Charge Migration Phenomena in γ-Irradiated Costacking Complexes of DNA Nucleotides: I. A Computer-Assisted ESR Analysis of dAMP · dTMP Complexes in Frozen Solution

Gregoli, Silvano; Olast, M.; Bertinchamps, Albert

doi:10.2307/3574585

Cited by 20 publications

(9 citation statements)

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“…In the first, the SP •+ radical is generated beyond the radius of an ionization cluster (described in radiation chemical jargon as a spur, blob, or short track); in this case, a neutral deoxyribose radical, SP(−H) • , will be trapped and be observable by EPR at 4 K. When the samples are warmed to room temperature, a large fraction (∼90%) of the radicals trapped at 4 K are annealed out , due to combination reactions such as reactions 3, 4, and 5 but primarily via reactions within the base stack, e.g., Pyr •- + Base •+ . Warming the sample mobilizes Base •+ (primarily as Gua •+ ), allowing it to hop between guanines. , If Gua •+ comes close enough to a deoxyribose radical, reaction 3 may occur. In this circumstance, however, the deoxyribose radicals are detectable at 4 K, a temperature where Gua •+ is for the most part immobilized by reversible deprotonation at N1.…”

Section: Discussionmentioning

confidence: 99%

An Investigation into the Mechanisms of DNA Strand Breakage by Direct Ionization of Variably Hydrated Plasmid DNA

2006

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The mechanisms by which ionizing radiation directly causes strand breaks in DNA were investigated by comparing the chemical yield of DNA-trapped free radicals to the chemical yield of DNA single strand break (ssb) and double strand break (dsb), as a function of hydration (Gamma). Solid-state films of plasmid pUC18, hydrated to 2.5 < Gamma < 22.5 mol, were X-irradiated at 4 K, warmed to room temperature, and dissolved in water. Free radical yields were determined by EPR at 4 K. With use of the same samples, Gel electrophoresis was used to measure the chemical yield of total strand breaks, which includes prompt plus heat labile ssb; G'total(ssb) decreased from 0.092 +/- 0.016 micromol/J at Gamma= 2.5 to 0.066 +/- 0.008 micromol/J at Gamma= 22.5. Most provocative is that at Gamma= 2.5 the yield of total ssb exceeds the yield of trapped deoxyribose radicals: G'total(ssb) - G'sugar(fr) = 0.06 +/- 0.02 micromol/J. Nearly 2/3 of the strand breaks are derived from precursors other than radicals trapped on the deoxyribose moiety. To account for these nonradical precursors, we hypothesize that strand breaks are produced by two one-electron oxidations at a single deoxyribose residue within an ionization cluster.

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Section: Discussionmentioning

confidence: 99%

An Investigation into the Mechanisms of DNA Strand Breakage by Direct Ionization of Variably Hydrated Plasmid DNA

2006

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“…The procedure of Gassman and Mansfield29 was followed, except that deuterium was used in place of hydrogen in the catalytic hydrogenation step: 'H NMR (200 MHz, acetone-</6) & 0.74 (d, J = 1.9 Hz, 2 H), 1.06 (dtt, J = 10.5, 2.0, 2.0 Hz, 1 H), 1.16 (d, J = 10.5 Hz, 1 H), 5.05 (d, / = 2.0 Hz, 2 H); 2H NMR (61.4 MHz, C6D6) 6 0.79. 2,3,4,5,. Cyclopentadiene-rf6 was synthesized according to the procedure of Lambert and Finzel.30 A 10% NaOD-D20 solution was prepared by adding Na (11 g) in portions to 100 mL of D20 cooled to 0 °C.…”

Section: Methodsmentioning

confidence: 99%

“…(1) The automorphism group Aut(G,) of this graph consists of two permutations: II = Aug(G,) = (ir,,ir2| where ir, = (1)(2)(3)(4)(5)(6)(7)(8) and *2 = (1)(2) (3,6) (4,7)(5,8). ( 2) Calculate the cycle index for each permutation:…”

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confidence: 99%