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111.
The title complexes were obtained as MIIM′II species [(bpy)2M(μ-abpy)M′(bpy)2](PF6)4, M,M′ = Ru or Os, using the new mononuclear precursor [(bpy)2Os(abpy)](PF6)2 for the osmium-containing dinuclear complexes. One-electron reduction produces radical complexes [(bpy)2M(μ-abpy)M′(bpy)2]3+ and [(bpy)2M(abpy)]+ with significant contributions from the metals, as evident from the EPR effects on successive replacement of ruthenium by osmium with its much higher spin-orbit coupling constant. The diruthenium and diosmium radical complexes were also studied by EPR at high-frequency (285 GHz), the latter shows an unusually large g anisotropy g1 − g3 = 0.25 in frozen solution. Further reduction was monitored by UV/Vis spectroelectrochemistry. Oxidation produced OsIII EPR signals for [(bpy)2Os(abpy)]3+ and [(bpy)2Os(μ-abpy)Ru(bpy)2]5+, indicating a RuIIOsIII species for the latter. The diosmium(III,II) and diruthenium(III,II) mixed-valent species remained EPR silent at 4 K, however, they exhibit weak inter-valence charge transfer (IVCT) bands at about 1460 nm. Whereas the cyclic voltammetric response towards reduction is only marginally different for the three dinuclear complexes, successive replacement of ruthenium by osmium causes the first oxidation potential to decrease. The much higher comproportionation constant Kc for the mixed valent diosmium(III,II) state (Kc > 1015) in comparison to the diruthenium(III,II) analogue with Kc = 1010 confirms the electron transfer alternative for the valence exchange mechanism, in contrast to the hole transfer established for analogous dinuclear complexes with the formally related diacylhydrazido(2−) bridging ligands. 相似文献
112.
Speranza G Morelli CF Cairoli P Müller B Schink B 《Biochemical and biophysical research communications》2006,349(2):480-484
Triethanolamine (TEA) is converted into acetate and ammonia by a strictly anaerobic, gram-positive Acetobacterium strain LuTria3. Fermentation experiments with resting cell suspensions and specifically deuterated substrates indicate that in the acetate molecule the carboxylate and the methyl groups correspond to the alcoholic function and to its adjacent methylene group, respectively, of the 2-hydroxyethyl unit of TEA. A 1,2 shift of a hydrogen (deuterium) atom from -CH2-O- to =N-CH2- without exchange with the medium was observed. This fact gives evidence that a radical mechanism occurs involving the enzyme and/or coenzyme molecule as a hydrogen carrier. Such a biodegradation appears analogous to the conversion of 2-phenoxyethanol into acetate mediated by another strain of the anaerobic homoacetogenic bacterium Acetobacterium. 相似文献
113.
Antioxidant properties of polysaccharide fractions with different molecular mass extracted with hot-water from rice bran 总被引:2,自引:0,他引:2
Xue-Qiang Zha Jun-Hui Wang Xue-Fei Yang Hao Liang Ling-Ling Zhao Su-Hua Bao Jian-Ping Luo Ying-Yin Xu Bin-Bin Zhou 《Carbohydrate polymers》2009,78(3):570-575
Polysaccharides were extracted with hot-water from rice bran and precipitated with 40% ethanol (PW1), 60% ethanol (PW2) and 80% ethanol (PW3) in turn. PW1 and PW3 were composed of Glu, Man, Gal, Rib and Ara with molar percent of 54.1%, 10.5%, 21.7%, 7.4% and 6.3% for PW1 and 50.7%, 10.1%, 32.7%, 2.4% and 4.1% for PW3. Man was not observed in PW2. The molecular weight distribution of PW1, PW2 and PW3 ranged from 1.2 × 105 to 6.3 × 106 Da, 3.5 × 104 to 7.4 × 104 Da and 5.3 × 103 to 2.3 × 104 Da, respectively. Antioxidant activity tests revealed that PW1 showed good capability of scavenging superoxide radical, hydroxyl free radical and anti-lipid peroxidation at 1.0 mg/mL. In the meanwhile PW3 exhibited the good potential for reducing power, chelating ferrous ions, scavenging 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonate), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide effects. 相似文献
114.
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116.
Amanda A. Brindley Richard Zajicek Martin J. Warren Stuart J. Ferguson 《FEBS letters》2010,584(11):2461-18265
NirJ is involved in the transformation of precorrin-2 into heme d1, although its precise role in the process has not been established. The purified protein was found to contain a 4Fe-4S centre, in line with the prediction that it belongs to the radical SAM class of enzymes. This was further confirmed by binding of S-adenosyl-l-methionine (SAM) to dithionite-reduced NirJ, which resulted in a decrease in the signal intensity and in a shift to higher field of the [4Fe-4S]1+ EPR signal. Significantly, though, this approach also led to the appearance of a small but reproducible organic radical signal that was associated with about 2% of the NirJ molecules and was affected by the incorporation of SAM deuterated at the 5′ adenosyl group. 相似文献
117.
118.
Two new iridoid glucosides, namely, 2'-O-[(2E,4E)-5-phenylpenta-2,4-dienoyl]mussaenosidic acid (1; mussaenosidic acid = [1S-(1alpha,4aalpha,7alpha,7aalpha)]-1-(beta-D-glucopyranosyloxy)-1,4a,5,6,7,7a-hexahydro-7-hydroxy-7-methylcyclopenta[c]pyran-4-carboxylic acid) and 2'-O-(4-methoxycinnamoyl)mussaenosidic acid (2), were isolated from the aerial parts of the mangrove plant Avicennia marina. Beside that, one known iridoid glucoside, 2'-O-coumaroylmussaenosidic acid (3) and four known flavones (flavone = 2-phenyl-4H-1-benzopyran-4-one) including 4',5-dihydroxy-3',7-dimethoxyflavone (4), 4',5-dihydroxy-3',5',7-trimethoxyflavone (5), 4',5,7-trihydroxyflavone (6), and 3',4',5-trihydroxy-7-methoxyflavone (7) were also isolated and identified. The structures of these compounds were elucidated by NMR spectroscopy and by low- and high-resolution mass spectrometry. The chemotaxonomic significance of these findings was discussed. In addition, each isolated compound was evaluated for the ability of alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radical-scavenging activity. 相似文献
119.
Soto-Otero R Sanmartín-Suárez C Sánchez-Iglesias S Hermida-Ameijeiras A Sánchez-Sellero I Méndez-Alvarez E 《Journal of biochemical and molecular toxicology》2006,20(5):209-220
Tetrahydropapaveroline (THP) is a compound derived from dopamine monoamine oxidase-mediated metabolism, particularly present in the brain of parkinsonian patients receiving L-dopa therapy, and is capable of causing dopaminergic neurodegeneration. The aim of this work was to evaluate the potential of THP to cause oxidative stress on mitochondrial preparations and to gain insight into the molecular mechanisms responsible for its neurotoxicity. Our data show that THP autoxidation occurs with a continuous generation of hydroxyl radicals (*OH) and without the involvement of the Fenton reaction. The presence of ascorbate enhances this process by establishing a redox cycle, which regenerates THP from its quinolic forms. It has been shown that the production of *OH is not affected by the presence of either ferrous or ferric iron. Although THP does not affect lipid peroxidation, it is capable of reducing the high levels of thiobarbituric acid-reactive substances obtained in the presence of ascorbate and/or iron. However, THP autoxidation in the presence of ascorbate causes both an increase in protein carbonyl content and a reduction in protein-free thiol content. THP also increases protein carbonyl content when the autoxidation occurs in the presence of iron. The remarkable role played by ascorbate in the production of oxidative stress by THP autoxidation is of particular interest. 相似文献
120.
Investigations of the structure and properties of paramagnetic carotenoid radical cations and diamagnetic carotenoid dications using electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in conjunction with electrochemical, optical, and HPLC measurements, and molecular orbital calculations are described. These methods were applied to determine how the carotenoid radical cations and dications can be formed, their electron-transfer properties and stability in various media, and the mechanism by which carotenoid radical cations can isomerize. 相似文献