Guanine Radicals Generated in Telomeric G-Quadruplexes by Direct Absorption of Low-Energy UV Photons: Effect of Potassium Ions

Evangelos Balanikas (1) , Akos Banyasz (2, 1) , Gérard Baldacchino (1) , Dimitra Markovitsi (1)

1 LIDyl - Laboratoire Interactions, Dynamiques et Lasers (ex SPAM)
2 LC - Laboratoire de Chimie - UMR5182

The study deals with the primary species, ejected electrons, and guanine radicals, leading to oxidative damage, that is generated in four-stranded DNA structures (guanine quadruplexes) following photo-ionization by low-energy UV radiation. Performed by nanosecond transient absorption spectroscopy with 266 nm excitation, it focusses on quadruplexes formed by folding of GGG(TTAGGG)$_3$ single strands in the presence of K$^+$ ions, TEL21/K$^+$. The quantum yield for one-photon ionization (9.4 × 10$^{−3}$) was found to be twice as high as that reported previously for TEL21/Na$^+$. The overall population of guanine radicals decayed faster, their half times being, respectively, 1.4 and 6.7 ms. Deprotonation of radical cations extended over four orders of magnitude of time; the faster step, concerning 40% of their population, was completed within 500 ns. A reaction intermediate, issued from radicals, whose absorption spectrum peaked around 390 nm, was detected.

Keywords: oxidative damage; photo-ionization; DNA; guanine-quadruplexes; electron holes; guanine radicals; reaction dynamics; time-resolved spectroscopy

Domains: Chemical Physics [physics.chem-ph]

Evangelos Balanikas, Akos Banyasz, Gérard Baldacchino, Dimitra Markovitsi. Guanine Radicals Generated in Telomeric G-Quadruplexes by Direct Absorption of Low-Energy UV Photons: Effect of Potassium Ions. Molecules, 2020, 25 (9), pp.2094. ⟨10.3390/molecules25092094⟩. ⟨cea-02571985⟩