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Open AccessArticle

Populations and Dynamics of Guanine Radicals in DNA strands—Direct versus Indirect Generation

1
LIDYL, CEA, CNRS, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
2
Univ Lyon, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, Laboratoire de Chimie, F-69342 Lyon, France
*
Author to whom correspondence should be addressed.
Academic Editor: Chryssostomos Chatgilialoglu
Molecules 2019, 24(13), 2347; https://doi.org/10.3390/molecules24132347
Received: 22 May 2019 / Revised: 14 June 2019 / Accepted: 18 June 2019 / Published: 26 June 2019
(This article belongs to the Special Issue Biomimetic Radical Chemistry and Applications)
Guanine radicals, known to be involved in the damage of the genetic code and aging, are studied by nanosecond transient absorption spectroscopy. They are generated in single, double and four-stranded structures (G-quadruplexes) by one and two-photon ionization at 266 nm, corresponding to a photon energy lower than the ionization potential of nucleobases. The quantum yield of the one-photon process determined for telomeric G-quadruplexes (TEL25/Na+) is (5.2 ± 0.3) × 10−3, significantly higher than that found for duplexes containing in their structure GGG and GG sequences, (2.1 ± 0.4) × 10−3. The radical population is quantified in respect of the ejected electrons. Deprotonation of radical cations gives rise to (G-H1) and (G-H2) radicals for duplexes and G-quadruplexes, respectively. The lifetimes of deprotonated radicals determined for a given secondary structure strongly depend on the base sequence. The multiscale non-exponential dynamics of these radicals are discussed in terms of inhomogeneity of the reaction space and continuous conformational motions. The deviation from classical kinetic models developed for homogeneous reaction conditions could also be one reason for discrepancies between the results obtained by photoionization and indirect oxidation, involving a bi-molecular reaction between an oxidant and the nucleic acid. View Full-Text
Keywords: DNA; guanine quadruplexes; radicals; electron holes; oxidative damage; photo-ionization; time-resolved spectroscopy; inhomogeneous reactions DNA; guanine quadruplexes; radicals; electron holes; oxidative damage; photo-ionization; time-resolved spectroscopy; inhomogeneous reactions
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Balanikas, E.; Banyasz, A.; Baldacchino, G.; Markovitsi, D. Populations and Dynamics of Guanine Radicals in DNA strands—Direct versus Indirect Generation. Molecules 2019, 24, 2347.

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