Mechanistic aspects of hydration of guanine radical cations in DNA

Yekaterina Rokhlenko, Jean Cadet, Nicholas Geacintov, Vladimir Shafirovich

Research output: Contribution to journalArticle

Abstract

The mechanistic aspects of hydration of guanine radical cations, G •+ in double- and single-stranded oligonucleotides were investigated by direct time-resolved spectroscopic monitoring methods. The G•+ radical one-electron oxidation products were generated by SO4•- radical anions derived from the photolysis of S 2O8 2- anions by 308 nm laser pulses. In neutral aqueous solutions (pH 7.0), after the complete decay of SO4•- radicals (∼5 μs after the actinic laser flash) the transient absorbance of neutral guanine radicals, G(-H)• with maximum at 312 nm, is dominant. The kinetics of decay of G(-H)• radicals depend strongly on the DNA secondary structure. In double-stranded DNA, the G(-H)• decay is biphasic with one component decaying with a lifetime of ∼2.2 ms and the other with a lifetime of ∼0.18 s. By contrast, in single-stranded DNA the G(-H)• radicals decay monophasically with a ∼ 0.28 s lifetime. The ms decay component in double-stranded DNA is correlated with the enhancement of 8-oxo-7,8-dihydroguanine (8-oxoG) yields which are ∼7 greater than in single-stranded DNA. In double-stranded DNA, it is proposed that the G(-H)• radicals retain radical cation character by sharing the N1-proton with the N3-site of C in the [G•+:C] base pair. This [G(-H)•:H +C G•+:C] equilibrium allows for the hydration of G•+ followed by formation of 8-oxoG. By contrast, in single-stranded DNA, deprotonation of G•+ and the irreversible escape of the proton into the aqueous phase competes more effectively with the hydration mechanism, thus diminishing the yield of 8-oxoG, as observed experimentally.

Original languageEnglish (US)
Pages (from-to)5956-5962
Number of pages7
JournalJournal of the American Chemical Society
Volume136
Issue number16
DOIs
StatePublished - Apr 23 2014

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Guanine
Hydration
Cations
Single-Stranded DNA
DNA
Positive ions
Anions
Protons
Lasers
Deprotonation
Photolysis
Oligonucleotides
Base Pairing
Negative ions
Laser pulses
Electrons
Oxidation
Kinetics
Monitoring
8-hydroxyguanine

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Mechanistic aspects of hydration of guanine radical cations in DNA. / Rokhlenko, Yekaterina; Cadet, Jean; Geacintov, Nicholas; Shafirovich, Vladimir.

In: Journal of the American Chemical Society, Vol. 136, No. 16, 23.04.2014, p. 5956-5962.

Research output: Contribution to journalArticle

Rokhlenko, Yekaterina ; Cadet, Jean ; Geacintov, Nicholas ; Shafirovich, Vladimir. / Mechanistic aspects of hydration of guanine radical cations in DNA. In: Journal of the American Chemical Society. 2014 ; Vol. 136, No. 16. pp. 5956-5962.
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abstract = "The mechanistic aspects of hydration of guanine radical cations, G •+ in double- and single-stranded oligonucleotides were investigated by direct time-resolved spectroscopic monitoring methods. The G•+ radical one-electron oxidation products were generated by SO4•- radical anions derived from the photolysis of S 2O8 2- anions by 308 nm laser pulses. In neutral aqueous solutions (pH 7.0), after the complete decay of SO4•- radicals (∼5 μs after the actinic laser flash) the transient absorbance of neutral guanine radicals, G(-H)• with maximum at 312 nm, is dominant. The kinetics of decay of G(-H)• radicals depend strongly on the DNA secondary structure. In double-stranded DNA, the G(-H)• decay is biphasic with one component decaying with a lifetime of ∼2.2 ms and the other with a lifetime of ∼0.18 s. By contrast, in single-stranded DNA the G(-H)• radicals decay monophasically with a ∼ 0.28 s lifetime. The ms decay component in double-stranded DNA is correlated with the enhancement of 8-oxo-7,8-dihydroguanine (8-oxoG) yields which are ∼7 greater than in single-stranded DNA. In double-stranded DNA, it is proposed that the G(-H)• radicals retain radical cation character by sharing the N1-proton with the N3-site of C in the [G•+:C] base pair. This [G(-H)•:H +C G•+:C] equilibrium allows for the hydration of G•+ followed by formation of 8-oxoG. By contrast, in single-stranded DNA, deprotonation of G•+ and the irreversible escape of the proton into the aqueous phase competes more effectively with the hydration mechanism, thus diminishing the yield of 8-oxoG, as observed experimentally.",
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