Importance of Protonation State of Guanine Radical Cation During Hole Transfer in DNA

Kawai, Kiyoshi; Osakada, Yasuko; Majima, Tetsuro

doi:10.1002/cphc.200900148

Cited by 17 publications

(20 citation statements)

References 44 publications

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“…4.5 (Adhikary et al 2009). As a result, the intra-base pair proton transfer equilibrium of the guanine cation radical in the G:C base pair (G• + :C) formed via one-electron oxidation shifts to favor protonation at the 5-Me-C and this has indeed been shown by employing laser flash photolysis of the 5-Me-C incorporated dsDNA-oligomers (Kawai et al 2009). However, replacement of C by 5-Me-C in a dsDNA-oligomer in aqueous solution at room temperature does not affect the extent of hole (unpaired spin) trapping at G sites (Kanvah and Schuster, 2004).…”

Section: Introductionmentioning

confidence: 95%

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Reactions of 5-methylcytosine cation radicals in DNA and model systems: Thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

Adhikary

Kumar

Palmer

et al. 2014

International Journal of Radiation Biology

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Purpose To study the formation and subsequent reactions of the 5-methyl-2′-deoxycytidine cation radical (5-Me-2′-dC•+) in nucleosides and DNA-oligomers and compare to one electron oxidized thymidine. Materials and methods Employing electron spin resonance (ESR), cation radical formation and its reactions were investigated in 5-Me-2′-dC, thymidine (Thd) and their derivatives, in fully double stranded (ds) d[GC*GC*GC*GC*]2 and in the 5-Me-C/A mismatched, d[GGAC*AAGC:CCTAATCG], where C* = 5-Me-C. Results We report 5-Me-2′-dC•+ production by one-electron oxidation of 5-Me-2′-dC by Cl2•− via annealing in the dark at 155 K. Progressive annealing of 5-Me-2′-dC•+ at 155 K produces the allylic radical (C-CH2•). However, photoexcitation of 5-Me-2′-dC•+ by 405 nm laser or by photoflood lamp leads to only C3′• formation. Photoexcitation of N3-deprotonated thyminyl radical in Thd and its 5′-nucleotides leads to C3′• formation but not in 3′-TMP which resulted in the allylic radical (U-CH2•) and C5′• production. For excited 5-Me-2′,3′-ddC•+, absence of the 3′-OH group does not prevent C3′• formation. For d[GC*GC*GC*GC*]2 and d[GGAC*AAGC:CCTAATCG], intra-base paired proton transferred form of G cation radical (G(N1-H)•:C(+H+)) is found with no observable 5-Me-2′-dC•+ formation. Photoexcitation of (G(N1-H)•:C(+H+)) in d[GC*GC*GC*GC*]2 produced only C1′• and not the expected photoproducts from 5-Me-2′-dC•+. However, photoexcitation of (G(N1-H)•:C(+H+)) in d[GGAC*AAGC:CCTAATCG] led to C5′• and C1′• formation. Conclusions C-CH2• formation from 5-Me-2′-dC•+ occurs via ground state deprotonation from C5-methyl group on the base. In the excited 5-Me-2′-dC•+ and 5-Me-2′,3′-ddC•+, spin and charge localization at C3′ followed by deprotonation leads to C3′• formation. Thus, deprotonation from C3′ in the excited cation radical is kinetically controlled and sugar C-H bond energies are not the only controlling factor in these deprotonations.

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Section: Introductionmentioning

confidence: 95%

“…Also, due to the electron donating methyl group, the p K a of the 5-Me-C(H + ) becomes ca. 4.7 (Kawai et al 2002, 2009) whereas the corresponding p K a of C(H + ) is ca. 4.5 (Adhikary et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Reactions of 5-methylcytosine cation radicals in DNA and model systems: Thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

Adhikary

Kumar

Palmer

et al. 2014

International Journal of Radiation Biology

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“…They are : the intra-base proton transfer process (represented as 1) within the one-electron oxidized G:C base pair, and the proton transfer processes (2, 3 and 4) from the one-electron oxidized G:C base pair to the surrounding water. 1 – 3, 8 – 11, 16 – 20 …”

Section: Introductionmentioning

confidence: 99%

“…Measurements of rate constants for hole transfer with the aid of laser flash photolysis in 5-bromocytosine incorporated ds DNA oligomers vis-à-vis in ds DNA oligomers containing cytosine yields results in accordance with this equilibrium between G• + :C and G(N1-H)•:C(+H + ). 20 …”

Section: Introductionmentioning

confidence: 99%

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Prototropic equilibria in DNA containing one-electron oxidized GC: intra-duplex vs. duplex to solvent deprotonation

Adhikary

Kumar

Munafo

et al. 2010

Phys. Chem. Chem. Phys.

183

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By use of ESR and UV-vis spectral studies, this work identifies the protonation states of one-electron oxidized G:C (viz. G•+:C, G(N1-H)•:C(+H+), G(N1-H)•:C, and G(N2-H)•:C) in a DNA oligomer d[TGCGCGCA]2. Benchmark ESR and UV-vis spectra from one electron oxidized 1-Me-dGuo are employed to analyze the spectral data obtained in one-electron oxidized d[TGCGCGCA]2 at various pHs. At pH ≥7, the initial site of deprotonation of one-electron oxidized d[TGCGCGCA]2 to the surrounding solvent is found to be at N1 forming G(N1-H)•:C at 155 K. However, upon annealing to 175 K, the site of deprotonation to the solvent shifts to an equilibrium mixture of G(N1-H)•:C and G(N2-H)•:C. For the first time, the presence of G(N2-H)•:C in a ds DNA-oligomer is shown to be easily distinguished from the other prototropic forms, owing to its readily observable nitrogen hyperfine coupling (Azz(N2)= 16 G). In addition, for the oligomer in H2O, an additional 8 G N2-H proton HFCC is found. This ESR identification is supported by a UV-vis absorption at 630 nm which is characteristic for G(N2-H)• in model compounds and oligomers. We find that the extent of photo-conversion to the C1′ sugar radical (C1′•) in the one-electron oxidized d[TGCGCGCA]2 allows for a clear distinction among the various G:C protonation states which can not be easily distinguished by ESR or UV-vis spectroscopies with this order for the extent of photo-conversion: G•+:C > G(N1-H)•:C(+H+) >> G(N1-H)•:C. We propose that it is the G•+:C form that undergoes deprotonation at the sugar and this requires reprotonation of G within the lifetime of exited state.

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Chemical Repair of Radical Damage to the GC Base Pair by DNA-Bound Bisbenzimidazoles

Anderson,

Shinde,

Andrau

et al. 2024

J. Phys. Chem. B

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The migration of an electron-loss center (hole) in calf thymus DNA to bisbenzimidazole ligands bound in the minor groove is followed by pulse radiolysis combined with time-resolved spectrophotometry. The initially observed absorption spectrum upon oxidation of DNA by the selenite radical is consistent with spin on cytosine (C), as the GC • pair neutral radical, followed by the spectra of oxidized ligands. The rate of oxidation of bound ligands increased with an increase in the ratio (r) ligands per base pair from 0.005 to 0.04. Both the rate of ligand oxidation and the estimated range of hole transfer (up to 30 DNA base pairs) decrease with the decrease in one-electron reduction potential between the GC • pair neutral radical of ca. 1.54 V and that of the ligand radicals (E 0 ′, 0.90−0.99 V). Linear plots of log of the rate of hole transfer versus r give a common intercept at r = 0 and a free energy change of 12.2 ± 0.3 kcal mol −1 , ascribed to the GC • pair neutral radical undergoing a structural change, which is in competition to the observed hole transfer along DNA. The rate of hole transfer to the ligands at distance, R, from the GC • pair radical, k 2 , is described by the relationship k 2 = k 0 exp(constant/R), where k 0 includes the rate constant for surmounting a small barrier.

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Importance of Protonation State of Guanine Radical Cation During Hole Transfer in DNA

Cited by 17 publications

References 44 publications

Reactions of 5-methylcytosine cation radicals in DNA and model systems: Thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

Reactions of 5-methylcytosine cation radicals in DNA and model systems: Thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

Prototropic equilibria in DNA containing one-electron oxidized GC: intra-duplex vs. duplex to solvent deprotonation

Chemical Repair of Radical Damage to the GC Base Pair by DNA-Bound Bisbenzimidazoles

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