowing down of fluctuations compared to bulk water. Here, both the more rigid heterogeneous structure of the first water layer around DNA and the less efficient resonant energy transfer between water molecules are relevant.

Ultrafast vibrational dynamics of hydrated DNA studied by 2D infrared spectroscopy

244th National Meeting (2012)

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