Direct observation of the oxidation of DNA bases by phosphate radicals formed under radiation: a model of the backbone-to-base hole transfer

In irradiated DNA, by the base-to-base and backbone-to-base hole transfer processes, the hole (i.e., the unpaired spin) localizes on the most electropositive base, guanine. Phosphate radicals formed via ionization events in the DNA-backbone must play an important role in the backbone-to-base hole tr...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2018, Vol.20 (21), p.14927-14937
Main Authors: Ma, Jun, Marignier, Jean-Louis, Pernot, Pascal, Houée-Levin, Chantal, Kumar, Anil, Sevilla, Michael D, Adhikary, Amitava, Mostafavi, Mehran
Format: Article
Language:English
Subjects:
Backbone
Base Sequence
Chemical Sciences
Cytosine - chemistry
Deoxyribonucleic acid
DNA
DNA - chemistry
Electron transfer
Electropositivity
Free Radicals - chemistry
Ionization
Kinetics
Oxidation
Oxidation-Reduction
Phosphates - chemistry
Protonation
Radicals
Radiolysis
Thermodynamics
Thymine
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Summary:In irradiated DNA, by the base-to-base and backbone-to-base hole transfer processes, the hole (i.e., the unpaired spin) localizes on the most electropositive base, guanine. Phosphate radicals formed via ionization events in the DNA-backbone must play an important role in the backbone-to-base hole transfer process. However, earlier studies on irradiated hydrated DNA, on irradiated DNA-models in frozen aqueous solution and in neat dimethyl phosphate showed the formation of carbon-centered radicals and not phosphate radicals. Therefore, to model the backbone-to-base hole transfer process, we report picosecond pulse radiolysis studies of the reactions between H2PO4˙ with the DNA bases - G, A, T, and C in 6 M H3PO4 at 22 °C. The time-resolved observations show that in 6 M H3PO4, H2PO4˙ causes the one-electron oxidation of adenine, guanine and thymine, by forming the cation radicals via a single electron transfer (SET) process; however, the rate constant of the reaction of H2PO4˙ with cytosine is too low (
ISSN:1463-9076
1463-9084
DOI:10.1039/c8cp00352a