Artículos de revistas: "Quinone"

1

Weiss, Sophie A. y Lars J. C. Jeuken. "Electrodes modified with lipid membranes to study quinone oxidoreductases". Biochemical Society Transactions 37, n.º 4 (22 de julio de 2009): 707–12. http://dx.doi.org/10.1042/bst0370707.

Texto completo

Resumen

Quinone oxidoreductases are a class of membrane enzymes that catalyse the oxidation or reduction of membrane-bound quinols/quinones. The conversion of quinone/quinol by these enzymes is difficult to study because of the hydrophobic nature of the enzymes and their substrates. We describe some biochemical properties of quinones and quinone oxidoreductases and then look in more detail at two model membranes that can be used to study quinone oxidoreductases in a native-like membrane environment with their native lipophilic quinone substrates. The results obtained with these model membranes are compared with classical enzyme assays that use water-soluble quinone analogues.

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Wang, Zhen-Hua, Xiao-Hui Fu, Qun Li, Yong You, Lei Yang, Jian-Qiang Zhao, Yan-Ping Zhang y Wei-Cheng Yuan. "Recent Advances in the Domino Annulation Reaction of Quinone Imines". Molecules 29, n.º 11 (24 de mayo de 2024): 2481. http://dx.doi.org/10.3390/molecules29112481.

Texto completo

Resumen

Quinone imines are important derivatives of quinones with a wide range of applications in organic synthesis and the pharmaceutical industry. The attack of nucleophilic reagents on quinone imines tends to lead to aromatization of the quinone skeleton, resulting in both the high reactivity and the unique reactivity of quinone imines. The extreme value of quinone imines in the construction of nitrogen- or oxygen-containing heterocycles has attracted widespread attention, and remarkable advances have been reported recently. This review provides an overview of the application of quinone imines in the synthesis of cyclic compounds via the domino annulation reaction.

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Jensen,, Kenneth A., Zachary C. Ryan, Amber Vanden Wymelenberg, Daniel Cullen y Kenneth E. Hammel. "An NADH:Quinone Oxidoreductase Active during Biodegradation by the Brown-Rot Basidiomycete Gloeophyllum trabeum". Applied and Environmental Microbiology 68, n.º 6 (junio de 2002): 2699–703. http://dx.doi.org/10.1128/aem.68.6.2699-2703.2002.

Texto completo

Resumen

ABSTRACT The brown-rot basidiomycete Gloeophyllum trabeum uses a quinone redox cycle to generate extracellular Fenton reagent, a key component of the biodegradative system expressed by this highly destructive wood decay fungus. The hitherto uncharacterized quinone reductase that drives this cycle is a potential target for inhibitors of wood decay. We have identified the major quinone reductase expressed by G. trabeum under conditions that elicit high levels of quinone redox cycling. The enzyme comprises two identical 22-kDa subunits, each with one molecule of flavin mononucleotide. It is specific for NADH as the reductant and uses the quinones produced by G. trabeum (2,5-dimethoxy-1,4-benzoquinone and 4,5-dimethoxy-1,2-benzoquinone) as electron acceptors. The affinity of the reductase for these quinones is so high that precise kinetic parameters were not obtainable, but it is clear that k cat/Km for the quinones is greater than 108 M−1 s−1. The reductase is encoded by a gene with substantial similarity to NAD(P)H:quinone reductase genes from other fungi. The G. trabeum quinone reductase may function in quinone detoxification, a role often proposed for these enzymes, but we hypothesize that the fungus has recruited it to drive extracellular oxyradical production.

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Miseviciene, Lina, Zilvinas Anusevicius, Jonas Sarlauskas, Richard J. Harris, Nigel S. Scrutton y Narimantas Cenas. "Two-electron reduction of quinones by Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase: quantitative structure-activity relationships." Acta Biochimica Polonica 54, n.º 2 (4 de junio de 2007): 379–85. http://dx.doi.org/10.18388/abp.2007_3260.

Texto completo

Resumen

In order to clarify the poorly understood mechanisms of two-electron reduction of quinones by flavoenzymes, we examined the quinone reductase reactions of a member of a structurally distinct old yellow enzyme family, Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase (PETNR). PETNR catalyzes two-electron reduction of quinones according to a 'ping-pong' scheme. A multiparameter analysis shows that the reactivity of quinones increases with an increase in their single-electron reduction potential and pK(a) of their semiquinones (a three-step (e(-),H(+),e(-)) hydride transfer scheme), or with an increase in their hydride-transfer potential (E(7)(H(-))) (a single-step (H(-)) hydride transfer scheme), and decreases with a decrease in their van der Waals volume. However, the pH-dependence of PETNR reactivity is more consistent with a single-step hydride transfer. A comparison of X-ray data of PETNR, mammalian NAD(P)H : quinone oxidoreductase (NQO1), and Enterobacter cloacae nitroreductase, which reduce quinones in a two-electron way, and their reactivity revealed that PETNR is much less reactive, and much less sensitive to the quinone substrate steric effects than NQO1. This may be attributed to the lack of pi-pi stacking between quinone and the displaced aromatic amino acid in the active center, e.g., with Phe-178' in NQO1.

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Vienozinskis, J., A. Butkus, N. Cenas y J. Kulys. "The mechanism of the quinone reductase reaction of pig heart lipoamide dehydrogenase". Biochemical Journal 269, n.º 1 (1 de julio de 1990): 101–5. http://dx.doi.org/10.1042/bj2690101.

Texto completo

Resumen

The relationship between the NADH:lipoamide reductase and NADH:quinone reductase reactions of pig heart lipoamide dehydrogenase (EC 1.6.4.3) was investigated. At pH 7.0 the catalytic constant of the quinone reductase reaction (kcat.) is 70 s-1 and the rate constant of the active-centre reduction by NADH (kcat./Km) is 9.2 x 10(5) M-1.s-1. These constants are almost an order lower than those for the lipoamide reductase reaction. The maximal quinone reductase activity is observed at pH 6.0-5.5. The use of [4(S)-2H]NADH as substrate decreases kcat./Km for the lipoamide reductase reaction and both kcat. and kcat./Km for the quinone reductase reaction. The kcat./Km values for quinones in this case are decreased 1.85-3.0-fold. NAD+ is a more effective inhibitor in the quinone reductase reaction than in the lipoamide reductase reaction. The pattern of inhibition reflects the shift of the reaction equilibrium. Various forms of the four-electron-reduced enzyme are believed to reduce quinones. Simple and ‘hybrid ping-pong’ mechanisms of this reaction are discussed. The logarithms of kcat./Km for quinones are hyperbolically dependent on their single-electron reduction potentials (E1(7]. A three-step mechanism for a mixed one-electron and two-electron reduction of quinones by lipoamide dehydrogenase is proposed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Giulivi, C. y E. Cadenas. "One- and two-electron reduction of 2-methyl-1,4-naphthoquinone bioreductive alkylating agents: kinetic studies, free-radical production, thiol oxidation and DNA-strand-break formation". Biochemical Journal 301, n.º 1 (1 de julio de 1994): 21–30. http://dx.doi.org/10.1042/bj3010021.

Texto completo

Resumen

The one- and two-electron enzymic reduction of the bioreductive alkylating agents 2-methylmethoxynaphthoquinone (quinone I) and 2-chloromethylnaphthoquinone (quinone II) was studied with purified NADPH-cytochrome P-450 reductase and DT-diaphorase respectively, and characterized in terms of kinetic constants, oxyradical production, thiol oxidation and DNA-strand-break formation. The catalytic-centre activity values indicated that DT-diaphorase catalysed the reduction of quinone I far more efficiently than NADPH-cytochrome P-450 reductase, although the Km values of the two enzymes for this quinone were similar (1.2-3.0 microM). The one-electron-transfer flavoenzyme also catalysed the reduction of quinone II, but the behaviour of DT-diaphorase towards this quinone did not permit calculation of kinetic constants. A salient feature of the redox transitions caused by the one- and two-electron catalysis of these quinones was the different contributions of disproportionation and autoxidation reactions respectively. In the former case, about 26% of NADPH consumed was accounted for in terms of autoxidation (as H2O2 formation), whereas in the latter, the autoxidation component accounted for most (98%) of the NADPH consumed. This difference was abrogated by superoxide dismutase, which enhanced autoxidation during NADPH-cytochrome P-450 catalysis to a maximal value. E.s.r. analysis indicated the formation of superoxide radicals, the signal of which was suppressed by superoxide dismutase and unaffected by catalase. The one- and two-electron reduction of these quinones in the presence of GSH was accompanied by formation of thiyl radicals. Although superoxide dismutase suppressed the thiol radical e.s.r. signal in both instances, the enzyme enhanced GSSG accumulation during NADPH-cytochrome P-450 catalysis of quinone I, whereas it inhibited GSSG formation during reduction of the quinone by DT-diaphorase. One- and two-electron reduction of quinone I led to calf thymus DNA-strand-break formation, a process that (a) was substantially decreased in experiments performed with dialysed DNA and in the presence of desferal and (b) was partially sensitive to superoxide dismutase and/or catalase. These findings are rationalized in terms of the occurrence of metal ions ligated to DNA, protecting against the toxic effects of superoxide radicals generated during enzymic reduction of quinones.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

Breker, Johannes, Reinhard Schmutzler, Bernd Dorbath y Markus Wieber. "Reaktionen von unsymmetrischen λ5P – λ3P-Diphosphorverbindungen und von Diphosphinen (λ3P – λ3P) mit o-Chinonen / Reactions of Unsymmetrical λ5Ρ – λ3Ρ Diphosphorus Compounds and of Diphosphines (λ3P – λ3P) with o-Quinones". Zeitschrift für Naturforschung B 45, n.º 8 (1 de agosto de 1990): 1177–86. http://dx.doi.org/10.1515/znb-1990-0812.

Texto completo

Resumen

The reaction of λ5Ρ – λ3Ρ diphosphorus compounds with o-quinones, e.g. tetrachloro-o-benzoquinone or 2,5-di-tert-butyl-o-benzoquinone, led not only to oxidative addition of the o-quinone to λ3Ρ but also to insertion of a further molecule of o-quinone into the P–P bond (i.e. λ5Ρ – λ3Ρ diphosphorus compound and o-quinone reacted in a molar ratio 1:2). In the course of these oxidative addition and insertion reactions the o-quinones were converted into the corresponding hydroquinones (i.e. catechols). The products of these reactions were characterized by NMR and mass spectrometric methods, and by elemental analysis. The hydrolysis of the 1:2 addition products proceeded with cleavage of a P–O–C (hydroquinone) bond and formation of mononuclear products, involving λ4Ρ and λ5Ρ, respectively. A mechanism of this hydrolysis is proposed and has been elucidated by independent synthesis of some products. Diphosphines, i.e. symmetrical λ3Ρ – λ3Ρ diphosphorus compounds, were found to react with o-quinones in the same fashion in a molar ratio 1:3, i.e. with oxidative addition of the o-quinone to both λ3P atoms and insertion of tetrachloro-o-catechol into the P–P bond.

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

Monks, Terrence y Douglas Jones. "The Metabolism and Toxicity of Quinones, Quinonimines, Quinone Methides, and Quinone-Thioethers". Current Drug Metabolism 3, n.º 4 (1 de agosto de 2002): 425–38. http://dx.doi.org/10.2174/1389200023337388.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

Flynn, Noah R., Michael D. Ward, Mary A. Schleiff, Corentine M. C. Laurin, Rohit Farmer, Stuart J. Conway, Gunnar Boysen, S. Joshua Swamidass y Grover P. Miller. "Bioactivation of Isoxazole-Containing Bromodomain and Extra-Terminal Domain (BET) Inhibitors". Metabolites 11, n.º 6 (15 de junio de 2021): 390. http://dx.doi.org/10.3390/metabo11060390.

Texto completo

Resumen

The 3,5-dimethylisoxazole motif has become a useful and popular acetyl-lysine mimic employed in isoxazole-containing bromodomain and extra-terminal (BET) inhibitors but may introduce the potential for bioactivations into toxic reactive metabolites. As a test, we coupled deep neural models for quinone formation, metabolite structures, and biomolecule reactivity to predict bioactivation pathways for 32 BET inhibitors and validate the bioactivation of select inhibitors experimentally. Based on model predictions, inhibitors were more likely to undergo bioactivation than reported non-bioactivated molecules containing isoxazoles. The model outputs varied with substituents indicating the ability to scale their impact on bioactivation. We selected OXFBD02, OXFBD04, and I-BET151 for more in-depth analysis. OXFBD’s bioactivations were evenly split between traditional quinones and novel extended quinone-methides involving the isoxazole yet strongly favored the latter quinones. Subsequent experimental studies confirmed the formation of both types of quinones for OXFBD molecules, yet traditional quinones were the dominant reactive metabolites. Modeled I-BET151 bioactivations led to extended quinone-methides, which were not verified experimentally. The differences in observed and predicted bioactivations reflected the need to improve overall bioactivation scaling. Nevertheless, our coupled modeling approach predicted BET inhibitor bioactivations including novel extended quinone methides, and we experimentally verified those pathways highlighting potential concerns for toxicity in the development of these new drug leads.

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Xu, Wei, William R. Dolbier, Jian-Xin Duan, Yian Zhai, Katsu Ogawa, Merle A. Battiste y Ion Ghiviriga. "Octafluoro[2.2]paracyclophane (AF4) Quinone". Collection of Czechoslovak Chemical Communications 73, n.º 12 (2008): 1764–76. http://dx.doi.org/10.1135/cccc20081764.

Texto completo

Resumen

Octafluoro[2.2]paracyclophane (AF4) has been oxidized by treatment with HIO3 in CF3CO2H to form the corresponding p-quinone along with a unique triketone. This quinone undergoes reduction to the respective hydroquinone as well as a Diels-Alder reaction with 1,3-cyclohexadiene. Its reduction potential was obtained by cyclic voltammetry and is discussed in the context of other quinones.

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Gready, JE, K. Hata, S. Sternhell y CW Tansey. "N.M.R.-Study of Bond Orders in o- and p-Quinone". Australian Journal of Chemistry 43, n.º 3 (1990): 593. http://dx.doi.org/10.1071/ch9900593.

Texto completo

Resumen

The 4J(Me-CC-H) coupling constant, previously established as a probe of bond order,1-3 was used to examine bond orders in a number of quinones. It was found that the presence of a quinone moiety does not cause bond localization in aromatic rings adjacent to the quinone ring.

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Li, Jin, Kattesh V. Katti, Ronald G. Cavell, A. Alan Pinkerton y Herbert Nar. "Synthesis and characterization of phosphinimine-substituted trifluoro- or trichloro-p-benzoquinones and their cationic Rh(I) complexes. The crystal and molecular structure of 3,5,6-trichloro-2-(triphenylphosphinimino)-p-benzoquinone". Canadian Journal of Chemistry 74, n.º 11 (1 de noviembre de 1996): 2378–85. http://dx.doi.org/10.1139/v96-265.

Texto completo

Resumen

Reaction of tetrafluoro- or tetrachloro-p-benzoquinone with silylated phosphoranimines R2R′P=NSiMe3 (R = Ph, Me) yields very highly colored monosubstituted derivatives of the p-quinone that act as two-electron acceptors showing clean, reversible CV traces. The molar absorptivity values are typical of dyes. These ligands also form chelate complexes with Rh(I) precursors using the quinone oxygen and the imine nitrogen donor sites. One of the quinone derivatives, 3,5,6-trichloro-2-(triphenylphosphinimino)-p-benzoquinone, has been structurally characterized. The iminated quinone shows a normal P=N bond length (1.597(2) Å) and P-N-C angle (P-N-C(3) 132.7(2)°). The N—C(3) bond, 1.327(3) Å, is a little shorter as is expected for the establishment of a conjugated structure between the phosphinimine substituent and the quinone ring. Some steric crowding pushes the Cl and N substituents on the quinone ring out of the plane of the ring. Key words: quinones, phosphinimines, fluorine, chlorine, rhodium.

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Ellis, Jessie, Xueyan Fu, J. Philip Karl, Patrick Radcliffe, Jason Soares, Laurel Doherty, Christopher Hernandez, Joel Mason, Angela Oliverio y Sarah Booth. "Investigation of Vitamin K Quinone Metabolism by Human Gut Bacteria". Current Developments in Nutrition 4, Supplement_2 (29 de mayo de 2020): 392. http://dx.doi.org/10.1093/cdn/nzaa045_025.

Texto completo

Resumen

Abstract Objectives Vitamin K (VK) is a family of structurally-related quinones, phylloquinone (PK) and menaquinones (MKn, n = prenyl units in side chain), that share a common napthoquinone ring (menadione, MD). VK quinones function as an essential dietary nutrient for humans. MD is considered a pro-vitamin form of VK. Plants and bacteria that produce VK quinones (PK and MKn, respectively) use them as an electron carrier in energy production. Little is known about the interaction of dietary VK quinones with gut bacteria, which may be bi-directional. The objective of this study was to investigate the influence of VK quinones and MD on human gut bacteria composition and MKn production. Methods Stool from 5 healthy male donors was pooled and inoculated in bioreactors under conditions mimicking the colon (anaerobic, pH 6.8, 37°C) for 48 h. Bioreactors were treated with deuterium (2H)-labeled quinones (2H-PK, 2H-MK4, 2H-MK9 or 2H-MD); no quinones (cell controls); or 2H-quinone treatment with no stool (cell-free controls). Culture aliquots were collected at 0, 5, 10, 24, and 48 h, and separated into pellet and supernatant fractions. Experiments were conducted in triplicate. All fractions were analyzed for VK quinone content using LC-MS. DNA from 0 and 24 h pellet fractions was extracted and amplified for paired-end 16S sequencing on an Illumina MiSeq 2500. Differences in bacterial composition were assessed using PERMANOVA. Results Supplemented 2H-quinones accumulated in the pellet fraction over time. This was not observed in cell-free controls and was thus not a function of culture media solubility. Endogenous (unlabeled) production of MKn was unaffected by supplementation of 2H-quinones. Generated 2H-MKn (2H-MK4, 2H-MK9, 2H-MK10, and 2H-MK11) were only detected in 2H-MD supplemented vessels. Community-wide bacterial composition significantly differed between 0 h and 24 h (r2 = 0.85, P = 0.001), but not by quinone treatment. Conclusions PK and MKn, dietary viamin K quinones, were not transformed by gut microbes to MKn in vitro, whereas the pro-vitamin quinone MD was transformed to MKn of multiple side chain lengths. Although no quinone induced community-wide changes in bacteria composition, additional analyses are needed to assess species-specific growth promotion. Funding Sources USDA ARS and DOD Health Program.

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Begleiter, Asher. "The contribution of alkylation to the activity of quinone antitumor agents". Canadian Journal of Physiology and Pharmacology 64, n.º 5 (1 de mayo de 1986): 581–85. http://dx.doi.org/10.1139/y86-096.

Texto completo

Resumen

Studies have shown that the quinone group can produce tumor cell kill by a mechanism involving active oxygen species. This cytotoxic activity can be correlated with the induction of DNA double strand breaks and is enhanced by the ability of the quinone compound to bind to DNA by alkylation. The cytotoxic activity and the production of DNA damage by model quinone antitumor agents were compared in L5178Y cells, sensitive and resistant to alkylating agents, to assess the contribution of alkylation to the activity of these agents. The resistant L5178Y/HN2 cells were found to be two fold and six fold more resistant to the alkylating quinones, benzoquinone mustard and benzoquinone dimustard, respectively, than parent L5178Y cells. In contrast, the L5178 Y/HN2 cells showed no resistance to the nonalkylating quinones, hydrolyzed benzoquinone mustard and bis(dimethylamino)benzoquinone. The alkylating quinones produced approximately two fold less cross-linking in L5178Y/HN2 cells compared with L5178Y sensitive cells. DNA double strand break formation by hydrolyzed benzoquinone mustard and bis(dimethylamino)benzoquinone was not significantly different in sensitive and resistant cells. However, the induction of double strand breaks by the alkylating quinones benzoquinone mustard and benzoquinone dimustard was reduced by 5-fold and 15-fold, respectively, in L5178Y/HN2 cells. These results show that the alkylating activity of the alkylating quinones cannot directly explain all of the enhanced cytotoxic activity of these agents. Furthermore, they provide strong evidence that the enhanced formation of DNA double strand breaks by alkylating quinone agents is directly related to the ability of these agents to bind to DNA. This increased formation of strand breaks may account for the enhanced cytotoxic activity of the alkylating quinones.

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Lima, Larissa S., Luiz Cláudio de A. Barbosa, Elson S. de Alvarenga, Antônio J. Demuner y Antônio A. da Silva. "Synthesis and Phytotoxicity Evaluation of Substituted para-Benzoquinones". Australian Journal of Chemistry 56, n.º 6 (2003): 625. http://dx.doi.org/10.1071/ch02032.

Texto completo

Resumen

Sorgoleone (1) is one of the major constituents of sorghum root exudates. Sorgoleone is an allelochemical that reduces the growth of broad-leaf plants. The 3,5-dimethoxybenzylic alcohol (3) was used as starting material for the synthesis of 2-methoxy-6-(non-1-yl)benzo-1,4-quinone (9) in 69% yield. Acetylation of (9) with acetic anhydride gave the triacetate (10) in 82% yield. The triacetate (10) was then converted in two steps in 2-hydroxy-5-methoxy-3-(non-1-yl)benzo-1,4-quinone (11) and 2-acetoxy-5-methoxy-3-(non-1-yl)benzo-1,4-quinone (12) in 8% and 37% yield, respectively. Quinone (11) was obtained also by reaction of (12) with DBU in 63% yield. Alkylation of (3) and oxidation with chromic anhydride formed the new quinones (16) (17) and (18) in 23%, 16% and 12% overall yield, respectively. The effect of these quinones and sorgoleone (1) at concentrations of 5.5 μg g–1 on the development of radicle and aerial parts of Cucumis sativus, Brachiaria decumbens, Hyptis lophanta, and Euphorbia heterophylla was tested.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Russell, RA, BA Pilley, RW Irvine y RN Warrener. "Anthracyclines. XVI. Further Comments Concerning the Phthalide Anion Annelation of Quinone Monoacetals". Australian Journal of Chemistry 40, n.º 2 (1987): 311. http://dx.doi.org/10.1071/ch9870311.

Texto completo

Resumen

.Yields of tricyclic and tetracyclic quinones prepared by annelation of quinone monoacetals with the anion of 3-phenylsulfonylphthalides are shown to be sensitive to the substituent on both the phthalide and the quinone monoacetal partner. In contrast, reactions with the anions of 3-cyanophthalides afford high yields of condensed products in all cases examined.

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Juliasih, Ni Luh Gede Ratna, Lee Chang Yuan, Yuki Sago, Yoichi Atsuta y Hiroyuki Daimon. "Supercritical Fluid Extraction of Quinones from Compost for Microbial Community Analysis". Journal of Chemistry 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/717616.

Texto completo

Resumen

Supercritical fluid extraction (SFE) was used to extract quinones from compost to monitor the microbial community dynamics during composting. The 0.3 g of dried compost was extracted using 3 mL min−1of carbon dioxide (90%) and methanol (10%) at 45°C and 25 MPa for a 30 min extraction time. The extracted quinones were analysed using ultra performance liquid chromatography (UPLC) with 0.3 mL min−1of methanol mobile phase for a 50 min chromatographic run time. A comparable detected amount of quinones was obtained using the developed method and an organic solvent extraction method, being 36.06 μmol kg−1and 34.54 μmol kg−1, respectively. Significantly low value of dissimilarity index (D) between the two methods (0.05) indicated that the quinone profile obtained by both methods was considered identical. The developed method was then applied to determine the maturity of the compost by monitoring the change of quinone during composting. The UQ-9 and MK-7 were predominant quinones in the initial stage of composting. The diversity of quinone became more complex during the cooling and maturation stages. This study showed that SFE had successfully extracted quinones from a complex matrix with simplification and rapidity of the analysis that is beneficial for routine analysis.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Ito, Shosuke, Manickam Sugumaran y Kazumasa Wakamatsu. "Chemical Reactivities of ortho-Quinones Produced in Living Organisms: Fate of Quinonoid Products Formed by Tyrosinase and Phenoloxidase Action on Phenols and Catechols". International Journal of Molecular Sciences 21, n.º 17 (24 de agosto de 2020): 6080. http://dx.doi.org/10.3390/ijms21176080.

Texto completo

Resumen

Tyrosinase catalyzes the oxidation of phenols and catechols (o-diphenols) to o-quinones. The reactivities of o-quinones thus generated are responsible for oxidative browning of plant products, sclerotization of insect cuticle, defense reaction in arthropods, tunichrome biochemistry in tunicates, production of mussel glue, and most importantly melanin biosynthesis in all organisms. These reactions also form a set of major reactions that are of nonenzymatic origin in nature. In this review, we summarized the chemical fates of o-quinones. Many of the reactions of o-quinones proceed extremely fast with a half-life of less than a second. As a result, the corresponding quinone production can only be detected through rapid scanning spectrophotometry. Michael-1,6-addition with thiols, intramolecular cyclization reaction with side chain amino groups, and the redox regeneration to original catechol represent some of the fast reactions exhibited by o-quinones, while, nucleophilic addition of carboxyl group, alcoholic group, and water are mostly slow reactions. A variety of catecholamines also exhibit side chain desaturation through tautomeric quinone methide formation. Therefore, quinone methide tautomers also play a pivotal role in the fate of numerous o-quinones. Armed with such wide and dangerous reactivity, o-quinones are capable of modifying the structure of important cellular components especially proteins and DNA and causing severe cytotoxicity and carcinogenic effects. The reactivities of different o-quinones involved in these processes along with special emphasis on mechanism of melanogenesis are discussed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Khetan, Abhishek. "High-Throughput Virtual Screening of Quinones for Aqueous Redox Flow Batteries: Status and Perspectives". Batteries 9, n.º 1 (28 de diciembre de 2022): 24. http://dx.doi.org/10.3390/batteries9010024.

Texto completo

Resumen

Quinones are one of the most promising and widely investigated classes of redox active materials for organic aqueous redox flow batteries. However, quinone-based flow batteries still lack the necessary performance in terms of metrics, such as specific capacity, power density, and long-term stability, to achieve mass market adoption. These performance metrics are directly related to the physicochemical properties of the quinone molecules, including their equilibrium redox potential, aqueous solubility, and chemical stability. Given the enormous chemical and configurational space of possible quinones and the high tunability of their properties, there has been a recent surge in the use of high-throughput virtual screening (HTVS) for the rational design and discovery of new high-performing molecules. In this review article, HTVS efforts for the computational design and discovery of quinones are reviewed with a special focus on the enumerated space of core quinone motif, the methods and approximations used for the estimation of performance descriptors, and the emergent structure-property relationships. The knowledge and methodological gaps in conventional HTVS efforts are discussed, and strategies for improvement are suggested.

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Norkov, Sergey V., Anton V. Cherkasov, Andrey S. Shavyrin, Maxim V. Arsenyev, Viacheslav A. Kuropatov y Vladimir K. Cherkasov. "Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands". Beilstein Journal of Organic Chemistry 17 (27 de enero de 2021): 273–82. http://dx.doi.org/10.3762/bjoc.17.26.

Texto completo

Resumen

The fused 1,3-dithiole spacer seems to be very suitable for the functionalization of sterically hindered o-quinones with additional groups capable of coordination of metal ions and/or possessing a redox activity. An effective method for the synthesis of sterically hindered o-quinones containing 1,3-diketonate, dinitrile and p-quinone-methide functional groups at the periphery of the ligand has been developed. The novel compounds have rigid and conjugated structures and exhibit properties typical of o-quinones. A study of their monoreduced semiquinone derivatives reveal that the spin density is delocalized across the whole molecule, including peripheral fragments. The first stable o-quinone derivative bearing an annulated thiete heterocycle has been isolated and characterized.

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Wiraswati, Hesti L., Fida M. Warganegara, Akhmaloka Akhmaloka y Muhamad A. Martoprawiro. "Molecular Docking Studies of ROS Agent from Quinone Family to Reductase Enzymes:Implication in Finding Anticancer Drug Candidate". Biomedical and Pharmacology Journal 14, n.º 02 (30 de junio de 2021): 681–89. http://dx.doi.org/10.13005/bpj/2170.

Texto completo

Resumen

Understanding the metabolism of cytotoxic compounds of quinone family is importance in cancer therapy because they have been successfully explored for their anti-tumor activity. Quinone which form radical semiquinone (by reductase enzymes) to generate Reactive Oxygen Species (ROS) is associated to be anticancer drug candidate. However, molecular mechanism of those compounds to reductase enzymes has not yet clearly understood.This study aimed to understand molecular interaction of quinones to oxidoreductase enzymes such as cytochrome P450 reductase or ubiquinone reductase (NQO1), or apoptosis inducing factor (AIF) which is recently reported as NADH:quinone reductase. In silico approach was applied to find the best affinity of each compound to enzymes. Optimize ligands were employed using Marvin sketch program. Molecular interaction using autodockvina software was built to measure important residues for quinone reduction. Docking analysis showed that generally quinones prefer bound to cytochrome P450 reductase rather than NQO1 or AIF. The number of ring seems affect to the affinity, but not for its functional groups. Residues analysis confirmed that reduction of quinone is NAD(P)H: dependent. The result revealedthat all ligands have high possibility to compete with their redox coupleswhich is needed in its capacity as an anti-cancer drug.

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Kass, G. E., S. K. Duddy y S. Orrenius. "Activation of hepatocyte protein kinase C by redox-cycling quinones". Biochemical Journal 260, n.º 2 (1 de junio de 1989): 499–507. http://dx.doi.org/10.1042/bj2600499.

Texto completo

Resumen

The effects of quinone-generated active oxygen species on rat hepatocyte protein kinase C were investigated. The specific activity of cytosolic protein kinase C was increased 2-3-fold in hepatocytes incubated with the redox-cycling quinones, menadione, duroquinone or 2,3-dimethoxy-1,4-naphthoquinone, without alterations in particulate protein kinase C specific activity or Ca2+- and lipid-independent kinase activities. Redox-cycling quinones did not stimulate translocation of protein kinase C; however, activated protein kinase C was redistributed from cytosol to the particulate fraction when quinone-treated hepatocytes were exposed to 12-O-tetradecanoylphorbol 13-acetate (TPA). Quinone treatment did not alter cytosolic phorbol 12,13-dibutyrate (PDBu) binding capacity, and the cytosol of both control and quinone-treated hepatocytes exhibited a Kd for PDBu binding of 2 nM. Quinone-mediated activation of cytosolic protein kinase C was reversed by incubation with 10 mM-beta-mercaptoethanol, dithiothreitol or GSH, at 4 degrees C for 24 h. Furthermore, protein kinase C specific activity in control cytosol incubated in air increased by over 100% within 3 h; this increase was reversed by thiol-reducing agents. Similarly, incubation of partially-purified rat brain protein kinase C in air, or with low concentrations of GSSG in the presence of GSH, resulted in a 2-2.5-fold increase in Ca2+- and lipid-dependent kinase activity. In contrast with the effects of the redox-cycling quinones, when hepatocytes were treated with the thiol agents N-ethylmaleimide (NEM), p-benzoquinone (pBQ) or p-chloromercuribenzoic acid (pCMB), the cytosolic Ca2+- and lipid-dependent kinase activity was significantly inhibited, but the particulate-associated protein kinase C activity was unaffected. The Ca2+- and lipid-independent kinase activity of both the cytosolic and particulate fractions was significantly stimulated by NEM, but was unaffected by pBQ and pCMB. These results show that hepatocyte cytosolic protein kinase C is activated to a high-Vmax form by quinone-generated active oxygen species, and this effect is due to a reduction-sensitive modification of the thiol/disulphide status of protein kinase C.

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Luo, Yu Jiao, Ling Feng Qiu, Yi Ming Chen y Jian Zhang. "Preliminary Discussion on the Activity of Denitrifying Phosphorus-Removing Bacteria in Sequencing Batch Reactors by Quinone Profile Analysis". Advanced Materials Research 518-523 (mayo de 2012): 440–43. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.440.

Texto completo

Resumen

Based on DPBs (Denitrifying Phosphorus-removing Bacteria) obtained from a lab-scale SBR, a quinone profile system had been established to analyze quinones in sludge samples. There existed a positive correlation between the contents of UQ-8 extracted from the sludge samples and the denitrifying and phosphorus removal efficiency of the treating system. With quinone profiles taken as a new important index, it was evidently feasible to determine the removal effect.

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Oliveira, Joyce C., Renato L. de Carvalho, Hugo G. S. Sampaio, João Honorato, Javier A. Ellena, Felipe T. Martins, João V. M. Pereira et al. "It Takes Two to Tango, Part II: Synthesis of A-Ring Functionalised Quinones Containing Two Redox-Active Centres with Antitumour Activities". Molecules 28, n.º 5 (27 de febrero de 2023): 2222. http://dx.doi.org/10.3390/molecules28052222.

Texto completo

Resumen

In 2021, our research group published the prominent anticancer activity achieved through the successful combination of two redox centres (ortho-quinone/para-quinone or quinone/selenium-containing triazole) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The combination of two naphthoquinoidal substrates towards a synergetic product was indicated, but not fully explored. Herein, we report the synthesis of 15 new quinone-based derivatives prepared from click chemistry reactions and their subsequent evaluation against nine cancer cell lines and the murine fibroblast line L929. Our strategy was based on the modification of the A-ring of para-naphthoquinones and subsequent conjugation with different ortho-quinoidal moieties. As anticipated, our study identified several compounds with IC50 values below 0.5 µM in tumour cell lines. Some of the compounds described here also exhibited an excellent selectivity index and low cytotoxicity on L929, the control cell line. The antitumour evaluation of the compounds separately and in their conjugated form proved that the activity is strongly enhanced in the derivatives containing two redox centres. Thus, our study confirms the efficiency of using A-ring functionalized para-quinones coupled with ortho-quinones to obtain a diverse range of two redox centre compounds with potential applications against cancer cell lines. Here as well, it literally takes two for an efficient tango!

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

MacDonald, Michael J. "Stimulation of insulin release from pancreatic islets by quinones". Bioscience Reports 11, n.º 3 (1 de junio de 1991): 165–70. http://dx.doi.org/10.1007/bf01182485.

Texto completo

Resumen

Coenzyme Q (CoQ0) and other quinones were shown to be potent insulin secretagogues in the isolated pancreatic islet. The order of potency was CoQ0≅benzoquinone≅hydroquinonemenadione. CoQ6 and CoQ10 (ubiquinone), duroquinone and durohydroquinone did not stimulate insulin release. CoQ0's insulinotropism was enhanced in calcium-free medium and CoQ0 appeared to stimulate only the second phase of insulin release. CoQ0 inhibited inositol mono-, bis- and trisphosphate formation. Inhibitors of mitochondrial respiration (rotenone, antimycin A, FCCP and cyanide) and the calcium channel blocker verapamil, did not inhibit CoQ0-induced insulin release. Dicumarol, an inhibitor of quinone reductase, did not inhibit CoQ0-induced insulin release, but it did inhibit glucose-induced insulin release suggesting that the enzyme and quinones play a role in glucose-induced insulin release. Quinones may stimulate insulin release by mimicking physiologically-occuring quinones, such as CoQ10, by acting on the plasma membrane or in the cytosol. Exogenous quinones may bypass the quinone reductase reaction, as well as many reactions important for exocytosis.

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Lian, Xiao-Lei, Alafate Adili, Bin Liu, Zhong-Lin Tao y Zhi-Yong Han. "Enantioselective [4 + 1] cycloaddition of ortho-quinone methides and bromomalonates under phase-transfer catalysis". Organic & Biomolecular Chemistry 15, n.º 17 (2017): 3670–73. http://dx.doi.org/10.1039/c7ob00484b.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Webster, Richard David. "Utilizing Redox Transformations of Quinones to Modulate Weak Donor and Acceptor Bonding Interactions with H₂o and CO₂ in Organic Solvents". ECS Meeting Abstracts MA2023-01, n.º 41 (28 de agosto de 2023): 2335. http://dx.doi.org/10.1149/ma2023-01412335mtgabs.

Texto completo

Resumen

Redox chemical transformations can be used to modulate supramolecular interactions between reduced quinones and acceptor molecules, with the application of an electric potential enabling the interactions to be switched on and off. The supramolecular interactions targeted include weak solution phase processes involving H-bonding with water molecules, and interactions between dissolved molecular gases such as CO2 and solution phase electroactive species. The advantage of this approach is that it enables the supramolecular complexing abilities of one molecule to be improved and tuned simply by changing its redox state. For instance, in one redox state the compound may undergo no supramolecular interactions, but once it is oxidized or reduced it undergoes very strong interactions. This enables the development of potential sensing devices as well as the ability to gain fundamental information regarding interactions that are difficult to quantify, including H-bonding. In aprotic organic solvents, neutral quinones (Q) undergo an EE reduction mechanism (E signifies an electron transfer) to first give a radical anion or semiquinone (Q•–) at potential E Q1, followed by an aromatic dianion (Q2–) at a more negative potential, E Q2. When water is progressively added to the solvent, the second reduction wave (E Q2) progressively moves towards more positive potentials until it eventually merges with the first reduction wave (E Q1), so the two electrons transfer at close to one potential. The reason for the shift in potential is because the quinone anions, especially the dianions, undergo very strong H-bonding interactions through the highly electronegative oxygen atoms in the reduced quinones with the hydrogen atoms from the water molecules. In order to be able to quantitatively study the reactions with water, it is essential that the exact water content of the solvent is known, and the water content can be precisely controlled. By performing careful calibration experiments using Karl Fischer coulometric titrations, it was possible to establish working curves of water content versus E Q2 – E Q1 (= ΔE) that enabled the accurate calculation of the water content of an organic solvent simply by recording one voltammogram in the presence of a quinone. Therefore, using this procedure, a voltammetric method for quickly estimating water contents of organic solvents down to the low ppm levels was established. In addition to H-bonding interactions, recent experiments have demonstrated that reduced quinones undergo interactions with CO2 and this has been proposed as a method for removing CO2 from industrial gas streams.The technique involves purging the gas through an ionic liquid containing a quinone and applying a reducing potential to produce the quinone dianion which interacts strongly with CO2 in a similar supramolecular mechanism as for H2O [Figure 1(a)]. Once the CO2 is “trapped”, the [quinone–(CO2)2]2– molecules can be separated, and an oxidizing potential applied which results in the [quinone–(CO2)2]2– complex being oxidized back to the starting material and the CO2 being released. Figure 1(b) shows the results from cyclic voltammetry and electrolysis experiments for the reduction of a quinone in the presence and absence of CO2. Under an argon atmosphere, two one-electron reduction processes are evident due to the reduction to the anion radical then at more negative potentials the dianion. However, when the solution is purged with CO2 gas, the voltametric waves immediately merge into one two-electron process due to the formation of the [quinone–(CO2)2]2– supramolecular complex This species is stable under electrolysis conditions and can exist in the bulk solution for long periods (hours). The mechanism can be varied by purging the solution containing the [quinone–(CO2)2]2– complex with an inert gas such as Ar or N2, resulting in two major pathways.In one pathway, the [quinone–(CO2)2]2– complex can be made to release the CO2 •– and leave the neutral quinone, and in the other pathway the charge remains on the quinone and the neutral CO2 is released as shown in Figure 1(c). Figure 1. (a) Reduction mechanism of 1,4-napthoquinone in the presence of CO2. The counterion for the anionic species is the electrolyte cation, n-Bu4N+. (b) Cyclic voltammograms for 1,4-napthoquinone in the presence and absence of CO2. (c) Proposed pathways for the reaction of NQ(CO2)2 2 – with excess argon gas. Figure 1

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Laatsch, Hartmut. "Methylierung 3,3′-dihydroxylierter 2,2′-Binaphthyl-1,4;1′,4′-dichinone / Methylation of 3,3′-Dihydroxylated 2,2′-Binaphtho-1,4;1′,4′-quinones". Zeitschrift für Naturforschung B 45, n.º 3 (1 de marzo de 1990): 393–400. http://dx.doi.org/10.1515/znb-1990-0316.

Texto completo

Resumen

Monomeric hydroxy-p-quinones (1) are in equilibrium with the corresponding o-quinones (2) and on methylation, a mixture of both isomeric ethers is obtained. In contrast, dimeric hydroxynaphthoquinones with the 3 a-skeleton in treatment with diazomethane are yielding only p-quinone ethers of type 3b.

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Tsou, Yun-Jie, Ren-You Guan y Jeng-Liang Han. "Enantioselective organocatalytic vinylogous aldol-cyclization cascade reaction of 3-alkylidene oxindoles with o-quinones". Organic & Biomolecular Chemistry 19, n.º 26 (2021): 5836–43. http://dx.doi.org/10.1039/d1ob00888a.

Texto completo

Resumen

A enantioselective organocatalytic vinylogous aldol-cyclization cascade reaction of 3-alkylidene oxindoles to o-quinones afforded chiral spirocyclic o-quinone analogues in good to excellent yields with high enantioselectivities.

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Jovanovic, S. V., K. Kónya y J. C. Scaiano. "Redox reactions of 3,5-di-tert-butyl-1,2-benzoquinone. Implications for reversal of paper yellowing". Canadian Journal of Chemistry 73, n.º 11 (1 de noviembre de 1995): 1803–10. http://dx.doi.org/10.1139/v95-222.

Texto completo

Resumen

One- and two-electron transfer reactions of 3,5-di-tert-butylcatechol and the corresponding quinone were studied by fast kinetic spectroscopy coupled with laser photolysis and pulse radiolysis, and by cyclic voltammetry in aqueous solutions. Photoionization of catechol yields the same semiquinone radical as the formate-radical-induced quinone reduction in the pulse radiolysis experiment. The neutral semiquinone radical deprotonates at pKr = 6.0 ± 0.1, as deduced from the pH induced changes in the radical spectra. The two-electron reduction potentials of quinone and catechol were measured by cyclic voltammetry in aqueous solutions containing 25% methanol in the pH range 3–14. The pH dependence has two linear parts with slopes of 0.056 and 0.03 V/pH, intersecting at pKa = 10.0. This is in excellent agreement with pKa = 10.05 ± 0.05 obtained spectrophotometrically. The reduction potential of 3,5-di-tert-butyl quinone, E7 = 0.01 ± 0.04 V, was obtained from the one-electron transfer equilibrium of the quinone with the oxygen/superoxide redox couple by pulse radiolysis. The rate constant of the reaction of quinone with the superoxide radical, k = 1.2 × 109 M−1 s−1, is higher than those of the superoxide reduction by catechols and phenols (typically ~ 105 M−1 s−1); thus, lignin o-quinones could be efficient scavengers of superoxide under the conditions relevant for the photo-induced yellowing of lignin-rich paper. The reaction with [Formula: see text] effectively bleaches yellow quinone and generates metastable furanone, which hydrolyses to muconic acid, thus completely eliminating yellow quinone. 3,5-Di-tert-butylquinone also undergoes rapid bleaching with ascorbate, k = 600 ± 100 M−1 s−1, in methanol. The reaction has a 1:1 stoichiometry and leads to complete reduction of quinone to catechol with concomitant oxidation of ascorbate to dehydroascorbate. This unusual selectivity and the fact that the reaction of the milder oxidant 3,5-di-tert-butylquinone is an order of magnitude faster than that of stronger oxidant p-benzoquinone (k = 60 ± 10 M−1 s−1) suggest that a nucleophilic attack of quinone at the ascorbate double bond initiates the reaction. Keywords: superoxide, lignin, photochemistry, quinone.

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Field, J. A., F. J. Cervantes, F. P. van der Zee y G. Lettinga. "Role of quinones in the biodegradation of priority pollutants: a review". Water Science and Technology 42, n.º 5-6 (1 de septiembre de 2000): 215–22. http://dx.doi.org/10.2166/wst.2000.0516.

Texto completo

Resumen

Evidence is accumulating that inert humic substances can play important roles in the anaerobic degradation of priority pollutants by shuttling electrons. This paper reviews the roles of humus and quinone analogues as electron acceptors, redox mediators and electron donors for microbial and abiotic degradation processes. An eventual technology based on pumping quinones as terminal electron acceptors into aquifers and sediments to stimulate xenobiotic degradation offers promising potential. Also quinone redox mediators can be considered to accelerate reductive transformations (e.g. dechlorination, azo cleavage) of priority pollutants.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Sekulic, Tatjana, Lj V. Vujisic, B. P. M. Curcic, B. M. Mandic, D. Z. Antic, Snezana Trifunovic, D. M. Godjevac, Vlatka Vajs, V. T. Tomic y S. E. Makarov. "Quinones and non-quinones from the defensive secretion of Unciger transsilvanicus (Verhoeff, 1899) (Diplopoda, Julida, Julidae), from Serbia". Archives of Biological Sciences 66, n.º 1 (2014): 385–90. http://dx.doi.org/10.2298/abs1401385s.

Texto completo

Resumen

A complex mixture of compounds was identified from the secretion of specimens of Unciger transsilvanicus. Phenol and p-cresol were detected for the first time in the family Julidae, and for the second time in the order Julida. Thirteen quinones were identified, with a great relative abundance of toloquinone and 2-methoxy-3-methyl-1,4-benzoquinone. Hydroquinone was detected for the first time in the order Julida. Besides these compounds, isopentyl hexacosatetraenoate and isopentyl esters of saturated and unsaturated fatty acids with chain lengths from C14 to C20were identified. The most abundant non-quinone compound was isopentyl eicosenoate. The relative abundance of quinone and non-quinone in the defensive fluid of U. transsilvanicus was 77% and 23%, respectively. The phylogenetic importance of the registered compounds is briefly discussed.

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Hu, H. Y., B. R. Lim, N. Goto, V. K. Bhupathiraju y K. Fujie. "Characterization of microbial community in an activated sludge process treating domestic wastewater using quinone profiles". Water Science and Technology 43, n.º 1 (1 de enero de 2001): 99–106. http://dx.doi.org/10.2166/wst.2001.0024.

Texto completo

Resumen

The dynamics of microbial community structure of activated sludges in a small-scale domestic wastewater treatment process were examined using a novel approach of quinone profiles. The composition and content of quinones in the activated sludges were analyzed monthly over a period of one year. More than 4 types of ubiquinones and 12 types of menaquinones were observed in the activated sludges, with the dominant quinones being ubiquinone (UQ) -8, menaquinone (MK) -7, followed by UQ-10, MK-8 and MK-6. The total quinone contents in the activated sludges varied from 0.93 to 2.28μmol per gram of particle organic carbon. The molar ratio of ubiquinones to menaquinones (UK/MK) changed from 0.38 to 0.98, indicating that anaerobic bacteria dominated the microbial community of the activated sludges examined. The ratio of UQ/MK varied similar to that of dissolved oxygen in the bulk. The microbial diversity of the activated sludges calculated from the quinone compositions was 13.4–16.8. The diversity of menaquinones was much higher than that of ubiquinones, and increased slightly with increasing temperature. The microorganisms containing menaquinones appear to be sensitive to the change in temperature than those containing ubiquinones.

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

Elgawish, Mohamed Saleh, Naoya Kishikawa, Mohamed A. Helal, Kaname Ohyama y Naotaka Kuroda. "Molecular modeling and spectroscopic study of quinone–protein adducts: insight into toxicity, selectivity, and reversibility". Toxicology Research 4, n.º 4 (2015): 843–47. http://dx.doi.org/10.1039/c5tx00098j.

Texto completo

Resumen

The toxicity, reversibility and selectivity of quinone–protein adducts were studied using molecular modeling and molecular spectroscopy. Adduction of quinones with proteins could affect their redox potential, bioavailability, and intracellular distribution.

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Nozawa, Mamie, Hong-Ying Hu, Koichi Fujie, Tomohiko Tsuchida y Kohei Urano. "Population dynamics of chromate reducing bacteria in a bioreactor system developed for the treatment of chromate wastewater". Water Science and Technology 37, n.º 4-5 (1 de febrero de 1998): 109–12. http://dx.doi.org/10.2166/wst.1998.0595.

Texto completo

Resumen

The population dynamics of microbes was investigated in a bioreactor system for the treatment of chromate wastewater supplemented with chromate reducing bacteria Enterobacter cloacae strain HO-1. In this study, respiratory quinone profile and PCR techniques were used to analyse the microbial population. The change in microbial community structure and density was observed on the basis of the respiratory quinone profile since the predominant quinone of HO-1 is ubiquinone-8 (Q-8) and the amount of quinone is proportional to the cell mass. the quantity of microbes and the Q-8 fraction of the total quinones were increased after cultivation with aeration, while long-term operation brought about a decrease in the fraction of Q-8. In addition, the amount of HO-1 was determined by the PCR amplification rate under conditions where the amplification was exponential to the reaction cycles. The cell density of HO-1 and total microbes determined from these procedures compared well with the numbers of HO-1 cells counted selectively using agar plates containing chromate.

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Baxter, Ryan, Akil Hamsath y Jordan Galloway. "Quinone C–H Alkylations via Oxidative Radical Processes". Synthesis 50, n.º 15 (6 de junio de 2018): 2915–23. http://dx.doi.org/10.1055/s-0037-1610005.

Texto completo

Resumen

A brief survey of radical additions to quinones is reported. Carboxylic acids, aldehydes, and unprotected amino acids are compared as alkyl radical precursors for the mono- or bis- C–H alkylation of several quinones. Two methods for radical initiation are discussed comparing inorganic persulfates and Selectfluor as stoichiometric oxidants. Kinetic analysis reveals dramatic differences in the rate of radical initiation depending on the identity of the radical precursor and oxidant. Synthetic strategies for efficiently producing alkyl-quinones are discussed in the context of selecting optimum radical precursors and initiators depending on quinone identity and functional groups present.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

Fujie, Koichi, Hong-Ying Hu, Hajime Tanaka y Kohei Urano. "Ecological Studies of Aerobic Submerged Biofilter on the Basis of Respiratory Quinone Profiles". Water Science and Technology 29, n.º 7 (1 de abril de 1994): 373–76. http://dx.doi.org/10.2166/wst.1994.0364.

Texto completo

Resumen

Respiratory quinone profiles were applied as tools for identifying different bacterial populations in the aerobic submerged biofilter along with the change of environment such as the temperature and the loading of hard-biodegradable chemicals. To begin with, a novel and simplified analytical operation of respiratory quinones was developed. A diversity in microbial population was observed in the film cultivated at the higher temperature. The change of microbial population in the course of acclimation to hard-biodegradable chemicals such as dimethylformamide(DMF, hereafter) was clarified on the basis of quinone profile.

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Sladic, Dusan, Irena Novakovic, Zoran Vujcic, Tatjana Bozic, Natasa Bozic, Dragan Milic, Bogdan Solaja y Miroslav Gasic. "Protein covalent modification of biologically active quinones". Journal of the Serbian Chemical Society 69, n.º 11 (2004): 901–7. http://dx.doi.org/10.2298/jsc0411901s.

Texto completo

Resumen

The avarone/avarol quinone/hydroquinone couple shows considerable antitumor activity. In this work, covalent modification of ?-lactoglobulin by avarone and its derivatives as well as by the synthetic steroidal quinone 2,5(10)-estradiene- 1,4,17-trione and its derivatives were studied. The techniques for studying chemical modification of ?-lactoglobulin by quinones were: UV/Vis spectrophotometry, SDS PAGE and isoelectrofocusing. SDS PAGE results suggest that polymerization of the protein occurs. It could be seen that the protein of 18 kD gives the bands of 20 kD, 36 kD, 40 kD, 45 kD, 64 kD and 128 kD depending on modification agent. The shift of the pI of the protein (5.4) upon modification toward lower values (from pI 5.0 to 5.3) indicated that lysine amino groups are the principal site of the reaction of ?-lactoglobulin with the quinones.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Gutiérrez, Isela, Sonia G. Bertolotti, M. A. Biasutti, Arnaldo T. Soltermann y Norman A. García. "Quinones and hydroxyquinones as generators and quenchers of singlet molecular oxygen". Canadian Journal of Chemistry 75, n.º 4 (1 de abril de 1997): 423–28. http://dx.doi.org/10.1139/v97-048.

Texto completo

Resumen

The role of quinones and hydroxyquinones as sensitizers and as quenchers in Type II photooxygenations has been examined. The second aspect is discussed here, through a systematic study, for the first time in the open literature. Quinonic compounds are excellent generators of O2(1Δg) in aprotic solvents (excluding those quinones possessing substituents in positions adjacent to the carbonyl groups, in the case of anthraquinone derivatives). Benzoquinones, anthraquinones, and hydroxy derivatives are good O2(1Δg) quenchers upon dye-sensitized photoirradiation. The excited oxygen species is deactivated with rate constants in the range 106–107 M−1 s−1 depending on the solvent employed. The quenching process deactivates O2(1Δg) without further destruction of the quinone. The main interaction with O2(1Δg) is driven by the quinone moiety, in spite of the presence of potentially active nuclear substituents. The quenching mechanism could involve a reversible charge transfer intermediate, with the quinonic compound acting as an electron donor. Keywords: photooxidation, quenching, quinones, rose bengal, singlet oxygen.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

Kianmehr, Ebrahim, Mehran Rezazadeh Khalkhali, Masoud Rezaeefard, Khalid Mohammed Khan y Seik Weng Ng. "Pd-Catalyzed Dehydrogenative Cross-Coupling of 1,4-Quinones with N,N′-Dialkyluracils". Australian Journal of Chemistry 68, n.º 1 (2015): 165. http://dx.doi.org/10.1071/ch14412.

Texto completo

Resumen

A straightforward and efficient method for the palladium-catalyzed direct cross-coupling of quinones with N,N′-dialkyluracils via 2-fold C–H activation has been developed to rapidly construct uracil substituted quinone structural motifs.

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Sugumaran, M., H. Dali y V. Semensi. "Mechanistic studies on tyrosinase-catalysed oxidative decarboxylation of 3,4-dihydroxymandelic acid". Biochemical Journal 281, n.º 2 (15 de enero de 1992): 353–57. http://dx.doi.org/10.1042/bj2810353.

Texto completo

Resumen

Mushroom tyrosinase, which is known to convert a variety of o-diphenols into o-benzoquinones, has been shown to catalyse an unusual oxidative decarboxylation of 3,4-dihydroxymandelic acid to 3,4-dihydroxybenzaldehyde [Sugumaran (1986) Biochemistry 25, 4489-4492]. The mechanism of this reaction was re-investigated. Although visible-region spectral studies of the reaction mixture containing 3,4-dihydroxymandelic acid and tyrosinase failed to generate the spectrum of a quinone product during the steady state of the reaction, both trapping experiments and non-steady-state kinetic experiments provided evidence for the transient formation of unstable 3,4-mandeloquinone in the reaction mixture. The visible-region spectrum of mandeloquinone resembled related quinones and exhibited an absorbance maximum at 394 nm. Since attempts to trap the second intermediate, namely alpha,2-dihydroxy-p-quinone methide, were in vain, mechanistic studies were undertaken to provide evidence for its participation. The decarboxylative quinone methide formation from 3,4-mandeloquinone dictates the retention of a proton on the alpha-carbon atom. Hence, if we replace this proton with deuterium, the resultant 3,4-dihydroxybenzaldehyde should retain the deuterium present in the original substrate. To test this hypothesis, we chemoenzymically synthesized alpha-deuterated 3,4-dihydroxymandelic acid and examined its enzymic oxidation. Our studies reveal that the resultant 3,4-dihydroxybenzaldehyde retained nearly 90% of the deuterium, strongly indicating the transient formation of quinone methide. On the basis of these findings it is concluded that the enzymic oxidation of 3,4-dihydroxymandelic acid generates the conventional quinone product, which, owing to its unstability, is rapidly decarboxylated to generate transient alpha,2-dihydroxy-p-quinone methide. The coupled dienone-phenol re-arrangement and keto-enol tautomerism of this quinone methide produce the observed 3,4-dihydroxybenzaldehyde.

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Grushevskaya, H. V. y N. G. Krylova. "Carbon Nanotubes as A High-Performance Platform for Target Delivery of Anticancer Quinones". Current Pharmaceutical Design 24, n.º 43 (28 de marzo de 2019): 5207–18. http://dx.doi.org/10.2174/1381612825666190117095132.

Texto completo

Resumen

Background: In spite of considerable efforts of researchers the cancer deseases remain to be incurable and a percentage of cancer deseases in the structure of mortality increases every year. At that, high systemic toxicity of antitumor drugs hampers their effective use. Because of this fact, the development of nanosystems for targeted delivery of antitumor drugs is one of the leading problem in nanomedicine and nanopharmacy. Objective: To critically examine the modern strategies for carbon nanotubes (CNTs)-based delivery of anticancer quinones and to summarize the mechanisms which can provide high effectiveness and multifunctionality of the CNT-based quinone delivery platform. Results: Quinones, including anthracycline antibiotics – doxorubicin and daunorubicin, are among the most prospective group of natural and syntetic compounds which exhibit high antitumor activity against different type of tumors. In this review, we focus on the possibilities of using CNTs for targeted delivery of antitumor compounds with quinoid moiety which is ordinarily characterized by high specific interaction with DNA molecules. Quinones can be non-covalently adsorbed on CNT surface due to their aromatic structure and π-conjugated system of double bonds. The characteristic features of doxorubicine-CNT complex are high loading efficiency, pH-dependent release in acidic tumor microenviroment, enough stability in biological fluid. Different types of CNT functionalization, targeting strategies and designs for multifunctional CNT-based doxorubicine delivery platform are disscussed. Conclusion: Nanosystems based on functionalized CNTs are very promising platform for quinone delivery resulting in significant enhancement of cancer treatment efficiency. Functionalization of CNTs with the polymeric shell, especially DNA-based shells, can provide the greatest affinity and mimicry with biological structures.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Hiraishi, Akira, Taichi Umezawa, Hiroyuki Yamamoto, Kenji Kato y Yonosuke Maki. "Changes in Quinone Profiles of Hot Spring Microbial Mats with a Thermal Gradient". Applied and Environmental Microbiology 65, n.º 1 (1 de enero de 1999): 198–205. http://dx.doi.org/10.1128/aem.65.1.198-205.1999.

Texto completo

Resumen

ABSTRACT The respiratory and photosynthetic quinones of microbial mats which occurred in Japanese sulfide-containing neutral-pH hot springs at different temperatures were analyzed by spectrochromatography and mass spectrometry. All of the microbial mats that developed at high temperatures (temperatures above 68°C) were so-called sulfur-turf bacterial mats and produced methionaquinones (MTKs) as the major quinones. A 78°C hot spring sediment had a similar quinone profile.Chloroflexus-mixed mats occurred at temperatures of 61 to 65°C and contained menaquinone 10 (MK-10) as the major component together with significant amounts of either MTKs or plastoquinone 9 (PQ-9). The sunlight-exposed biomats growing at temperatures of 45 to 56°C were all cyanobacterial mats, in which the photosynthetic quinones (PQ-9 and phylloquinone) predominated and MK-10 was the next most abundant component in most cases. Ubiquinones (UQs) were not found or were detected in only small amounts in the biomats growing at temperatures of 50°C and above, whereas the majority of the quinones of a purple photosynthetic mat growing at 34°C were UQs. A numerical analysis of the quinone profiles was performed by using the following three parameters: dissimilarity index (D), microbial divergence index (MDq ), and bioenergetic divergence index (BDq ). A D matrix tree analysis showed that the hot spring mats consisting of the sulfur-turf bacteria, Chloroflexus spp., cyanobacteria, and purple phototrophic bacteria formed distinct clusters. Analyses ofMDq and BDq values indicated that the microbial diversity of hot spring mats decreased as the temperature of the environment increased. The changes in quinone profiles and physiological types of microbial mats in hot springs with thermal gradients are discussed from evolutionary viewpoints.

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Hui, Pan, Mathieu Branca, Benoît Limoges y François Mavré. "An autocatalytic organic reaction network based on cross-catalysis". Chemical Communications 57, n.º 86 (2021): 11374–77. http://dx.doi.org/10.1039/d1cc05121k.

Texto completo

Resumen

A simple autocatalytic organic reaction network based on cross-catalysis is here illustrated. It involves the redox chemistry of quinones and reactive oxygen species, requiring only an pro-quinone boronate probe and ascorbate in an aerated solution.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Li, Zhi y Xiao-Long Xu. "Deciphering the Redox Chain Mechanism in the Catalytic Alkylation of Quinones". Synlett 29, n.º 14 (14 de mayo de 2018): 1807–13. http://dx.doi.org/10.1055/s-0037-1610125.

Texto completo

Resumen

Alkylation of p-quinones with allylic and benzylic esters is achieved by using a strong Lewis acid as the catalyst. This transformation likely follows an unusual redox chain mechanism. In this mechanism, quinone undergoes a sequence of reactions: it is reduced to hydroquinone (HQ), functionalized in a Lewis acid-catalyzed Friedel–Crafts alkylation, and then oxidized back to quinone. The last step is concurrent with the first step of a second quinone molecule, which is reduced to new HQ and functionalized, and thus propagates the redox chain reaction. The autoinitiation mechanism of the redox chain is not well understood, but additive HQ or Hantzsch ester can serve as effective initiators. The likelihood of this mechanism was elaborated by kinetic studies and various control experiments.1 Introduction2 Discovery of Catalytic Alkylation Reactions of Quinones3 Proposed Redox Chain Reaction Mechanism and Experimental Evidence4 Substrate Scope5 Conclusion

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Caldwell, Sharon L., Joe B. Gilroy, Rajsapan Jain, Evan Crawford, Brian O. Patrick y Robin G. Hicks. "Synthesis and redox properties of a phosphine-subsituted para-dioxolene and its bimetallic palladium complex". Canadian Journal of Chemistry 86, n.º 10 (1 de octubre de 2008): 976–81. http://dx.doi.org/10.1139/v08-127.

Texto completo

Resumen

Oxidation of 2,5-bis(diphenylphosphino)-1,4-hydroquinone (8) with iodobenzene diacetate produces the corresponding bis(phosphine) substituted benzoquinone (9), the first phosphine-substitued quinone. Cyclic voltammetry studies reveal that the redox functionality of the quinone unit in 9 is retained, and the reduction potentials render this compound slightly more easily reduced than the parent p-benzoquinone. Reaction of the precursor hydroquinone 8 with Pd(hfac)2 affords a binuclear complex 10 with the hydroquinonate ligand bridging two Pd(hfac) substrates. The redox activity of the bridging dioxolene ligand is retained in complex 10, although there are significant changes in the redox potentials relative to those of the free quinone 9. Chemical oxidation of 10 with AgPF6 yields a persistent cationic complex 11, which, based on EPR and electronic spectroscopy, can be formulated as containing a bridging semiquinone ligand.Key words: p-quinones, phosphines, bridging ligands, redox properties.

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Silva, Raquel L., Daniel P. Demarque, Renata G. Dusi, João Paulo B. Sousa, Lorena C. Albernaz y Laila S. Espindola. "Residual Larvicidal Activity of Quinones against Aedes aegypti". Molecules 25, n.º 17 (31 de agosto de 2020): 3978. http://dx.doi.org/10.3390/molecules25173978.

Texto completo

Resumen

The number of documented dengue cases has increased dramatically in recent years due to transmission through the Aedes aegypti mosquito bite. Vector control remains the most effective measure to protect against this and other arboviral diseases including Zika, chikungunya and (urban) yellow fever, with an established vaccine only available for yellow fever. Although the quinone class shows potential as leading compounds for larvicide development, limited information restricts the development of optimized structures and/or formulations. Thus, in this contribution we investigated the larvicidal and pupicidal activity of three quinone compounds isolated from a Connarus suberosus root wood ethyl acetate extract together with 28 quinones from other sources. Eight quinones demonstrated larvicidal activity, of which tectoquinone (4) proved to be the most active (LC50 1.1 µg/mL). The essential residual effect parameter of four of these quinones was evaluated in laboratory trials, with tectoquinone (4) and 2-ethylanthraquinone (7) presenting the most prolonged activity. In small-scale field residual tests, tectoquinone (4) caused 100% larvae mortality over 5 days, supporting its selection for formulation trials to develop a prototype larvicide to control Ae. aegypti.

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

Agalidis, I., E. Rivas y F. Reiss-Husson. "Characterization of Reaction Center-B875 Complex of Rhodocyclus gelatinosus: QB Site Properties Derived from Reconstitution Experiments". Zeitschrift für Naturforschung C 46, n.º 1-2 (1 de febrero de 1991): 99–105. http://dx.doi.org/10.1515/znc-1991-1-216.

Texto completo

Resumen

Abstract Purified reaction center-B875 pigment-protein complex isolated from Rc. gelatinosus (I. Agalidis, E. Rivas, and F. Reiss-Husson, Photosynth. Res. 23, 249 - 255 (1990)) was further characterized. In the chromatophores, the quinone content was shown to be 6 menaquinones 8 and 16 ubiquinones 8 per reaction center, indicating that the pool contained both quinone types. Besides the primary (MK8) and secondary (UQ8 ) electron acceptors of the reaction center, the complex contains residual quinones from the membrane pool (about 3 MK8 and 5 UQ8) probably associated with the phospholipids. Apparent particle weight of the complex including bound detergent was 520 ± 46 kDa. The secondary quinone QB was partially removed from the RC by treatment with 2 -3 % octaethyleneglycol dodecyl ether and 3 -4 mᴍ orthophenanthroline. Reconstitution experiments showed that UQ6, UQ9 and UQ10 could replace QB but that MK8 and MK9 could not. It was concluded that QB site has a clear specificity towards ubiquinone binding.

Los estilos APA, Harvard, Vancouver, ISO, etc.

49

Moullet, O. y J. L. Dreyer. "Selective inhibition of adenylate cyclase in bovine cortex by quinones: a novel cellular substrate for quinone cytotoxicity". Biochemical Journal 300, n.º 1 (15 de mayo de 1994): 99–106. http://dx.doi.org/10.1042/bj3000099.

Texto completo

Resumen

Quinones are widely distributed substances of often potential toxicological significance. On the other hand, cyclic AMP is known to promote a cell-survival response and to retard apoptosis [Berridge, Tan and Hilton (1993) Exp. Hematol. 21, 269-276]. Therefore the effects of quinones on adenylate cyclase were tested. Adenylate cyclase is rapidly inhibited by quinones, with IC50 values of 40-45 microM for p-benzoquinone (BQ) or 200 microM for dichlorophenol-indophenol (DCIP), with 2-substituted quinones being inactive. Membrane solubilization decreases the IC50 values for BQ and DCIP to 18 microM and 40 microM respectively. The inhibition is not affected by GTP, GDP or analogues, or by cholera and pertussis toxins; therefore it is not mediated by a G-protein or the activation of a defined receptor. Further, the inhibition stoichiometrically competes with forskolin activation of adenylate cyclase, equimolar concentrations of quinone and forskolin restoring the enzyme activity to its basal value. Reduction of BQ with sodium dithionite stoichiometrically prevents the inhibition of adenylate cyclase; in turn, oxidation of hydroquinone with ferricyanide fully restores it, indicating that the oxidized state of the quinone is required for inhibition. In addition, BQ is cytotoxic in vivo on HepG2, a human hepatocellular carcinoma cell line, but the effect can be prevented with forskolin. In plasma membranes, BQ tightly binds only one major and two minor proteins; these BQ-binding proteins were purified by means of labelling with [14C]BQ followed by PAGE under native conditions. Together these observations indicate that the action of quinone can be traced to targeting a limited number of proteins at the plasma membrane in a highly selective way and to affecting key enzymes such as adenylate cyclase.

Los estilos APA, Harvard, Vancouver, ISO, etc.

50

Mas y mas, Sarah, Cécile Giustini, Jean-Luc Ferrer, Norbert Rolland, Gilles Curien y David Cobessi. "Analytical ultracentrifugation and preliminary X-ray studies of the chloroplast envelope quinone oxidoreductase homologue fromArabidopsis thaliana". Acta Crystallographica Section F Structural Biology Communications 71, n.º 4 (20 de marzo de 2015): 455–58. http://dx.doi.org/10.1107/s2053230x1500480x.

Texto completo

Resumen

Quinone oxidoreductases reduce a broad range of quinones and are widely distributed among living organisms. The chloroplast envelope quinone oxidoreductase homologue (ceQORH) fromArabidopsis thalianabinds NADPH, lacks a classical N-terminal and cleavable chloroplast transit peptide, and is transported through the chloroplast envelope membrane by an unknown alternative pathway without cleavage of its internal chloroplast targeting sequence. To unravel the fold of this targeting sequence and its substrate specificity, ceQORH fromA. thalianawas overexpressed inEscherichia coli, purified and crystallized. Crystals of apo ceQORH were obtained and a complete data set was collected at 2.34 Å resolution. The crystals belonged to space groupC2221, with two molecules in the asymmetric unit.

Los estilos APA, Harvard, Vancouver, ISO, etc.

Artículos de revistas sobre el tema "Quinone"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros