- Kinetic characterization of the oxidation of chlorogenic acid by polyphenol oxidase and peroxidase. Characteristics of the o-quinone
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Chlorogenic acid is the major diphenol of many fruits, where it is oxidized enzymatically by polyphenol oxidase (PPO) or peroxidase (POD) to its o-quinone. In spectrophotometric studies of chlorogenic acid oxidation with a periodate ratio of [CGA]0/[lO4-]0 0/[IO4-]0 > 1, the o-quinone was characterized as follows: λmax at 400 nm and ε = 2000 and 2200 M-1 cm-1 at pH 4.5 and 7.0, respectively. In studies of o-quinone generated by the oxidation of chlorogenic acid using a periodate at ratio of [CGA]0/[lO4-]0 > 1, a reaction with the remaining substrate was detected, showing rate constants of k = 2.73 ± 0.17 M-1 s-1 and k = 0.05 ± 0.01 M-1 s-1 at the above pH values. A Chronometric spectrophotometric method is proposed to kinetically characterize the action of the PPO or POD on the basis of measuring the time it takes for a given amount of ascorbic acid to be consumed in the reaction with the o-quinone. The kinetic constants of mushroom PPO and horseradish POD are determined.
- Munoz,Garcia-Molina,Varon,Rodriguez-Lopez,Garcia-Ruiz,Garcia-Canovas,Tudela
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- Electrochemical biosensor for detection of 17β-estradiol using semi-conducting polymer and horseradish peroxidase
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A convenient electrochemical sensing pathway for 17β-estradiol detection was investigated. The system is based on a conducting polymer and horseradish peroxidase (HRP) modified platinum (Pt) electrode. The miniature estradiol biosensor was developed and constructed through the immobilization of HRP in an electroactive surface of the electrode covered with electroconducting polymer-poly(4,7-bis(5-(3,4-ethylenedioxythiophene)thiophen-2-yl)benzothiadiazole). The detection strategy is based on the fact that 17β-estradiol (E2) and pyrocatechol (H2Q) are co-substrates for the HRP enzyme. HRP, which does not react with E2, in the presence of H2O2 catalyses the oxidation of H2Q to o-benzoquinone (Q). With the optimized conditions, such constructed biosensing system demonstrated a convenient level of sensitivity, selectivity in a broad linear range-0.1 to 200 μM with a detection limit of 105 nM. Furthermore, the method was successfully applied for hormone detection in the presence of potential interfering compounds (ascorbic acid, estriol, estrone, uric acid and cholesterol).
- Cabaj, Joanna,Spychalska, Kamila,Zaj?c, Dorota
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- Inhibition of mushroom tyrosinase by a newly synthesized ligand: Inhibition kinetics and computational simulations
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Alterations in the synthesis of melanin contribute to a number of diseases; therefore, the design of new tyrosinase inhibitors is very important. Mushroom tyrosinase (MT) is a metalloenzyme, which plays an important role in melanin biosynthesis. In this study, the inhibitory effect of a novel designed compound, i.e. 2-((1Z)-(2-(2,4-dinitrophenyl)hydrazin-1-ylidene)methyl) phenol, as a specific ligand which can bind to the copper ion of MT, has been assessed. The ligand was found to competitively inhibit both the cresolase and catecholase activities of MT, with small inhibition constants of 2.8 and 2.6 μM, respectively. Intrinsic fluorescence studies were performed to gain more information on the binding constants. Docking results indicated that the ligand binds to copper ions in the active site of MT via the OH group of the ligand. The ligand makes four hydrogen bonds with aspartic acid and one hydrogen bond with the histidine residue in the active site. Molecular dynamics results show that ligand binds to the MT via both electrostatic and hydrophobic interactions with its different parts. Copyright
- Alijanianzadeh, Mahdi,Saboury, Ali Akbar,Hadi-Alijanvanda, Hamid,Moosavi-Movahedia, Ali Akbar,Ganjali, Mohammad Reza
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- Alzheimer's disease related copper(II)-β-amyloid peptide exhibits phenol monooxygenase and catechol oxidase activities
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(Chemical Equation Presented) A gray area in gray matter: The Cu II complex of a truncated β-amyloid, CuAβ1-20, catalyzes the oxidation of catechol and the hydroxylation and oxidation of phenol (see picture) with dramatic rate accelerations (≈ 10 5-106-fold increases). The Cu-oxygen chemistry of CuAβ may offer both a better understanding of the chemical effect in the brains of patients who suffer from Alzheimer's disease as well as possible treatment strategies of this disease.
- Da Silva, Giordano F. Z.,Ming, Li-June
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- Complex Nonlinear Behavior in the Bromate–2-Aminophenol Reaction
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The bromate–2-aminophenol reaction in a batch reactor was investigated in this research, in which both simple and sequential oscillations were observed. The occurrence of sequential oscillations were found to be very sensitive to changes of the initial concentrations, where decreasing the concentration of sulfuric acid or sodium bromate or increasing the 2-aminophenol concentration caused the two oscillation windows to coalesce. Lowering the reaction temperature from 30 to 5°C also caused the two oscillation windows to merge into one. A phase diagram in the bromate–sulfuric acid concentration plane demonstrates that sequential oscillations only occur within a narrow band of conditions. Mechanistic studies of the system through employing 1H NMR and mass spectrometry suggest that a dibrominated ortho-benzoquinone is a major product. The oxidation of 2-aminophenol, on the other hand, can lead to the formation of pyrocatechol, which may be the substrate responsible for the second set of oscillations.
- Tang, Alexander,Bell, Jeffrey G.,Green, James R.,Wang, Jichang
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- How well should the active site and the specific recognition be defined for proficient catalysis? - Effective and cooperative polyphenol/catechol oxidation and oxidative dna cleavage by a copper(II)-binding and H-bonding copolymer
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Despite the mainly inhomogeneous and unstructured nature of linear polymers, the CuII complex of a vinylpyridine-acrylamide copolymer exhibits very efficient 2-electron catalysis toward the oxidation of catechol and derivatives to form quinones with and without 80 mM (0.27%) H 2O2, showing remarkable (0.114-2.67) × 10 5 and (2.83-9.60) × 104-fold rate enhancements, respectively, in terms of first-order rate constant relative to auto-oxidation of the substrates in an aqueous environment under mild conditions. Metal-binding profiles suggest the presence of cooperativity in the catalysis. The oxidation catalysis is inhibited by the di-copper tyrosinase specific kojic acid. Moreover, electron paramagnetic resonance spectra reveal magnetic interaction of the CuII ions. On the basis of the results, the catalysis by this CuII-polymer seems to be consistent with the mechanism of type-3 di-copper oxidases. This complex also shows effective single- and double-stranded DNA cleavage in the presence of 1.0% H2O2. These studies suggest this CuII-polymer complex can serve as a unique chemical nuclease and a versatile chemical system for further exploration of Cu-oxygen chemistry. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Lykourinou, Vasiliki,Hanafy, Ahmed I.,Da Silva, Giordano F. Z.,Bisht, Kirpal S.,Larsen, Randy W.,Livingston, Brian T.,Angerhofer, Alexander,Ming, Li-June
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- The enthalpies of formation of o-, m-, and p-benzoquinone: Gas-phase ion energetics, combustion calorimetry, and quantum chemical computations combined
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Radical anions of o-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to
- Fattahi, Alireza,Kass, Steven R.,Liebman, Joel F.,Matos, M. Agostinha R.,Miranda, Margarida S.,Morais, Victor M. F.
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- Synthesis and studies of the inhibitory effect of hydroxylated phenylpropanoids and biphenols derivatives on tyrosinase and laccase enzymes
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The impaired activity of tyrosinase and laccase can provoke serious concerns in the life cycles of mammals, insects and microorganisms. Investigation of inhibitors of these two enzymes may lead to the discovery of whitening agents, medicinal products, anti-browning substances and compounds for controlling harmful insects and bacteria. A small collection of novel reversible tyrosinase and laccase inhibitors with a phenylpropanoid and hydroxylated biphenyl core was prepared using naturally occurring compounds and their activity was measured by spectrophotometric and electrochemical assays. Biosensors based on tyrosinase and laccase enzymes were constructed and used to detect the type of protein-ligand interaction and half maximal inhibitory concentration (IC50). Most of the inhibitors showed an IC50 in a range of 20–423 nM for tyrosinase and 23–2619 nM for laccase. Due to the safety concerns of conventional tyrosinase and laccase inhibitors, the viability of the new compounds was assayed on PC12 cells, four of which showed a viability of roughly 80% at 40 μM. In silico studies on the crystal structure of laccase enzyme identified a hydroxylated biphenyl bearing a prenylated chain as the lead structure, which activated strong and effective interactions at the active site of the enzyme. These data were confirmed by in vivo experiments performed on the insect model Tenebrio molitur.
- Dettori, Maria Antonietta,Fabbri, Davide,Dessì, Alessandro,Dallocchio, Roberto,Carta, Paola,Honisch, Claudia,Ruzza, Paolo,Farina, Donatella,Migheli, Rossana,Serra, Pier Andrea,Pantaleoni, Roberto A.,Fois, Xenia,Rocchitta, Gaia,Delogu, Giovanna
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- Dearomatization of Electron-Deficient Phenols to ortho-Quinones: Bidentate Nitrogen-Ligated Iodine(V) Reagents
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Despite their broad utility, the synthesis of ortho-quinones remains a significant challenge, in particular, access to electron-deficient derivatives remains an unsolved problem. Reported here is the first general method for the synthesis of electron-deficient ortho-quinones by direct oxidation of phenols. The reaction is enabled by a novel bidentate nitrogen-ligated iodine(V) reagent, a previously unexplored class of compounds which we have termed Bi(N)-HVIs. The reaction is extremely general and proceeds with excellent regioselectivity for the ortho over para isomer. Functionalization of the ortho-quinone products was examined, resulting in a facile one-pot synthesis of catechols, as well as the incorporation of a variety of heteroatom nucleophiles. This method represents the first synthetic application of Bi(N)-HVIs and demonstrates their potential as a platform for the further development of highly reactive, but also highly tunable, I(V) reagents.
- Xiao, Xiao,Greenwood, Nathaniel S.,Wengryniuk, Sarah E.
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supporting information
p. 16181 - 16187
(2019/11/05)
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- The Study of Mg(II) Ion Influence on Catechol Autoxidation in Weakly Alkaline Aqueous Solution
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Abstract: High performance liquid chromatography with diode array detection (HPLC-DAD) and electron spin resonance (ESR) spectroscopy were used to study Mg(II) ion influence on the autoxidation of catechol in weakly alkaline solution. The presence of Mg(II) ions greatly enhanced the catechol autoxidation rate and probably influenced the mechanism of reaction thus enabling formation of reaction products not obtained in the absence of metal ions. Consecutive formation of 1,2-benzoquinone, 2,3-oxanthrenediol, and 2,3-oxanthrenedione with intermediate o-semiquinone anion radicals during the initial stages of catechol autoxidation was suggested based on the detailed analysis of experimental HPLC-DAD and ESR data. The results of this study may help in better understanding of autoxidation of some biologically important catecholic molecules in real systems, where Mg(II) ions are ubiquitously present. Because of the possible toxicity of simple quinone molecules, it is important that the formation of relatively stable quinoid autoxidation products were detected in this study.
- Nikoli?,?ivanovi?,Krsti?,Nikoli?
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p. 2656 - 2660
(2020/01/23)
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- Fabrication of a novel PbO2 electrode with a graphene nanosheet interlayer for electrochemical oxidation of 2-chlorophenol
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A novel PbO2 electrode with a graphene nanosheet interlayer (marked as GNS-PbO2) was prepared combining electrophoretic deposition and electro-deposition technologies. The micro morphology, crystal structure and surface chemical states of GNS-PbO2 electrodes were characterized using scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Their electrochemical properties and stability were determined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ·OH radicals test and accelerated life test, and compared with traditional PbO2 electrodes. Besides, their potential application in the electrochemical degradation of 2-chlorophenol (2-CP) was investigated. The GNS-PbO2 electrode possessed perfect octahedral β-PbO2 microcrystals, and its grain size was much smaller than that of traditional PbO2 electrode. It exhibited higher electrochemical activity than traditional PbO2 electrode due to its larger electrochemical active surface area and stronger ·OH radicals generation ability. The service lifetime of GNS-PbO2 electrode (107.9?h) was 1.93 times longer than that of traditional PbO2 electrode (55.9?h). The electrochemical degradation rate constant of 2-CP on GNS-PbO2 electrode (kapp?=?2.75?×?10?2?min?1) is much higher than for PbO2 electrode (kapp?=?1.76?×?10?2?min?1). 2-CP oxidation yielded intermediates including aromatic compounds (catechol, phenol and ortho-benzoquinone) and organic acids (oxalic acid, maleic acid and glutaconic acid), and a possible degradation pathway for 2-CP was proposed accordingly.
- Duan, Xiaoyue,Zhao, Cuimei,Liu, Wei,Zhao, Xuesong,Chang, Limin
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p. 424 - 436
(2017/04/28)
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- Accessing Polyoxygenated Dibenzofurans via the Union of Phenols and o-Benzoquinones: Rapid Syntheses of Metabolites Isolated from Ribes takare
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The construction of polyoxygenated dibenzo[b,d]furan frameworks from the union of substituted phenols/naphthols and o-benzoquinones via a Michael-oxidation-oxa-Michael cascade is reported. The power of this transformation is demonstrated in the generation of a library of highly substituted dibenzofurans, featuring specifically substituted molecules containing broad ranges of functionality. The utility of this method is showcased in the total syntheses of two dibenzofurans isolated from Ribes takare, assembling the carbon scaffold of both natural products in one operation.
- Zhang, Meng Yao,Barrow, Russell A.
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supporting information
p. 2302 - 2305
(2017/05/12)
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- Synthesis, structural, catecholase, tyrosinase and DFT studies of pyrazoloquinoxaline derivatives
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Six functional multidentate ligands: 2,3-bis(3,5-dimethyl-1H-pyrazol-1-yl) quinoxaline, L1, 2,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-nitroquinoxaline, L2, 2,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylquinoxaline, L3, 2-(3,5-dimethyl-1H-pyrazol-1-yl)-3-hydrazinyl-6-nitroquinoxaline L4, 2-chloro-3-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylquinoxaline, L5, 2-chloro-3-(3,5-dimethyl-1H-pyrazol-1-yl) quinoxaline, L6, and a new copper (II) complex, were prepared and evaluated for their catecholase activities at aerobic conditions. We found that, the reaction rate depends on: The nature of the substituents in the quinoxaline ring, counter anion, metal, concentration of ligand and the used solvent. The complex obtained in-situ from reaction of one equivalent of ligand L1 and two equivalents of Cu(CH3COO)2 in methanol showed the highest oxidation rate activity (V?=?33.48?μmol?L?1. min?1). In addition, geometry optimizations of the complexes in order to get better insight into the geometry and the electronic structure and chemical reactivity were carried out by means of DFT calculations.
- Bouanane, Zohra,Bounekhel, Mahmoud,Elkolli, Meriem,Abrigach, Farid,Khoutoul, Mohamed,Bouyala, Rabab,Touzani, Rachid,Hellal, Abdelkader
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p. 238 - 246
(2017/03/22)
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- Efficient mineralization of phenol by a temperature-responsive polyoxometalate catalyst under wet peroxide oxidation at lower temperatures
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Herein, a temperature-responsive polyoxometalate (POM) catalyst [C16H33(CH3)3N]3[PO4{WO(O2)2}4]/poly(N-isopropylacrylamide) (abbreviated as (C16PW(O2)2/PNIPAM) was prepared and used in the catalytic wet peroxide oxidation (CWPO) of phenol under mild conditions. The POM catalyst C16PW(O2)2/PNIPAM showed a higher degradation efficiency and mineralization of phenol with H2O2 at room temperature or even at lower temperature (0 °C) within a short time (120 min). The high efficiency at lower temperature was attributed to its temperature-responsive property, wherein the lattice of the temperature-sensitive polymer relaxed at lower temperature and then wrinkled at higher temperature. These characteristics also permitted C16PW(O2)2/PNIPAM to be easily separated for recycling. The leaching test indicated that the POM catalyst exhibited excellent stability and little leaching and can be used as a thermosensitive catalyst for about six times. C16PW(O2)2/PNIPAM has potential application in the CWPO of phenol without the limitation of temperature and pH conditions.
- Li, Yiming,Zhang, Xueyan,Zhang, Dan,Li, Yue,Wang, Xiaohong,Wang, Shengtian
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p. 43681 - 43688
(2017/09/22)
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- An electrochemical biosensing platform based on 1-formylpyrene functionalized reduced graphene oxide for sensitive determination of phenol
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A highly efficient enzyme-based screen printed electrode (SPE) was developed based on the covalent immobilization of tyrosinase (Tyr) on 1-formylpyrene (1-FP) functionalized reduced graphene oxide (rGO). Here, the bifunctional molecule 1-FP was assembled onto rGO sheets. Subsequently, a Tyr molecule was immobilized on the 1-FP forming a biocompatible nanocomposite, which was further coated onto the working electrode surface of the SPE. The performance of as-prepared biosensor was investigated by the detection of phenol in the presence of molecular oxygen. Wide linear range, low detection limit and high sensitivity were obtained with this biosensor due to the good conductivity of rGO as well as the high bioactivity of Tyr well retained by the 1-FP/rGO platform. Finally, the proposed biosensor was successfully employed for the detection of phenol in real water samples with satisfactory results. These findings suggest that this novel biosensor could offer great potential for rapid, cost-effective and on-field analysis of phenolic compounds.
- Hua, Zulin,Qin, Qin,Bai, Xue,Huang, Xin,Zhang, Qi
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p. 25427 - 25434
(2016/03/22)
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- Electrochemical oxidation of guaiacol to increase its biodegradability or just remove COD in terms of anodes and electrolytes
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To assess the role of electrochemical oxidation as a single mineralization technique or a pretreatment (for biotreatment) of lignin-containing wastewater, Ti/Sb-SnO2 and Ti/Pb3O4 were used as comparable anode materials to degrade the lignin monomer guaiacol. The electrode catalytic activity was examined by cyclic voltammetry. Then the guaiacol degradation was analyzed. Finally, the main intermediates and products were identified. The results show that Ti/Sb-SnO2 is non-selective in treating guaiacol and its intermediates while Ti/Pb3O4 has a weaker ability in degrading the intermediates. A chlorine-containing media is suitable to perform total organic removal with a high rate, but the active chlorine and organochlorine may ruin the follow-up biological treatment. Electrochemical oxidation (EO) pretreatment could save 50-70% electric energy and reduce the burden of subsequent biotreatment. Quinones and dimers are important intermediates that could be used to distinguish the capability of anodes and the function of Cl-.
- Shao, Dan,Chu, Wei,Li, Xiaoliang,Yan, Wei,Xu, Hao
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p. 4858 - 4866
(2016/01/29)
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- Mechanistic insights into phenol oxidation by a copper(II) complex of a pyridine- And amide-containing copolymer in an aqueous medium
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A CuII complex of a pyridine- and amide-containing copolymer (Cu-P1) exhibits effective activity toward phenol hydroxylation in 50% aqueous methanol solution at apparent pH 8.0 and 25°C. The complex shows significant first-order rate accelerations of 4.2 × 105 and 1.4 × 105 relative to phenol autoxidation in air and in the presence of 20 mM H2O2, respectively. The reaction mechanisms with H2O2 and air are different on the basis of (a) the different activity profiles for Cu binding, (b) the different deuterium kinetic isotope effects (2.8 in 20 mM H2O2 and 1.2 aerobically), and (c) the formation of a dinuclear substrate-(Cu-P1) complex with H2O2 but a mononuclear one aerobically. The mechanism in the presence of H2O2 is consistent with that of the type-3 dicopper tyrosinase. Although oxidized di-CuII tyrosinase can only use H2O2 for phenol hydroxylation, CuII-P1 can use either air or H2O2 for this process. The studies herein introduce a versatile chemical system for the further exploration of Cu-oxygen chemistry and other types of metal-centered chemistry and for the aerobic degradation of aromatic compounds in environmental and green chemistry.
- Lykourinou, Vasiliki,Ming, Li-June
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p. 375 - 381
(2015/01/30)
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- Catalytic oxygenation of various monophenols by copper(I) complexes with bis(pyrazolyl)methane ligands: Differences in reactivity
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Three new mononuclear copper(I) complexes supported by the symmetric ligands 1,1′-methylenebis-1H-pyrazole (BPM), 1,1′-methylenebis(3-methyl-1H-pyrazole) (mBPM), and 1,1′-methylenebis(3,5-di-methyl-1H-pyrazole) (dmBPM) were synthesized as catalytic model systems of tyrosinase. The influence of various functional groups on the catalytic conversion of monophenols is investigated and the formation of the corresponding ortho-quinones is monitored using UV/vis and NMR spectroscopy. Comparison of various monophenols reveals the differences in reactivity which are analyzed and interpreted based on key intermediates of the mechanistic cycle.
- Hamann, Jessica Nadine,Schneider, Rebecca,Tuczek, Felix
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p. 3259 - 3271
(2015/09/22)
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- Tris(2,2′-azobispyridine) complexes of copper(II): X-ray structures, reactivities, and the radical nonradical bis(ligand) analogues
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Tris(abpy) complexes of types mer-[CuII(abpy)3][PF6]2 (mer-12+[PF6-]2) and ctc-[CuII(abpy)2(bpy)][PF6]2 (ctc-22+[PF6-]2) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of mer-12+ and ctc-22+ ions with catechol, o-aminophenol, p-phenylenediamine, and diphenylamine (Ph-NH-Ph) in 2:1 molar ratio afford [CuI(abpy)2]+ (3+) and corresponding quinone derivatives. The similar reactions of [CuII(bpy)3]2+ and [CuII(phen)3]2+ with these substrates yielding [CuI(bpy)2]+ and [CuI(phen)2]+ imply that these complexes undergo reduction-induced ligand dissociation reactions (phen = 1,10-phenanthroline). The average -N=N- lengths in mer-12+[PF6-]2 and ctc-22+[PF6-]2 are 1.248(4), while that in 3+[PF6-]·2CH2Cl2 is relatively longer, 1.275(2) ?, due to dCu → πazo back bonding. In cyclic voltammetry, mer-12+ exhibits one quasi-reversible wave at -0.42 V due to CuII/CuI and abpy/abpy?- couples and two reversible waves at -0.90 and -1.28 V due to abpy/abpy?- couple, while those of ctc-22+ ion appear at -0.44, -0.86, and -1.10 V versus Fc+/Fc couple. The anodic 32+/3+ and the cathodic 3+/3 redox waves at +0.33 and -0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy?-) in 3, which is defined as a hybrid state of [CuI(abpy0.5?-)(abpy0.5?-)] and [CuII(abpy?-)(abpy?-)] states. 32+ ion is a neutral abpy complex of copper(II) of type [CuII(abpy)2]2+. 3 exhibits a near-IR absorption band at 2400-3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH2Cl2.
- Maity, Suvendu,Kundu, Suman,Weyhermüller, Thomas,Ghosh, Prasanta
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p. 1300 - 1313
(2015/06/11)
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- SELECTIVE AEROBIC ALCOHOL OXIDATION METHOD FOR CONVERSION OF LIGNIN INTO SIMPLE AROMATIC COMPOUNDS
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Described is a method to oxidize lignin or lignin sub-units. The method includes oxidation of secondary benzylic alcohol in the lignin or lignin sub-unit to a corresponding ketone in the presence of unprotected primarily aliphatic alcohol in the lignin or lignin sub-unit. The optimal catalyst system consists of HNO3 in combination with another Br?nsted acid, in the absence of a metal-containing catalyst, thereby yielding a selectively oxidized lignin or lignin sub-unit. The method may be carried out in the presence or absence of additional reagents including TEMPO and TEMPO derivatives.
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- New catalytic model systems of tyrosinase: Fine tuning of the reactivity with pyrazole-based N-donor ligands
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Two new Cu(I) complexes have been synthesized and investigated as model systems of the enzyme tyrosinase. The corresponding ligands are based on a combination of an imine function with two different pyrazole groups. The reactivity of the prepared systems with respect to the conversion of monophenols to the corresponding ortho-quinones is investigated. The resulting data are compared to results obtained for other catalytic model systems of tyrosinase. The Royal Society of Chemistry 2014.
- Hamann, Jessica Nadine,Tuczek, Felix
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supporting information
p. 2298 - 2300
(2014/03/21)
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- Rabbit 3-hydroxyhexobarbital dehydrogenase is a NADPH-preferring reductase with broad substrate specificity for ketosteroids, prostaglandin D2, and other endogenous and xenobiotic carbonyl compounds
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3-Hydroxyhexobarbital dehydrogenase (3HBD) catalyzes NAD(P) +-linked oxidation of 3-hydroxyhexobarbital into 3-oxohexobarbital. The enzyme has been thought to act as a dehydrogenase for xenobiotic alcohols and some hydroxysteroids, but its physiological function remains unknown. We have purified rabbit 3HBD, isolated its cDNA, and examined its specificity for coenzymes and substrates, reaction directionality and tissue distribution. 3HBD is a member (AKR1C29) of the aldo-keto reductase (AKR) superfamily, and exhibited high preference for NADP(H) over NAD(H) at a physiological pH of 7.4. In the NADPH-linked reduction, 3HBD showed broad substrate specificity for a variety of quinones, ketones and aldehydes, including 3-, 17- and 20-ketosteroids and prostaglandin D2, which were converted to 3α-, 17β- and 20α-hydroxysteroids and 9α,11β- prostaglandin F2, respectively. Especially, α-diketones (such as isatin and diacetyl) and lipid peroxidation-derived aldehydes (such as 4-oxo- and 4-hydroxy-2-nonenals) were excellent substrates showing low Km values (0.1-5.9 μM). In 3HBD-overexpressed cells, 3-oxohexobarbital and 5β-androstan-3α-ol-17-one were metabolized into 3-hydroxyhexobarbital and 5β-androstane-3α,17β-diol, respectively, but the reverse reactions did not proceed. The overexpression of the enzyme in the cells decreased the cytotoxicity of 4-oxo-2-nonenal. The mRNA for 3HBD was ubiquitously expressed in rabbit tissues. The results suggest that 3HBD is an NADPH-preferring reductase, and plays roles in the metabolisms of steroids, prostaglandin D2, carbohydrates and xenobiotics, as well as a defense system, protecting against reactive carbonyl compounds.
- Endo, Satoshi,Matsunaga, Toshiyuki,Matsumoto, Atsuko,Arai, Yuki,Ohno, Satoshi,El-Kabbani, Ossama,Tajima, Kazuo,Bunai, Yasuo,Yamano, Shigeru,Hara, Akira,Kitade, Yukio
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p. 1366 - 1375
(2013/11/19)
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- Chemo-selective oxidation of hydroxybenzyl alcohols with IBX in the presence of hemicucurbit[6]uril
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The chemo-selective oxidation of bifunctional substrates via a supramolecular strategy has been achieved. IBX (o-iodoxybenzoic acid) oxidations of hydroxybenzyl alcohols produce the corresponding aldehyde and o-quinones, while the presence of HemiQ[6] can restrain the IBX oxidation of phenolic hydroxyl groups to afford the aldehyde product. The conversion and reaction rate are greatly affected by the structures of substrates, and the stereo effect and electronic effect play very important roles in the selective oxidation system. Various spectroscopies, including 1H NMR (proton nuclear magnetic resonance), IR (infrared), and UV-vis (ultra violet-visible) have been employed to confirm the host-guest interaction of HemiQ[6] with hydroxybenzyl alcohols.
- Cong, Hang,Yamato, Takehiko,Tao, Zhu
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p. 3778 - 3783
(2013/11/06)
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- Effect of chloride and sulfate ions on the advanced photo Fenton and modified photo Fenton degradation process of Alizarin Red S
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The degradation of Alizarin Red S (ARS) was carried out by heterogeneous advanced photo Fenton processes (HAPFP) of the type Fe0/H 2O2/UV and heterogeneous modified photo Fenton process (HMPFP) of the type Fe0/ammonium persulfate (APS)/UV. The influence of various reaction parameters like pH, catalyst loading, concentration of the oxidants and the influence of inorganic anions such as Chloride (Cl-) and Sulfate (SO42-) ions on processes were investigated. Quenching of the hydroxyl radical by inorganic anions was confirmed by the decrease in the degradation rate constant for the HAPFP from 3.33 × 10-2 to 0.19 × 10-2 (for Cl- (1 M)) and 0.29 × 10-2 min-1 (for SO42- (1 M)). Similar decrease in rate constant for HMPFP is from 4.67 × 10 -2 to 0.41 × 10-2(for Cl- (1 M)) and 0.51 × 10-2 min-1 (for SO42- (1 M)) process. The combined effect of concentration of sulfate and chloride ions on the rate constant for the degradation of ARS with APS and H2O 2 as oxidants is investigated. The initial degradation mechanism involves the cleavage of a quinone group to catechol as detected by UV-visible and GC-MS analysis.
- Devi, L. Gomathi,Munikrishnappa,Nagaraj,Rajashekhar, K. Eraiah
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p. 125 - 131
(2013/06/27)
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- The influence of hydroquinone on tyrosinase kinetics
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In vitro studies, using combined spectrophotometry and oximetry together with hplc/ms examination of the products of tyrosinase action demonstrate that hydroquinone is not a primary substrate for the enzyme but is vicariously oxidised by a redox exchange mechanism in the presence of either catechol, l-3,4-dihydroxyphenylalanine or 4-ethylphenol. Secondary addition products formed in the presence of hydroquinone are shown to stimulate, rather than inhibit, the kinetics of substrate oxidation.
- Stratford, Michael R.L.,Ramsden, Christopher A.,Riley, Patrick A.
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experimental part
p. 4364 - 4370
(2012/08/28)
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- Nitration of phenolic compounds and oxidation of hydroquinones using tetrabutylammonium chromate and dichromate under aprotic conditions
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In this work, we have reported a mild, efficient and selective method for the mononitration of phenolic compounds using sodium nitrite in the presence of tetrabutylammonium dichromate (TBAD) and oxidation of hydroquinones to quinones with TBAD in CH2Cl2. Using this method, high yields of nitrophenols and quinones were obtained under neutral aprotic conditions. Tetrabutylammonium chromate (TBAC) can also be used as oxidant at same conditions. Indian Academy of Sciences.
- Pourali, Ali Reza,Goli, Arezou
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scheme or table
p. 63 - 67
(2012/01/13)
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- Reactivity of dpph in the oxidation of catechol and catechin
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A kinetic study of the reduction of pyrocatechol and catechin by dpph radical has been carried out in various ratios of CH 3OH/H2O mixed solvent at pH 5.5-7.5, μ = 0.10 M [(n-Bu)4N]ClO4, and T = 25°C. The rate constants of oxidation in aqueous solvent, kH2O, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H 2O plots at each pH value. A linear relationship between k H2O and 1/[H+] was observed for both flavonoids with kH2O = k1Ka1/[H+], where K a1 was the first acid dissociation constant on the catechol ring and k1 is the rate constant of the oxidation of the mononegative species HX-. The values of k1 obtained from the slopes of the plots are (8.2 ± 0.2) × - 105 and (6.1 ± 0.1) × - 105 M-1 s-1 for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer-sphere electron transfer reaction yielded a value of 3.7 × - 103 M-1 s-1 for the self-exchange rate constant of dpph/dpphH couple.
- Chen, Wei-Lin,Li, Wei-Shuen,Fu, Ping-Jou,Yeh, Andrew
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supporting information; scheme or table
p. 147 - 153
(2011/10/02)
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- Investigation of acid-base catalysis in the extradiol and intradiol catechol dioxygenase reactions using a broad specificity mutant enzyme and model chemistry
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The extradiol and intradiol catechol dioxygenase reaction mechanisms proceed via a common proximal hydroperoxide intermediate, which is processed via different Criegee 1,2-rearrangements. An R215W mutant of extradiol dioxygenase MhpB, able to produce a mi
- Brivio, Michela,Schlosrich, Janne,Ahmad, Mark,Tolond, Caroline,Bugg, Timothy D. H.
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experimental part
p. 1368 - 1373
(2009/12/04)
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- Isoquinolinium bromochromate; new, efficient and stable reagent for oxidation of aromatic amines and phenols
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The new chromium(VI) oxidizing reagent isoquinolinium bromochromate (IQBC) was prepared and characterized. This new compound has been found to be an efficient reagent for oxidation of primary amines and phenols. The oxidation of primary amines and phenols with isoquinolinium bromochromate proceeded smoothly to afford corresponding azobenzenes and quinones in good to excellent yield. The synthesized isoquinolinium bromochromate is more ideal reagent, with number of specifications including higher yield, mild conditions and easy preparation. The results obtained with isoquinolinium bromochromate are satisfactory and suggest that this new reagent is valuable addition to the existing chromium(VI) reagents.
- Khansole, Sandeep V.,Patwari, Shivaji B.,Vibhute, Yeshwant B.
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experimental part
p. 1343 - 1346
(2010/08/19)
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- Facile one-pot synthesis of 2-(3,4-dihydroxyphenyl)-2-phenyl-2H-indene derivatives via electrochemical oxidation of catechols in the presence of 2-phenyl-1,3-indandione
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The electrooxidation of 3-substituted catechols (1a-1c) has been studied in the presence of 2-phenyl-1,3-indandione (3) in water + acetonitrile (90/10 v/v) solution, using the electrochemical and spectroelectrochemical methods. The o-benzoquinones (2a-2c) derived from catechols (1a-1c) precipitate out according to Michael addition reactions with 2-phenyl-1,3-indandione (3) to form the corresponding 2-(3,4-dihydroxyphenyl)-2-phenyl-2H-indene derivatives (5a-5c). An EC mechanism was proposed for the electrode process. The efficient electrochemical syntheses of the new catechol derivatives (5a-5c) were performed at a carbon rod electrode in an undivided cell at high yields.
- Shamsipur,Hosseiny Davarani,Bayandori-Moghaddam,Nematollahi,Fakhari, Ali Reza
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p. 237 - 247
(2008/02/11)
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- Solid state oxidation of phenols to quinones with ammonium persulfate/wet SiO2
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A solid state method for the oxidation of phenols to quinones is described using ammonium persulfate/wet silica gel as oxidant.
- Hashemi, Mohammed M.,Karimi-Jaberi, Zahed,Eftekhari-Sis, Bagher
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p. 160 - 161
(2007/10/03)
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- Structural characterization of a new manganese(III)-salen complex [H2salen = N,N′-bis(salicylidene)ethane-1,2-diamine] and study of its electron transfer kinetics with hydroquinone and catechol
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The octahedral manganese(III) complex, [Mn(salen)Cl(H2O)]·H2O (H2salen = N,N′-bis(salicylidene)ethane-1,2-diamine), has been synthesized and structurally characterized by single-crystal X-ray diffraction study. The X-ray structural analysis shows that the metal center is six-coordinate with distorted octahedral geometry. In this compound, the Mn-Cl and Mn-OH2 bond lengths are 2.621(6) and 2.333(2) A?, respectively, slightly longer than the usual values. The kinetics of electron transfer reaction of the complex with catechol and hydroquinone has been followed spectrophotometrically over the pH range 5.75-8.15 at 30 °C. The nature of the kinetic trace is indicative of a biphasic reaction with each reductant. Detailed analysis of kinetic data supports the formation of a relatively stable intermediate complex between manganese(III) and the dihydroxybenzenes (H2A) at the initial stage. The decay of the intermediate is the bimolecular electron transfer process involving another molecule of reductants leading to the manganese(II) complex and benzoquinones. MnIII(salen)(H2O)(OH) generated in situ from the aquation and proton equilibrium of the parent complex has been assigned to be the reactive species during the formation of the intermediate. The corresponding species for the redox step is MnIII(L)(H2O)(HA), sufficient experimental evidence for which has been gathered from pH-rate profiles.
- Panja, Anangamohan,Shaikh, Nizamuddin,Ali, Mahammad,Vojtí?ek, Pavel,Banerjee, Pradyot
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p. 1191 - 1198
(2008/10/08)
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- Oxidation of Aromatic Amines to Quinones by Iodic Acid under Microwave Irradiation in the Presence of Montmorillonite K10 and Silica Gel
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A variety of aromatic amines are oxidized to their corresponding quinones in excellent yields by supported iodic acid under microwave irradiation and solvent free conditions.
- Hashemi, Mohammed M.,Akhbari, Maryam
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p. 1561 - 1563
(2007/10/03)
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- Diphenol radical cations and semiquinone radicals as direct products of the free electron transfer from catechol, resorcinol and hydroquinone to parent solvent radical cations
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In the pulse radiolysis of solutions of catechol, resorcinol and hydroquinone in n-butylchloride, dihydroxybenzene radical cations (40%) as well as semiquinone radicals (60%) are observed as direct synchronously formed products of the electron transfer from the solvent parent ions to the solute. This is explained in terms of free electron transfer succeeding in nearly every encounter of the reactants, which in the case of the studied dihydroxybenzenes involves femtosecond molecular dynamics effects. The rotation of the C-OH bond causes cycling of the molecule through transient conformations also exhibiting different electron distributions. From the more chemical point of view, the diphenol radical cations represent the first and till now unknown intermediates of oxidative semiquinone radical formation.
- Brede, Ortwin,Kapoor, Sudhir,Mukherjee, Tulsi,Hermann, Ralf,Naumov, Sergej
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p. 5096 - 5104
(2007/10/03)
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- Cetyltrimethylammonium cerium nitrate: A phase transferring oxidant
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A phase transferring oxidant, cetyltrimethylammoniumceric nitrate (CTACN) has been prepared and characterized from elemental analysis and spectral data. An aggregation phenomenon has been observed at 1.25 × 10-3 M of CTACN in water medium. Application of this reagent to oxidise benzyl alcohol, hydroquinone, 8-hydroxyquinoline, 2-aminophenol, 1-naphthol and 2-naphthol has been reported.
- Mishra,Kuanar,Sharma,Nayak
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p. 724 - 726
(2007/10/03)
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- Preparation of 1,4-dioxenes from α-diazo-β-ketoesters
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A novel preparation of 1,4-dioxenes is reported in which a rhodium carbenoid generated from an α-diazo-β-ketoester reacts with a 1,2-diol. Insertion of the carbenoid into the O-H bond followed by hemiacetal formation and acid-catalyzed dehydration generates the targeted 1,4-dioxene.
- Hilgenkamp, Ramona,Brogan, John B.,Zercher, Charles K.
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p. 1073 - 1078
(2007/10/03)
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- Sodium hypochlorite/Dowex 1X8-200: An effective oxidant for the oxidation of aromatic amines to quinones
-
Polymer supported hypochlorite ion is a useful oxidant for the oxidation of aromatic amines to the corresponding quinones.
- Hashemi, Mohammed M.,Beni, Yousef A.
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p. 672 - 673
(2007/10/03)
-
- Oxidation by Chemical Manganese Dioxide. Part 3.1 Oxidation of Benzylic and Allylic Alcohols, Hydroxyarenes and Aminoarenes
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The combined use of chemical manganese dioxide (CMD) and molecular sieves in hexane (or in acetone) in general or CMD alone in particular cases enables the convenient and efficient oxidation of benzylic and allylic alcohols, phenols and amines under relatively mild conditions.
- Hirano, Masao,Yakabe, Sigetaka,Chikamori, Hideki,Clark, James H.,Morimoto, Takashi
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p. 770 - 771
(2007/10/03)
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- Selective Oxidations using Alumina-supported Iodobenzene Diacetate under Solvent-free Conditions
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The solid reagent system iodobenzene diacetate-alumina expeditiously and selectively oxidises Sulfides to sulfoxides and alcohols to carbonyl compounds in high yields under the influence of microwaves.
- Varma, Rajender S.,Saini, Rajesh K.,Dahiya, Rajender
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p. 120 - 121
(2007/10/03)
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- Pyrazine-based polymeric complex of oxodiperoxochromium (VI) compound as a new stable, mild, efficient and versatile oxidant in organic synthesis
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The title compound was prepared and characterized by conventional methods. Its uses as stoichiometric oxidizing agent for a variety of organic compounds are described. With this reagent alcohols are converted to the corresponding carbonyl compounds. With 1,2-dioles C-C bond cleavage occurs. Decarboxylation of α-hydroxy acids proceeds quantitatively. Also thiols are converted to disulfides, hydroxy phenols to quinones, benzylamines to carbonyl compounds, tertiaryamines to the N-oxides, phosphines to phosphine oxides, sulfides to sulfoxides, and anthracene and phenanthrene to quinones. Deprotection of oximes and oxidative deprotection of silyl ethers proceed easily.
- Tamami, Bahman,Yeganeh, Hamid
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p. 7889 - 7896
(2007/10/03)
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- Iodobenzene diacetate on alumina: Rapid oxidation of alcohols to carbonyl compounds in solventless system using microwaves
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In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compounds using alumina-supported iodobenzene diacetate (lBD) as an oxidant under microwave irradiation.
- Varma, Rajender S.,Dahiya, Rajender,Saini, Rajesh K.
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p. 7029 - 7032
(2007/10/03)
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- Intermediates and products formed during the periodic reaction between phenol and bromate
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The course of the oscillatory reaction between phenol and bromate has been studied using HPLC for analyzing the intermediates and products formed from phenol before, during and after the oscillatory regime.The time evolution of 9 detected species has been followed; 6 of them were identified as 1.2-benzoquinone, 1.2-dihyroxybenzene, 2-bromophenol, 4-bromophenol, 2.4-dibromophenol, and 2.4.6-tribromophenol, the others are supposed to be bromoderivatives of 1.2-dihydroxybenzene and 1.2-benzoquinone.In the light of our results some unidentified species listed in the skeleton mechanisms suggested earlier for explaining the oscillatory behavior could be specified.
- Orban, Miklos,Szokan, Gyula
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p. 179 - 190
(2007/10/03)
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- BIOMIMETIC OXIDATIONS. OXYGENATION REACTIONS BY PHOTOEXCITED IRON PORPHYRINS
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A pyrazine-bridged Fe(II) protoporphyrin polymeric species is observed to react with oxygen giving rise to the formation of a mixed Fe(II)-Fe(III) porphyrin polynuclear complex which is stable in air for several days in neutral or slightly acidic solution.The effect of the presence of pyridine or pyrazine on the photocatalytic properties of Fe(III) protoporphyrin or Fe(III) octaethylporphyrin is investigated.It is observed that the irradiation of these systems in the presence of benzene as a substrate leads to the formation of phenol, benzohydroquinones and benzoquinones.A similar behaviour is observed with phenol which, indeed, is also oxidized to quinones.No appreciable amounts of oxidation products are formed in the absence of pyrazine or pyridine and under conditions where pyrazine-bridged polymeric species are formed.This is taken as an evidence of a considerable trans effect of the nitrogen ligands, favouring the coordination and the activation of O2.
- Maldotti, Andrea,Bartocci, Carlo,Amadelli, Rossano,Varani, Graziano,Pietrogrande, Maria Chiara,Carassiti, Vittorio
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p. 411 - 414
(2007/10/02)
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- Preparation of Unstable Quinones in Aqueous Solution via Pulse Radiolytic One-electron Oxidation of Dihydroxybenzenes
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The stoichiometry of the reactions of semiquinones resulting from the one-electron oxidation of various dihydroxybenzenes is examined.It is verified that the semiquinones of hydroquinone and catechol disproportionate completely to give p-benzoquinone and o-benzoquinone, respectively.With resorcinol, however, the corresponding semioxidised radical reaction is different, giving unstable dimers which subsequently rearrange to tetrahydroxybiphenyls.The usefulness of catechol one-electron oxidation followed by o-semiquinone disproportionation as a means of preparing biologically important unstable o-quinones is exemplified by three new examples: (1) The o-quinone of oestradiol which may have melanocytotoxic properties; (2) the o-quinone of salsolinol whose oxidative metabolites may be responsible for neuronal damage in alcoholism and (3) o-quinone of tetrahydropapaveroline whose oxidative metabolism may play a role in both alcohol addiction and Parkinson's disease.
- Land, Edward J.
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p. 803 - 810
(2007/10/02)
-
- Zinc Bismuthate Zn(BiO3)2. I. A Useful Oxidizing Agent for the Efficient Oxidation of Organic Compounds
-
Zinc bismuthate is an easily prepared and a stable compound.It could be used as an oxidant in organic solvents under aprotic or in the presence of a catalytic amount of a protic solvent.Primary and secondary saturated, allylic, and benzylic alcohols are converted to their carbonyl compounds in high yields.Mildness of the reagent is shown by the oxidation of thiols to their disulfides in excellent yields.Thioethers are also oxidized to their corresponding sulfoxides in good yields.
- Firouzabadi, Habib,Mohammadpour-Baltork, Iraj
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p. 1131 - 1134
(2007/10/02)
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- Electrocatalytic Oxidation of Allylic Ethers, Dihydropyran and Phenol Using a Polypyridyl Complex of Ruthenium(IV)
-
An electrocatalytic procedure is described for the oxidation of allyl butyl ether, (E/Z)-2-butenyl butyl ether, dihydropyran and phenol using the ruthenium(IV) oxidant 2+.The resulting products were respectively, butyl acrylate (42percent), butyl (E/Z)-2-butenoate (53percent), 2,3-dihydro-4-pyranone (40percent) and o-benzoquinone (71percent).
- Campos, Jose Luiz,Giovani, Wagner F. De,Romero, Jose Ricardo
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p. 597 - 599
(2007/10/02)
-
- Kinetics of the Oxidation of Ascorbic Acid and Substituted 1,2- and 1,4-Dihydroxybenzenes by the Hexacyanoruthenate(III) Ion in Acidic Perchlorate Media
-
The kinetics of oxidation of ascorbic acid and a series of substituted 1,2- and 1,4-dihydroxybenzene compounds (H2Q) by 3- have been investigated in acidic perchlorate media.The inverse dependences of the rate constants on acid concentrations for 2,3-dicyano-1,4-dihydroxybenzene, 4,5-dihydroxybenzene-1,3-disulphonate, and ascorbic acid have been attributed to concurrent rate-determining pathways involving the one-electron oxidations of H2Q or HQ(-) by 3- to the corresponding semiquinone or ascorbate radical intermediate.The cross-reaction rate constants have been correlated with the semiquinone or ascorbate reduction potentials in terms of the Marcus relationship to yield a 3--4- electron self-exchange rate constant of (1.0 +/- 0.8) . 105 dm3mol-1s-1.This is compared with those for other low-spin d5-d6 transition-metal complex couples and discussed in terms of the inner-sphere and solvent reorganization energies.
- Hoddenbagh, J. Mark A.,Macartney, Donal H.
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p. 615 - 620
(2007/10/02)
-
- Barium Ferrate Monohydrate BaFeO4.H2O, a Useful Oxidant for the Oxidation of Organic Compounds under Aprotic Conditions
-
Preparation of barium ferrate monohydrate with a slight modification is described.It is shown that this reagent is capable of oxidizing different organic compounds and could be used as a versatile reagent in organic synthesis.Primary and secondary alcohols are converted to their carbonyl compounds, α-hydroxy ketones to their diketones, and hydroquinones to their quinones.Aromatic amines are converted to their azo compounds, benzylamine to benzaldehyde, phenylhydrazones and oximes to their carbonyl compounds.Thiols are also converted to their disulfides in high yields.This reagent seems to be a non-toxic and a non-pollutant compound.
- Firouzabadi, Habib,Mohajer, Daryoush,Entezari-Moghadam, Mohsen
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p. 2185 - 2190
(2007/10/02)
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