N鈥揌 Stretching Vibrations of Guanosine鈥揅ytidine Base Pairs in Solution: Ultrafast Dynamics, Couplings, and Line Shapes

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• 作者：Henk Fidder ; Ming Yang ; Erik T. J. Nibbering ; Thomas Elsaesser ; Katharina R枚ttger ; Friedrich Temps
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：February 7, 2013
• 年：2013
• 卷：117
• 期：5
• 页码：845-854
• 全文大小：714K
• 年卷期：v.117,no.5(February 7, 2013)
• ISSN：1520-5215

文摘

Dynamics and couplings of N鈥揌 stretching vibrations of chemically modified guanosine鈥揷ytidine (G路C) base pairs in chloroform are investigated with linear infrared spectroscopy and ultrafast two-dimensional infrared (2D-IR) spectroscopy. Comparison of G路C absorption spectra before and after H/D exchange reveals significant N鈥揌 stretching absorption in the region from 2500 up to 3300 cm^鈥?. Both of the local stretching modes 谓_C(NH₂)_b of the hydrogen-bonded N鈥揌 moiety of the cytidine NH₂ group and 谓_G(NH) of the guanosine N鈥揌 group contribute to this broad absorption band. Its complex line shape is attributed to Fermi resonances of the N鈥揌 stretching modes with combination and overtones of fingerprint vibrations and anharmonic couplings to low-frequency modes. Cross-peaks in the nonlinear 2D spectra between the 3491 cm^鈥? free N鈥揌 oscillator band and the bands centered at 3145 and 3303 cm^鈥? imply N鈥揌路路路O鈺怌 hydrogen bond character for both of these transitions. Time evolution illustrates that the 3303 cm^鈥? band is composed of a nearly homogeneous band absorbing at 3301 cm^鈥?, ascribed to 谓_G(NH₂)_b, and a broad inhomogeneous band peaking at 3380 cm^鈥? with mainly guanosine carbonyl overtone character. Kinetics and signal strengths indicate a <0.2 ps virtually complete population transfer from the excited 谓_G(NH₂)_b mode to the 谓_G(NH) mode at 3145 cm^鈥?, suggesting lifetime broadening as the dominant source for the homogeneous line shape of the 3301 cm^鈥? transition. For the 3145 cm^鈥? band, a 0.3 ps population lifetime was obtained.