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The enzyme activity of catechol oxidase (CO) give rise to enzymatic browning, leading to undesirable changes in fruits and vegetables. The aim of this work is to investigate the inhibitory effect of five essential oils (EOs) on CO from date fruits (Phoenix dactylifera). Catechol oxidase has been purified from date fruit through three-phase partitioning (TPP). Essential oils were extracts from Artemisia herba-alba, Artemisia campestris, Thymus vulgaris, Origanum vulgare, and Salvia Rosmarinus, and were tested against CO. The composition of these five essential oils was then identified using GC-MS. Major constituents identified were camphor (20.91%) and davanone D (19%) for A. herba alba, capillene (47.79%) for A. compestris, thymol (33.75%) and linalool (30.44%) for T. vulgaris, carvacrol (68.60%) for O. vulgare, and camphor (33.89%) for S. Rosmarinus. The EO from A. campestris was the most potent inhibitor of enzyme (IC50 = 3.44±0.09 mg/mL) while the weakest effect was observed for EO of O. vulgare (IC50 = 10.24±0.29 mg/mL). Different mechanism of inhibition was obtained. Hence, a competitive inhibition for both EOs of A. herba-alba and T. vulgaris, uncompetitive behavior for A. campestris, noncompetitive mechanism for S. rosmarinus and O. vulgare were observed. The docking molecular of those major constituents was investigated using crystal structure of CO from Ipomoea batatas (1BT1). The best-docked compound was davanone D (-5.55 kcal/mol) while camphor show weaker docking scores (3.79 kcal/mol). Thus, the results from our work could be important and offer an approach of control enzymatic browning using essential oils. [ABSTRACT FROM AUTHOR]

Given the widespread and diverse effects of transition metal ions such as copper and zinc in multiple biological processes, this research endeavor addresses herein the microwave‐aided synthesis of two novel tetradentate ONNO (L1) and tridentate NNO (L2) donor Schiff base ligands derived from 4,5‐dimethyl‐1,2‐phenylenediamine and 4‐bromo‐2‐hydroxybenzaldehyde in a 1:2 ratio and from 4,5‐dimethyl‐1,2‐phenylenediamine and 5‐methoxy‐2‐hydroxybenzaldehyde in a 1:1 ratio, with their respective zinc, ZnL1(1) and ZnL2(3), and copper, CuL1(2) and CuL2(4), Schiff base metal complexes, which are comprehensively characterized utilizing physiochemical and analytical techniques, along with geometry optimization using the DFT approach. Spectrophotometric analyses have been used to assess the biomimetic activity in the conversion of 3,5‐DTBC to 3,5‐DTBQ with turnover numbers 53.4 and 78 h−1 in methanol for 2 and 4, whereas the zinc complexes are found to be ineffective. With CT‐DNA, possible modes of interaction with the synthesized complexes have been explored using absorption spectroscopy, where the associated binding constants ranged between 1.541 × 105 and 2.186 × 105 M−1. EtBr‐bound DNA was used in the fluorescence quenching experiments with Stern–Volmer constant (Ksv) values in the range 4.084 × 104 and 3.402 × 104 M−1, showing a stronger association with CT‐DNA. The compounds' ability to inhibit bacterial strains was also examined in vitro, as well as their ability to reduce inflammation, through the protein denaturation method and the DPPH assay for antioxidant activity have been performed. Furthermore, molecular docking simulations have been carried out to obtain a deeper comprehension of the molecular‐level interactions with CT‐DNA and cyclooxygenase‐2 (COX‐2). [ABSTRACT FROM AUTHOR]

Several novel quinazoline derivatives bearing phenolic hydroxyl moiety (2–7) have been produced with good yields and screened for biological activities. All the title compounds were characterized using spectroscopic techniques such as 1H NMR, 13C NMR, FTIR, and HRMS. Then, the anti-browning effects of synthesized quinazoline derivatives were investigated in vitro. The IC50 values for molecules 2–7 were calculated as 0.085, 1.145, 0.106, 6.86, 0.52, 7.07 µM, respectively. Ki constants, which are inhibitory-enzyme binding constants, were calculated by using Lineweaver–Burk graphs as 0.16 ± 0.0620, 0.906 ± 0.3029, 0.055 ± 0.0171, 9.363 ± 2.5809, 0.773 ± 0.3204, 7.863 ± 1.9107 µM, respectively. In computer-aided analysis, to gain insights electrochemical properties, synthesized compounds were analysed theoretically by density functional theory. Molecular docking studies and MD simulations were performed to identify possible inhibitor-enzyme binding interactions. According to obtained results, all the compounds formed hydrogen bonds with Asn 112 and Asn 414, and showed π-cation interaction with Phe2 70, gatekeeper residue in target protein. Supporting the nm level inhibition, MD simulations indicate that protein-inhibitor complex maintain the stability and have high number of hydrogen bond formation during the simulation. [ABSTRACT FROM AUTHOR]

The trend of modelling native enzymes is increasing day by day with the motive of mechanistic elucidation of enzyme-catalyzed reactions and the efficiency of catalysts. Most of the metalloenzymes are capable to activate molecular oxygen due to the presence of metal ions. Among these, copper-based metalloenzyme catechol oxidase has an attractive feature of its oxidizing ability to generate ortho-quinones from catechol. Moreover, the conversion of catechol to ortho-quinones is an important tool for the determination of hormonally active catecholamines such as adrenaline, noradrenaline, and dopa. Nevertheless, the use of native enzymes is highly expensive and the employment of biomimetic models can be the best alternative. This review summarizes some of the widely used modelling methods and their successful applications. Additionally, we also briefly elucidated the structure–activity relationship, kinetic studies of the catalytic oxidation of the substrate, and different external factors influencing the catalytic cycle such as pH, temperature, etc. [ABSTRACT FROM AUTHOR]

Tyrosinase is the most predominant member of the coupled binuclear copper (CBC) protein family. The recent trapping and spectroscopic definition of the elusive catalytic ternary intermediate (enzyme/O2/monophenol) of tyrosinase dictates a monooxygenation mechanism that revises previous proposals and involves cleavage of the μ‐η2:η2‐peroxide dicopper(II) O–O bond to accept the phenolic proton, followed by monophenolate coordination to copper concomitant with aromatic hydroxylation by the non‐protonated μ‐oxo. Here, we compare and contrast previously proposed and current mechanistic models for monophenol monooxygenation of tyrosinase. Next, we discuss how these recent insights provide new opportunities towards uncovering structure–function relationships in CBC enzymes, as well as understanding fundamental principles for O2 activation and reactivity by bioinorganic active sites. [ABSTRACT FROM AUTHOR]

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Within the framework of the present study, a polydentate ligand with S and N donor sites along with its CuII‐based chelates were prepared and characterized. Elemental and thermal analyses, μeff and ΛM measurements as well as spectroscopy techniques including FT‐IR, electronic spectra, and EPR are the characterization tools. Computational chemistry calculations were applied to confirm the geometrical assignments of the penta and hexa coordinated perchlorato and chloro derivatives, respectively. Octahedral and trigonal bipyramidal stereochemistries were assigned for these copper(II) chelates. Powder X‐ray spectroscopy data were processed by Expo 2014 computer program for the structural illustration of one of the existing octahedral metal complexes. Biomimicking of copper(II) containing proteins phenoxazinone synthase and catechol oxidase was studied and the obtained results demonstrated promising oxidase‐like activity of the present CuII‐base complexes. Kinetic measurements were also performed to identify the potential catalytic pathways of the studied oxidation processes. The type of the counter‐anion included in the complexes significantly controls the structural features and the catalytic properties. [ABSTRACT FROM AUTHOR]

A new series of MnII and FeIII chelates containing pyridine and phenolate‐based ligands was synthesized by treating the metal salt in ethanol with the Schiff‐bases, which were formed in situ. Analytical (C, H, N, and M), thermal analysis (thermogravimetric analysis & differential thermogravimetric), and spectroscopic techniques (IR, UV–Vis, ESR) in addition to molar conductance and magnetic measurements were employed to characterize the prepared metal chelates. Mono‐nuclear metal complexes, with N5 donor containing pentadentate Schiff‐base ligands were obtained. In addition, two dibridged homobinuclear iron(III) complexes with N4O donors containing phenolate‐based ligand were successfully isolated. Six‐coordinate complex species in an octahedral environment is proposed for both MnII and FeIII metal complexes. The density function theory study was used to optimize the geometrical shapes of three of the existing metal complexes and to identify some global reactivity descriptors. In addition, spectral data of PXRD with Expo 2014's structural solution software were utilized in the structural illustration of a representative MnII and FeIII complexes. Aerobic catalytic oxidation of 4‐tert‐butylcatechol (4‐TBCH2) and o‐aminophenol under catalytic conditions was studied by using the present manganese(II) and iron(III) complexes. The synthesized MnII and FeIII chelates exhibited a promising catalytic activity and probable catalytic sequences have been discussed. [ABSTRACT FROM AUTHOR]

Polyphenol oxidases (PPOs) comprise tyrosinases (TYRs) and catechol oxidases (COs), which catalyse the initial reactions in the biosynthesis of melanin. TYRs hydroxylate monophenolic (monophenolase activity) and oxidize diphenolic (diphenolase activity) substrates, whereas COs react only with diphenols. In order to elucidate the biochemical basis for the different reactions in PPOs, cDNA from walnut leaves was synthesized, the target gene encoding the latent walnut tyrosinase (jrPPO1) was cloned, and the enzyme was heterologously expressed in Escherichia coli. Mutations targeting the two activity controller residues (Asn240 and Leu244) as well as the gatekeeper residue (Phe260) were designed to impair monophenolase activity of jrPPO1. For the first time, monophenolase activity of jrPPO1 towards L-tyrosine was blocked in two double mutants (Asn240Lys/Leu244Arg and Asn240Thr/Leu244Arg) while its diphenolase activity was partially preserved, thereby converting jrPPO1 into a CO. Kinetic data show that recombinant jrPPO1 resembles the natural enzyme, and spectrophotometric investigations proved that the copper content remains unaffected by the mutations. The results presented herein provide experimental evidence that a precisely tuned interplay between the amino acids located around the active center controls the substrate specificity and therewith the mono- versus diphenolase activity in the type-III copper enzyme jrPPO1. [ABSTRACT FROM AUTHOR]

A template Schiff condensation of 2,6‐pyridine dicarbaldehyde or 2,6‐diformyl‐4‐ bromophenol and 1,3–diamino‐2‐hydroxy propane or 3,4‐diaminotoluene in the presence of copper(II) salts (CuX2) (X = Cl, Br, CH3COO, or ClO4) affords different types of copper(II) complexes. Depending on the employed molar ratio of the dicarbonyl compounds and diamines, different types of copper(II) complexes formed during the template condensation reaction. Structural formulation of the complexes was confirmed by elemental analysis (C, H, N, and M), physical measurements such as thermal analysis (TAG & DTG), molar conductivity, and magnetic moments in addition to spectral studies (UV–Vis, IR, and ESR). Homobinuclear in a four‐coordinate square planar and five‐coordinate square pyramidal and trigonal bipyramidal in monomeric structures are proposed. A mononuclear hexa‐coordinate in an octahedral geometry is suggested as well. Oxidase biomimetic catalytic activity of these newly synthesized copper(II) complexes was examined toward the aerobic oxidation of 4‐tert‐butylcatechol (4‐TBCH2) and o‐aminophenol under catalytic conditions. Both catalytic and kinetic investigations demonstrate promising oxidase catalytic activity and based on the kinetic results, probable mechanistic catalytic implications are discussed. Geometrical structures of representative copper(II) complexes were determined by optimizing their bond lengths, bond angles, dihedral angles, and the structural index (τ). [ABSTRACT FROM AUTHOR]

The napthyl/pyridine-pyrazole-derived complexes, [Mn(L1)Cl2] (1), [Co(L1)Cl2] (2), [Cu(µ-Cl)(Cl)(L)]2 (3), [Cu2(L)2(N3)3(µ2-N3)] (4), and [Co(L2)Cl2] (5) (where L1 = bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-napthalen-1-ylmethyl-amine (L1), L = 5-methyl-pyrazol-1-ylmethyl) -napthalen-1-ylmethyl-amine (L) and L2 = 2-[2-(3,5-dimethyl-pyrazol-1-yl)-1-methyl-ethyl]-pyridine), exhibited phenoxazinone synthase activity in methanol in the range 5–54 h−1. Binuclear copper(II) derivatives 3 and 4 show better catalytic activities than manganese(II) and cobalt(II) derivatives. The kinetic studies reveal that phenoxazinone chromophore is produced via a complex-substrate intermediate. Further, 3 and 4 show catecholase activity in methanol in the presence of oxygen. All the complexes showed potent antimicrobial activity against the tested strains of bacteria and fungi. Complex 1 was synthesized for the first time by mixing L1 and MnCl2 (1:1) and characterized by single-crystal X-ray crystallography, cyclic voltammetry, density functional theory, and thermogravimetry analysis. The present study suggests that napthyl/pyridyl-anchored pyrazole metal complexes are interesting scaffolds for the development of novel model compounds for biochemical reaction and efficient antimicrobial agents. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rational ligand design approaches allowed {Cu2(μ-OH/OMe)} cores to be accommodated within μ-phenoxido bis(tetradentate) and μ-phenoxido bis(tridentate) ligands having thioether donors. The complexes [Cu2(μ-H2L1)(μ-OH)](ClO4)2·2H2O (1), [Cu2(μ-L2)(μ-OH)(OH2)](ClO4)2 (2a) and [Cu2(μ-L2)(μ-OCH3)(OH2)](ClO4)2 (2b) were obtained from an N2O3S2 donor set bearing the H3L1 ligand (2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) and N2OS2 donor set containing the HL2 ligand (4-methyl-2,6-bis-[{2-(methylthio)phenylimino}methyl]phenol) without showing double phenoxido bridging or any type of preformed inter-fragment aggregation. Previously, we showed that H3L (2,6-bis[((2-(2-hydroxyethoxy)ethyl)imino)methyl]-4-methylphenol), the ether analogue of H3L1, in the presence of carboxylate anions, was responsible for the self-aggregation of preformed {Cu2} fragments and gave two types of [Cu4] complexes comprising [Cu4O] and [Cu4(OH)2] cores (T. S. Mahapatra, A. Bauzá, D. Dutta, S. Mishra, A. Frontera and D. Ray, ChemistrySelect, 2016, 1, 64–74). The molecular structures of 1, 2a and 2b were determined via single crystal X-ray diffraction and solution studies, which indicated the presence of [Cu2] species. This was further confirmed via UV-vis spectroscopy and HRMS analysis. The synthesized complexes were screened for their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2). A change in the mechanism of catalytic oxidation was observed with a change in the ligand backbone. All three complexes also showed DNA binding properties, which were further substantiated via molecular docking studies. Their DNA binding affinities were quantitatively ascertained using their intrinsic binding constant, Kb, values which were found to be 4.2 × 104, 5.6 × 104 and 4.8 × 104 M−1, respectively. Furthermore, the complexes displayed efficient DNA cleavage behaviour with pBR322 and the oxidative path was established in presence of ROS, singlet oxygen, 1O2, and the superoxide anion, O2·−. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the synthesis and characterization of Cu(II) and Fe(III) complexes of a newly synthesized Mannich base N-[4-hydroxy-3-[[4-(pyridin-2-yl)piperazin-1-yl]methyl]phenyl]acetamide. The spectro-analytical techniques employed include 1H, 13C NMR, IR, UV spectroscopy, conductivity measurements, and elemental analysis. Both mononuclear and dinuclear metal complexes were encountered in the study. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, catecholase activity of all four complexes was evaluated with the detailed kinetic studies reported. The nature of the bonding of the thiocyanate is discussed based on the observation of νCN (2150-2050 cm−1). All the metal complexes are catalytically active with turn over numbers ranging from 9.47 to 31.86 h−1 in DMF.Graphical abstract: [ABSTRACT FROM AUTHOR]

Copper(II) complexes of five peptide ligands containing at least three histidine residues have been tested as catalysts in catechol oxidation and superoxide dismutation. All systems exhibit considerable catechol oxidase-like activity, and the Michaelis-Menten enzyme kinetic model is applicable in all cases. Beside the Michaelis-Menten parameters, the effects of pH, catalyst and dioxygen concentration on the reaction rates are also reported. Considering the rather different sequences, the observed oxidase activity seems to be a general behavior of copper(II) complexes with multihistidine peptides. Interestingly, in all cases {Nim/2Nim,2N−} coordinated complexes are the pre-active species, the bound amide nitrogens were proposed to be an acid/base site for facilitating substrate binding. The studied copper(II)-peptide complexes are also able to effectively dismutate superoxide radical in the neutral pH range. [ABSTRACT FROM AUTHOR]

Synthetic CuII2 complexes have been widely investigated as model systems for catechol oxidase enzymes. The catechol oxidase reactivity of MnII2 complexes has been less explored, and the effect of metal substitution in catecholase mimics has not been explored. A series of MnII2 and CuII2 complexes supported by the same poly-benzimidazole ligand framework have been synthesised and investigated in catecholase activity in acetonitrile medium using 3,5-di-tert-butylcatechol (3,5-DTBC) as a substrate. The CuII2 complexes proved to be good catechol oxidase mimics with moderate kcat values (∼45 h−1). The kinetic parameters for MnII2 complexes exhibited lower kcat values (∼8–40 h−1) when compared to the CuII2 complexes. Our findings demonstrate that later transition metals supported by relatively electron rich ligands yield the highest kcat values for catechol oxidation. [ABSTRACT FROM AUTHOR]

The silkworm, Bombyxmori L., has developed various defense mechanisms that reducethe negative effects of adverse environmental conditions. However, the mechanisms by which many physiological and ecological aspects work, including the functioning of the prophenoloxidase (pro-PO) system in Bombyxmori (BmPPO), are not completely understood. In our previous study, we found that eicosanoids mediated the innate immunity of the Chinese oak silkworm, Antheraeapernyi. To investigate the role of the pro-PO system in the silk-producing insect, Bombyxmori, the transcripts and activity of BmPPO were studied. We found that lipopolysaccharides (LPS) could induce the transcripts of BmPPO1, while eicosanoids could mediatethe induction of BmPPO1 gene expression in hemocytes. Most interestingly, the expression of BmPPO2 had no response to LPS challenge and treatment with eicosanoids. These results support the hypothesis that the B.mori pro-POsystem is associated with the eicosanoids signaling pathway. [ABSTRACT FROM AUTHOR]

Coupled binuclear copper (CBC) enzymes have a conserved type 3 copper site that binds molecular oxygen to oxidize various mono- and diphenolic compounds. In this study, we found a new crystal form of catechol oxidase from Aspergillus oryzae (AoCO4) and solved two new structures from two different crystals at 1.8-Å and at 2.5-Å resolutions. These structures showed different copper site forms (met/deoxy and deoxy) and also differed from the copper site observed in the previously solved structure of AoCO4. We also analysed the electron density maps of all of the 56 CBC enzyme structures available in the protein data bank (PDB) and found that many of the published structures have vague copper sites. Some of the copper sites were then re-refined to find a better fit to the observed electron density. General problems in the refinement of metalloproteins and metal centres are discussed. [ABSTRACT FROM AUTHOR]

The development of low-cost catalytic systems that mimic the activity of tyrosinase enzymes (Catechol oxidase) is of great promise for future biochemistry technologic demands. Herein, we report the synthesis of new biomolecules systems based on hydrazone derivatives containing a pyrazole moiety (L1-L6) with superior catecholase activity. Crystal structures of L1 and L2 biomolecules were determined by X-ray single crystal diffraction (XRD). Optimized geometrical parameters were calculated by density functional theory (DFT) at B3LYP/6-31G (d, p) level and were found to be in good agreement with single crystal XRD data. Copper (II) complexes of the compounds (L1-L6), generated in-situ, were investigated for their catalytic activities towards the oxidation reaction of catechol to ortho-quinone with the atmospheric dioxygen, in an attempt to model the activity of the copper containing enzyme tyrosinase. The studies showed that the activities depend on four parameters: the nature of the ligand, the nature of counter anion, the nature of solvent and the concentration of ligand. The Cu(II)-ligands, given here, present the highest catalytic activity (72.920 μmol.L-1.min-1) among the catalysts recently reported in the existing literature. [ABSTRACT FROM AUTHOR]

Copper(ii) complexes of a new polydentate tripodal ligand trenpyz (L, tris[2-(5-pyrazolylmethyl)aminoethyl]amine) were characterized in both solution and solid states. A combined evaluation of potentiometric UV-Vis and EPR data provided both thermodynamic and structural information on the complexes formed in solution. In equimolar solution the highly stable square pyramidal CuHL and trigonal bipyramidal CuL are the dominant species at around pH 3 and 5–8, respectively. Above pH 8 further deprotonation was observed (pK = 9.56), which is related to the formation of a copper(ii)-bound pyrazolate anion. This creates the possibility for the formation of oligonuclear complexes, through pyrazolate bridges, and at a 3/2 Cu(ii)/L ratio three trinuclear complexes were identified, similar to the copper(ii)–tachpyz (N,N′,N′′-tris(5-pyrazolylmethyl)-1,3,5-cis,cis-triamino-cyclohexane) system studied earlier. The trinuclear complexes of the two ligands have considerably different speciations, due to the different denticities of tripodal platforms. At the optimal pH the catechol oxidase activities of the triply deprotonated trinuclear complexes of trenpyz and tachpyz are similar, but the pH-rate constant profiles are significantly different, as a consequence of the deviations in their speciation. Consequently, the H2dtbc oxidation promoted by these trinuclear complexes can be easily controlled by the denticity of the tripodal ligands, since it affects the coordination environment of the central metal ion, which is proposed to be the main actor during the reaction. [ABSTRACT FROM AUTHOR]

Unique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co3L4] and planar disc-like [Co7L6] compounds: [CoII3L2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [CoII7(μ-L)6(μ-OMe)6]Cl2 (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L−, water and a trifluoroacetate anion, while 2 grows around a central CoII ion surrounded by a {CoII6} hexagon bound to methoxide and L−. Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (kcat) 2 is more effective than 1 for oxidation of 3,5-DTBCH2. [ABSTRACT FROM AUTHOR]

Tyrosinase and peroxidase content in various fruits and vegetables was compared. Avocado pulp was found to be a rich source of tyrosinase yielding around 4.5U/g. Avocado seeds, Datura metel and Coccinia grandis were found to be the next best sources. The tyrosinase rich sources gave comparatively poor yield of peroxidase with the exception of C. grandis. Tyrosinases from Avacado (ATy) functioned optimally at pH 6.5 and was stable over a broad range of pH from 5.5-9. C. grandis tyrosinase (CTy) was an alkaline tyrosinase with an optimum pH of 9.5-10. Optimum temperature of C grandis peroxidase (CPox) was 50 °C. ATy, CTy and CPox retained 100% activity at 40 °C, 60 °C and 75 °C respectively for 30min. The KM for Catechol was 3.2-3.3 mM for both CTy and ATy. KM for Dopa was 3.3 and 1.27mM for ATy and CTy respectively. CPox exhibited a strong affinity for hydrogen peroxide with a KM of 87 μM. [ABSTRACT FROM AUTHOR]

The authors report on a nonenzymatic catechol sensor that is based on the immobilization of ferrocene (Fc) on graphene oxide (GO). A glassy carbon electrode (GCE) was modified with GO which then was silanized with (3-aminopropyl)trimethoxysilane. Ferrocenecarboxaldehyde was then immobilized on GO via formation of a Schiff base. The immobilization process was monitored stepwise by using FTIR spectroscopy, X-ray diffraction, cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Investigation of the modified electrode by CV revealed a pair of well-defined redox peaks with anodic and cathodic peak potentials at +0.380 and +0.277 V, corresponding to the Fc/Fc redox couple. The Fc modified electrode exhibits excellent electrocatalytic activity towards the oxidation of catechol at a typical working voltage of +0.45 V (vs. Ag/AgCl). The response is linear in the 3 to 112 μM catechol concentration range, the detection limit is 1.1 μM, and the sensitivity is 1184.3 μA·mM·cm. The sensor is stable, reproducible and reasonably selective. It was successfully applied to the determination of catechol in spiked tap water and lake water samples. [ABSTRACT FROM AUTHOR]

This report describes the syntheses, crystal structures, electrospray ionisation mass spectra, catechol oxidase activity and magnetic properties of a tetracopper(ii) cluster [CuII4L2(µ3-OH)2(NCO)4]·2H2O (1) and a one-dimensional (1D) coordination polymer [{{CuII2L(µ1,1-N3)}2(µ1,1-N3)2}(µ1,3-N3)2]n (2) derived from a Schiff base ligand (HL; 1 : 2 condensation product of 4-ethyl-2,6-diformylphenol and 3-morpholinopropylamine). Compound 1 may be considered a dimer of two µ-phenoxo-µ3-hydroxido dicopper(ii) units, where the dimerisation takes place through the two µ3-hydroxido moieties. Compound 2 is a µ-phenoxo-µ1,1-azido dicopper(ii)-based 1D polymer, where the dicopper(ii) units are interlinked by two end-on azide bridges to form a dimer of dinuclear-type tetracopper(ii) moieties, which, in turn, are self-assembled by end-to-end azide bridges. Magnetic investigations reveal a strong antiferromagnetic interaction in the dicopper(ii) basic unit in both cases, with J values of −382 cm−1 for 1 and −220 cm−1 for 2. Both compounds have been found to be functional models for catechol oxidase activity in N,N-dimethylformamide (DMF) and acetonitrile, with Kcat values around 15 h−1 for 1 and 13 h−1 for 2. Interestingly, compound 2 is a unique example in which a dimer of a dinuclear metal unit is the node for a versatile and well-explored linker, azide, to generate a coordination polymer. It is also interesting that a coordination polymer, 2, has been identified as the functional model of catechol oxidase activity. [ABSTRACT FROM AUTHOR]

Background: Many fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic polysaccharide monooxygenases (LPMOs). The application of LPMOs is expected to contribute to ecologically friendly conversion of biomass into fuels and chemicals. Moreover, applications of LPMO-modified cellulose-based products may be envisaged within the food or material industry. Results: Here, we show an up to 75-fold improvement in LPMO-driven cellulose degradation using polyphenol oxidase- activated lignin building blocks. This concerted enzymatic process involves the initial conversion of monophenols into diphenols by the polyphenol oxidase MtPPO7 from Myceliophthora thermophila C1 and the subsequent oxidation of cellulose by MtLPMO9B. Interestingly, MtPPO7 shows preference towards lignin-derived methoxylated monophenols. Sequence analysis of genomes of 336 Ascomycota and 208 Basidiomycota reveals a high correlation between MtPPO7 and AA9 LPMO genes. Conclusions: The activity towards methoxylated phenolic compounds distinguishes MtPPO7 from well-known PPOs, such as tyrosinases, and ensures that MtPPO7 is an excellent redox partner of LPMOs. The correlation between MtPPO7 and AA9 LPMO genes is indicative for the importance of the coupled action of different monooxygenases in the concerted degradation of lignocellulosic biomass. These results will contribute to a better understanding in both lignin deconstruction and enzymatic lignocellulose oxidation and potentially improve the exploration of eco-friendly routes for biomass utilization in a circular economy. [ABSTRACT FROM AUTHOR]

Two new tripodal peptides containing non-protected N-terminal (L1, tren3his) and C-terminal (L2, nta3his) histidines have been synthesized in order to combine the structuring effect of tripodal scaffolds and the strong metal binding properties of histidine moieties. In the present work the copper(ii) complexes of these ligands have been studied by combined pH-metric, UV-Vis, CD, EPR and MS methods. At a 1 : 1 metal-to-ligand ratio the two ligands behave as the corresponding dipeptides containing N/C-terminal histidines, but above pH 9 the participation of the tertiary amine in the fused chelate rings results in unique binding modes in the case of both ligands. Besides, the formation of oligonuclear complexes also confirms the positive influence of tripodal platforms on metal coordination, and provides the potential to be efficient functional models of oxidase enzymes. Accordingly, the oligonuclear complexes of both ligands exhibit considerable catecholase-like activity. The oxidation of 3,5-di-tert-butyl-catechol proceeds with the participation of separated Cu2+ centers in the presence of L1 complexes. However, the proximity of the two metal ions in the dinuclear complexes of L2 allows their cooperation along the catalytic cycle. Substrate binding modes, effects of reactants, intermediate and side product formation have also been studied, allowing us to propose a plausible catalytic mechanism for each copper(ii)–ligand system. [ABSTRACT FROM AUTHOR]

A series of N-phenylthiourea derivatives was built starting from the X-ray structure in the molecular mechanics framework and the interaction profile in the complex with the catechol oxidase was traced using molecular dynamics simulation. The results showed that the geometry and interactions between ligand and receptor were highly related to the position of the substituted side chains of phenyl moiety. At the end of molecular dynamics run, a concentrated multicenter hydrogen bond was created between the substituted ligand and receptor. The conformation of the ligand itself were also restricted in the receptor pocket. Furthermore, the simulation time of 50 ns were found to be long enough to explore the relevant conformational space and the stationary behavior of the molecular dynamic could be observed. [ABSTRACT FROM AUTHOR]

Four new neutral diclofenac-based complexes, [Co(dicl)2(2-pyet)2] 1, [Ni(dicl)2(2-pyet)2] 2, [Cu2(dicl)2(2-pyet)2] 3, and [Cu2(dicl)2(2-pypr)2] 4 have been synthesized and characterized by elemental analysis, FT-IR, thermal analysis. Complexes 1, 3, and 4 have also been characterized by X-ray single-crystal structural analysis. The compounds of Co(II) and Ni(II) have octahedral geometry with two diclofenac and two 2-pyridineethanol ligands in the coordination sphere. The compounds of Cu(II) have square-pyramidal geometry and Cu(II) ions are linked via oxygens to the bridging 2-pyridineethanol or 2-pyridinepropanol ligands. The Δν values acquired by FT-IR are in agreement with the single XRD data. Studies on the thermal properties are reported and the complexes are stable to 196, 216, 215, and 201 °C in air, respectively. Two dinuclear Cu(II) complexes have demonstrated catalytic activity on oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone showing saturation kinetics at high substrate concentrations. The diclofenac complexes are investigated as inhibitors of the human cytosolic isoforms hCA I and II. The complexes are good as hCA I inhibitors (Kis of 1.52–55.06 μM) but only moderately efficient as hCA II inhibitors (Kis of 0.23–5.61 μM). [ABSTRACT FROM PUBLISHER]

An unprecedented solid of coper(II) complexes, [Cu(dpa)NCS][Cu(dpa)(NCS)](ClO) ( 1) [dpa = 2,2′-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically characterized with the aim to study the catecholase activity. The Cu(II) complex mimics the full catalytic cycle of the active site of catechol oxidase enzyme in acetonitrile medium with a turnover number of 4.788×10 h along with the production of semiquinone radical and hydrogen peroxide. In situ generation of Cu(I) species in the catalytic pathway of catechol oxidation was established by electrochemical study and further confirmed by electron paramagnetic resonance (EPR) spectroscopy. [ABSTRACT FROM AUTHOR]

Unique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co3L4] and planar disc-like [Co7L6] compounds: [CoII3L2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [CoII7(μ-L)6(μ-OMe)6]Cl2 (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L−, water and a trifluoroacetate anion, while 2 grows around a central CoII ion surrounded by a {CoII6} hexagon bound to methoxide and L−. Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (kcat) 2 is more effective than 1 for oxidation of 3,5-DTBCH2. [ABSTRACT FROM AUTHOR]

Four new imidazole-based ligands, 4-((1 H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (L 1), 4-((1 H-imidazol-4-yl)methyl)-2-( tert-butyl)-4,5-dihydrooxyzole (L 2), 4-((1 H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (L 3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1 H-imidazol-4-yl-)ethyl amine ( L 1), have been synthesized. The corresponding copper(I) complexes [Cu(I)( L 1)(CHCN)]PF (Cu L 1), [Cu(I)( L 2)(CHCN)]PF (Cu L 2), [Cu(I)( L 3)(CHCN)]PF (Cu L 3), [Cu(I)( L 1)(CHCN)]PF (Cu L 1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)( BIMZ)(CHCN)]PF (Cu BIMZ), are screened as catalysts for the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC-H) to 3,5-di- tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di- tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order Cu L 3 ≈ Cu L 1 > Cu BIMZ > Cu L 2 > Cu L 1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di- tert-butylphenol (2,4-DTBP-H), 3- tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl- l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (Cu L 1 and Cu BIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed. [ABSTRACT FROM AUTHOR]

Tyrosinases and catechol oxidases belong to the family of polyphenol oxidases (PPOs). Tyrosinases catalyze the o-hydroxylation and oxidation of phenolic compounds, whereas catechol oxidases were so far defined to lack the hydroxylation activity and catalyze solely the oxidation of o-diphenolic compounds. Aurone synthase from Coreopsis grandiflora (AUS1) is a specialized plant PPO involved in the anabolic pathway of aurones. We present, to our knowledge, the first crystal structures of a latent plant PPO, its mature active and inactive form, caused by a sulfation of a copper binding histidine. Analysis of the latent proenzyme's interface between the shielding C-terminal domain and the main core provides insights into its activation mechanisms. As AUS1 did not accept common tyrosinase substrates (tyrosine and tyramine), the enzyme is classified as a catechol oxidase. However, AUS1 showed hydroxylase activity toward its natural substrate (isoliquiritigenin), revealing that the hydroxylase activity is not correlated with the acceptance of common tyrosinase substrates. Therefore, we propose that the hydroxylase reaction is a general functionality of PPOs. Molecular dynamics simulations of docked substrate-enzyme complexes were performed, and a key residue was identified that influences the plant PPO's acceptance or rejection of tyramine. Based on the evidenced hydroxylase activity and the interactions of specific residueswith the substrates during the molecular dynamics simulations, a novel catalytic reaction mechanism for plant PPOs is proposed. The presented results strongly suggest that the physiological role of plant catechol oxidases were previously underestimated, as they might hydroxylate their--so far unknown--natural substrates in vivo. [ABSTRACT FROM AUTHOR]

Tyrosinases mediate the ortho-hydroxylation and two-electron oxidation of monophenols to ortho-quinones. Catechol oxidases only catalyze the oxidation of diphenols. Although it is of significant interest, the origin of the functional discrimination between tyrosinases and catechol oxidases has been unclear. Recently, it has been postulated that a glutamate and an asparagine bind and activate a conserved water molecule towards deprotonation of monophenols. Here we demonstrate for the first time that a polyphenoloxidase, which exhibits only diphenolase activity, can be transformed to a tyrosinase by mutation to introduce an asparagine. The asparagine and a conserved glutamate are necessary to properly orient the conserved water in order to abstract a proton from the monophenol. These results provide direct evidence for the crucial importance of a proton shuttle for tyrosinase activity of type 3 copper proteins, allowing a consistent understanding of their different chemical reactivities. [ABSTRACT FROM AUTHOR]

Tyrosinases and catechol oxidases are members of the class of type III copper enzymes. While tyrosinases accept both mono- and o-diphenols as substrates, only the latter substrate is converted by catechol oxidases. Researchers have been working for decades to elucidate the monophenolase/ diphenolase specificity on a structural level and have introduced an early hypothesis that states that the reason for the lack of monophenolase activity in catechol oxidases may be its structurally restricted active site. However, recent structural and biochemical studies of this enzyme class have raised doubts about this theory. Herein, the first crystal structure of a plant tyrosinase (from Juglans regia) is presented. The structure reveals that the distinction between mono- and diphenolase activity does not depend on the degree of restriction of the active site, and thus a more important role for amino acid residues located at the entrance to and in the second shell of the active site is proposed. [ABSTRACT FROM AUTHOR]

Tyrosinases are metalloenzymes belonging to the type-3 copper protein family which contain two copper ions in the active site. They are found in various prokaryotes as well as in plants, fungi, arthropods, and mammals and are responsible for pigmentation, wound healing, radiation protection, and primary immune response. Tyrosinases perform two sequential enzymatic reactions: hydroxylation of monophenols and oxidation of diphenols to form quinones which polymerize spontaneously to melanin. Two other members of this family are catechol oxidases, which are prevalent mainly in plants and perform only the second oxidation step, and hemocyanins, which lack enzymatic activity and are oxygen carriers. In the last decade, several structures of plant and bacterial tyrosinases were determined, some with substrates or inhibitors, highlighting features and residues which are important for copper uptake and catalysis. This review summarizes the updated information on structure-function correlations in tyrosinases along with comparison to other type-3 copper proteins. [ABSTRACT FROM AUTHOR]

A large library of CuII complexes with mononucleating and dinucleating ligands was synthesized to investigate their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC). X-ray structure determination for a number of these complexes revealed relatively large Cu…Cu distances and the formation of polymeric species. Comparison of the 3,5-DTBC oxidation rates showed that ligands that stabilize the biomimetic dinuclear CuIIμ-thiolate complex also result in copper compounds that are much more active in the oxidation of 3,5-DTBC. This oxidation activity is however inhibited by the presence of chloride ions. The highest kcat that was observed was 6900 h−1, which is one of the highest turnover frequencies reported so far for catechol oxidation in CH3CN. [ABSTRACT FROM AUTHOR]

Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aerobic auto-oxidation of 3,5-di- tert-butylcatechol to the corresponding o-benzoquinone at room temperature and displaying catalase activity for the hydrogen peroxide dismutation with remarkable activity (TON up to 4000). [ABSTRACT FROM AUTHOR]

Syntheses, crystal structures, magnetic properties and catechol oxidation behavior are presented for [Mn3] and [Mn4] aggregates, [MnIII2MnII(O2CMe)4(dmp)2(H2O)2]·2H2O (1·2H2O), [MnIII2MnII(O2CCH2Cl)4(dmp)2(H2O)2]·H2O·MeOH (2·H2O·MeOH), [MnIII4(μ3-O)(dmp)4(μ-DMSO)(N3)(DMSO)(H2O)]ClO4·DMSO (3·ClO4·DMSO), and [MnIII4(μ3-O)(dmp)4(μ-DMSO)(ClO4)(DMSO)(H2O)]ClO4·DMSO (4·ClO4·DMSO), developed with single type ligand H2dmp, 2-[(2-hydroxy-1,1-dimethyl-ethylimino)-methyl]-phenol. The successful isolation of 1–4 resulted from a systematic exploration of the effect of MnII salts, added carboxylates, Mn/H2dmp ratio, presence of azide, and other reaction conditions. The cores of 1 and 2 are similar and consist of a linear MnIIIMnIIMnIII unit in a carboxylate and H2dmp environment, revealing a central MnII ion in a different environment and terminal MnIII ions available for the introduction of structural and magnetic anisotropy to the system. The cores of 3 and 4 are also similar and consist of a distorted incomplete-adamantane type Mn4 coordination assembly in a carboxylate-free environment built on a triangular [MnIII3(μ3-O)] unit. The magnetic behavior of complexes 1–3 is dominated by antiferromagnetic exchange coupling that results in ground state spin values of S = 3/2 for 1 and 2 and S = 0 for 3. In solution, all four complexes 1–4 show catechol oxidation activity towards 3,5-DTBC. The catalytic activity for the oxidation of 3,5-DTBC in air followed the order 4 ＜ 3 ＜ 1 ＜ 2. [ABSTRACT FROM AUTHOR]

The reaction of CuX2 (X− = ClO4− and BF4−) with a new 1,3,5-tris(isonicotinoyloxymethyl)benzene (L) ligand gives rise to 3D coordination networks, [Cu3L4(CH3CN)6](X)6, with a new topology of the Schläfli point symbol {4·82}4{42·82·102}2{84·122}. [Cu3L4(CH3CN)6](ClO4)6 and [Cu3L4(CH3CN)6](BF4)6 networks have useful oval-shaped pores of 11.2 × 11.2 × 24.8 Å3 and 11.1 × 11.1 × 24.4 Å3 dimensions, respectively. These porous coordination networks act as good heterogeneous catalysts, oxidizing the catechols in the order 3,5-di-tert-butylcatechol (3,5-DBuCat) ＞ 4-tert-butylcatechol (4-BuCat) ＞ 4-chlorocatechol (4-ClCat). The catalytic effect of [Cu3L4(CH3CN)6](BF4)6 is slightly higher than that of [Cu3L4(CH3CN)6](ClO4)6. The pores of the 3D networks reversibly adsorb the solvents in the order chloroform ＞ tetrahydrofuran ＞ acetone. [ABSTRACT FROM AUTHOR]

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Electrochemical oxidation of catechol has been studied in the presence of thioacetamide (TAM) in a phosphate buffer solution (0.2 mol L-1, pH=6.0) at the surface of glassy carbon electrode by means of cyclic voltammetry. After the cyclic voltammetric investigation of the reaction mechanism of TAM with catechol, TAM has been determinated by means of the differential pulse voltammetry technique. The results showed that the cathodic peak current of catechol reduced in the presence of various concentrations of TAM and that catechol can participate in a 1,4-Michael addition reaction with TAM under an EC mechanism. The decreasing of the cathodic current of catechol showed a linear relationship with the TAM concentration that can be used for the determination of TAM with a detection limit less than 3 μmol L-1. [ABSTRACT FROM AUTHOR]

The work in this investigation deals with the syntheses, characterization, crystal structures and catechol oxidase activity of four diphenoxo-bridged CoIIICoIII compounds of composition [CoIIICoIIILMe-pn-(N3)4]·6H2O (1), [CoIIICoIIILMe-pn(N3)4]·4H2O (2), [CoIIICoIIILEt-pn(N3)4]·3.5H2O (3) and [CoIIICoIIILEt-pn-(N3)4]·CH3CN·2.5H2O (4), and two diphenoxo-bridged CoIIICoII compounds of composition [CoIIICoIILMe-Me2pn(N3)3]·2H2O (5) and [CoIIICoIILEt-Me2pn(N3)3]·H2O (6). In these compounds, H2LMe-pn, H2LEt-pn, H2LMe-Me2pn and H2LEt-Me2pn are four Robson type tetraiminodiphenolate macrocyclic ligands, in which the superscript Me and Et indicate that the dialdehyde components are 4-methyl-2,6-diformylphenol and 4-ethyl-2,6-diformyl-phenol, respectively, while pn and Me2pn indicate that the diamine components are 1,3-diaminopropane and 2,2-dimethyl-1,3-diaminopropane, respectively. The CoIIICoIII compounds 1-4 are further characterized by 1H NMR spectra. Compounds 1 and 3 are prepared following a metal-templated synthesis, while compounds 2 and 4 are prepared by direct synthesis, which includes using a pre-isolated macrocycle, [H4LMe-pn](ClO4)2/[H4LEt-pn](ClO4)2, as a reactant. On changing the diamine component of the corresponding macrocycle from 1,3-diaminopropane to 2,2-dimethyl-1,3-diaminopropane, but otherwise following the similar reaction procedure (both direct and template), the CoIIICoII compounds [CoIIICoIILMe-Me2pn(N3)3]·2H2O (5), [CoIIICoIILEt-Me2pn(N3)3]·H2O (6), [CoIIICoIILMe-Me2pn(N3)3]·0.5MeCN·0.27H2O (5A; Inorg. Chim. Acta, 2014, 412, 38) and [CoIIICoIILEt-Me2pn(N3)3]·MeCN (6A; Dalton Trans., 2013, 42, 4561) are formed, rather than CoIIICoIII compounds. Like compounds 5A and 6A, all the compounds 1-6 show catechol oxidase activity (substrate: 3,5-di-tert-butyl catechol). The kinetic parameters for 1, 3 and 6 have been determined. Their Kcat values are, respectively, 212.6, 188.0 and 191.3 h-1. ESI-MS (positive) spectra of some representative cases (with and without the substrate) have been recorded and the positive species have been assigned well. Unprecedented and surprising aspects of the composition/structure and properties of the complexes in this investigation have been discussed. [ABSTRACT FROM AUTHOR]

To explore the effect of Cu-Cu distance in the structure of copper complexes on their catechol oxidase and nuclease activity, six copper complexes with a similar coordination sphere but different Cu-Cu distances were synthesized and characterized with elemental analysis, single-crystal X-ray diffraction, molar conductivity measurements, IR and UV-visible spectroscopy. Complex 1 is a binuclear copper complex and complex 4 is a polynuclear complex with a Z-chain structure, as evidenced by their crystal structures. Complementary characterizations showed that complexes 2 and 3 have a similar binuclear structure to the complex 1; and complexes 5 and 6 are analogous to complex 4. The catechol oxidase activity of complexes 1, 2, 3 is quite akin to that of 4, 5, 6, suggesting that the catechol oxidase activity of the complexes was determined by the coordination environment of the copper center, when Cu-Cu distance is large. In contrast, DNA cleavage activity of the complexes 1, 2 and 3 are much higher than that of 4, 5 and 6, indicating that the planar ligand structure in the complexes 4, 5 and 6 is more critical than the copper coordination sphere and the Cu-Cu distance for their nuclease activity. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Stand aside, potatoes! A mononuclear manganese(III) complex [MnIII(L)2(OAc)(AcOH)] (1) exhibits catechol oxidation in the presence of molecular oxygen by generation of a hydroxyl radical with a turnover number of the same order as that of catechol oxidase from sweet potatoes. [ABSTRACT FROM AUTHOR]

Catechol oxidases (EC 1.10.3.1) catalyse the oxidation of o-diphenols to their corresponding o-quinones. These oxidases contain two copper ions (CuA and CuB) within the so-called coupled type 3 copper site as found in tyrosinases (EC 1.14.18.1) and haemocyanins. The crystal structures of a limited number of bacterial and fungal tyrosinases and plant catechol oxidases have been solved. In this study, we present the first crystal structure of a fungal catechol oxidase from Aspergillus oryzae (AoCO4) at 2.5-Å resolution. AoCO4 belongs to the newly discovered family of short-tyrosinases, which are distinct from other tyrosinases and catechol oxidases because of their lack of the conserved C-terminal domain and differences in the histidine pattern for CuA. The sequence identity of AoCO4 with other structurally known enzymes is low (less than 30 %), and the crystal structure of AoCO4 diverges from that of enzymes belonging to the conventional tyrosinase family in several ways, particularly around the central α-helical core region. A diatomic oxygen moiety was identified as a bridging molecule between the two copper ions CuA and CuB separated by a distance of 4.2–4.3 Å. The UV/vis absorption spectrum of AoCO4 exhibits a distinct maximum of absorbance at 350 nm, which has been reported to be typical of the oxy form of type 3 copper enzymes. [ABSTRACT FROM AUTHOR]

Two new dinucleating phenol-based ligands ( m-HLSMe and p-HLSMe) bearing pyridine-containing pendant arms with a SMe group on one pyridine ( meta or para position relative to the pyridine nitrogen atom) have been synthesized. After coordination by two copper(II) ions, the corresponding μ-phenoxido, μ-hydroxido dicopper(II) complexes were isolated and characterized by UV/Vis, EPR spectroscopy, single-crystal X-ray analysis (for the complex with the SMe substituent at the meta position) and electrochemistry. The presented compounds mimic the active site of type 3 copper enzymes and in particular the distinct environments of the copper ions.Both complexes are active as catalysts for the oxidation of 3, 5-di- tert-butylcatechol to the respective quinone. The catalytic properties of the complexes depend on substrate binding, as reflected by the KM values determined for the complexes in presence of 3, 5-dtbc and are not correlated directly with the redox properties of the dicopper center. [ABSTRACT FROM AUTHOR]

Background: Tyrosinases, tyrosinase-related proteins, catechol oxidases and hemocyanins comprise the type-3 copper protein family and are involved in a variety of biological processes, including pigment formation, innate immunity and oxygen transport. Although this family is present in the three domains of life, its origin and early evolution are not well understood. Previous analyses of type-3 copper proteins largely have focussed on specific animal and plant phyla. Results: Here, we combine genomic, phylogenetic and structural analyses to show that the original type-3 copper protein possessed a signal peptide and may have been secreted (we designate proteins of this type the α subclass). This ancestral type-3 copper protein gene underwent two duplication events, the first prior to the divergence of the unikont eukaryotic lineages and the second before the diversification of animals. The former duplication gave rise to a cytosolic form (β) and the latter to a membrane-bound form (γ). Structural comparisons reveal that the active site of α and γ forms are covered by aliphatic amino acids, and the β form has a highly conserved aromatic residue in this position. The subsequent evolution of this gene family in modern lineages of multicellular eukaryotes is typified by the loss of one or more of these three subclasses and the lineage-specific expansion of one or both of the remaining subclasses. Conclusions: The diversity of type-3 copper proteins in animals and other eukaryotes is consistent with two ancient gene duplication events leading to α, β and γ subclasses, followed by the differential loss and expansion of one or more of these subclasses in specific kingdoms and phyla. This has led to many lineage-specific type-3 copper protein repertoires and in some cases the independent evolution of functionally-classified tyrosinases and hemocyanins. For example, the oxygen-carrying hemocyanins in arthropods evolved from a β-subclass tyrosinase, whilst hemocyanins in molluscs and urochordates evolved independently from an α-subclass tyrosinase. Minor conformational changes at the active site of α, β and γ forms can produce type-3 copper proteins with capacities to either carry oxygen (hemocyanins), oxidize diphenols (catechol oxidase) or o-hydroxylate monophenols (tyrosinases) and appear to underlie some functional convergences. [ABSTRACT FROM AUTHOR]

A series of seven heterocyclic compounds based on pyridazinone and thiopyridazinone moieties: 5-(2-chlorobenzyl)-6-methylpyridazin-3-one L1; 5-[(2-chlorobenzyl)hydroxyl)methyl]6-methylpyridazin-3-one L2; 5-(2-chlorobenzyl)-2,6-dimethylpyridazin-3-one L3; 5-(2-chlorobenzyl)-2-(hydroxyethyl)-6-methylpyridazin-3-one L4; ethyl-4-(2-chloro-benzyl)-3-methyl-6-oxopyridazin-1(6H)-yl)acetate L5; 5-(2-chlorobenzyl)-2-(hydroxyethyl)-6-methylpyridazin-3-thione L6, and ethyl-4-(2-chloro-benzyl)-3-methyl-6-thioxopyridazin-1(6H)-yl)acetate L7 were tested for the oxidation of catechol to o-quinone for miming microorganism in the O activation for electrophilic non substituted aromatic. The in situ generated Cu(II), Fe(II) and Zn(II) complexes of these ligands ( L1- L7) were examined for such catalytic activities. We found that all these substrates catalyze the oxidation reaction of catechol to o-quinone with the presence of atmospheric dioxygen. The rates of this oxidation depend on two parameters: the nature of the ligand and the nature of ion salts. We found that the combination of L7 [ Cu( CH COO)] leads to the fastest catalytic processes. [ABSTRACT FROM AUTHOR]

Asymmetrical N-tripodal ligands have been synthesized in three steps. Diversity has been introduced at the first step of the synthesis by adding pyrazine, pyridine, benzyl and thiophene rings. The corresponding CuII complexes have been prepared by reaction with CuCl2 and characterized by Electron Paramagnetic Resonance (EPR), UV-Vis spectroscopies and cyclic voltammetry. The data show that the ligand coordinates to CuII in a mononuclear fashion in solution and that the complexes display a square pyramidal geometry. All complexes are characterized by a quasi-reversible one-electron redox behavior in acetonitrile. The ability of the complexes to oxidize 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone has been studied and the results show that the rate of the reaction depends on the basicity and the steric hindrance of the heterocyclic donor. Best results have been obtained with CuII complexes coordinated to bidentate ligands, since they facilitate the approach and the coordination of catechol to the metal. Particularly, the introduction of a thiophenyl group to mimic the sulfur atom at proximity to the catalytic center in the catechol oxidase protein structure improves the catalytic activity of the complex. [ABSTRACT FROM AUTHOR]

The synthesis of new tetradentate Schiff-base containing N4 donors is described along with the preparation of a series of copper complexes derived from this ligand. These complexes have the form [CuLX]X′, X = OH−, X′ =  (1) or X = X′ = Cl− (2); and [CuL]H2O(ClO4)2 (3), in addition to a copper(I) complex [Cu2L2](ClO4)2 (4). The synthesized compounds were spectroscopically characterized, showing the N4 donor ligand. The single-crystal X-ray structural analysis of 4 demonstrated the dimeric structure and univalent copper. This dimer consists of , two uncoordinated , and one acetonitrile. Each ligand is tetradentate via pyridyl and azomethine nitrogen atoms, providing a strongly distorted tetrahedron around copper(I) despite the pseudo-macrocyclic skeleton of the ligand. These complexes have been evaluated as functional model systems for catechol oxidase enzyme using 3,5-di-tert-butylcatechol (3,5-DTBC) as the test substrate. The catalytic performance of the air oxidation of 3,5-DTBC to the corresponding light absorbing 3,5-di-tert-butylquinone (3,5-DTBQ) at ambient conditions was studied using UV-Vis absorption spectra. Complex 4 exhibits the highest catalytic activity with turnover number of 33 h−1. A kinetic treatment on the basis of the Michaelis–Menten model was applied. Correlation among reactivity, binding constants, electrochemical properties, and the geometry was determined. These correlations showed that the rate of oxidation is linearly correlated with the binding constants for the five coordinate 1 and 2. The catalytic investigations demonstrate that geometrical effects are only one facet of the activity. The probable mechanistic implications of the catalyzed oxidation reactions are discussed. [ABSTRACT FROM PUBLISHER]