Abstract:The relationship between γ proton hyperfine couplings and conformation in alkoxy radicals was investigated. It is shown that large γ proton couplings are present in alkoxy radicals in which significant spin polarization of the Cβ–Cγ bonding orbitals is expected. This principle finds application in analyzing the proton hyperfine couplings observed for the alkoxy radical in irradiated deoxycytidine monophosphate. The g tensor and hyperfine coupling tensors which characterize this radical were determined from ESR… Show more
“…The only identified product associated with radiation damage to the deoxyribose moiety is a secondary alkoxy radical observed at 10 K and stable on warming to ca. 65 K. This radical was correctly identified by Box et al, 24 and although ENDOR lines from this radical were detected in the present work (Figure 1), no new experimental results on this radical are reported here. It is important to note, however, that this radical exhibits a number of weak hyperfine couplings that appear only 5-8 MHz from the free proton ENDOR signal (36.5 MHz at K-band), which interfered with the weak couplings from radicals R1 and R2.…”
Section: Oxidation Of the Deoxyribose Moiety (Radical R3)supporting
confidence: 82%
“… 1 (A) K-band ENDOR spectrum from a nondeuterated single crystal of 5‘dCMP, X-irradiated and measured at 10 K. Low-dose (crystal irradiated with 55 kVp (kilovolts peak), 10 mA X-rays for 1 h) study for rotation about the 〈 a 〉 crystallographic axis, H o parallel to the 〈 c 〉 axis. ENDOR lines marked * are from the alkoxy radical (ref ). (B) The ENDOR lines at ca.…”
Section: Results and Analysismentioning
confidence: 99%
“…Sugar Radicals. Identification of an alkoxy radical in 5‘dCMP initially led to several incorrect assignments. , However, ENDOR results by Box et al, which accounted for one β-proton and three γ-proton couplings, leave no doubt that the alkoxy radical in 5‘dCMP is a secondary alkoxy radical located at O3‘.…”
Section: Discussionmentioning
confidence: 99%
“…(C) Simulation of the EPR powder spectrum of radical R6. However, ENDOR results by Box et al, 24 which accounted for one β-proton and three γ-proton couplings, leave no doubt that the alkoxy radical in 5′dCMP is a secondary alkoxy radical located at O3′. Some time ago it was suggested by Hu ¨ttermann 38 that in DNA there is a shift away from damage to the sugar.…”
The EPR spectra of single crystals of deoxycytidine 5‘-phosphate monohydrate (5‘dCMP), X-irradiated at 10
K, exhibit signals from several distinct radical species. Analysis of the ENDOR spectra from two of these
radicals indicates that these result from oxidation and reduction of the cytosine base. The reduced species
exhibits hyperfine coupling to the C6−Hα proton, and an additional small exchangeable hyperfine coupling
from the N3−H proton. No additional couplings that may be associated with protonation of the amino group
have been observed. Since the native molecule is protonated at N3, it appears that reduction of the cytosine
base does not result in any further protonation. The oxidized species exhibits hyperfine couplings to C5−Hα
and C1‘−Hβ, and two small exchangeable couplings from the C4−NH2 protons. Since no hyperfine coupling
to N3−H was observed, the oxidized species is believed to be the N3−H deprotonated cation. At high X-ray
dose there is also evidence for both C5 and C6 H-addition radicals at 10 K. The fate of these radicals has
been studied under controlled warming conditions. Attempts have been made to relate the fate of the low-temperature radicals with several radicals that have been detected previously at 77 K and at room temperature.
“…The only identified product associated with radiation damage to the deoxyribose moiety is a secondary alkoxy radical observed at 10 K and stable on warming to ca. 65 K. This radical was correctly identified by Box et al, 24 and although ENDOR lines from this radical were detected in the present work (Figure 1), no new experimental results on this radical are reported here. It is important to note, however, that this radical exhibits a number of weak hyperfine couplings that appear only 5-8 MHz from the free proton ENDOR signal (36.5 MHz at K-band), which interfered with the weak couplings from radicals R1 and R2.…”
Section: Oxidation Of the Deoxyribose Moiety (Radical R3)supporting
confidence: 82%
“… 1 (A) K-band ENDOR spectrum from a nondeuterated single crystal of 5‘dCMP, X-irradiated and measured at 10 K. Low-dose (crystal irradiated with 55 kVp (kilovolts peak), 10 mA X-rays for 1 h) study for rotation about the 〈 a 〉 crystallographic axis, H o parallel to the 〈 c 〉 axis. ENDOR lines marked * are from the alkoxy radical (ref ). (B) The ENDOR lines at ca.…”
Section: Results and Analysismentioning
confidence: 99%
“…Sugar Radicals. Identification of an alkoxy radical in 5‘dCMP initially led to several incorrect assignments. , However, ENDOR results by Box et al, which accounted for one β-proton and three γ-proton couplings, leave no doubt that the alkoxy radical in 5‘dCMP is a secondary alkoxy radical located at O3‘.…”
Section: Discussionmentioning
confidence: 99%
“…(C) Simulation of the EPR powder spectrum of radical R6. However, ENDOR results by Box et al, 24 which accounted for one β-proton and three γ-proton couplings, leave no doubt that the alkoxy radical in 5′dCMP is a secondary alkoxy radical located at O3′. Some time ago it was suggested by Hu ¨ttermann 38 that in DNA there is a shift away from damage to the sugar.…”
The EPR spectra of single crystals of deoxycytidine 5‘-phosphate monohydrate (5‘dCMP), X-irradiated at 10
K, exhibit signals from several distinct radical species. Analysis of the ENDOR spectra from two of these
radicals indicates that these result from oxidation and reduction of the cytosine base. The reduced species
exhibits hyperfine coupling to the C6−Hα proton, and an additional small exchangeable hyperfine coupling
from the N3−H proton. No additional couplings that may be associated with protonation of the amino group
have been observed. Since the native molecule is protonated at N3, it appears that reduction of the cytosine
base does not result in any further protonation. The oxidized species exhibits hyperfine couplings to C5−Hα
and C1‘−Hβ, and two small exchangeable couplings from the C4−NH2 protons. Since no hyperfine coupling
to N3−H was observed, the oxidized species is believed to be the N3−H deprotonated cation. At high X-ray
dose there is also evidence for both C5 and C6 H-addition radicals at 10 K. The fate of these radicals has
been studied under controlled warming conditions. Attempts have been made to relate the fate of the low-temperature radicals with several radicals that have been detected previously at 77 K and at room temperature.
“…The unpaired electron in alkoxy radicals resides mainly on an oxygen atom and consequently has a very characteristic g tensor. Alkoxy radicals also have distinctive hyperfine couplings with gamma protons as well as beta protons contributing significantly to the hyperfine patterns (18).…”
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