The Kinetic Deuterium Isotope Effect as a Probe of a Proton Coupled Electron Transfer Mechanism in the Oxidation of Guanine by 2-Aminopurine Radicals

Vladimir Shafirovich, Alexander Dourandin, Natalia P. Luneva, Nicholas Geacintov

Research output: Contribution to journalArticle

Abstract

Photoexcitation of 2-aminopurine riboside (2APr, 2-amino-9-β-D-ribofuranosylpurine) and 2-aminopurine (2AP) in oxygenated aqueous buffer solutions (pH 7.0) with 308 nm XeCl excimer laser pulses (fwhm = 12 ns, ca. 70 mJ/pulse/cm 2) results in the consecutive two-photon ionization of the aromatic 2APr (or 2AP) residues. In neutral solutions, the 2APr (or 2AP) radical cations rapidly deprotonate (<100 ns). The 2APr(-H) · (or 2AP(-H) · neutral radicals thus formed reversibly oxidize 2-deoxyguanosine 5′-monophosphate (dGMP) on μs time scales, resulting in the formation of dGMP(-H) · neutral radicals. Transient absorption measurements show that a remarkable solvent isotope effect is observed on the kinetics of oxidation of dGMP by 2APr(-H) · (or 2AP(-H) ·) radicals in H 2O and D 2O solutions. In H 2O, the rate constants of dGMP(-H) · formation, as well as the rate constants of the reverse reaction of the 2APr (or 2AP) oxidation by dGMP(-H) · is larger than in D 2O by a factor of 1.5-2. This kinetic isotope effect indicates that the electron-transfer reaction from dGMP to 2APr(-H) · (or to 2AP(-H) ·), and the reverse electron transfer from 2APr (or 2AP) to dGMP(-H) ·, is coupled to a deprotonation of the primary electron-transfer radical cation products, dGMP ·+ and 2APr ·+ (or 2AP ·+). Therefore, these reactions, involving redox equilibria between different nucleobases, can be considered in terms of proton-coupled electron-transfer reactions.

Original languageEnglish (US)
Pages (from-to)137-139
Number of pages3
JournalJournal of Physical Chemistry B
Volume104
Issue number1
StatePublished - Jan 13 2000

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2-Aminopurine
guanines
Deuterium
Guanine
Isotopes
isotope effect
Protons
deuterium
electron transfer
Oxidation
oxidation
Kinetics
protons
Electrons
probes
kinetics
Rate constants
Positive ions
Deprotonation
Photoexcitation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

The Kinetic Deuterium Isotope Effect as a Probe of a Proton Coupled Electron Transfer Mechanism in the Oxidation of Guanine by 2-Aminopurine Radicals. / Shafirovich, Vladimir; Dourandin, Alexander; Luneva, Natalia P.; Geacintov, Nicholas.

In: Journal of Physical Chemistry B, Vol. 104, No. 1, 13.01.2000, p. 137-139.

Research output: Contribution to journalArticle

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abstract = "Photoexcitation of 2-aminopurine riboside (2APr, 2-amino-9-β-D-ribofuranosylpurine) and 2-aminopurine (2AP) in oxygenated aqueous buffer solutions (pH 7.0) with 308 nm XeCl excimer laser pulses (fwhm = 12 ns, ca. 70 mJ/pulse/cm 2) results in the consecutive two-photon ionization of the aromatic 2APr (or 2AP) residues. In neutral solutions, the 2APr (or 2AP) radical cations rapidly deprotonate (<100 ns). The 2APr(-H) · (or 2AP(-H) · neutral radicals thus formed reversibly oxidize 2-deoxyguanosine 5′-monophosphate (dGMP) on μs time scales, resulting in the formation of dGMP(-H) · neutral radicals. Transient absorption measurements show that a remarkable solvent isotope effect is observed on the kinetics of oxidation of dGMP by 2APr(-H) · (or 2AP(-H) ·) radicals in H 2O and D 2O solutions. In H 2O, the rate constants of dGMP(-H) · formation, as well as the rate constants of the reverse reaction of the 2APr (or 2AP) oxidation by dGMP(-H) · is larger than in D 2O by a factor of 1.5-2. This kinetic isotope effect indicates that the electron-transfer reaction from dGMP to 2APr(-H) · (or to 2AP(-H) ·), and the reverse electron transfer from 2APr (or 2AP) to dGMP(-H) ·, is coupled to a deprotonation of the primary electron-transfer radical cation products, dGMP ·+ and 2APr ·+ (or 2AP ·+). Therefore, these reactions, involving redox equilibria between different nucleobases, can be considered in terms of proton-coupled electron-transfer reactions.",
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