Oxidation Of Pyrocatechol Research Articles

Determination of Folic Acid in both Pure and Pharmaceutical Preparations via Oxidative Coupling Reaction

In this study, the development of an indirect spectrophotometric method for the determination of folic acid in pure and pharmaceutical preparations is described. The method is based on the oxidation of pyrocatechol with iron (III) in an acidic medium, followed by the reaction with folic acid (FA) to produce a stable, water-soluble orange compound with maximum absorption at 350 nm versus the blank reagent. The complex of charge transfer was studied under optimal conditions; the titration graph was linear over the range of 0.5-25 μg/mL with a relative error of 1.2-2.8 and a relative standard deviation of 2.43-1.45 depending on the concentration level.

Histamine derived dimer of µ-Chlorido-µ-Phenoxido Dicopper(II) complex as a potential enzyme mimic with catecholase activity

A new copper(II) complex, [Cu2(L1)(µ-Cl)2]2 (C1), of the binucleating 2,6-bis((2-(4′-imidazolyl)ethyl)aminomethylidene)-4-methylphenol (HL1) with N4O binding sites, has been synthesized to investigate as potential structural and functional model for catecholase activity of the dicopper(II) site. It has been characterized by spectroscopic techniques and X-ray crystallography. The complex C1 exists as chlorido bridged dimer of binuclear copper(II) units, each possessing one end-off compartmental ligand (L1) with endogenous µ-phenoxido and exogenous µ-chlorido groups leading to intermetallic distance Cu1···Cu2 of 3.129 Å and Cu1-O1(phenoxo)-Cu2 angle of 107.67(10)o. Each copper(II) center has distorted octahedral geometry with bridging by chlorides in the tetranuclear dimer. The crystal system is monoclinc with space group P21/c. Magnetic measurements reveal that C1 is strongly antiferromagnetically coupled with J = − 115.663 ± 0.82547 cm−1. The catecholase activity of the complex has been evaluated by oxidation of 3,5-di(tert-butyl)catechol and 4-methyl catechol to the corresponding quinones under aerobic conditions. A kinetic treatment on the basis of the Michaelis-Menten model has been applied for the kinetic study. The complex is found to be selective for the substrates with higher Vmax = 8.2726x10−8 M s−1 and Km = 0.0107 M for 3,5-DTBC at 30 °C as compared to Vmax = 5.0371x10−8 M s−1 and Km = 0.027 M for 4-methyl catechol at 50 °C while it is found to be practically inactive for dopamine, 2,3-dihydroxy naphthalene and pyrocatechol oxidation.

A quantitative method for the detection and validation of catalase activity at physiological concentration in human serum, plasma and erythrocytes

A novel method has been proposed to develop a simple, rapid, sensitive and affordable chromogenic attempt for the quantification of catalase (CAT) activity in blood samples. The method is based on the oxidation of pyrocatechol (PC) to give quinone form which by oxidative coupling with aminyl radical of 4-aminoantipyrine (4-AAP) resulting from H2O2/CAT to produce a pink colored quinone-imine product with λmax = 530 nm in a 100 mmol/L of tris buffer of pH 9.8 at room temperature (30 °C). The linearity of CAT assay was between 0.316 and 10 U/mL. The accuracy ranges for CAT having concentrations of 1.25, 5 and 7.5 μmol/L were 89–105.52, 90–107%, and 91–104.58% respectively. Within-run and between-run precision studies showed CV’s of 1.98–3.02% (n = 7) and 2.97–4.40% (n = 7), respectively. The detection and quantification limits of CAT were 0.12 and 0.225 μmol/L, respectively. The Michaelis-Menten constant and maximum velocity of the reaction was Km = 1.052 mM and Vmax = 0.168 μmol/min, respectively. The present method provides a convenient means for investigating the usefulness of CAT measurements in biological sample assessing the potential for free radical-induced pathology.

Inhibitory effect of Malaysian coastal plants on banana (Musa acuminata colla "Lakatan"), ginger (Zingiber officinale Roscoe) and sweet potato (Ipomoea batatas) polyphenol oxidase.

Undesired browning reaction catalyzed by polyphenol oxidase (PPO) has reduced the nutritional quality and customer acceptance of the products. The inhibitory effects of six coastal plants including Sonneratia alba, Rhizophora apiculata, Syzygium grande, Rhizophora mucronata, Hibiscus tiliaceus and Bruguiera gymnorhiza on PPO in banana, sweet potato and ginger were studied based on oxidation of pyrocatechol. Banana exhibited the highest PPO activity (141,600 U), followed by sweet potato (43,440 U) and ginger (26,880 U). Banana PPO was strongly inhibited by R. apiculata (70.87%) and sweet potato PPO was strongly inhibited by S. alba (82.00%). In general, most banana PPO was the most susceptible to inhibition with all inhibitors having inhibition higher than 60.00% at 0.5mg/ml and ginger PPO was the least susceptible with all inhibitors showing less than 50.00% inhibition at 0.5mg/ml. Coastal plant extracts are potentially to be developed as natural inhibitors for preventing enzymatic browning of fruits and vegetables.

Manipulating the Polymerization of 3,5-Diaminobenzoic Acid with a Bromate Oscillator

Manifestation of the properties of 3,5-diaminobenzoic acid polymer film was explored by polymerizing 3,5-diaminobenzoic acid in the presence of bromate. Depending on the initial concentration of bromate, the 3,5-diaminobenzoic acid solution was observed to transit from steady to oscillatory evolution in a batch reactor. The thus-fabricated film on Au electrodes exhibited different activities toward the electrochemical oxidation of pyrocatechol. The film synthesized at nonoscillatory conditions has a primary oxidation peak of pyrocatechol at about 0.20 V (vs Hg/Hg2SO4 electrode), as opposed to 0.0 V with the film that was prepared under oscillatory conditions. A phase diagram in the bromate–sulfuric acid phase was constructed to demonstrate the influence of each parameter on the emergence of oscillatory behavior in the 3,5-diaminobenzoic acid system. Experiments showed that an increase in the concentrations of sulfuric acid and bromate greatly increased the frequency and reduced the induction period of the...

Tyrosinase immobilization on functionalized porous silicon surface for optical monitoring of pyrocatechol

Immobilized Tyrosinase enzyme was widely investigated for developing sensitive and specific biosensors for determination of phenolic compounds. However, the performance and stability of these biosensors largely depend upon the used support material and method of enzyme immobilization. In this work, covalent and stable attachment of active Tyrosinase on porous silicon (PSi) support for the detection of phenolic derivatives was achieved. A multistep functionalization strategy was developed in mild conditions allowing the activity retention of the immobilized enzyme. The surface was characterized with contact angle measurements, SEM microscopy and FTIR spectroscopy. The results confirmed the attachment of Tyrosinase enzyme on the functionalized PSi surface. The enzymatic activity of immobilized Tyrosinase and the optical detection of pyrocatechol were studied basing on the assessment of the UV/Vis absorbance at 500 nm of a colored azo-dye product formed from the reaction of 3-methyl-2-benothiazolinone hydrazone (MBTH) reagent with the Quinone issuing from the enzymatic oxidation of pyrocatechol. The surface concentration of active Tyrosinase was estimated to be Γ = 1.135 × 1015 molecules covering the whole PSi surface. The calibration curve of pyrocatechol detection shows linearity over a wide concentration range (1–100 μM) with a correlation coefficient of 0.995 and a detection limit of 0.43 μM. These results show the efficiency of the Tyrosinase-modified PSi surface for phenol detection and the possibility to use the structure in real applications.

Highly sensitive and stable laccase based amperometric biosensor developed on nano-composite matrix for detecting pyrocatechol in environmental samples

The present study aims at fabricating a laccase based amperometric biosensor for detection of pyrocatechol in environmental samples. Trametes versicolor laccase was co-immobilized in a nanocomposite matrix comprising of osmium tetroxide on poly 4-vinylpyridine, multiwalled carbon nanotubes, Nafion and carbon black on glassy carbon electrode. The nanocomposite matrix provides a porous structure for easy immobilization of the enzyme as evident from the SEM images and a highly electroactive surface for facile diffusion free electron transfer kinetics as discerned from the cyclic voltametric studies. The heterogeneous electron transfer rate constant (Ks) and surface concentration of the ionic species (Γ) of the bioelectrode were 0.67s−1 and 1.32×10−8molcm−2, respectively. The response of the constructed biosensor was generated at a potential of 0.14V from the electrocatalyzed reduction of 1,2-benzoquinone formed from the biocatalyzed oxidation of pyrocatechol. The bioelectrode when subjected to differential pulse voltammetry exhibited a linear faradaic current response against pyrocatechol in the concentration range of 3.98nM–16.71nM with a minimum detection limit of 2.82nM and a sensitivity of 3.82±0.31nAnM−1. The bioelectrode also shows high operational stability and optimum storage stability up to 3 weeks. The nanocomposite based fabrication method of the laccase bioelectrode thus shows a great promise for developing a highly sensitive, selective and stable biosensor for detection of pyrocatechol in environmental samples.

Development of a very sensitive electrochemical magneto immunosensor for the direct determination of ochratoxin A in red wine

An electrochemical immunosensor (EI) for the determination of ochratoxin A (OTA) in red wine samples was developed. This immunosensor was based on Protein G functionalized magnetic beads (MBs) as solid phase for affinity reaction between OTA and OTA monoclonal antibody (mAbOTA). A carbon screen printed-electrodes (CSPE) system was used as electrochemical transduction element. This immunosensor was based on a direct competitive assay between OTA in wine samples and OTA labeled with horseradish peroxidase (HRP) (OTA–HRP). The HRP, in the presence of hydrogen peroxide catalyzes the oxidation of pyrocatechol to benzoquinone, whose back electrochemical reduction was detected on a CSPE by square wave voltammetry (SWV). The experimental variables involved in the immunosensor response to OTA were evaluated. The performance obtained for the EI was an analytical range of 0.01–20ppb, limit of detection (LOD) of 0.008ppb, and IC50=0.272±0.081ppb. In addition, an acceptable accuracy with a relative standard deviation (RSD) of 5.56% and very good recoveries (92–110%) were found. This work shows the potential of our EI for the direct measurement of OTA in red wine samples combining SWV as electroanalytical technique with the MBs and CSPE. This EI has great advantages as direct measurement of red wine samples without a prior pretreatment, the small volume of sample, the short time consuming of experiences and LOD well below those established by the Regulatory Commission of the European Community (2μgkg−1).

Kinetics and Thermodynamics of the Thermal Inactivation of Polyphenol Oxidase in an Aqueous Extract from Agaricus bisporus

The kinetics and thermodynamics of the thermal inactivation of polyphenol oxidase (PPO) in an aqueous extract from mushroom Agaricus bisporus (J.E. Lange) Imbach was studied, using pyrocatechol as a substrate. Optimal conditions for enzymatic studies were determined to be pH 7.0 and 35-40 °C. The kinetics of PPO-catalyzed oxidation of pyrocatechol followed the Haldane model with an optimum substrate concentration of 20 mM. Thermal inactivation of PPO was examined in more detail between 50 and 73 °C and in relation to exposure time. Obtained monophasic kinetics were adequately described by a first-order model, with significant inactivation occurring with increasing temperature (less than 10% preserved activity after 6 min at 65 °C). Arrhenius plot determination and calculated thermodynamic parameters suggest that the PPO in aqueous extract from Agaricus bisporus mushroom is a structurally robust yet temperature-sensitive biocatalyst whose inactivation process is mainly entropy-driven.

Calcium-dioxolene complexes: Rate constants of pyrocatechol oxidation in the presence of Ca2+

The effect of calcium ions on the rate of pyrocatechol autoxidation at pH 9.0 has been studied by mathematical modeling. The effect of Ca2+ on the oxygen absorption rate has been studied, and a kinetic model has been suggested, which takes different stages of interaction of pyrocatechol and its radical form with oxygen into account. It has been shown that the prooxidant action of Ca2+ is related to an abrupt increase (approximately by three orders of magnitude) in the rate constant of comproportionation (reaction of chain branching and formation of o-semiquinonates) and a marked decrease (by two orders of magnitude, from 1.4 10(7) to 0.6 10(5) M(-1)s(-1)) in the rate constant of disproportionation of o-semiquinones. The system can be used as a model for studying the prooxidant action of calcium ions.

New 14-membered trans-di-substituted ‘tet-a’ macrocycles and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

Copper(II) and nickel(II) complexes of new trans-di-substituted macrocyclic ligands incorporating three different benzoyl groups, 1,8-bis-(benzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 1), 1,8-bis-(2-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 2), and 1,8-bis-(4-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 3) have been synthesized. The ligands and complexes were characterized by elemental and spectral analysis. Further, the X-ray crystal structure of one of the ligand, L 1, has been determined. N-benzoylation causes red shift in the λ max values of the complexes. The cyclic voltammogram of the complexes of ligand L 1 shows one-electron, quasi-reversible reduction wave in the region −0.94 to −1.00 V, whereas that of L 2 and L 3 show two quasi-reversible reduction peaks corresponding to ligand and metal. Nickel complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.92 to +1.21 V. The Cu(II) complexes have a magnetic moment value close to the spin-only value with four hyperfine EPR signals. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The complexes containing electron-withdrawing group shows higher rate-constant values than that with no electron-withdrawing group. All the complexes were screened for antifungal and antibacterial activity.

Synthesis, characterization, crystal structure and antimicrobial activities of new transN, N-substituted macrocyclic dioxocyclam and their copper(II) and nickel(II) complexes

New trans-disubstituted macrocyclic ligands, 1,8-[ N,N-bis(3-formyl-12-hydroxy-5-methyl)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 1), 1,8-[ N,N-bis(3-formyl-12-hydroxy-5-bromo)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 2), N, N-bis[1,8-dibenzoyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 3), N, N-bis[1,8-(2-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 4), and N, N-bis[1,8-(4-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 5) were synthesized. The ligands were characterized by elemental analysis, FT IR, 1H NMR and mass spectrometry studies. The crystal structure of L 1 is also reported. The copper(II) and nickel(II) complexes of these ligands were prepared and characterized by elemental analysis, FT IR, UV–Vis and mass spectral studies. The cyclic voltammogram of the complexes of ligand L 1–3 show one-electron quasi-reversible reduction wave in the region −0.65 to −1.13 V, whereas that of L 4 and L 5 show two quasi-reversible reduction peaks. Nickel(II) complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.95 to +1.06 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μ eff 1.70–1.73 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

N-benzoylated 1,4,8,11-tetraazacyclotetradecane and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

A series of N-benzoylated cyclam ligands incorporating three different benzoyl groups 1,4,8,11-tetra-(benzoyl)-1,4,8,11-tetraazacyclotetradecane (L 1), 1,4,8,11-tetra-(2-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 2) and 1,4,8,11-tetra-(4-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 3) and their nickel(II) and copper(II) complexes are described. Crystal structure of L 1 is also reported. The ligands and complexes were characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. N-benzoylation causes red shift in the λ max values of the complexes. The cyclic voltammogram of the complexes of ligand L 1 show one-electron, quasi-reversible reduction wave in the region −1.00 to −1.04 V, whereas that of L 2 and L 3 show two quasi-reversible reduction peaks. Nickel complexes show one-electron quasi-reversible oxidation wave at a positive potential in the range +1.05 to +1.15 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment values μ eff 1.70–1.73 BM which is close to the spin-only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. All the ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

Synthesis, characterization, and antimicrobial activities of nickel(II) and copper(II) Schiff-base complexes

Ni(II) and Cu(II) metal complexes of simple unsymmetrical Schiff-base ligands derived from salicylaldehyde/5-methylsalicylaldehyde and ethylenediamine or diaminomaleonitrile (DMN) were synthesized. The ligands and their complexes were characterized by elemental analysis, 1H NMR, FT IR, and mass spectroscopy. The electronic spectra of the complexes show d–d transitions in the region at 450–600 nm. Electrochemical studies of the complexes reveal that all mononuclear complexes show a one-electron quasi-reversible reduction wave in the cathodic region. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts were also carried out. The in vitro antimicrobial activity of the investigated compounds was tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa and Escherichia coli. The antifungal activity was tested against Candida albicans. Generally, the metal complexes have higher antimicrobial activity than the free ligands.

Synthesis, spectral, magnetic, electrochemical and catalytic studies of cyclam-based copper(II) and nickel(II) complexes–effect of N-substitution

New N-substituted cyclam ligands 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-1,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane (L1–L4) were synthesized and mononuclear copper(II) and nickel(II) complexes prepared. The ligands and complexes were characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. N-alkylation causes red shifts in the λmax values of the complexes. Copper(II) complexes show one-electron, quasi-reversible reduction waves in the range −1.04 to −1.00 V. The nickel(II) complexes show one-electron, quasi-reversible reduction waves in the range −1.18 to −1.30 V and one-electron, quasi-reversible oxidation waves in the range +1.20 to +1.40 V. The reduction potential of the copper(II) and nickel(II) complexes of the ligands L1 to L2 and L3 to L4 shift anodically on N-alkylation. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μeff = 1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalyst were carried out. The tetra-N-substituted complexes have higher rate constants than the corresponding disubstituted complexes.

Effect of Group II Metal Cations on Catecholate Oxidation

The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation.

Iron oxide and pyrocatechol: a spectroscopy study of the reaction products

The reaction of 1,2-dihydroxy-benzene (pyrocatechol) (C6H6O2) with iron oxide (Fe2O3) and sodium thiosulfate (Na2S2O3) in aqueous medium (pH 7) was investigated. Pyrocatechol suffers autoxidation and coordinates with Fe3+ in solution. The presence of S2O32- in solution was fundamental to generate and stabilize the pyrocatechol oxidation products as o-semiquinones. This compound was isolated and its structure characterized using FT-IR, EPR and UV-Vis Spectroscopy as [CTA][Fe(SQ)2(Cat)]. A thermal mass loss mechanism was proposed based on Thermogravimetric Analysis (TG) to support the structural characterization.

Synthesis of new ‘end-off’ μ-phenoxo and bis-μ-acetato tri-bridged copper(II), nickel(II) and zinc(II) complexes: Spectral, magnetic, electrochemical and catalytic studies

A new end-off type acyclic ligand with two N-methyl piperazine arms, 2,6-bis[(4-methyl piperazin-1-yl)]-4-formyl phenol [L], has been synthesized by a simple Mannich reaction. The mono and binuclear complexes of Cu(II), Ni(II) and Zn(II) have been prepared. The complexes were characterized by elemental and spectral analysis. The EPR spectrum of the mononuclear copper complex shows four hyperfine splittings and the binuclear complex shows a broad signal due to an anti-ferromagnetic interaction. The room temperature magnetic moment of the mono and binuclear copper complexes are found to be 1.72 μ B ( μ eff) and 1.58 μ B ( μ eff), respectively. The mononuclear Ni(II) complex is square planar and diamagnetic, whereas the six-coordinated binuclear Ni(II) complex shows a magnetic moment value of 2.98 μ B ( μ eff). Cyclic voltammetric studies evidenced one irreversible reduction wave for all the mononuclear complexes and two irreversible one-electron reduction waves for the binuclear complexes are obtained in the cathodic region. In the anodic region, one irreversible oxidation wave for the mononuclear nickel(II) complex and two irreversible oxidation waves for the binuclear nickel(II) complexes are obtained. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the mono and binuclear copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the mono and binuclear copper(II), nickel(II) and zinc(II) complexes as catalysts were carried out. The binuclear complexes have higher rate constant values than those of the corresponding mononuclear complexes. The rate constant values for the complexes for the hydrolysis are in the order nickel(II) > copper(II) > zinc(II).

Extracellular Oxidases of the Lignin-Degrading Fungus Panus tigrinus

Two extracellular oxidases (laccases) were isolated from the extracellular fluid of the fungus Panus (Lentinus) tigrinus cultivated in low-nitrogen medium supplemented with birch sawdust. The enzymes were purified by successive chromatography on columns with TEAE-cellulose and DEAE-Toyopearl 650M. Both oxidases catalyze oxidation of pyrocatechol and ABTS. Moreover, oxidase 1 also catalyzes oxidation of guaiacol, o-phenylenediamine, and syringaldazine. The enzymes have identical pH (7.0) and temperature (60-65 degrees C) optimums. Absorption spectra of the oxidases differ from the spectra of typical "blue" laccases and are similar to the spectrum of yellow oxidase.

Coordination properties of a dicompartmental ligand with tetra- and hexadentate coordination sites towards copper (II) and nickel (II) ions

A new dicompartmental ligand, N, N′-bis[2-iminomethyl-4-methyl-6-(4-methylpiperazin-1-ylmethyl)1-hydroxybenzene]1,8,naphthalene (H 2L) possessing contiguous tetra- and hexadentate coordination sites has been synthesized in simple route by the Schiff’s base condensation of the precursor compound (PC) 2-formyl-4-methyl-6[4-methyl-6-(4-methylpiperazin-1-yl)methyl]phenol with 1,8-diaminonaphthalene.The mononuclear and binuclear Cu(II) and Ni(II) complexes of this ligand have been prepared and characterized by elemental analysis, IR, NMR and UV–Vis spectra.The electronic spectra of the mono- and binuclear Cu(II) complexes and mononuclear Ni(II) complex revealed one d–d transition in the region 570–600 nm, whereas the binuclear Ni(II) complex showed three d–d transitions at 800 nm ( ε ∼ 95 M −1 cm −1), 620 nm ( ε ∼ 140 M −1 cm −1) and 560 nm ( ε ∼ 250 M −1 cm −1), which were assigned to 3A 2g → 3T 2g, 3A 2g → 3T 1g, 3A 2g → 3T 1g(P), and these spin allowed electronic transitions are characteristic of an octahedral Ni 2+ centre.The electrochemical studies evidenced for the mononuclear Cu(II) complex shows a single quasireversible one electron wave at −0.83 V ( E pc).The binuclear Cu(II) complex shows two quasireversible one electron reduction waves at - 0.68 V ( E pc 1 ) and - 1.35 V ( E pc 2 ) in the cathodic region.The mononuclear Ni(II) complex shows one quasireversible reduction potential at −0.80 V ( E pc) and the binuclear Ni(II) complex shows two irreversible reduction potentials at - 1.10 V ( E pc 1 ) and - 1.40 V ( E pc 2 ) in the cathodic region.The room-temperature magnetic moment value for the mononuclear Cu(II) complex is 1.72 μ B( μ eff) and for the binuclear Cu(II), 2.05 μ B( μ eff). The mononuclear Ni(II) complex is square planar and diamagnetic whereas the binuclear Ni(II) complex has a magnetic moment value of 3.05 μ B ( μ eff). Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper (II) complexes and hydrolysis of 4-nitrophenyl phosphate using the nickel (II) complexes as catalysts showed that the binuclear complexes have higher rate constant values than that of the corresponding mononuclear complexes.