- Hemo-acrylic polymers as catalyst for the oxidative dehalogenation of 2,4,6-trichlorophenol. Chloroperoxidase's mimic imprinting effects
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Acrylic polymers with catalytic activity for the oxidative degradation of 2,4,6-trichlorophenol (TCP) were developed. In order to mimic the active site of chloroperoxidase (CPO), chloro-iron(III)-protoporphyrin IX was used as the catalytic centre, and methacrylamide (MA) and 4-vinylpyridine (VPY) were used as the monomers that build up the active sites. Taking as basis 3:1 (w/w) acid:basic aminoacidic composition of CPO, three MA:VPY combinations were tested: one keeping the same ratio (3:1) i.e. 25% VPY in the functional monomer mixture, one with lower content of the basic monomer (9:1) i.e. 10% VPY, and one with higher concentration of it (1:1) i.e. 50% VPY. Polymers synthesized with the lowest VPY content exhibited the highest catalytic efficiency, which was improved by the creation of specific TCP binding sites through molecular imprinting technology. In these way, synthetic enzymes with useful properties for analytical and bioremediation applications were obtained.
- Díaz-Díaz, Goretti,Blanco-López, M. Carmen,Lobo-Casta?ón, M. Jesús,Miranda-Ordieres, Arturo J.,Tu?ón-Blanco, Paulino
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- A green method for the electroorganic synthesis of new 1,3-indandione derivatives
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This is an environmentally friendly method in the field of electroorganic reactions under controlled potential electrolysis, without toxic reagents at a carbon electrode in an undivided cell which involves the (EC) mechanism reaction and comprises two ste
- Moghaddam, Abdolmajid Bayandori,Ganjali, Mohammad Reza,Norouzi, Parviz,Latifi, Maryam
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- Mechanisms of Reduction of trans-Cyclohexane-1,2-diamine-NNN'N'-tetra-acetatomanganate(III) by Hydrazine, Hydroxylamine, and Substituted Benzene-1,2-diols
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The kinetics and mechanism of reduction of trans-cyclohexane-1,2-diamine-NNN'N'-tetra-acetatomanganate(III), III(cdta)(H2O)>-, by hydrazine hydroxylamine, and a series of substituted benzene-1,2-diols C6H3(OH)2R (R=H, 4-Me, 4-CO2H, or 3-CO2H) have been investigated by the stopped-flow technique.Simple first-order dependence on MnIII complex and reductant concentrations has been observed for hydrazine, which shows a rate with +>-1 dependence.For hydroxylamine, complex kinetic dependences on reductant and hydrogen-ion concentration suggest a composite inner-sphere mechanism.Also, in the case of the diols an inner-sphere mechanism, through intermediate association, is proposed; for these substrates experimental rates, higher than those computed with the Marcus cross relation, and limiting kinetics are in agreement with the lability of the oxidizing complex.
- Arselli, Patrizia,Mentasti, Edoardo
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- Synthesis and DNA interaction of ethylenediamine platinum(II) complexes linked to DNA intercalants
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A series of ethylenediamine platinum(II) complexes connected through semi-rigid chains of 1,2-bis(4-pyridyl)ethane to DNA intercalating subunits (naphthalene, anthracene or phenazine) has been synthesized, and their interactions with calf thymus (CT) DNA
- Duskova, Katerina,Sierra, Sara,Fernández, María-José,Gude, Lourdes,Lorente, Antonio
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- Copper-Aβ Peptides and Oxidation of Catecholic Substrates: Reactivity and Endogenous Peptide Damage
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The oxidative reactivity of copper complexes with Aβ peptides 1–16 and 1–28 (Aβ16 and Aβ28) against dopamine and related catechols under physiological conditions has been investigated in parallel with the competitive oxidative modification undergone by the peptides. It was found that both Aβ16 and Aβ28 markedly increase the oxidative reactivity of copper(II) towards the catechol compounds, up to a molar ratio of about 4:1 of peptide/copper(II). Copper redox cycling during the catalytic activity induces the competitive modification of the peptide at selected amino acid residues. The main modifications consist of oxidation of His13/14 to 2-oxohistidine and Phe19/20 to ortho-tyrosine, and the formation of a covalent His6-catechol adduct. Competition by the endogenous peptide is rather efficient, as approximately one peptide molecule is oxidized every 10 molecules of 4-methylcatechol.
- Pirota, Valentina,Dell'Acqua, Simone,Monzani, Enrico,Nicolis, Stefania,Casella, Luigi
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- Enhanced enzymatic reaction of tyrosinase-immobilized polyacrylamide- (γ-cyclodextrin) membrane coated on a platinum disk electrode in acetonitrile
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A functionalized stable film, polyacrylamide-(γ-cyclodextrin) (PAA-γ-CD), synthesized from polyacrylamide (PAA) and γ-cyclodextrin (γ-CD), was used to immobilize enzyme. The membrane containing γ-CD provided an excellent environment for enzymatic kinetics
- Nakamura, Toshio,Ji, Xueping,Endo, Kazuyoshi,Takano, Daisuke
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- Purification and antiradical properties of the structural unit of betalains
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Betalamic acid [4-(2-oxoethylidene)-1,2,3,4-tetrahydropyridine- 2,6-dicarboxylic acid] is a naturally occurring compound that is normally found condensed with amino acids, amines, cyclo-DOPA, and cyclo-DOPA derivatives to form the betalains. Betalains are
- Gandia-Herrero, Fernando,Escribano, Josefa,Garcia-Carmona, Francisco
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- On the development of NAD(P)H-sensitive fluorescent probes
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In contrast to current, multi-reagent assay systems, the development of a single reagent that can be used to assay NAD(P)H is described. The reagent eliminates the fluorophore 4-methylumbelliferone from a quinoxalinium adduct upon reduction and the chemistry of this process is described. The Royal Society of Chemistry.
- Maidwell, Nicola L.,Reza Rezai,Roeschlaub, Carl A.,Sammes, Peter G.
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- Photometric assay for polyphenol oxidase activity in olives, olive pastes, and virgin olive oils
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A photometric method is proposed that allows the determination of phenolase activity in olive fruits, olive pastes, and virgin olive oil. The method can also be used to quantify partially purified phenolase from olives, and is based on the coupling betwee
- Valgimigli, Luca,Sanjust, Enrico,Curreli, Nicoletta,Rinaldi, Augusto,Pedulli, Gian F.,Rescigno, Antonio
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- Quinone-induced protein modifications: Kinetic preference for reaction of 1,2-benzoquinones with thiol groups in proteins
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Oxidation of polyphenols to quinones serves as an antioxidative mechanism, but the resulting quinones may induce damage to proteins as they react through a Michael addition with nucleophilic groups, such as thiols and amines to give protein adducts. In this study, rate constants for the reaction of 4-methylbenzoquinone (4MBQ) with proteins, thiol and amine compounds were determined under pseudo first-order conditions by UV-vis stopped-flow spectrophotometry. The chemical structures of the adducts were identified by LC-ESI-MS/MS. Proteins with free thiols were rapidly modified by 4MBQ with apparent second order rate constants, k2 of (3.1±0.2)×104 M-1 s-1 for bovine serum albumin (BSA) and (4.8±0.2)×103 M-1 s-1 for human serum albumin at pH 7.0. These values are at least 12-fold greater than that for α-lactalbumin (4.0±0.2)×102 M-1 s-1, which does not contain any free thiols. Reaction of Cys-34 of BSA with N-ethylmaleimide reduced the thiol concentration by ~59%, which resulted in a decrease in k2 by a similar percentage, consistent with rapid adduction at Cys-34. Reaction of 4MBQ with amines (Gly, Nα-acetyl-l-Lys, N?-acetyl-l-Lys and l-Lys) and the guanidine group of Nα-acetyl-l-Arg was at least 5×105 slower than with low-molecular-mass thiols (l-Cys, Nα-acetyl-l-Cys, glutathione). The thiol-quinone interactions formed colorless thiol-phenol products via an intermediate adduct, while the amine-quinone interactions generated colored amine-quinone products that require oxygen involvement. These data provide strong evidence for rapid modification of protein thiols by quinone species which may be of considerable significance for biological and food systems.
- Li, Yuting,Jongberg, Sisse,Andersen, Mogens L.,Davies, Michael J.,Lund, Marianne N.
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- Characterization of immobilized tyrosinase-an enzyme that is stable in organic solvent at 100 °C
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Tyrosinase is a copper-containing enzyme present in plant and animal tissues, which catalyzes the production of melanin and other pigments. In organic solvent, tyrosinase can convert N-acetyl-l-tyrosine ethyl ester (insoluble in aqueous) to a derivative o
- Wu, Lidong,Rathi, Brijesh,Chen, Yi,Wu, Xiuhong,Liu, Huan,Li, Jincheng,Ming, Anjie,Han, Gang
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- REACTIONS OF 4-METHYL-o-BENZOQUINONE, GENERATED CHEMICALLY OR ENZYMATICALLY, IN THE PRESENCE OF L-PROLINE
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The reactions of 4-methyl-o-benzoquinone in the presence of L- proline were studied by rapid scanning spectrophotometry.It was concluded that it was transformed into 5-methyl-4-N-prolyl-o-benzoquinone, according to the equation: 2(4-methyl-o-benzoquinone) + L-proline->4-methylcatechol + 5-methyl-4-N-prolyl-o-benzoquinone.Rate constants for the reaction of 4-methyl-o-benzoquinone with water and L-proline have been measured.Key Word Index-Tyrosinase; 4-methylcatechol; 4-methyl-o-benzoquinone; L-proline.
- Valero, Edelmira,Escribano, Josefa,Garcia-Carmona, Francisco
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- Catechol Oxidase versus Tyrosinase Classification Revisited by Site-Directed Mutagenesis Studies
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Catechol oxidases (COs) and tyrosinases (TYRs) are both polyphenol oxidases (PPOs) that catalyze the oxidation of ortho-diphenols to the corresponding quinones. By the official classification, only TYRs can also catalyze the hydroxylation of monophenols to ortho-diphenols. Researchers have been trying to find the molecular reason for the mono-/diphenolase specificity for decades. However, the hypotheses for the lack of monophenolase activity of plant COs are only based on crystal structures so far. To test these hypotheses, we performed site-directed mutagenesis studies and phylogenetic analyses with dandelion PPOs offering high phylogenetic diversity, the results of which refute the structure-based hypotheses. While plant PPOs of phylogenetic group 2 solely exhibit diphenolase activity, plant PPOs of phylogenetic group 1 unexpectedly also show monophenolase activity. This finding sheds new light upon the molecular basis for mono-/diphenol substrate specificity and challenges the current practice of generally naming plant PPOs as COs.
- Prexler, Sarah M.,Frassek, Martin,Moerschbacher, Bruno M.,Dirks-Hofmeister, Mareike E.
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- Diels-Alder reactions of a 6-arenyl fulvene with dienes and dienophiles and related chemistryl
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6-(2-Phenyl ethenyl) fulvene has been shown to participate both as diene and dienophile in Diels-Alder reactions and a facile photochemical transformation of the resulting bicyclo[2.2.2]-octenediones leading to extensively conjugated benzofulvenes has bee
- Nair, Vijay,Anilkumar,Radhakrishnan,Sheela,Rath, Nigam P.
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- Differential activation of a latent polyphenol oxidase mediated by sodium dodecyl sulfate
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A kinetic study of the activity of soluble and membrane-bound latent polyphenol oxidase (PPO) extracted from beet root (Beta vulgaris) was carried out. For the first time, two types of behavior (hyperbolic and sigmoid) are reported in the same enzyme for
- Gandia-Herrero, Fernando,Jimenez-Atienzar, Mercedes,Cabanes, Juana,Garcia-Carmona, Francisco,Escribano, Josefa
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- Formation of a blue adduct between 4-tert-butyl-1,2-benzoquinone and 4- amino-N,N-diethylaniline
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The reaction of 4-tert-butyl-1,2-benzoquinone (BQ) with 4-amino-N,N- diethylaniline (ADA) produces a stable blue adduct with λ(max) 625 nm (ε 11,120 M-1 cm-1). This makes the reaction a sensitive analytical tool, suitable for the detection and spectrophotometric determination of this quinone even in the presence of biological compounds. The adduct was identified as 3-tert-butyl-4-(4'-diethylamino)phenylimino-6-hydroxycyclohexa- 2,5-dien-1-one. (C) 2000 Elsevier Science Ltd.
- Valgimigli, Luca,Pedulli, Gian Franco,Cabiddu, Salvatore,Sanjust, Enrico,Rescigno, Antonio
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- Aminomethylene-Phosphonate Analogue as a Cu(II) Chelator: Characterization and Application as an Inhibitor of Oxidation Induced by the Cu(II)-Prion Peptide Complex
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Recently, we reported on a series of aminomethylene-phosphonate (AMP) analogues, bearing one or two heterocyclic groups on the aminomethylene moiety, as promising Zn(II) chelators. Given the strong Zn(II) binding properties of these compounds, they may fi
- Pariente Cohen, Natalie,Lo Presti, Eliana,Dell'Acqua, Simone,Jantz, Thomas,Shimon, Linda J. W.,Levy, Naomi,Nassir, Molhm,Elbaz, Lior,Casella, Luigi,Fischer, Bilha
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- Laccase-mediated multi-step homo- and heteromolecular reactions of ortho-dihydroxylated aromatic compounds and mono- or diaminated substances resulting in C-C, C-O and C-N bonds
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Three types of reactions involving oxidation, inter- and intramolecular Michael-addition as well as homo-intermolecular dimerization, catalyzed by laccase [E.C. 1.10.3.2] of Pycnoporus cinnabarinus in the presence of oxygen, resulted in the formation of dimeric, trimeric and cyclic products with yields up to 44% (non-optimized reactions). For heteromolecular reactions a number of different aminated five- and six-membered aromatic compounds were used. The first reaction type involved the oxidation of catechol, 3- or 4-methylcatechol to o-quinone and subsequent Michael-addition of the amino compounds with C-N bond formation. Conclusive analytical data (UV-vis data, MS spectra) for the respective o-quinone are provided. The second type of reaction included a homo-intermolecular dimerization probably with C-C and C-O bond formation to the proposed dibenzofuran derivatives. The heteromolecular reaction with the amino compounds yielded trimers consisting of homomolecular dimers and the amino compound connected via a C-N bond. The third reaction type started from epinephrine (adrenaline) which was oxidized by laccase and underwent an intramolecular Michael-addition to adrenochrome. The subsequent heteromolecular reaction resulted in the unusual substance class of cyclooctenes (diazocines). Differences between the reaction types in regard to the kind of o-hydroquinone, amino compound used and the types of product recovered are discussed.
- Hahn, Veronika,Mikolasch, Annett,Kuhlisch, Cornelius,Schauer, Frieder
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- Synthesis, structure, polyphenol oxidase mimicking and bactericidal activity of a zinc-schiff base complex
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Focusing on the important biological functions of metallo-enzymes and metallo-therapeutics in living world, this research work demonstrates the synthesis, crystal structure, supramolecular architecture, 4-methylcatechol oxidation and bactericidal activity
- Mahato, Shreya,Meheta, Nishith,Kotakonda, Muddukrishnaiah,Joshi, Mayank,Shit, Madhusudan,Choudhury, Angshuman Roy,Biswas, Bhaskar
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supporting information
(2020/12/13)
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- Synthesis and spectroscopic characterization of ternary copper(ii) complexes containing nitrogen and oxygen donors as functional mimics of catechol oxidase and phenoxazinone synthase
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Two ternary copper(ii) complexes 1 [(Cu2Me4en)4(EDTA)] and 2 [(CuMe4en)2(MIDA)] containing the mixed ligand system of 1,1′,4,4′-tetramethylethylenediamine (Me4en) (L) and N-methyliminodiace
- Abdel-Rahman, Adel A.-H.,Al-Harbi, Sami A.,Ibrahim, Mohamed M.,Omar, Walid,Ramadan, Abd El-Motaleb M.,Sallam, Shehab A.,Shaban, Shaban Y.
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p. 6331 - 6345
(2020/05/13)
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- The impact of an isoreticular expansion strategy on the performance of iodine catalysts supported in multivariate zirconium and aluminum metal-organic frameworks
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Iodine functionalized variants of DUT-5 (Al) and UiO-67 (Zr) were prepared as expanded-pore analogues of MIL-53 (Al) and UiO-67 (Zr). They were prepared using a combination of multivariate and isorecticular expansion strategies. Multivariate MOFs with a 25% iodine-containing linker was chosen to achieve an ideal balance between a high density of catalytic sites and sufficient space for efficient diffusion. Changes to the oxidation potential of the catalyst as a result of the pore-expansion strategy led to a decrease in activity with electron rich substrates. On the other hand, these larger frameworks proved to be more efficient catalysts for substrates with higher oxidation potentials. Recyclability tests for these larger MOFs showed sustained catalytic activity over multiple recycles.
- Tahmouresilerd, Babak,Moody, Michael,Agogo, Louis,Cozzolino, Anthony F.
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supporting information
p. 6445 - 6454
(2019/05/24)
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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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- A Catalyst-Controlled Aerobic Coupling of ortho-Quinones and Phenols Applied to the Synthesis of Aryl Ethers
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ortho-Quinones are underutilized six-carbon-atom building blocks. We herein describe an approach for controlling their reactivity with copper that gives rise to a catalytic aerobic cross-coupling with phenols. The resulting aryl ethers are generated in high yield across a broad substrate scope under mild conditions. This method represents a unique example where the covalent modification of an ortho-quinone is catalyzed by a transition metal, creating new opportunities for their utilization in synthesis.
- Huang, Zheng,Lumb, Jean-Philip
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supporting information
p. 11543 - 11547
(2016/11/17)
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- Biomolecular interaction, catecholase like activity and alkane oxidation in ionic liquids of a phenylcarbohydrazone-based monocopper(II) complex
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A phenylcarbohydrazone-based Schiff base type ligand (E)-N′-(2-hydroxy-5-methylbenzylidene)benzohydrazide (HL) and its monocopper(II) complex [CuL(NO3)(H2O)]·(H2O) (CuL) are synthesized and structurally characterized including single-crystal X-ray crystallography. The DNA interacting efficacy of the synthesized CuL with CT (calf thymus) DNA has been investigated using different spectral and viscosity measurements. The DNA binding constant (Kb?=?2.1 (±1.11)?×?105?M?1) and binding site size (s?=?0.31), viscosity data together with circular dichroism studies, revealed that the CuL could interact with DNA via intercalation. The protein binding ability of CuL with BSA (Bovine Serum Albumin) was investigated by absorption, fluorescence and synchronous fluorescence methods and a static quenching mechanism was observed for their interaction with BSA. CuL acts as an efficient catalyst for the aerobic oxidation of catechols (4-methylcatechol, 3,5-ditertiarybutylcatechol, 3-methoxycatechol and 3-nitrocatechol) to the corresponding quinones, in methanol/0.02?M HEPES medium at pH?=?8.0 and at 25?°C. The highest activity is observed for the substituted catechol with the electron donor tert-butyl group, resulting in a turnover frequency (TOF) value of 1.45?×?104?h?1. CuL also mimics the action of other copper enzymes, being capable of catalyzing the peroxidative oxidation of cyclohexane, under in mild conditions and in several media. The best results were obtained in an ionic liquid, with a TOF of 1220?h?1.
- Anbu, Sellamuthu,Paul, Anup,Ribeiro, Ana P.C.,Guedes da Silva, M. Fatima C.,Kuznetsov, Maxim L.,Pombeiro, Armando J.L.
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p. 426 - 436
(2016/07/20)
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- Reactions of flavonoids with o-quinones interfere with the spectrophotometric assay of tyrosinase activity
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Flavonoids are important food components with antioxidant properties and many of them have been described as tyrosinase inhibitors. Oxidation of quercetin, kaempferol, morin, catechin, and naringenin by mushroom tyrosinase and their influence on the oxidation of l-dopa and l-tyrosine was studied. Reaction rates measured spectrophotometrically and by oxygen consumption differed substantially. All tested flavonoids reacted with 4-tert-butyl-o-benzoquinone and/or 4-methyl-o-benzoquinone, although at different rates. These reactions generated products whose UV-vis spectra either overlapped or did not overlap with the spectrum of dopachrome. They therefore strongly influence the kinetic analysis performed by measuring the absorbance at 475 nm during oxidation of l-dopa or l-tyrosine generating false inhibition or activation effects. This method is therefore inappropriate for monitoring the activity of this enzyme in the presence of flavonoids and other compounds possessing strong nucleophilic or reducing groups.
- Gasowska-Bajger, Beata,Wojtasek, Hubert
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p. 5417 - 5427
(2016/07/19)
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- Associative chemosensing by fluorescent macrocycle-dye complexes-a versatile enzyme assay platform beyond indicator displacement
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A label-free in situ method to monitor reactions in real time by using fluorescent supramolecular chemosensors based on cucurbit[8]uril is presented. It allows sensing of enzymatic activity, inhibitor and activator screening, and analyte detection with unprecedented versatility and high sensitivity.
- Biedermann, Frank,Hathazi, Denisa,Nau, Werner M.
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supporting information
p. 4977 - 4980
(2015/03/30)
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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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- Kinetic characterisation of o-aminophenols and aromatic o-diamines as suicide substrates of tyrosinase
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We study the suicide inactivation of tyrosinase acting on o-aminophenols and aromatic o-diamines and compare the results with those obtained for the corresponding o-diphenols. The catalytic constants follow the order aromatic o-diamines max/KmS, follows this order: o-diphenols > o-aminophenols > aromatic o-diamines.
- Munoz-Munoz, Jose Luis,Garcia-Molina, Francisco,Berna, Jose,Garcia-Ruiz, Pedro Antonio,Varon, Ramon,Tudela, Jose,Rodriguez-Lopez, Jose N.,Garcia-Canovas, Francisco
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experimental part
p. 647 - 655
(2012/08/08)
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- Anodic oxidation of catechols in the presence of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring: Selective α-arylation reaction
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The electrochemical oxidation of catechols leads to the formation of o-benzoquinones. This property has been applied to effectively synthesize α-arylated products of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring.
- Zeng, Cheng-Chu,Ping, Da-Wei,Hu, Li-Ming,Song, Xiu-Qing,Zhong, Ru-Gang
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body text
p. 2465 - 2472
(2010/07/06)
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- Studies of the competing rates of catechol oxidation and suicide inactivation of tyrosinase
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Tyrosinase oxidation of catechols to ortho-quinones is accompanied by suicide inactivation of the enzyme. The rates of these competing processes vary and depend on the nature of ring substituents. For a series of 4-substituted catechols the relationships between structure and reaction rates have been examined using multiple regression. Significant but different structure-rate relationships were found for each process. The oxidation rate (k1) is greatest for short hydrophobic substituents; there is an optimum substituent hydrophobicity (π 0.7) for the rate of inactivation (k2). ARKAT USA, Inc.
- Ramsden, Christopher A.,Riley, Patrick A.
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experimental part
p. 248 - 254
(2011/02/22)
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- Electrochemical oxidation of 4-methylcatechol in the presence of β-diketones
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Electrochemical oxidation of 4-methylcatechol (1) in the presence of, benzoylacetone (2), dibenzoylmethane (3), 3-hydroxy-1H-phenalen-l-one (4), acetylacetone (5), dimedone (6), and 2-acetylcyclohexanone (7) as nucleophiles has been studied in detail by cyclic voltammetry and controlled-potential coulometry. The results indicate that the electro-chemically generated quinone participates in Michael addition reaction with 2-7 via various mechanisms to produce new organic compounds. Furthermore, our studies show that the structure of intermediates play a crucial role in product selectivity under controlled-potential conditions. Various types of products were also obtained through the selective oxidation at the surface of a carbon electrode in an undivided cell.
- Nematollahi, Davood,Rafiee, Mohammad,Khavasi, Hamid Reza
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experimental part
p. 1505 - 1511
(2009/05/06)
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- Polyphenol oxidase from yacon roots (Smallanthus sonchifolius)
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Polyphenol oxidase (E.C. 1.14.18.1) (PPO) extracted from yacon roots (Smallanthus sonchifolius) was partially purified by ammonium sulfate fractionation and separation on Sephadex G-100. The enzyme had a molecular weight of 45 490 ± 3500 Da and Km/s
- Neves, Valdir Augusto,Da Silva, Maraiza Aparecida
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p. 2424 - 2430
(2008/02/07)
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- Use of experimental design methodology to prepare Maillard reaction products from glucose and cysteine inhibitors of polyphenol oxidase from eggplant (Solanum melongena)
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Polyphenol oxidase (PPO) from eggplant was extracted and partially purified by a two-step fractionation-precipitation using ammonium sulfate and phenylsepharose hydrophobic interaction chromatography. The eggplant PPO extract was characterized concerning
- Cheriot, Sophie C.,Billaud, Catherine,Nicolas, Jacques
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p. 5120 - 5126
(2008/04/03)
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- Purification and characterization of Ocimum basilicum L. polyphenol oxidase
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A partial characterization of polyphenol oxidase (PPO) activity in Ocimum basilicum L. is described. PPO in O. basilicum L. was extracted and purified through (NH4)2SO4 precipitation, dialysis, and a Sepharose 4B-L-tyrosin
- Dogan, Serap,Turan, Pinar,Dogan, Mehmet,Arslan, Oktay,Alkan, Mahir
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p. 10224 - 10230
(2007/10/03)
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- Effects of electron-withdrawing substituents on DPPH radical scavenging reactions of protocatechuic acid and its analogues in alcoholic solvents
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The DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity of protocatechuic acid (3,4-dihydroxybenzoic acid) and its related catechols was examined. Compounds possessing strong electron-withdrawing substituents showed high activity. NMR analysis of the reaction mixtures of catechols and DPPH radical in methanol showed the formation of methanol adducts. The results suggest that high radical scavenging activity of catechols in alcohol is due to a nucleophilic addition of an alcohol molecule on o-quinones, which leads to a regeneration of a catechol structure. Furthermore, the radical scavenging activity in alcohols would largely depend on the electron-withdrawing/donating substituents, since they affect the susceptibility toward nucleophilic attacks on o-quinone.
- Saito, Shizuka,Kawabata, Jun
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p. 8101 - 8108
(2007/10/03)
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- Regioselective oxidation of phenols to o-quinones with o-iodoxybenzoic acid (IBX)
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Chemical equation presented An efficient regioselective method for oxidation of phenols to o-quinones is reported. When this procedure is combined with a subsequent reduction, it proves to be useful for the construction of a variety of catechols.
- Magdziak, Derek,Rodriguez, Andy A.,Van De Water, Ryan W.,Pettus, Thomas R. R.
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p. 285 - 288
(2007/10/03)
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- Enhancement of tyrosinase activity by macrocycles in the oxidation of p-cresol in organic solvents
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The activity of tyrosinase, suspended in dry halogenated solvents, can be considerably increased upon the addition of macrocycles to the reaction medium.
- Broos, Jaap,Arends, Renate,Van Dijk, Gerrit B.,Verboom, Willem,Engbersen, Johan F. J.,Reinhoudt, David N.
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p. 1415 - 1417
(2007/10/03)
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- N.M.R. Study of Bond Orders in o- and p-Quinones
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The 4J(Me-CC-H) coupling constsnt, 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.
- Gready, Jill E.,Hata, Kazumi,Sternhell, Sever,Tansey, Charles W.
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p. 593 - 600
(2007/10/02)
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- ROLES OF o-QUINONES AND THEIR POLYMERS IN THE ENZYMIC BROWNING OF APPLES
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Enzymic browning and the bleaching produced by the addition of ascorbic acid have been studied simultaneously in crushed apple tissue and in pure solutions of (+)-catechin and chlorogenic acid.Spectrophotocolorimetry was used to study crushed apple tissue
- Rouet-Mayer, Marie-Aude,Ralambosoa, Justin,Philippon, Jean
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p. 435 - 440
(2007/10/02)
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- Multiple Electron Oxidation of Phenols by an Oxo Complex of Ruthenium(IV)
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The kinetics of oxidation of phenol and alkylated phenol derivatives by (2+) and (2+) (bpy is 2,2'-bipyridine and py is pyridine) to give the corresponding quinones have been studied in aqueous solution and in acetonitrile.The reactions are first order in both phenol and Ru(IV)=O(2+) or Ru(III)-OH(2+).They proceed via a detectable intermediate, which is a Ru(II) complex. 18O isotopic labeling experiments show that transfer of the oxo group from Ru(IV)=O(2+) to phenol is quantitative.The reactions are facile.With Ru(IV)=O(2+) as oxidant k(25 deg C, CH3CN) = 1.9 (+/-0.4) E2M-1s-1; with Ru(III)-OH(2+) as oxidant k(25 deg C, CH3CN) = 4.0 (+/-0.4) E1M-1s-1.On the basis of the rate laws, the magnitude of OH/OD and CH/CD kinetic isotope effects, and the 18O labeling results, the most reasonable mechanisms for oxidation of phenol by Ru(IV)=O(2+) appears to be electrophilic attack on the aromatic ring.For Ru(III)-OH(2+), oxidation appears to occur by CH/H atom transfer in CH3CN and OH/H atom transfer in water.
- Seok, Won K.,Meyer, Thomas J.
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p. 7358 - 7367
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- Regioselective Oxidation of Phenols Catalyzed by Polyphenol Oxidase in Chloroform
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Mushroom polyphenol oxidase can catalyze the oxidation of a number of phenols to o-quinones in chloroform.While in water the enzymatic oxidation results in negligible yields due to rapid inactivation of the enzyme and spontaneous polymerization of the quinones, in chloroform a quantitative conversion has been achieved; the quinones produced have been nonenzymatically reduced to catechols, thereby affording a net regioselective polyphenol oxidase catalyzed hydroxylation of phenols.
- Kazandjian, Rafi Z.,Klibanov, Alexander M.
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p. 5448 - 5450
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Acetanilide and para-Substituted Acetanilides by HClO4-Phenyliodosyl Acetate System
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Oxidation of acetanilide and p-methyl-, p-chloro-, p-bromo- and p-nitro-acetanilides by phenyliodosyl acetate (PIA) in the presence of HClO4 in aqueous medium is first order in and fractional order each in and .Increase in percentage of HOAc in the solvent mixture increases the rate.A probable reaction mechanism and rate law consistent with it have been discussed.
- Radhakrishnamurti, P. S.,Sasmal, B. M.,Patnaik, D. P.
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p. 106 - 108
(2007/10/02)
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- The Synthesis of Propellane Compounds from 2,3-Disubstituted Indoles and o-Benzoquinones
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The reaction of 2,3-dihydro-1H-cyclopentindole 3 and 1,2,3,4-tetrahydrocarbazole 4 with substituted o-benzoquinones yielded - and propellanes, respectively.The physical and chemical properties of the propellane compounds were investigated
- Omote, Yoshimori,Harada, Kazuo,Tomotake, Atsushi,Kashima, Choji
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p. 1841 - 1844
(2007/10/02)
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- Spectroelectrochemical Examination of Charge Transfer between Chlorpromazine Cation Radical and Catecholamines
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With chlorpromazine (CPZ) and dopamine (DA) in their reduced forms in solution, the potential of a platinum electrode was stepped to a value where both species were oxidized at diffusion controlled rates.The CPZ+. cation radical so generated then diffused away from the electrode and encountered reduced DA, which it oxidized.The rate of oxidation was determined by monitoring the absorbance due to CPZ+. or dopamine quinone (DPQ) using the glancing incidence reflection spectroelectrochemical technique.The kinetics of the process indicate that the rate law is first order in both CPZ+. and DA, implying that the first encouter of the two molecules is the rate limiting step, rather than some subsequent process.The rate constant for dopamine was compared with those for three other catechols, and the rate constant increased monotonically with driving force, as measured by the difference in redox potentials between catechol and CPZ.The advantages of the technique for studying homogeneous charge transfer reactions are noted, as is the implication of the results on the CPZ+./DA reaction on the biological effects of CPZ.
- Mayausky, J. S.,McCreery, R. L.
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p. 308 - 312
(2007/10/02)
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- Kinetics of V(IV) Catalysed Oxidation of Phenols by Acid Bromate
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The oxidation of phenol and substituted phenols was studied using KBrO3 as oxidant in presence of V(IV) in binary solvent mixtures of acetic acid in water.Order with respect to oxidant is one and the order with respect to substrate and the catalyst is found to be fractional.The behaviour of acid shows that the order in acid is different under different acid concentrations.Effects of temperatures and percentage composition of acetic acid were studied.A suitable mechanism in presence of catalyst is given explaining the experimental facts.The effect of substituents was also studied and discussed.
- Parimala, N.,Lakshmi, Vijaya,Sundaram, E. V.
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p. 667 - 669
(2007/10/02)
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