Excited state dynamics of thienoguanosine, an isomorphic highly fluorescent analogue of guanosine.
Fiche publication
Date publication
mars 2019
Journal
Chemistry (Weinheim an der Bergstrasse, Germany)
Auteurs
Membres identifiés du Cancéropôle Est :
Pr MELY Yves, Dr RICHERT Ludovic
Tous les auteurs :
Martinez-Fernandez L, Gavvala K, Sharma R, Pascal D, Richert L, Segarra Martì J, Mori M, Mely Y, Improta R
Lien Pubmed
Résumé
Thienoguanosine (thG) is an isomorphic analogue of guanosine with promising potentialities as fluorescent DNA label. As a free probe in protic solvents, thG exists in two tautomeric forms, identified as H1, the only one observed in non protic solvents, and H3 keto-amino tautomers. We here investigate the photophysics of thG in solvents of different polarity, from water to dioxane by combining time-resolved fluorescence with PCM/TD-DFT and CASSCF calculations. Fluorescence lifetimes of 14.5-20.5 ns and 7-13 ns were observed for the H1 and H3 tautomers, respectively in the tested solvents. In methanol and ethanol, an additional fluorescent decay lifetime ( ~ 3 ns) at the blue emission side (~430 nm) as well as a 0.5 ns component with negative amplitude at the red edge of the spectrum, typical of an excited-state reaction, were observed. Our computational analysis explains the solvent effects observed on the tautomeric equilibrium. The main radiative and non-radiative deactivation routes have been mapped by PCM/TD-DFT in solution and CASSCF in the gas phase. The most easily accessible conical intersection, involving an out-of plane motion of the sulphur atom in the five membered ring of thG, is separated by a sizeable energy barrier (≥ 0.4 eV) from the minimum of the spectroscopic state, which explains the large experimental fluorescence quantum yield.
Référence
Chemistry. 2019 Mar 18;: