Electron paramagnetic resonance studies of vitamin K and vitamin E quinones

Fritsch, John M.; Tatwawadi, S. V.; Adams, Ralph N.

doi:10.1021/j100861a019

Cited by 43 publications

(10 citation statements)

References 2 publications

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“…Experiments on NQ •- in various solvents ,, have given magnitudes of the H2 and H3 hfccs which range from 3.22 to 3.32, in excellent agreement with our calculated values of 2.9−3.3. For the H6 and H7 protons, our calculations predict hfcc magnitudes of 0.7−0.8, which is in reasonable agreement with the experimental range 0.57−0.655.…”

Section: Resultssupporting

confidence: 87%

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

Grafton

Wheeler

1997

J. Phys. Chem. A

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The hybrid Hartree−Fock/density functional B3LYP has been used to predict a variety of properties of 1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 2,3-dimethyl-1,4-naphthoquinone, and 9,10-anthraquinone, as well as their radical anions. Geometries and spin properties show good agreement with experiment. The calculated adiabatic electron affinities show excellent agreement with previously determined experimental values, where available. An electron affinity of 1.63 eV is predicted for 2,3-dimethyl-1,4-naphthoquinone. A complete analysis of the vibrational spectra of each neutral molecule is provided and compared with available experimental and previous theoretical results. In each case, the CO antisymmetric stretching vibration is found to be slightly higher in frequency than the CO symmetric stretch. The first full analysis of the vibrational spectra of each of the radical anions is presented, and a comparison is made with the spectra of the neutral molecules. It is found that B3LYP/6-31G(d) theory consistently overestimates vibrational frequencies by 4−5%, in agreement with previous tests, but also does an excellent job of predicting the correct relative ordering of vibrational modes. Unrestricted Hartree−Fock geometries and frequencies are also provided for comparison.

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Section: Resultssupporting

confidence: 87%

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

Grafton

Wheeler

1997

J. Phys. Chem. A

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“…UQ 10 •- can be stabilized owing to the possible formation of an intramolecular hydrogen bond between the H atom of the methylene group and the negatively charged 1-C carbonyl oxygen atom, which is not possible for UQ 0 •- . Such an intramolecular H bond, which has also been proposed for vitamin K 1 , must reduce the proton affinity of UQ and facilitate the second electron transfer due to the decrease in the effective negative charge of UQ 10 •- .…”

Section: Resultsmentioning

confidence: 88%

Hydrogen-Bonding Effect on ¹³C and Proton Hyperfine Couplings of [4-¹³C]-Labeled Ubisemiquinones in Vitro

et al. 1996

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EPR spectra of ubiquinone-0 (UQ 0 ) and UQ 10 anion radicals selectively labeled with 13 C at the 4-CdO position are reported. The environmental effect on the 4-13 C splitting constant was studied in mixed solvents in which the molar fraction of the protic component was changed over a wide range. The quinones were electrochemically reduced, with cyclic voltammetry and concomitant optical spectroscopy being performed as controls. The value and the sign of the 4-13 C hyperfine splitting constant strongly depend on the H-bonding properties (proticity) of the solvent, due to the formation of mono-and disolvates through hydrogen bonding of the carbonyl oxygens in protic solvents. The formation of disolvates is less favorable by a factor of 80 than formation of the monosolvated anion. The results are discussed in light of recent EPR, FTIR, and NMR experiments on the primary 13 C-labeled acceptor quinone Q A in bacterial photosynthetic reaction centers. We propose that in the neutral state both carbonyls of Q A are not or only weakly hydrogen bonded to the protein and that formation of anionic Q A •-results in a much stronger H-bond for the 4-carbonyl only. The large shift of the 4-CdO IR signal reported for UQ in ViVo is in our view mostly due to a change in bond order induced by binding of UQ to the protein, perhaps through a change in sp 2 hybridization at the 4-C position.

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“…In liquid ammonia the absolute value of the ihfcs of the anion radicals at positions 2 and 3 of vitamin are equal, as K 3 with 2-methyl-1,4-benzoquinone.32 According to the literature, similar degeneracy can be found by EPR in DMF and in DMSO. 13 The relative permittivities are e \ 36.7 for DMF and e \ 46.6 for DMSO. Therefore in Fig.…”

Section: Resultsmentioning

confidence: 99%

EPR, ENDOR, TRIPLE resonance spectroscopy and MO studies on radical anion, neutral radical and radical cation of vitamin K3 in a selection of solvents

Joela¹,

Lehtovuori²

1999

Phys. Chem. Chem. Phys.

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All three radical species (radical anion, neutral radical and radical cation) from 2-methyl-1,4-naphthoquinone (vitamin were prepared in liquid solutions and measured by EPR and ENDOR/TRIPLE resonance K 3 ) spectroscopy. The methyl group protons showed the largest variation of isotropic hyperÐne coupling, from 8.3 MHz (anion) to 19.1 MHz (neutral) to 9.3 MHz (cation). Isotropic hyperÐne couplings of a proton in the quinoid ring and the methyl group protons in di †erent solutions were shown to be dependent on the relative permittivity of the solvent. A prominent alternating linewidth e †ect was detected in the EPR spectra of the radical anion of 2-methyl-1,4-naphthoquinone at di †erent concentrations and at di †erent temperatures in 1,2dimethoxyethane. This was explained as being due to the counter-cation Ñuctuation between the two quinodic oxygens. A solid dipotassium radical salt of vitamin was prepared and its EPR spectra measured. Isotropic K 3 hyperÐne coupling constants were also calculated for all three radical species using the UB3LYP density functional method.

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Electron paramagnetic resonance studies of vitamin K and vitamin E quinones

Cited by 43 publications

References 2 publications

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

Hydrogen-Bonding Effect on ¹³C and Proton Hyperfine Couplings of [4-¹³C]-Labeled Ubisemiquinones in Vitro

EPR, ENDOR, TRIPLE resonance spectroscopy and MO studies on radical anion, neutral radical and radical cation of vitamin K3 in a selection of solvents

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Electron paramagnetic resonance studies of vitamin K and vitamin E quinones

Cited by 43 publications

References 2 publications

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

A Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree−Fock and Hybrid Hartree−Fock/Density Functional Methods

Hydrogen-Bonding Effect on 13C and Proton Hyperfine Couplings of [4-13C]-Labeled Ubisemiquinones in Vitro

EPR, ENDOR, TRIPLE resonance spectroscopy and MO studies on radical anion, neutral radical and radical cation of vitamin K3 in a selection of solvents

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Hydrogen-Bonding Effect on ¹³C and Proton Hyperfine Couplings of [4-¹³C]-Labeled Ubisemiquinones in Vitro