EPR-detection of the guanosyl radical cation in aqueous solution. Quantum chemically supported assignment of nitrogen and proton hyperfine couplings

Bachler, Vinzenz; Hildenbrand, Knut

doi:10.1016/1359-0197(92)90141-2

Cited by 15 publications

(29 citation statements)

References 37 publications

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“…The simulated spectrum (black) match very well with those of the experimental spectrum (blue) of 1-Me-G(N2-H)• (see Figure 1B). We note here that the HFCC values for the C8-H atom used to simulate the experimental ESR spectrum of 1-Me-G(N2-H)• in the aqueous (D 2 O) glassy system (see Table 1) match very well with those of the already reported from experimental (ESR/ENDOR studies of X-ray irradiated single crystals 40 ) and theoretical (DFT/B3LYP/6-31G(d)) 21, 41a for the N2-deprotonated neutral radical (see Table T1 in supplemental information). These results establish that for the N2-deprotonated neutral radical (i) the N1 and N7 nitrogen atoms have very small HFCC couplings which could be neglected, and (ii) the methyl group at N1 does not have a significant effect on the hyperfine couplings and hence on the spin distribution at N1 and at other sites.…”

Section: Resultssupporting

confidence: 81%

“…Comparison of the simulated spectrum (black) with the experimentally recorded spectrum (green) shows that the hyperfine coupling components in the wings (A ∥ ) of the simulated spectrum match very well with those of the experimental spectrum. The HFCC values for the N2-H and C8-H atoms used to simulate the experimental ESR spectrum of 1-Me-dG(N2-H)• in the aqueous (H 2 O) glassy system (see Table 1) match very well with those of the already reported (ESR/ENDOR studies of the X-ray irradiated single crystals 40 and theoretical studies 21, 41a (see supplemental information Table T1)).…”

Section: Resultssupporting

confidence: 78%

“…Note that the N2-H is an exchangeable proton, thus we find that the N2-H hyperfine couplings are observed only in H 2 O and not in D 2 O. The A xx and A yy values for the N2-H hyperfine are not well determined by experiment and reasonable estimates from the published literature (ESR/ENDOR studies of the X-ray irradiated single crystals 40 and theoretical studies 21, 41a (see supplemental information Table T1) were employed in the simulations. For the A xx , A yy tensors, principal axes (x and y) were not collinear for the C8-H and N2-H protons and this has been taken into account in the simulation.…”

Section: Methodssupporting

confidence: 40%

“…We note here that the N2 deprotonated species is well-documented in previous ESR/ENDOR studies of X-ray irradiated single crystals. 40, 41a Our ESR work with dGuo in glassy system at low temperature 21 as well as pulse radiolysis studies with dGuo in aqueous solution at ambient temperature 17, 18 shows that G• + naturally deprotonates from N1 first to produce G(N1-H)• and subsequently from N2 to form G(−2H)• − . Therefore, to produce an authentic ESR benchmark spectrum of the neutral N2 deprotonated species, we employ 1-Me-dGuo or 1-Me-Guo, which can only deprotonate from N2 as the N1-H atom here has been replaced by the CH 3 group.…”

Section: Resultsmentioning

confidence: 80%

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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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Section: Resultssupporting

confidence: 81%

Section: Resultssupporting

confidence: 78%

Section: Methodssupporting

confidence: 40%

Section: Resultsmentioning

confidence: 80%

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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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“…The triggered dissociation of persulfate ions into SO 4 . radical anions in timeresolved pulse radiolysis or flash photolysis experiments has been previously employed by Steenken and co-workers (34 -36), O'Neill and Davies (37), and Bachler and Hildenbrand (38), to study the kinetics of reactions of the SO 4 . radical anions with nucleic acids.…”

Section: Materials-2ј-deoxyguanosinementioning

confidence: 99%

The Carbonate Radical Is a Site-selective Oxidizing Agent of Guanine in Double-stranded Oligonucleotides

Shafirovich

Dourandin

Huang

et al. 2001

Journal of Biological Chemistry

168

202

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The carbonate radical anion (CO 3 . ) is believed to be an . anions and the formation of G(؊H) ⅐ radicals are correlated with one another on the millisecond time scale, whereas the neutral guanine radicals decay on time scales of seconds. Alkali-labile guanine lesions are produced and are revealed by treatment of the irradiated oligonucleotides in hot piperidine solution. The DNA fragments thus formed are identified by a standard polyacrylamide gel electrophoresis assay, showing that strand cleavage occurs at the guanine sites only. The biological implications of these oxidative processes are discussed.There is growing evidence that bicarbonate and carbon dioxide, both present in biological systems in significant amounts, can alter the mechanisms and reaction pathways of reactive oxygen (1-4) and nitrogen (5-13) species formed during normal metabolic activity and under conditions of oxidative stress. It has been proposed that the mechanism of generation of carbonate radical anions (CO 3 . ) 1 from bicarbonate (HCO 3 Ϫ ) or CO 2 can involve the one-electron oxidation of HCO 3 Ϫ at the active site of copper-zinc superoxide dismutase (3, 4) and homolysis of the nitrosoperoxycarbonate anion (ONOOCO 2 Ϫ ) formed by the reaction of peroxynitrite with carbon dioxide (14 -18).The carbonate radical anion is a strong one-electron oxidant that oxidizes appropriate electron donors via electron transfer mechanisms (19). Detailed pulse radiolysis studies have shown that carbonate radicals can rapidly abstract electrons from aromatic amino acids (tyrosine and tryptophan). However, reactions of CO 3 . with sulfur-containing methionine and cysteine are less efficient (20 -22). Hydrogen atom abstraction by carbonate radicals is generally very slow (19), and their reactivities with other amino acids are negligible (20 -22). It is well established that carbonate radicals can play an important role in the modification of selective amino acids in proteins in cellular environments under conditions of oxidative stress, aging, and inflammatory processes (1,11,12). The role of HCO 3 Ϫ /CO 2 in potentiating oxidative DNA damage has received relatively little attention. It has been shown that the presence of HCO 3 Ϫ /CO 2 inhibits direct strand cleavage of DNA induced by ONOO Ϫ but enhances the formation of 8-nitroguanine, alkali-labile and formamidopyrimidine glycosylase-labile DNA lesions (23-25). Peroxynitrite causes direct DNA strand cleavage by oxidizing deoxyribose. However, in the presence of HCO 3 Ϫ /CO 2 there is a shift in product distribution from direct strand cleavage to the formation of oxidative modifications of guanines (26), suggesting that the carbonate radical anion could play an important role in this phenomenon (24). Although guanine is indeed the most easily oxidized base in DNA, the reactions of the carbonate radical anions with the different aromatic DNA residues have not yet been characterized.In this work, we explore the electron transfer reactions from guanine electron donor residues embedded in the self-comp...

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Oxidation of Guanine by Carbonate Radicals Derived from Photolysis of Carbonatotetramminecobalt(III) Complexes and the pH Dependence of Intrastrand DNA Cross‐Links Mediated by Guanine Radical Reactions

et al. 2008

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The carbonate radical anion CO3•− is a decomposition product of nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite, an important biological byproduct of the inflammatory response. The selective oxidation of guanine in DNA by CO3•− radicals is known to yield spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), and a novel intrastrand cross-linked product, 5’-d(CCATCG*CT*ACC) between guanine C8 (G*) and thymine N3 (T*) atoms in the oligonucleotide (Crean et al., Nucleic Acids Res., 2008, 36, 742–755). Involvement of the T-N3 (pKa of N3-H is 9.67) suggests that the formation of 5’-d(CCATCG*CT*ACC) might be pH – dependent. This hypothesis was tested generating CO3•− radicals by the photodissociation of carbonatotetramminecobalt(III) complexes by steady-state UV irradiation that allowed for studies of product yields in the pH 5.0 – 10.0 range. The yields of 5’-d(CCATCG*CT*ACC) is ~ 45 times greater at pH 10.0 than at pH 5.0, which is consistent with the proposed mechanism that requires N3(H) thymine proton dissociation followed by nucleophilic addition to the C8 guanine radical.

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EPR-detection of the guanosyl radical cation in aqueous solution. Quantum chemically supported assignment of nitrogen and proton hyperfine couplings

Cited by 15 publications

References 37 publications

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

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

The Carbonate Radical Is a Site-selective Oxidizing Agent of Guanine in Double-stranded Oligonucleotides

Oxidation of Guanine by Carbonate Radicals Derived from Photolysis of Carbonatotetramminecobalt(III) Complexes and the pH Dependence of Intrastrand DNA Cross‐Links Mediated by Guanine Radical Reactions

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