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One-electron oxidation of ds(5'-GGG-3') and ds(5'-G(8OG)G-3') and the nature of hole distribution: A density functional theory (DFT) study

Abstract

Of particular interest in radiation-induced charge transfer processes in DNA is the extent of hole localization immediately after ionization and subsequent relaxation. To address this, we considered double stranded oligomers containing guanine (G) and 8-oxoguanine (8OG), i.e., ds(5′-GGG-3′) and ds(5′-G8OGG-3′) in B-DNA conformation. Using DFT, we calculated a variety of properties, viz., vertical and adiabatic ionization potentials, spin density distributions in oxidized stacks, solvent and solute reorganization energies and one-electron oxidation potential (Eo) in the aqueous phase. Calculations for the vertical state of the -GGG- cation radical showed that the spin was found mainly (67%) on the middle G. However, upon relaxation to the adiabatic -GGG- cation radical, the spin localized (96%) to the 5′-G, as observed in experiments. Hole localizations on the middle G and 3′-G were higher in energy by 0.5 kcal/mol and 0.4 kcal/mol respectively than that of 5′-G. In -G8OGG- cation radical, the spin localized only on the 8OG in both vertical and adiabatic states. The calculated vertical ionization potentials of -GGG- and -G8OGG- stacks were found to be lower than that of the vertical ionization potential of a single G in DNA. The calculated Eo of -GGG- and –G8OGG- stacks are 1.15 and 0.90 V which owing to stacking effects are substantially lower than the corresponding experimental Eo values of their monomers (1.49 and 1.18 V). SOMO to HOMO level switching is observed in these oxidized stacks. Consequently, our calculations predict that local double oxidations in DNA will form triplet diradical states which are especially significant for high LET radiations.

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Supplementary files

Article information


Submitted
18 Nov 2019
Accepted
31 Jan 2020
First published
03 Feb 2020

Phys. Chem. Chem. Phys., 2020, Accepted Manuscript
Article type
Paper

One-electron oxidation of ds(5'-GGG-3') and ds(5'-G(8OG)G-3') and the nature of hole distribution: A density functional theory (DFT) study

A. Kumar, A. Adhikary, M. D. Sevilla and D. Close, Phys. Chem. Chem. Phys., 2020, Accepted Manuscript , DOI: 10.1039/C9CP06244K

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