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Photophysics of Deoxycytidine and 5-Methyldeoxycytidine in Solution: A Comprehensive Picture by Quantum Mechanical Calculations and Femtosecond Fluorescence Spectroscopy (32 visite)
J Am Chem Soc (ISSN: 1520-5126electronic, 0002-7863linking), 2017 Jun 14; 139(23): 7780-7791.
Tipo di articolo: Journal Article,
Impact factor: 13.858
Impact factor a 5 anni: 12.969
Parole chiave: Non disponibili.
Url: Non disponibile.
The study concerns the relaxation of electronic excited states of the DNA nucleoside deoxycytidine (dCyd) and its methylated analogue 5-methyldeoxycytidine (5mdCyd), known to be involved in the formation of UV-induced lesions of the genetic code. Due to the existence of four closely lying and potentially coupled excited states, the deactivation pathways in these systems are particularly complex and have not been assessed so far. Here, we provide a complete mechanistic picture of the excited state relaxation of dCyd/5mdCyd in three solvents-water, acetonitrile, and tetrahydrofuran-by combining femtosecond fluorescence experiments, addressing the effect of solvent proticity on the relaxation dynamics of dCyd and 5mdCyd for the first time, and two complementary quantum mechanical approaches (CASPT2/MM and PCM/TD-CAM-B3LYP). The lowest energy pipi* state is responsible for the sub-picosecond lifetime observed for dCyd in all the solvents. In addition, computed excited state absorption and transient IR spectra allow one, for the first time, to assign the tens of picoseconds time constant, reported previously, to a dark state (nOpi*) involving the carbonyl lone pair. A second low-lying dark state, involving the nitrogen lone pair (nNpi*), does significantly participate in the excited state dynamics. The 267 nm excitation of dCyd leads to a non-negligible population of the second bright pipi* state, which affects the dynamics, acting mainly as a "doorway" state for the nOpi* state. The solvent plays a key role governing the interplay between the different excited states; unexpectedly, water favors population of the dark states. In the case of 5mdCyd, an energy barrier present on the main nonradiative decay route explains the 6-fold lengthening of the excited state lifetime compared to that of dCyd, observed for all the examined solvents. Moreover, C5-methylation destabilizes both nOpi* and nNpi* dark states, thus preventing them from being populated.
*** IBB - CNR ***
Istituto di Biostrutture e Bioimmagini, CNR, Via Mezzocannone 16, I-80134 Napoli, Italy., Dipartimento di Chimica Industriale "T. Montanari", Universita di Bologna , Viale Risorgimento 4, I-40136 Bologna, Italy., Laboratoire de Chimie UMR 5182, Univ Lyon, ENS de Lyon, CNRS, Universite Lyon 1 , F-69342 Lyon, France., LIDYL, CEA, CNRS, Universite Paris-Saclay , F-91191 Gif-sur-Yvette, France.,
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