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Radicals Generated in Tetramolecular Guanine Quadruplexes by Photoionization: Spectral and Dynamical Features

Akos Banyasz 1 Evangelos Balanikas 1 Lara Martinez-Fernandez 1 Gérard Baldacchino 1 Thierry Douki 2, 3 Roberto Improta 1, 4 Dimitra Markovitsi 1, *
* Corresponding author
1 DICO - Biomolécules Excitées
IRAMIS - Institut Rayonnement Matière de Saclay, LIDyl - Laboratoire Interactions, Dynamiques et Lasers (ex SPAM)
2 CIBEST - Chimie Interface Biologie pour l’Environnement, la Santé et la Toxicologie
SYMMES - SYstèmes Moléculaires et nanoMatériaux pour l’Energie et la Santé : DRF/IRIG/SYMMES
Abstract : G-quadruplexes are four-stranded DNA structures playing a key role in many biological functions and are promising for applications in the field of nanoelectronics. Characterizing the generation and fate of radical cations (electron holes) within these systems is important in relation to the DNA oxidative damage and/or conductivity issues. This study focuses on guanine radicals in G-quadruplexes formed by association of four TGGGGT strands in the presence of Na$^+$ cations, (TG4T)$_4$/Na$^+$. Using nanosecond transient spectroscopy with 266 nm excitation, we quantitatively characterize hydrated ejected electrons and three types of guanine radicals. We show that, at an energy lower by 2.7 eV than the guanine ionization potential, one-photon ionization occurs with quantum yield of (3.5 $\pm$ 0.5) × 10$^-3$. Deprotonation of the radical cations is completed within 20 $\mu$s, leading to the formation of (G-H2)$^•$ radicals, following a strongly nonexponential decay pattern. Within 10 ms, the latter undergoes tautomerization to deprotonated (G-H1)$^•$ radicals. The dynamics of the various radicals determined for (TG4T)$_4$/Na$^+$, in connection to those reported previously for telomeric G-quadruplexes TEL$_{21}$/Na$^+$, is correlated with energetic factors computed by quantum chemical methods. The faster deprotonation of radical cations in (TG4T)$_4$/Na$^+$ compared to TEL$_{21}$/Na$^+$ explains that irradiation of the former does not generate 8-oxodGuo, which is readily detected by high-performance liquid chromatography/mass spectrometry in the case of TEL$_{21}$/Na$^+$.
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Submitted on : Tuesday, December 17, 2019 - 11:24:04 AM
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Akos Banyasz, Evangelos Balanikas, Lara Martinez-Fernandez, Gérard Baldacchino, Thierry Douki, et al.. Radicals Generated in Tetramolecular Guanine Quadruplexes by Photoionization: Spectral and Dynamical Features. Journal of Physical Chemistry B, American Chemical Society, 2019, 123 (23), pp.4950-4957. ⟨10.1021/acs.jpcb.9b02637⟩. ⟨cea-02160879v1⟩



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