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Showing 1 to 20 of 27 for “"semiquinone"”.
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Spectroscopic Studies of Some Semiquinone Radical Ions
Previous ESR and UV spectroscopic studies of semiquinone cations are reviewed. Cations of 4,4'-bipheno-semiquinones prepared by chemical oxidation of the corresponding diols and reduction of the quinones in sulphuric acid, were studied using ESR and UV spectroscopy. Oxidation of biphenyl-4,4'-diol …
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Characterization of the Electronic and Molecular Structures of Transition Metal Semiquinone and Catecholate Complexes
… when bonding to metals: {M(O)(quinone)}, {M(I) (semiquinone)}, and {M(II)(catecholate)}. The difference between these three formulations is related to the residence of electrons in either metal or ligand orbitals.
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Characterizations on bacterial photosynthesis and respiration with optical spectroscopy and magnetic resonance
… I have also examined the reactivity of the semiquinones in the LM dimer (Chapter 2). In accordance with previous reports, both semiquinones are less stable compared to their counterparts in the intact reaction center. Particularly, I have found that the oxidation of the QA- by the …
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Structural and Functional Studies on Cytochrome BO3 Ubiquinol Oxidase From Escherichia Coli and the Characterization of Its Quinone Binding Sites
… able to transiently form a one-electron reduced semiquinone radical during the catalytic cycle. The semiquinone is highly stabilized at the QH site, and it was postulated from the crystal structure that ArgI71, AspI75, HisI98 and GlnI101 are the hydrogen bond partners involved in quinone binding …
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Gas-Phase Formation of Environmentally Persistent Free Radicals from Thermal Degradation of Catechol, Hydroquinone, Phenols and Tobacco
… endogenous or exogenous redox cycling to form semiquinone type radicals responsible of Reactive Oxygen Species (ROS) formation. ROS such as hydroxyl radicals can cause severe oxidative stress on biological tissues and can provoke severe signaling pathways leading to cardiovascular and pulmonary …
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Part I. Studies of the substitution and formation reactions of rhenium carbonyl o-semiquinone compounds. Part II. Molecular mechanics studies of the steric interactions in chromium pentacarbonyl phosphine compounds
… thermal synthesis of (3,5-di-t-butyl-1,2-benzosemiquinone)Re(CO)$\sb4$ from the sodium semiquinone radical anion and Re(CO)$\sb5$Cl is reported. The substitution kinetics of (3,5-di-t-butyl-1,2-benzosemiquinone)Re(CO)$\sb4$ with P(n-Bu)$\sb3$ was studied by stopped-flow methods. The observed …
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Investigation of the quinone sites in reaction centers from Rhodobacter sphaeroides by pulsed EPR and spectral simulations
… oxidized ubiquinone molecule. The QA- and QB- semiquinone intermediate states can both be readily trapped by photoreduction or chemical reduction methods, making them well-suited for study by electron paramagnetic resonance (EPR). In this thesis, pulsed EPR is used to explore the magnetic …
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Biochemical characterization of a-type heme-copper oxidases in escherichia coli, bacillus subtilis and thermus thermophilus
… Asp75, His98, and Gln101) involved in ubiquinone semiquinone radical stabilization at quinone binding site in E. coli cytochrome bo3 oxidase. Similar result was reported on cytochrome aa3-600 oxidase in B. subtilis, a close homolog to cytochrome bo3 that uses menaquinone instead of ubiquinone. …
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The Binding Pockets of QA and QB in the Photosynthetic Reaction Center of Rba. sphaeroides Probed by Pulsed EPR
… ubiquinones can be stabilized in their reduced (semiquinone) state allowing for their binding pockets to be studied with EPR (electron paramagnetic resonance) spectroscopy. Using the pulsed EPR technique, ESEEM (electron spin echo envelope modulation) the interactions between the reaction center …
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Electron gating and mechanism of proton exit in quinol oxidation in cyt bc1 complex from R. sphaeroides
… bypass reactions mediated through the transient semiquinone intermediate at the Qo-site; pH dependence of Km; and the thermodynamic properties of redox cofactors. Our results could be interpreted in terms of two roles for the -PEWY- glutamate: (i) in facilitating electron transfer from …
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Ultrafast Dynamics of Flavin Cofactor in Photolyase/Cryptochrome Family
… 20 and 18 ps to the oxidized FAD and neutral semiquinone FADH<sup>•</sup>, respectively. The orientation factors were estimated from the acquired energy transfer rates and compared with values from the theoretical study. Both results demonstrate that MTHF-FADH¯ has the largest κ<sup>2</sup> …
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EPR and solid-state NMR studies on the mechanism of cytochrome bo3 ubiquinol oxidase from escherichia coli
… from these C43(DE3) auxotroph strains, and the semiquinone radicals at the QH-site of these samples were analyzed by pulsed EPR spectroscopy. Selective 15N labeling has revealed the Nε of R71 in the wild type cytochrome bo3 and the Nε of H75 in the D75H mutant cytochrome bo3 as the nitrogen …
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Qo site of the bc1 complex; unlocking the gate of the electron transport chain
… also lead to production toxic ROS formation from semiquinone intermediates. Its internal proton/electron shuttling and gating mechanisms have been a source of controversy and debate for decades. Structural and kinetic analysis of the bc1 complex suggests several proton-coupled electron transfer …
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Structure and Function Relationships in Cytochrome Bo(3) Oxidase and Cytochrome Bd-I Oxidase From Escherichia Coli
… the heme/copper superfamily, is found to have a semiquinone intermediate during turnover of quinol. Additionally, after the quinol is consumed and turnover stops, the enzyme is found in a mixture of oxidation states, one of which is the elusive Peroxy species. No free radical species is observed …
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Kinetics of electron transfer and binding of inhibitors in the two-electron gate of chloroplasts
… secondary plastoquinone, Q$\sb{\rm B}$, and its semiquinone, Q$\sb{\rm B}\sp-$, in the Q$\sb{\rm B}$ binding site and to characterize the two electron gate in chloroplasts with thermodynamical and kinetic parameters. There are three studies involved: (1) kinetics of an electron transfer reaction …
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Coordination Geometries in Metallobundles Enforcing Oxidative and Hydrolytic Catalysis and Designing Biomaterials for Use As Antimicrobials
… We investigated the influence metal has on semiquinone stabilization in DF bundles, a minimalist model representing active sites of more complex natural diiron and dimanganese proteins. Coordination sphere was modified in the original DF single chain version to incorporate a …
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Electron Transfer in the Reaction Center From Rhodopseudomonas Viridis (Photosynthesis, Bioenergetics, Bacteria)
… s-triazines) mimic the quinone rather than the semiquinone. The kinetics of charge recombination between the photooxidized primary donor, P('+), and the photoreduced quinone acceptors were measured. The temperature dependence of the P('+) Q(,A)('-) recovery kinetic revealed a novel indirect …
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Mössbauer studies of photsynthetic reaction centers from Rhodopseudomonas sphaeroides R-26
… broadened via the spin-spin interaction with the semiquinone free radical. In high field the spectra of Nand Rare similir, showing broad unresolved doublets at 4.2K, which resolve at higher temperatures. The width of the lower energy line has a minimum near 25K. Analysis of the magnetic data using …
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Formation and Stabilization of Combustion-Generated Environmentally Persistent Free Radicals on Transition Metal Oxides Supported on Silica
… a lower g-value of 2.0023-2.0043, and a second semiquinone-type radical, with a g-value of 2.0044-2.0085. In general, the yield of EPFRs on Ni(II)O are similar to Cu(II)O and differs by ~10× compared to Fe(III)2O3. The persistency of the EPFRs is highly dependent on the metals they are …
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Characterization of the major extrapallial fluid protein of the mollusc, Mytilus edulis: Implications for function
… resonance spectroscopy and shown to contain semiquinone radicals and Fe(III). In addition, Cu(II) and a second radical (g = 2.007) were found in cultivated threads.</p>
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