title: N-H stretching vibrations of guanosine-cytidine base pairs in solution: ultrafast dynamics, couplings, and line shapes.
abstract: Dynamics and couplings of N-H stretching vibrations of chemically modified guanosine-cytidine (G·C) base pairs in chloroform are investigated with linear infrared spectroscopy and ultrafast two-dimensional infrared (2D-IR) spectroscopy. Comparison of G·C absorption spectra before and after H/D exchange reveals significant N-H stretching absorption in the region from 2500 up to 3300 cm(-1). Both of the local stretching modes ν(C)(NH(2))(b) of the hydrogen-bonded N-H moiety of the cytidine NH(2) group and ν(G)(NH) of the guanosine N-H group contribute to this broad absorption band. Its complex line shape is attributed to Fermi resonances of the N-H 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(-1) free N-H oscillator band and the bands centered at 3145 and 3303 cm(-1) imply N-H···O═C hydrogen bond character for both of these transitions. Time evolution illustrates that the 3303 cm(-1) band is composed of a nearly homogeneous band absorbing at 3301 cm(-1), ascribed to ν(G)(NH(2))(b), and a broad inhomogeneous band peaking at 3380 cm(-1) with mainly guanosine carbonyl overtone character. Kinetics and signal strengths indicate a <0.2 ps virtually complete population transfer from the excited ν(G)(NH(2))(b) mode to the ν(G)(NH) mode at 3145 cm(-1), suggesting lifetime broadening as the dominant source for the homogeneous line shape of the 3301 cm(-1) transition. For the 3145 cm(-1) band, a 0.3 ps population lifetime was obtained.
authors: Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2 A, 12489 Berlin, Germany. fidder@mbi-berlin.de
authors: Henk
authors: H
authors: Fidder
authors: Ming
authors: M
authors: Yang
authors: Erik T J
authors: ET
authors: Nibbering
authors: Thomas
authors: T
authors: Elsaesser
authors: Katharina
authors: K
authors: Röttger
authors: Friedrich
authors: F
authors: Temps
mesh_terms: D020029:Base Pairing; D002725:Chloroform / Q000737:chemistry; D003562:Cytidine / Q000737:chemistry*; D041961:Deuterium Exchange Measurement; D006151:Guanosine / Q000737:chemistry*; D007700:Kinetics; D012996:Solutions; D013055:Spectrophotometry, Infrared
chemical_list: D012996:Solutions; D006151:Guanosine; D003562:Cytidine; D002725:Chloroform