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对苯二胺类彩色显影剂(PPDs)经两步电子转移依次生成半醌自由基(SQDIs)和醌二亚胺(QDIs)[1]。 相似文献
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本文研究了竹红菌甲素和还原型谷胱甘肽(GluSH)间的光诱导氧化还原作用。甲素是3,10-二羟基-4,10-苝醌衍生物。在GluSH作为电子给体时,甲素经受可见光诱导的单电子还原,生成年醌自由基或二氢甲素,取决于pH值,同时GluSH被氧化。甲素的单电子还原量子效率随pH值增加而增加。在充氧溶液中甲素敏化氧化GluSH的反应通过类型Ⅰ和Ⅱ的混合机制进行。用ESR检测到了通过Fenton反应产生的羟基自由基。在脂质体包裹的甲素溶液中用动力学测定方法证明了甲素敏化GluSH的氧化是通过类型Ⅱ机制进行的。 相似文献
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阿霉素的光谱电化学研究 总被引:4,自引:0,他引:4
利用循环伏安、紫外可见光谱电化学、荧光光谱电化学、圆二色光谱电化学等方法研究了阿霉素(ADM)在石墨电极上的电化学行为.结果发现,阿霉素在+0.2~+0.7V和-0.2~-0.7V范围内分别出现一对氧化还原峰.正电位下,蒽环上的酚羟基发生单电子氧化,并伴随后续化学反应.负电位范围内,阿霉素经历ECE电极反应过程,即蒽醌经单电子还原生成半醌自由基,半醌可发生不可逆的化学反应,脱去配氧糖基,转变为7-去氧柔毛霉醌(7-deoxyadriamycinone),后者在更负的电位下形成一对可逆的新的氧化还原峰. 相似文献
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《中国科学:化学》2015,(7)
卤代醌是一类具有致癌活性的化合物.最近,它们作为氯代消毒副产物在饮用水中被检测到.有机氢过氧化物(ROOH)可通过自由基和酶促反应氧化多不饱和脂肪酸产生.先前的研究表明,ROOH可被过渡金属催化分解产生烷氧自由基,从而启动脂质过氧化或进一步分解生成α,β-不饱和醛.然而,目前还不清楚卤代醌能否不依赖过渡金属离子与ROOH以类似方式生成烷氧自由基.综合采用电子自旋共振-自旋捕获、高分辨液相色谱质谱联用及其他分析方法,结果发现,2,5-二氯-1,4-苯醌(DCBQ)可显著增强典型的有机氢过氧化物叔丁基过氧化氢(t-BuO OH)分解,以不依赖金属离子的方式生成叔丁氧自由基.在以上发现的基础上,我们检测和鉴定出一类新型的以碳为中心的醌酮自由基,其是我们之前推测的以氧为中心的醌氧自由基的自旋异构体.我们进而将研究扩展到更具生理意义的内源性脂质氢过氧化物13-过氧羟基-9,11-十八碳二烯酸(13-HPODE)中,发现DCBQ也可以显著增加13-HPODE的分解,产生脂质烷基自由基和具有基因毒性的4-羟基-2-壬烯醛.其他卤代醌也具有类似作用.研究表明,致癌性卤代醌能通过一类新型的不依赖于金属离子的亲核取代和均裂分解的机制,促进有机氢过氧化物分解并生成具有较强反应活性的烷氧、醌酮和脂质烷基自由基,及具有基因毒性的4-羟基-2-壬烯醛.以上研究结果可部分解释卤代醌及其酚类前驱物为何具有潜在的基因毒性和致癌性. 相似文献
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A. S. Tatikolov 《Russian Chemical Bulletin》1997,46(6):1082-1088
Kinetics of the interaction of ketyl and neutral semiquinone radicals with dioxygen was studied by the flash photolysis technique.
The reactivity of neutral semiquinone radicals in the transfer of a hydrogen atom to O2 is lower than that of ketyl radicals and increases as the reduction ability of the radicals increases, which give evidence
for the charge transfer from the radicals to O2 in the transition state of the reaction. The deuterium kinetic isotope effect of the reaction (up to 2.6) suggests considerable
weakening of the O−H bond of the seminquinone radical in the transition state. A cyclic structure of the transition state
similar to that in the reactions of ketyl radicals with hydrogen atom acceptors is proposed. In aprotic volvents, solvation
has essentially no effect on the reactivity of neutral anthrasemiquinone radicals up to solvent nucleophilicityB≈240. In solvents with higher nucleophilicity and in protic solvents, their reactivity drops sharply. Hydrogen atom transfer
reactions involving ketyl and neutral semiquinone radicals are shown to involve concerted electron and proton transfers, and
to have transition states in which the partial transfer of an electron and a proton from the ketyl or semiquinone radical
to an acceptor occurs.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1131–1137, June, 1997. 相似文献
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《Radiation Physics and Chemistry》1999,53(2):161-164
Pulse radiolysis studies of VK1 were carried out in a nitrogen-saturated aqueous–isopropanol–acetone mixed solvent. We studied the spectroscopic characteristics of semiquinone radicals of VK1 and determined the kinetic parameters of formation and decay of the species. It was found that the decay process of semiquinone radicals of VK1 was according to a first-order reaction, this was different from the case in ethanol solution, possible reasons were also analyzed. 相似文献
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Rahimipour S Palivan C Barbosa F Bilkis I Koch Y Weiner L Fridkin M Mazur Y Gescheidt G 《Journal of the American Chemical Society》2003,125(5):1376-1384
Helianthrones 2-4 are a new class of synthetic photosensitizers, which have a molecular skeleton related to that of hypericin. We established that irradiation of heliantrones with visible light leads to the formation of semiquinone radicals and reactive oxygen species. The structures of the paramagnetic anion species produced by electron transfer were calculated on the density functional level and investigated by cyclovoltammetry, UV/vis, and EPR/ENDOR spectroscopy. As with hypericin, the pi system of the helianthrones was found to be considerably deviated from planarity, and, upon electron transfer, deprotonation in the bay region occurs. The structure of the semiquinone radicals was found to be identical in THF, DMF, and aqueous buffered solutions regardless of the means by which reduction was achieved. Semiquinone radicals can be formed via self-electron transfer between the excited state and the ground state or via electron transfer from an electron donor to the excited state of helianthrone. Therefore, the presence of an electron donor significantly enhanced the photogeneration of semiquinone and superoxide radical. The kinetic studies showed that no significant photochemical destruction of helianthrones occurred upon irradiation. Generation of superoxide and singlet oxygen upon irradiation of helianthrones was established by spin trapping techniques. This shows that both type I and type II mechanisms are of importance for the photodynamic action of these compounds. 相似文献
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Thermodynamic and kinetic acidities of 6-tert-butyl-2-hydroxy-4-triphenylmethylphenoxyl during its interaction with triethylamine in toluene have been studied by ESR. It has been shown that the protolysis of this radical is a two-pathway process, since tautomeric transitions, i.e. ammonium ion migration between oxygen atoms of the semiquinone radical anion, have been detected in the reaction products, that is, in contact ion pairs of the corresponding semiquinone radicals.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 81–84, January, 1993. 相似文献
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A method for determining the rate constant of disproportionation of 2,5-dichlorosemiquinone radicals (k
6) from unsteady-state kinetic data for the initiated chain reaction of N,N′-diphenyl-1,4-benzoquinone diimine with 2,5-dichlorohydroquinone have been developed, and two variants of this method are
presented. The method is based on the study of the unsteady-state disappearance kinetics of one of the initial reactants (quinone
diimine) in its initiated chain reaction with hydroquinone. The unsteadiness of the reaction is due to the presence of semiquinone
radicals or initiator radicals accumulated before the start of the reaction at a concentration exceeding the steady-state
concentration of semiquinone radicals in the chain reaction. The variants of the method differ in the order of mixing the
reactants and initiator, on which the nature and concentration of the radicals accumulated in the system before the reaction
depend. In the first variant, a quinone diimine + initiator solution is initially prepared and initiator radicals are accumulated.
Hydroquinone is added to this solution (start of the reaction). In the second variant, a hydroquinone + initiator solution
is initially prepared and semiquinone radicals from hydroquinone are accumulated. Quinone imine is then added to the solution
(start of the reaction). The disproportionation rate constant of semiquinone radicals (k
6) is derived from the dependence of the decrease in the quinone imine concentration in a certain short time (∼20 s) after
the start of the reaction on the initiation rate. The rate constant k
6 in benzene is (7.3 ± 3.7) × 106 l mol−1 s−1 according to the first variant of the method and (5.0 ± 2.2) × 106 l mol−1 s−1 according to the second one. 相似文献
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To explore the interactions between ubiquinones and oxygen in living organisms, the thermodynamics of a series of electron
and hydrogen transfer reactions between semiquinone radicals, as well as their corresponding protonated forms, and oxygen,
singlet or triplet, were studied using the hybrid Hartree–Fock–density functional theory method Becke's three parameter hybrid
method with the Lee, Yang, and Parr correlation functional. Effects of the solvent and of the isoprenyl tail on the electron
and hydrogen transfer reactions were also investigated. It is found that semiquinone radicals (semiquinone anion radicals
or protonated semiquinone radicals) cannot react with triplet oxygen to form the superoxide anion radical O2
−. In contrast, neutral quinones can scavenge O2
− efficiently. In the gas phase, only protonated semiquinone radicals can react spontaneously with singlet oxygen to produce
peroxyl radical (HO2). However, both semiquinone anion radicals and protonated semiquinone radicals can react with singlet oxygen to produce harmful
oxygen radicals (O2
−
a
l
l
b
u
l
l
and HO2, respectively) in aqueous and protein environments. The free-energy changes of the corresponding reactions obtained for different
ubiquinone systems are very similar. It clearly shows that the isoprenyl tail does not influence the electron and hydrogen
transfer reactions between semiquinone radicals and oxygen significantly. Results of electron affinities, vertical ionization
potentials, and proton affinities also show that the isoprenyl tail has no substantial effect on the electronic properties
of ubiquinones.
Received: 3 July 2000 / Accepted: 6 September 2000 / Published online: 21 December 2000 相似文献
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The semiquinone radicals produced by one-electron reduction of 9, 10-anthraquinone, 1-amino-9, 10-anthraquinone and 1-hydroxy-9, 10-anthraquinone have been characterized in aqueous-organic mixed solvent comprising of 30.2 mol dm−3 water, 5 mol dm−3 isopropanol and 1 mol dm−3 acetone, using the pulse radiolysis technique. Spectroscopic characteristics, the kinetic parameters of formation and decay and one acid dissociation constants of the semiquinones and one-electron reduction potentials of the quinones have been estimated. The characteristics of the present semiquinone systems have been compared with those of other similar systems. The observed differences in characteristics of the semiquinones due to different substitutions have been analysed. 相似文献
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Song Y Buettner GR Parkin S Wagner BA Robertson LW Lehmler HJ 《The Journal of organic chemistry》2008,73(21):8296-8304
Polychlorinated biphenyls (PCBs) comprise a group of persistent organic pollutants that differ significantly in their physicochemical properties, their persistence, and their biological activities. They can be metabolized via hydroxylated and dihydroxylated metabolites to PCB quinone intermediates. We have recently demonstrated that both dihydroxy PCBs and PCB quinones can form semiquinone radicals (SQ(*-)) in vitro. These semiquinone radicals are reactive intermediates that have been implicated in the toxicity of lower chlorinated PCB congeners. Here we describe the synthesis of selected PCB metabolites with differing degrees of chlorination on the oxygenated phenyl ring, e.g., 4,4'-dichloro-biphenyl-2,5-diol, 3,6,4'-trichloro-biphenyl-2,5-diol, 3,4,6,-trichloro-biphenyl-2,5-diol, and their corresponding quinones. In addition, two chlorinated o-hydroquinones were prepared, 6-chloro-biphenyl-3,4-diol and 6,4'-dichloro-biphenyl-3,4-diol. These PCB (hydro-)quinones readily react with oxygen or via comproportionation to yield the corresponding semiquinone free radicals, as detected by electron paramagnetic resonance spectroscopy (EPR alias ESR). The greater the number of chlorines on the (hydro-)quinone (oxygenated) ring, the higher the steady-state level of the resulting semiquinone radical at near neutral pH. 相似文献
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Pedersen JA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(6):1257-1270
From electron paramagnetic resonance (EPR) spectra of numerous semiquinone anion radicals we propose that the spin density distributions in benzo-, naphtho- and anthrasemiquinones are changed under the influence of various substituent in a comparable fashion, electron donating substituents having the opposite effect of withdrawing ones. These findings facilitate the work in obtaining correct assignments, further leading to safe identification of new radicals. Semiquinone anion radicals of para- and ortho-hydroquinones are demonstrated to exist at physiological pH in buffered solutions under continuous access to molecular oxygen. Reaction schemes are proposed for the formation of primary and tertiary radicals and hydroxylated products of ten quinols. From studies on crude plant extracts are three quinols, known as precursors in the biogenesis of chimaphilin, observed and identified in Chimaphila umbellata. Other studies demonstrate the power of using semiquinone radicals as chemotaxonomic markers. 相似文献
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《Analytical letters》2012,45(1):75-84
Abstract We analyzed the solid state and aqueous solution electron spin resonance (esr) spectra of Oyster River and Podzol soil fulvic and humic acids. Because the aqueous solution esr spectra mimic the behavior of the model compound para-benzosemiquinone, we conclude that semiquinone free radicals predominate in fulvic acid. In addition a decrease in spin concentration at a potential of 0.20 volts (vs. SCE) demonstrates that the semiquinone radicals are at least partially responsible for the reducing capability of humic materials. From the above results we devised a quantitative semiquinone analysis for humic materials. 相似文献