Heyne, K; Krishnan, GM; Kühn, O

JOURNAL OF PHYSICAL CHEMISTRY B 2008, 112(26), p. 7909-7915

The identification and characterization of NH₂ hydrogen-bonded stretching vibrations (v(NH₂)) in DNA oligomers is usually hampered by the all-dominating absorption of the water stretching band in the spectral range of 3050-3600 cm^-1. Here, we use the two-color IR pump-probe technique to overcome the limitations of linear absorption spectroscopy by exciting adenine-thymine A-T oligomer vibrations in the fingerprint region and analyzing induced transient spectral changes in the v(NH₂) spectral region. These transient changes are related to anharmonic couplings to the modes excited in the fingerprint region and to modes populated by intra- and intermolecular energy redistribution and relaxation. The combination of calculated anharmonic coupling parameters and experimental transient IR data allows the assignment of a transition at 3215 cm^-1 to the v(NH₂) vibration of adenine in dA₂₀-dT₂₀ DNA oligomers.

DOI 10.1021/jp711262y