title: Ultrashort fluorescence lifetimes of hydrogen-bonded base pairs of guanosine and cytidine in solution.
abstract: The optically excited electronic states of hydrogen-bonded homo- and heterodimers of guanosine (G) and deoxycytidine (C) were investigated by femtosecond fluorescence up-conversion spectroscopy. The base pairs were prepared in CHCl(3) solution by employing tert-butyldimethylsilyl (TBDMS) groups at the OH positions of the ribose (G) or deoxyribose (C) moieties to enhance the solubilities of the nucleosides in organic solvents. The H-bonded complexes that were obtained were characterized by FTIR spectroscopy. Fluorescence lifetime measurements were performed following electronic excitation at a series of UV wavelengths from lambda(pump) = 294 nm, close to the electronic origins of the bases, to lambda(pump) = 262 nm, where significant excess vibronic energy is deposited in the molecules, at nucleoside concentrations of c(0) = 0.1 and 1.0 mM. The experimental results revealed the existence of an ultrafast deactivation pathway for the optically prepared electronically excited state(s) of the G.C Watson-Crick base pair, which was found to have a lifetime of tau(GC) = 0.30(3) ps (with 2sigma error limits) irrespective of the pump wavelength. A similar short decay time, tau(GG) = 0.32(2) ps, was observed for the respective excited G.G homodimer. In contrast, the excited G monomer displayed a significantly longer-lived and wavelength-dependent deactivation, requiring three time constants, between 0.43(6) ps < or = tau(G,1) < or = 1.2(1) ps, 4.2(8) ps < or = tau(G,2) < or = 8(1) ps, and tau(G,3) = 195(32) ps. Self-complexation of C, on the other hand, led to a longer-lived excited state with a lifetime estimated between 1 ps < or = tau(CC) < or = 10 ps, compared to the dominant initial subpicosecond decay time of the C monomer of tau(C,1) = 0.80(4) ps.
authors: Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24098 Kiel, Germany. schwalb@phc.uni-kiel.de
authors: Nina K
authors: NK
authors: Schwalb
authors: Thomas
authors: T
authors: Michalak
authors: Friedrich
authors: F
authors: Temps
mesh_terms: D020029:Base Pairing; D003562:Cytidine / Q000737:chemistry*; D006151:Guanosine / Q000737:chemistry*; D006860:Hydrogen Bonding; D012996:Solutions / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013997:Time Factors
chemical_list: D012996:Solutions; D006151:Guanosine; D003562:Cytidine