Ultrafast Excited-State Deactivation of 8-Hydroxy-2鈥?deoxyguanosine Studied by Femtosecond Fluorescence Spectroscopy and Quantum-Chemical Calculations
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- 作者：Pascale Changenet-Barret ; Thomas Gustavsson ; Roberto Improta ; Dimitra Markovitsi
- 刊名：Journal of Physical Chemistry A
- 出版年：2015
- 出版时间：June 11, 2015
- 年：2015
- 卷：119
- 期：23
- 页码：6131-6139
- 全文大小：424K
- ISSN：1520-5215
文摘
The fluorescence properties of the 8-hydroxy-2鈥?deoxyguanosine (8-oxo-dG) in aqueous solution at pH 6.5 are studied by steady-state spectroscopy and femtosecond fluorescence up-conversion and compared with those of 2鈥?deoxyguanine (dG) and 2鈥?deoxyguanine monophosphate (dGMP). The steady-state fluorescence spectrum of 8-oxo-dG is composed of a broad band that peaks at 356 nm and extends over the entire visible spectral region, and its fluorescence quantum yield is twice that of dG/dGMP. After excitation at 267 nm, the initial fluorescence anisotropy at all wavelengths is lower than 0.1, giving evidence of an ultrafast internal conversion (<100 fs) between the two lowest excited 蟺蟺* states (Lb and La). The fluorescence decays of 8-oxo-dG are biexponential with an average lifetime of 0.7 卤 0.1 ps, which is about two times longer than that of dGMP. In contrast with dGMP, only a moderate dynamical shift (鈭?400 vs 10鈥?00 cm鈥?) of the fluorescence spectra of 8-oxo-dG is observed on the time scale of a few picoseconds without modification of the spectral shape. PCM/TD-DFT calculations, employing either the PBE0 or the M052X functionals, provide absorption spectra in good agreement with the experimental one and show that the deactivation path is similar to that proposed for dGMP, with a fast motion toward an energy plateau, where the purine ring keeps an almost planar geometry, followed by decay to S0, via out-of-the plane motion of amino substituent.