Catechol Oxidase Activity Research Articles

Catechol oxidase mimetic activity of copper(I) complexes of 3,5-dimethyl pyrazole derivatives: Coordination behavior, X-ray crystallography and electrochemical study

N1-substituted 3,5-dimethylpyrazole (dmpz) namely, methyl-3,5-dimethyl pyrazole-1-dithioate (L1) and benzyl-3,5-dimethyl-pyrazole-1-dithioate (L2) were reacted with zinc(II), copper(II) and cadmium(II) chloride to study their coordination behavior. Ligands L1 and L2 produced isostructural complexes with composition [CuI(L1)2][CuICl2] (1) and [CuI(L2)2][CuICl2] (2), respectively when reacted with CuCl2·2H2O. Copper (I) (d10 system) analogues, 1 and 2, exhibit prominent catechol oxidase activity in which a nice correlation-the easily oxidizable copper(I) center favoring the oxidation of 3,5-DTBC (3,5-ditertiary butyl catechol) is observed. Most importantly, these two compounds represent the class of copper(I) compounds that are rarely employed for the study of catecholase activity. The kinetics study exhibits a deuterium kinetic isotope effect in the catalytic oxidation of 3,5-DTBC by O2 as evidenced by about 1.9 times rate retardation in the deuterated solvent, suggesting the hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo species. With other d10 cations, zinc(II) and cadmium(II) the ligand L1and/or L2 undergoes dissociation into parent pyrazole unit i.e., 3,5-dimethylpyrazole (dmpz) during formation of a monomeric tetrahedral Zn(dmpz)2Cl2 (3) complex and a helical 1-D polymeric chain, [Cd(dmpz)2Cl2]n(4). The possible role of intramolecular hydrogen-bonding induced helicity has been explored in 4.

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Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: synthesis, magnetic properties and catechol oxidase activity.

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: [CoL2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [Co(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 Co(II) ion surrounded by a {Co} 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.

Radical pathways and O2 participation in benzyl alcohol oxidation, and catechol and o-aminophenol oxidase activity studies with novel zinc complexes: an experimental and theoretical investigation

Diphenoxo bridged dinuclear zinc complexes were found to be capable of oxidation of benzyl alcohol, catechol and o-aminophenol.

Enhanced Catechol Oxidase and Peroxidase Activities as Possible Markers for Measuring Chromium Tolerance in Sorghum (Sorghum bicolor L.) Genotypes

The aim of the present study was to estimate the effect of chromium on catechol oxidase and peroxidase activities in ten sorghum genotypes grown in soil amended by different concentrations of chromium. Ten sorghum genotypes, (Tabat, Wad Ahmed, L4, L7, L12, L14, L16, L25, L32 and L34) were obtained from the Department of Agronomy, Faculty of Agriculture University of Khartoum., Seeds were sown in polyethylene bags filled with 2 kg soil (clay and sand, 2:1). Two weeks after sowing, the seedlings were irrigated with eight levels of chromium (Cr-VI) concentrations (0, 2.5, 5, 10, 20, 30, 40, and 50 mg/l.). Samples for assaying enzyme (catechol oxidase and peroxidase) activities were taken three times (on the 8, 12, and 15 day) following chromium application. The results revealed that the level of enzyme activity of most genotypes was increased significantly with increasing chromium concentration. The magnitude of increase in enzymatic activity was also dependent on the genotype and duration of time after chromium treatment. These findings suggest that, the activities of both enzymes might be used as indicator for selecting chromium tolerant sorghum genotypes.

Oxidant dependent oxidation of copper bound catecholate: Catecholase versus catechol dioxygenase activity

A series of new mixed ligand copper complexes CuII(PBI)(O2Ncat) (1) (PBI=2-(2-pyridyl)-benzimidazole), CuII(DMPBI)(O2Ncat) (2) (DMPBI=5,6-dimethyl-2-(2-pyridyl)-benzimidazole), CuII(PBO)(O2Ncat) (3) (PBO=2-(2-pyridyl)-benzoxazole), CuII(PBT)(O2Ncat) (4) (PBT=2-(2-pyridyl)-benzothiazole), and Cu(TBA)(O2Ncat) (5) (TBA=4-(1H-1,3-benzodiazol-2-yl)-1,3-thiazole) have been synthesized by classic organic, bioinorganic methods. The complexes have been found to mimic catechol oxidase and catechol dioxygenase activity depending on the oxidant used. Triplet state dioxygen activates the complex leading to intradiol cleavage product, 2-nitromuconic acid while sterically more demanding tert-butyl hydroperoxide (TBHP) oxidizes the 4-nitrocatechol (4-O2NcatH2) ligand into 4-nitrobenzoquinone. We have also found that the electron density on the copper center significantly increase the reactivity toward the oxidant used.

Synthesis, structure, magnetism, and hydrolase and catecholase activity of a new trinuclear copper(II) complex

In this paper we report the synthesis of the new multidentate N,O-donor ligand H3L_2pyald=(N,N′-bis-(2-pyridylmethyl)-(2-hydroxy-3-carbonyl-5-methylbenzyl)-1,3-propanediamine-2-ol) and its first trinuclear copper(II) complex, [Cu3(L_2pyald)(μ-OAc)](ClO4)2 (1). The structure of 1 was determined by X-ray crystallography and variable-temperature magnetic data in the temperature range of 4–300K indicate weak antiferromagnetism (J1,2≅−1.0cm−1) between the Cu(1) and Cu(2) centers bridged by the μ-alkoxo and μ-acetate groups and weak ferromagnetic coupling (J1,3=J2,3≅+4.0cm−1) involving the {Cu(1)(μ-phenoxo)Cu(3)} and {Cu(2)(μ-phenoxo)Cu(3)} structural units. Complex 1 shows significant catalytic activity towards the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate (2,4-BDNPP) as well as catechol oxidase activity since it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone by dioxygen. A comparison of the catalytic efficiency of 1 with its dinuclear parent complex [Cu2(H2bbppnol)(μ-OAc)]2+ (H3bbppnol=N,N′,N,N′-bis[(2-hydroxybenzyl)(2-methylpyridyl)]-1,3-propanediamine-2-ol) reveals that the hydrolase efficiency (kcat/KM) is 12 times higher for 1, while the catecholase efficiencies of these two compounds are similar.

Syntheses, structures and catecholase activity of two cobalt(III) complexes derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine): A special host–guest system from a special ligand

The work in this report deals with syntheses, crystal structures, catechol oxidase activity and ESI-MS (positive) studies of two mononuclear cobalt(III) compounds [CoIIILOEt–en(N3)2⊃(H3O+)]·2MeOH (1) and [CoIIILOEt–en(NCS)(H2O)]·DMF·H2O (2), where H2LOEt–en is N,N′-ethylenebis(3-ethoxysalicylaldiimine). The metal center in both the compounds occupies N(imine)2O(phenoxo)2 compartment. Two apical coordination positions are occupied by one anionic ligand (thiocyanate) and one neutral ligand (water) in 2 but by two anionic ligands (azide) in 1. The extra negative charge in [CoIIILOEt–en(N3)2]− is balanced by an oxonium ion (H3O+), which is trapped in the O(phenoxo)2O(ethoxy)2 compartment to result in the formation of host–guest species [CoIIILOEt–en(N3)2⊃(H3O+)] in 1. Both the compounds show catechol oxidase activity (1 in MeCN, 2 in DMF) as monitored by the UV–Vis spectroscopy of the aerial oxidation of 3,5-DTBCH2 to 3,5-DTBQ. The kinetic parameters have been determined using Michaelis–Menten approach. The Kcat values for 1 in MeCN and 2 in DMF are 10.0h−1 and 11.2h−1, respectively. ESI-MS (positive) of 1 and the mixture of 1 and 3,5-DTBCH2 have been recorded and the positive ions have been well assigned. Interestingly, a 1:2 adduct of composition [CoIILOEt–en(3,5-DTBQ)2+H+]+ has been identified from the spectrum of the mixture of 1 and 3,5-DTBCH2. Unique features of 1 and 2 in terms of showing catechol oxidase activity and, more importantly, unique structural features of compound 1 have been discussed.

Ligand centered radical pathway in catechol oxidase activity with a trinuclear zinc-based model: Synthesis, structural characterization and luminescence properties

A new trinuclear zinc(II) complex, [Zn3(L)(NCS)2](NO3)2·CH3OH·H2O (1), of a (N,O)-donor compartmental Schiff base ligand (H2L=N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol), has been synthesized in crystalline phase. The zinc(II) complex has been characterized by elemental analysis, IR spectroscopy, UV–Vis spectroscopy, powder X-ray diffraction study (PXRD), 1H NMR, EI mass spectrometry and thermogravimetric analysis. PXRD revealed that 1 crystallizes in P−1 space group with a=9.218Å, b=10.849Å, c=18.339Å, with unit cell volume is 2179.713(Å)3. Fluorescence spectra in methanolic solution reflect that intensity of emission for 1 is much higher compared to H2L and both the compounds exhibit good fluorescence properties. The complex 1 exhibits significant catalytic activities of biological relevance, viz. catechol oxidase. In methanol, it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to corresponding quinone via formation of a dinuclear species as [Zn2(L)(3,5-DTBC)]. Electron Paramagnetic Resonance (EPR) experiment suggests generation of radicals in the presence of 3,5-DTBC and it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complex of redox-innocent Zn(II) ion.

Beyond brown: polyphenol oxidases as enzymes of plant specialized metabolism.

Most cloned and/or characterized plant polyphenol oxidases (PPOs) have catechol oxidase activity (i.e., they oxidize o-diphenols to o-quinones) and are localized or predicted to be localized to plastids. As a class, they have broad substrate specificity and are associated with browning of produce and other plant materials. Because PPOs are often induced by wounding or pathogen attack, they are most generally believed to play important roles in plant defense responses. However, a few well-characterized PPOs appear to have very specific roles in the biosynthesis of specialized metabolites via both tyrosinase (monophenol oxidase) and catechol oxidase activities. Here we detail a few examples of these and explore the possibility that there may be many more “biosynthetic” PPOs.

Anion coordination selective [Mn3] and [Mn4] assemblies: synthesis, structural diversity, magnetic properties and catechol oxidase activity.

Syntheses, crystal structures, magnetic properties and catechol oxidation behavior are presented for [Mn3] and [Mn4] aggregates, [MnMn(II)(O2CMe)4(dmp)2(H2O)2]·2H2O (1·2H2O), [MnMn(II)(O2CCH2Cl)4(dmp)2(H2O)2]·H2O·MeOH (2·H2O·MeOH), [Mn(μ3-O)(dmp)4(μ-DMSO)(N3)(DMSO)(H2O)]ClO4·DMSO (3·ClO4·DMSO), and [Mn(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 Mn(II) 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 Mn(III)Mn(II)Mn(III) unit in a carboxylate and H2dmp environment, revealing a central Mn(II) ion in a different environment and terminal Mn(III) 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 [Mn(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.

The activity of ascorbic acid and catechol oxidase, the rate of photosynthesis and respiration as related to plant organs, stage of development and copper supply

Some experiments were performed to investigate the physiological role of copper in oat and sunflower and to recognize some effects of copper deficiency. Oat and sunflower plants were grown in pots on a peat soil under copper deficiency conditions (–Cu) or with the optimal copper supply (+Cu). In plants the following measurements were carried out: 1) the activity of ascorbic acid oxidase (AAO) and of catechol oxidase (PPO) in different plant organs and at different stages of plant development, 2) the activity and the rate of photosynthesis, 3) the activity of RuDP-carboxylase, 4) the intensity of plant respiration. The activity of AAO and of PPO, and also the rate and the activity of photosynthesis were significantly lower under conditions of copper deficiency. The activity of both discussed oxidases depended on: 1) the plant species, 2) plant organs, 3) stage of plant development. Copper deficiency caused decrease of the respiration intensity of sunflower leaves but it increased to some extent the respiration of oat tops. Obtained results are consistent with the earlier suggestion of the authors that the PPO activity in sunflower leaves could be a sensitive indicator of copper supply of the plants, farther experiments are in progress.

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(II) complexes.

A series of copper(ii) complexes, viz. [Tp(MeMe)Cu(Cl)(H2O)] (), [Tp(MeMe)Cu(OAc)(H2O)] (), [Tp(MeMe)Cu(NO3)] () and [Tp(MeMe)Cu(ClO4)] () containing tris(3,5-dimethylpyrazolyl)borate (KTp(MeMe)), have been synthesized and fully characterized. The substitution reaction of with thiourea was studied under pseudo-first-order conditions as a function of concentration, temperature and pressure in methanol and acetonitrile as solvents. Two reaction steps that both depended on the nucleophile concentration were observed for both solvents. Substitution of coordinated methanol is about 40 times faster than the substitution of chloride. In acetonitrile, the rate constant for the displacement of coordinated acetonitrile was more than 20 times faster than the substitution of chloride. The reported activation parameters indicate that both reaction steps follow a dissociative mechanism in both solvents. On going from methanol to acetonitrile, the rate constant for the displacement of the solvent becomes more than 200 times faster due to the more labile acetonitrile, but the substitution mechanism remained to have a dissociative character. The antioxidant activities of were evaluated for superoxide dismutase (SOD), glutathione-s-transferase (GST0 and glutathione reduced (GSH-Rd) activity. and were found to show (p < 0.05) the highest antioxidant activity in comparison to and , which can be ascribed to the geometric configuration as well as the nature of the co-ligand. showed catechol oxidase activity with turnover numbers of 20 min(-1) and a coordination affinity for 3,5-DTBC of K1, = 31 mM(-1). K1 is rather large and seems to be typical for faster biomimetic models, and also for the enzyme itself (25 mM(-1)). The reaction rate depended linearly on the complex concentration, indicating a first-order dependence on the catalyst concentration.

Unprecedented dinuclear Robson type macrocyclic complexes having two +iii metal ions in two compartments and the role of the diimino moiety on the stability of metal ion oxidation states.

The work in this investigation deals with the syntheses, characterization, crystal structures and catechol oxidase activity of four diphenoxo-bridged Co(III)Co(III) compounds of composition [Co(III)Co(III)L(Me-pn)(N3)4]·6H2O (), [Co(III)Co(III)L(Me-pn)(N3)4]·4H2O (), [Co(III)Co(III)L(Et-pn)(N3)4]·3.5H2O () and [Co(III)Co(III)L(Et-pn)(N3)4]·CH3CN·2.5H2O (), and two diphenoxo-bridged Co(III)Co(II) compounds of composition [Co(III)Co(II)L(Me-Me2pn)(N3)3]·2H2O () and [Co(III)Co(II)L(Et-Me2pn)(N3)3]·H2O (). In these compounds, H2L(Me-pn), H2L(Et-pn), H2L(Me-Me2pn) and H2L(Et-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-diformyl-phenol 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 Co(III)Co(III) compounds are further characterized by (1)H NMR spectra. Compounds and are prepared following a metal-templated synthesis, while compounds and are prepared by direct synthesis, which includes using a pre-isolated macrocycle, [H4L(Me-pn)](ClO4)2/[H4L(Et-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 Co(III)Co(II) compounds [Co(III)Co(II)L(Me-Me2pn)(N3)3]·2H2O (), [Co(III)Co(II)L(Et-Me2pn)(N3)3]·H2O (), [Co(III)Co(II)L(Me-Me2pn)(N3)3]·0.5MeCN·0.27H2O (; Inorg. Chim. Acta, 2014, 412, 38) and [Co(III)Co(II)L(Et-Me2pn)(N3)3]·MeCN (; Dalton Trans., 2013, 42, 4561) are formed, rather than Co(III)Co(III) compounds. Like compounds and , all the compounds show catechol oxidase activity (substrate: 3,5-di-tert-butyl catechol). The kinetic parameters for , and 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.

The role of the testa during development and in establishment of dormancy of the legume seed.

Timing of seed germination is one of the key steps in plant life cycles. It determines the beginning of plant growth in natural or agricultural ecosystems. In the wild, many seeds exhibit dormancy and will only germinate after exposure to certain environmental conditions. In contrast, crop seeds germinate as soon as they are imbibed usually at planting time. These domestication-triggered changes represent adaptations to cultivation and human harvesting. Germination is one of the common sets of traits recorded in different crops and termed the “domestication syndrome.” Moreover, legume seed imbibition has a crucial role in cooking properties. Different seed dormancy classes exist among plant species. Physical dormancy (often called hardseededness), as found in legumes, involves the development of a water-impermeable seed coat, caused by the presence of phenolics- and suberin-impregnated layers of palisade cells. The dormancy release mechanism primarily involves seed responses to temperature changes in the habitat, resulting in testa permeability to water. The underlying genetic controls in legumes have not been identified yet. However, positive correlation was shown between phenolics content (e.g., pigmentation), the requirement for oxidation and the activity of catechol oxidase in relation to pea seed dormancy, while epicatechin levels showed a significant positive correlation with soybean hardseededness. myeloblastosis family of transcription factors, WD40 proteins and enzymes of the anthocyanin biosynthesis pathway were involved in seed testa color in soybean, pea and Medicago, but were not tested directly in relation to seed dormancy. These phenolic compounds play important roles in defense against pathogens, as well as affecting the nutritional quality of products, and because of their health benefits, they are of industrial and medicinal interest. In this review, we discuss the role of the testa in mediating legume seed germination, with a focus on structural and chemical aspects.

Effect of coordination sphere of the copper center and Cu―Cu distance on catechol oxidase and nuclease activities of the copper complexes

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 &amp; Sons, Ltd.

Mono and dinuclear copper(II) naproxenato complexes containing 3-picoline and 4-picoline: synthesis, structure, properties, catechol oxidase, and antimicrobial activities

Mononuclear and dinuclear copper(II) complexes [Cu2(μ-nap)4(3-pic)2] (1) and [Cu(nap)2(H2O)(4-pic)2] (2) have been synthesized in the presence of 3-picoline and 4-picoline. Two complexes were characterized by FT-IR, UV–vis spectroscopic methods and their thermal stabilities were determined by TG/DTA/DTG techniques. The crystal structures of 1 and 2 were established by X-ray analysis. X-ray structure analysis has shown that copper(II) has a distorted square-pyramidal geometry. Naproxenate is a bridging ligand in 1 and monodentate in 2. Two complexes have shown catalytic activity on oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations. The complexes were also screened for antimicrobial activity against pathogenic bacteria and fungi. The complexes exhibited antimicrobial activity against Entrococcus faecalis and Candida albicans.

Biochemical Processes at the Stage of Withering during Black Tea Production

We determined the molecular weight and some properties of multiple forms of phenol oxidase from tea leaves and four other perennial plants. It was shown that multiple high- and low-molecular forms of phenol oxidase differed in substrate specificity. Low-molecular forms of the enzyme mostly demonstrated hydroxylase activity, while high-molecular forms showed catechol oxidase activity. It was revealed that the withering stage of black tea production is accompanied by the formation of only high-molecular forms of phenol oxidase, which possess catechol oxidase activity crucial for the procurement of oxidative reactions and the quality of the product.

The C–H bond activation in 1-ethyl-3-methylimidazolium acetate–copper(ii) acetate–water–air (dioxygen) systems

Ionic liquid (1-ethyl-3-methylimidazolium acetate, [C2C1im][AcO])-copper(ii) diacetate monohydrate-water-air (O2) systems have been investigated by (13)C NMR, EPR, spectrophotometry, HPLC, and synthetic chemistry methods at different temperatures. The C-H bond activation of [C2C1im](+) with the formation of the unusual dication 1,1'-diethyl-3,3'-dimethyl-2,2'-biimidazolium ([(C2C1im)2](2+)) at 50 °C and 1-ethyl-3-methyl-1H-imidazol-2(3H)-one (C2C1imO) at 50-85 °C was revealed. Two new complexes with the above compounds, [(C2C1im)2][Cu(AcO)4] and Cu2(AcO)4(C2C1imO)2, were isolated from the systems and characterized by X-ray structural analysis. Catalytic cycles with the participation of copper(ii) acetate and dioxygen and the production of [(C2C1im)2](2+) and C2C1imO have been proposed. The catalysis presumably includes the formation of the Cu(II)(O2)Cu(II) active centre with μ-η(2):η(2)-peroxide bridging in analogy with tyrosinase and catechol oxidase activity.

Crystal structure, catecholase activity and ESI-MS of a mixed valence cobalt(III)–cobalt(II) complex derived from a macrocyclic ligand: Identification/proposition of hydrogen bonded metal complex⋯solvent aggregates in ESI-MS

This paper presents the synthesis, crystal structure, catechol oxidase activity and electrospray ionization mass spectra (ESI-MS positive) of a mixed-valence CoIIICoII compound [CoIIICoIIL(N3)3]· 0.5CH3CN·0.27H2O (1) derived from the Robson type tetraiminodiphenolate macrocyclic ligand H2L, which is the [2+2] condensation product of 2,6-diformyl-4-methylphenol and 2,2-dimethyl-1,3-diaminopropane. Compound 1 crystallizes in the monoclinic P21/n space group. The structure consists of two independent units of diphenoxo-bridged CoIIICoII moieties where the CoIII center is hexacoordinated (distorted octahedral) having O(phenoxo)2N(imine)2N(azide)2 environment, while CoII center is pentacoordinated (distorted square pyramidal) having O(phenoxo)2N(imine)2N(azide) environment. Catechol oxidase activity of 1 has been investigated using 3,5-di-tert-butylcatechol (3,5-DTBCH2) as the substrate, revealing that it is an active catalyst with Kcat value 114.24h–1. Electrospray ionization mass spectra (ESI-MS positive) of 1 and 1+3,5-DTBCH2 in acetonitrile have been recorded. No complex⋯substrate aggregate in the spectrum of 1+3,5-DTBCH2 has been identified. However, interestingly, two hydrogen bonded metal complex⋯solvent aggregates [{CoII(LH2)(N3)}⋯(CH3CN)]+ and [{CoIII(LH2)(N3)2}⋯(CH3CN)]+ have been identified in the spectrum of 1. Catecholase activity has also been studied with pyrocatechol and tetrachlorocatechol (TCCH2) as substrates. While no activity has been found with TCCH2, weak activity has been observed with pyrocatechol.