Oxygen-17 and carbon-13 hyperfine interactions in the electron paramagnetic resonance spectrum of the hydroquinone cation radical

Sullivan, Paul D.; Bolton, James R.; Geiger, William E.

doi:10.1021/ja00717a006

Cited by 42 publications

(26 citation statements)

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“…The reason for this wide range lies in the universal assumption of a McConnell-type relationship, namely aoH H = QoaHpo, hyperconjugative contributions being ignored. In this respect it is interesting to note that until recently, the closest agreement with the present value for QoH H was found in the work of Sullivan et al [15]. These authors made a careful study of all the tH, laC and 1~O splittings in the radical cation of hydroquinone.…”

Section: Resultssupporting

confidence: 86%

Temperature-dependent hyperfine coupling constants in electron spin resonance

Bullock

Howard

1974

Molecular Physics

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The temperature dependence of the hydroxyl proton splittings in the radical cation of 1,2,4,5-tetrahydroxybenzene has been measured over the temperature range -80~ to + 60~The ring proton split-tings show no significant dependence upon temperature. The hyperconjugative contribution to the hydroxyl proton coupling has been calculated as a function of temperature for a range of values of V0, the two-fold barrier to rotation of an individual hydroxyl group, using numerical solutions to the Mathieu equation. This, together with the results of McLachlan SCF-MO calculations for this system, leads to a value of V0 of 24_+ 2 kJ tool -1 and to an estimate of the spin-polarization parameter Qorr E of -3.87 4-0.05 mT.

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Section: Resultssupporting

confidence: 86%

Temperature-dependent hyperfine coupling constants in electron spin resonance

Bullock

Howard

1974

Molecular Physics

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“…Most of the unpaired electron spin in a semiquinone anion radical is concentrated at the carbon and oxygen atoms of the carbonyl groups [19,31]. Most of the unpaired electron spin in a semiquinone anion radical is concentrated at the carbon and oxygen atoms of the carbonyl groups [19,31].…”

Section: Discussionmentioning

confidence: 99%

ENDOR spectroscopic studies of stable semiquinone radicals bound to the Escherichia coli cytochrome bo₃ quinol oxidase

Hastings

Heathcote

Ingledew

et al. 2000

European Journal of Biochemistry

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The putative oxidation of ubiquinol by the cytochrome bo3 terminal oxidase of Escherichia coli in sequential one-electron steps requires stabilization of the semiquinone. ENDOR spectroscopy has recently been used to study the native ubisemiquinone radical formed in the cytochrome bo3 quinone-binding site [Veselov, A.V., Osborne, J.P., Gennis, R.B. & Scholes, C.P. (2000) Biochemistry 39, 3169-3175]. Comparison of these spectra with those from the decyl-ubisemiquinone radical in vitro indicated that the protein induced large changes in the electronic structure of the ubisemiquinone radical. We have used quinone-substitution experiments to obtain ENDOR spectra of ubisemiquinone, phyllosemiquinone and plastosemiquinone anion radicals bound at the cytochrome bo3 quinone-binding site. Large changes in the electronic structures of these semiquinone anion radicals are induced on binding to the cytochrome bo3 oxidase. The changes in electronic structure are, however, independent of the electronic structures of these semiquinones in vitro. Thus it is shown to be the structure of this binding site in the protein, not the covalent structure of the bound quinone, that determines the electronic structure of the protein-bound semiquinone.

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“…It has been reported that H 2 Q + C undergoes cis-trans isomerization in solution to give ESR spectra for a mixture of isomers at < À20 8C in www.chemeurj.org CH 3 NO 2 . [29] In addition, the cation radicals of hydroquinone and catechol are known to be strong acids with pK a values of À0.8 and À1.65, respectively. [30] In the case of PNC-H 2 Q (Figure 6a), there are three sets of hfc values as a result of two equivalents protons (4.6, 3.6, and 1.6 G).…”

Section: Full Papermentioning

confidence: 99%

Selective Inclusion of Electron‐Donating Molecules into Porphyrin Nanochannels Derived from the Self‐Assembly of Saddle‐Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

Kojima

Nakanishi

Harada

et al. 2007

Chemistry A European J

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A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p-hydroquinone and p-xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at lambda>340 nm at room temperature) of the PNC that contains p-hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively.

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Oxygen-17 and carbon-13 hyperfine interactions in the electron paramagnetic resonance spectrum of the hydroquinone cation radical

Cited by 42 publications

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Temperature-dependent hyperfine coupling constants in electron spin resonance

Temperature-dependent hyperfine coupling constants in electron spin resonance

ENDOR spectroscopic studies of stable semiquinone radicals bound to the Escherichia coli cytochrome bo₃ quinol oxidase

Selective Inclusion of Electron‐Donating Molecules into Porphyrin Nanochannels Derived from the Self‐Assembly of Saddle‐Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

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Oxygen-17 and carbon-13 hyperfine interactions in the electron paramagnetic resonance spectrum of the hydroquinone cation radical

Cited by 42 publications

References 0 publications

Temperature-dependent hyperfine coupling constants in electron spin resonance

Temperature-dependent hyperfine coupling constants in electron spin resonance

ENDOR spectroscopic studies of stable semiquinone radicals bound to the Escherichia coli cytochrome bo3 quinol oxidase

Selective Inclusion of Electron‐Donating Molecules into Porphyrin Nanochannels Derived from the Self‐Assembly of Saddle‐Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin Dications

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ENDOR spectroscopic studies of stable semiquinone radicals bound to the Escherichia coli cytochrome bo₃ quinol oxidase