Dynamics and couplings of N-H stretching excitations of guanosine-cytidine base pairs in solution.
N-H stretching vibrations of hydrogen-bonded guanosine-cytidine (G·C) base pairs in chloroform solution are studied with linear and ultrafast nonlinear infrared (IR) spectroscopy. Assignment of the IR-active bands in the linear spectrum is made possible by combining structural information on the hydrogen bonds in G·C base pairs with literature results of density functional theory calculations, and empirical relations connecting frequency shifts and intensity of the IR-active vibrations. A local mode representation of N-H stretching vibrations is adopted, consisting of ν(G)(NH(2))(f) and ν(C)(NH(2))(f) modes for free NH groups of G and C, and of ν(G)(NH(2))(b), ν(G)(NH), and ν(C)(NH(2))(b) modes associated with N-H stretching motions of hydrogen-bonded NH groups. The couplings and relaxation dynamics of the N-H stretching excitations are studied with femtosecond mid-infrared two-dimensional (2D) and pump-probe spectroscopy. The N-H stretching vibrations of the free NH groups of G and C have an average population lifetime of 2.4 ps. Besides a vibrational population lifetime shortening to subpicosecond values observed for the hydrogen-bonded N-H stretching vibrations, the 2D spectra reveal vibrational excitation transfer from the ν(G)(NH(2))(b) mode to the ν(G)(NH) and/or ν(C)(NH(2))(b) modes. The underlying intermode vibrational couplings are on the order of 10 cm(-1).
Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
Ming
M
Yang
Łukasz
Ł
Szyc
Katharina
K
Röttger
Henk
H
Fidder
Erik T J
ET
Nibbering
Thomas
T
Elsaesser
Friedrich
F
Temps
D020029:Base Pairing; D003562:Cytidine / Q000737:chemistry*; D006151:Guanosine / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D009584:Nitrogen / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013997:Time Factors
D012996:Solutions; D006151:Guanosine; D003562:Cytidine; D006859:Hydrogen; D009584:Nitrogen