Disproportionation Of Peroxide Research Articles

The Molecular Mechanism of the Catalase-like Activity in Horseradish Peroxidase.

Horseradish peroxidase (HRP) is one of the most relevant peroxidase enzymes, used extensively in immunochemistry and biocatalysis applications. Unlike the closely related catalase enzymes, it exhibits a low activity to disproportionate hydrogen peroxide (H2O2). The origin of this disparity remains unknown due to the lack of atomistic information on the catalase-like reaction in HRP. Using QM(DFT)/MM metadynamics simulations, we uncover the mechanism for reduction of the HRP Compound I intermediate by H2O2 at atomic detail. The reaction begins with a hydrogen atom transfer, forming a peroxyl radical and a Compound II-like species. Reorientation of the peroxyl radical in the active site, concomitant with the transfer of the second hydrogen atom, is the rate-limiting step, with a computed free energy barrier (18.7 kcal/mol, ∼ 6 kcal/mol higher than the one obtained for catalase) in good agreement with experiments. Our simulations reveal the crucial role played by the distal pocket residues in accommodating H2O2, enabling formation of a Compound II-like intermediate, similar to catalases. However, out of the two pathways for Compound II reduction found in catalases, only one is operative in HRP. Moreover, the hydrogen bond network in the distal side of HRP compensates less efficiently than in catalases for the energetic cost required to reorient the peroxyl radical at the rate-determining step. The distal Arg and a water molecule in the "wet" active site of HRP have a substantial impact on the reaction barrier, compared to the "dry" active site in catalase. Therefore, the lower catalase-like efficiency of heme peroxidases compared to catalases can be directly attributed to the different distal pocket architecture, providing hints to engineer peroxidases with a higher rate of H2O2 disproportionation.

Oxygen Reduction on Hafnium/Hafnium Carbide Nanoparticles

Non-precious metal nanoparticles are attractive candidates for oxygen electrocatalytic reduction in electrochemical energy conversion devices, such as fuel cells and batteries. Here we report for the first time electrocatalytic activity of hafnium/hafnium carbide nanoparticles towards the oxygen reduction reaction (ORR). While activity of hafnium oxynitride nanoparticles towards the ORR in acid has previously been reported [1] a little was known about the ability of Hf/HfC nanoparticles to reduce molecular oxygen. Here we demonstrate that molecular oxygen can be reduced on Hf/HfC nanoparticles both in acidic and alkaline environment. However, the reaction mechanism changes from 4 - to 2 - electron pathway, when switching from acidic to alkaline environment. Although the ORR in base occurs through the two-electron parthway, this reaction has a potential for a practical application because Hf/HfC catalyst demonstrates an activity toward the disproportionation of hydrogen peroxide to O2 and H2O. Onset potential for the ORR in 0.1 M KOH for non-optimized catalyst (-0.10 V vs AgAgCl ) is superior to that of the best reported to date MnO2 catalyst (-0.13 V vs Ag/AgCl). In acid, moderate catalytic activity towards the ORR is observed. The results suggests that Hf nanomaterials can be considered as a promising candidate for replacing noble metal catalysts in alkaline air electrodes. [1] CHISAKA, M. & MURAMOTO, H. 2014. Suppression and Evaluation of Hydrogen Peroxide Formation on Carbon-Supported Hafnium Oxynitride. ECS Electrochemistry Letters, 3, F1-F4.

MONO-, TRINUCLEAR NICKEL(II) AND COPPER(II) DIOXIME COMPLEXES: SYNTHESIS, CHARACTERIZATION, CATECHOLASE AND CATALASE-LIKE ACTIVITIES, DNA CLEAVAGE STUDIES

The synthesis and molecular structures of six new mono- and trinuclear complexes [M1L 2 {M2(phen)} 2 ](ClO 4 ) 2 [phen = 1,10-phenanthroline, H 2 L = dioxime ligand, M1, M2 =Ni(II) and Cu(II)] of the ligand, 4-(4-methylphenylamino)biphenylglyoxime are reported. Structural assignments are supported by a combination of FT-IR, elemental analyses, ICP-OES, magnetic susceptibility and molar conductivity studies. Furthermore these complexes were each tested for their ability to catalyze the oxidation of catechol substrates to quinone with dioxygen at 25oC and disproportionation of hydrogen peroxide in the presence of the added base imidazole. The catalytic results indicated that the heterotrinuclear Cu(II)Ni(II)Cu(II) complex (5) shows greater catecholase activity. On the other hand the trinuclear complexes display efficiency in disproportion reactions of hydrogen peroxide producing water and dioxygen in catalase-like activity and homotrinuclear Cu(II) (6) complex is more active towards catalytic decomposition of hydrogen peroxide. The interaction between these compounds with DNA has also been investigated by agarose gel electrophoresis, the trinuclear copper(II) complexes (5, 6) with H 2 O 2 as a cooxidant exhibited the strongest cleaving activity.

Paper-based electrochemiluminescence origami cyto-device for multiple cancer cells detection using porous AuPd alloy as catalytically promoted nanolabels

The detection of cancer cells is important and fundamental for cancer diagnosis and therapy, which has attracted considerable interest recently. Although traditional cyto-sensors have been widely explored due to their high sensitivity and selectivity, it is still a challenge to develop a low-cost, portable, disposable, fast, and easy-to-use cancer cell detection method for applying in the field of cancer diagnosis and therapy. Herein, to address these challenges, we developed a microfluidic paper-based electrochemiluminescence origami cyto-device (μ-PECLOC), in which aptamers modified 3D macroporous Au-paper electrodes were employed as the working electrodes and efficient platforms for the specific cancer cells capture. Owing to the effective disproportionation of hydrogen peroxide and specific recognition of mannose on cell surface, concanavalin-A conjugated porous AuPd alloy nanoparticles were introduced into this μ-PECLOC as the catalytically promoted nanolabels for peroxydisulfate ECL system. Under the optimal conditions, the proposed μ-PECLOC exhibited excellent analytical performance with good stability, reproducibility, and accuracy, towards the cyto-sensing of four types of cancer cells indicating the potential applications to facilitate effective and multiple early cancer diagnosis and clinical treatment.

An ionizable active-site tryptophan imparts catalase activity to a peroxidase core.

Catalase peroxidases (KatG's) are bifunctional heme proteins that can disproportionate hydrogen peroxide (catalatic reaction) despite their structural dissimilarity with monofunctional catalases. Using X-ray crystallography and QM/MM calculations, we demonstrate that the catalatic reaction of KatG's involves deprotonation of the active-site Trp, which plays a role similar to that of the distal His in monofunctional catalases. The interaction of a nearby mobile arginine with the distal Met-Tyr-Trp essential adduct (in/out) acts as an electronic switch, triggering deprotonation of the adduct Trp.

Efficiencies of the Copper(II) Adsorbed Zeolites in the H2O2Disproportionation Reaction

This work describes FT-IR studies results on adsorption of Cu(II) metal cation. Adsorption has been performed on 3A, 4A, 5A, AW-300, ammonium Y zeolite, organophilic, and molecular sieve zeolites using aqueous solution of the metal studied. Changes in intensities and positions of the pseudolattice bands corresponding to ring vibrations have been observed in the measured spectra. These changes are expected particularly in the pseudolattice bands connected with the presence of aluminoand silicooxygen tetrahedral rings in the zeolite structure. Also, Cu(II) adsorbed zeolites were each tested for their ability to catalyse the disproportionation of hydrogen peroxide in the presence of the added base imidazole. The Cu(II) adsorbed zeolites display e ciency in the disproportion reactions of hydrogen peroxide, producing water and dioxygen.

Studies on Catalase-Like Activity of Some Tc-99m Radiopharmaceuticals

Studies on Catalase-Like Activity of Some Tc-99m Radiopharmaceuticals E. C ceka,∗ and B. Dede Faculty of Science and Art, Mehmet Akif Ersoy University, Burdur, Turkey Faculty of Science and Art, Suleyman Demirel University, Isparta, Turkey Hydrogen peroxide is an ubiquitous metabolite in living systems, produced at increased levels in a variety of pathological situations. Therefore suppressing or at least controlling H2O2 production is important. Catalase enzymes can convert hydrogen peroxide into water and dioxygen and a similar role can be played by transition metal ions or some radiopharmaceuticals. (1) TcO4 , (2) Tc-99m mercaptoacetyltriglycine (MAG3) and (3) Tc-99m methoxyisobutylisonitrile (MIBI) were each tested for their ability to catalyse the disproportionation of hydrogen peroxide in the presence of the added base imidazole. It was found that (2) and (3) exhibit acceptable catalase-like activity compared to the Tc-99m pertechnetate.

New organocobaloxime derivatives – Synthesis, characterization, catalase-like activity and DFT studies

New organocobaloxime derivatives of the types [Co(HL)2(Bz)Py] and [CoL2(Bz)PyB2F4] [H2L = 4-(4-chlorophenylamino)biphenylglyoxime; Bz = Benzyl; Py = Pyridine] were synthesized and characterized by elemental analysis, molar conductance, FT-IR, 1H NMR and magnetic susceptibility measurements. The structural and vibrational spectroscopic data of the molecule in the ground state were calculated by the density functional method using the 6-31G(d) basis set. Isotropic chemical shifts (1H and 13C NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. In addition, the thermal decomposition of complexes with H2L was studied in nitrogen atmosphere. The IR spectra indicated that the complexes coordinate through the N atom of the oxime group of the ligand. The diamagnetic susceptibilities of the complexes indicated that they are diamagnetic (low-spin d6 octahedral). The catalase-like activities of the complexes for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The redox behaviors of the ligand and its complexes were investigated by cyclic voltammetry at the platinum electrode in DMF.

New insights into the effects of the herbicide imazethapyr on Cu(II) ecotoxicity to the aquatic unicellular alga Scenedesmus obliquus

Interactions between heavy metals and organic contaminants can result in speciation changes of heavy metals. Therefore, it is unknown whether organic contaminants in aquatic environments act as selective agents to mediate the toxicity of heavy metals. To elucidate these interactions, the effects of the herbicide imazethapyr (IM) on Cu(II) ecotoxicity to the aquatic unicellular alga Scenedesmus obliquus were investigated. It was found that the toxicity of Cu could be mediated by IM. To explore the mechanisms involved, complex formation, the catalytic activity of the complex, the Cu species and the distribution of Cu and Fe in the algal cell were characterized. The results showed that Cu(II) and IM formed an octahedral complex with an IM:Cu molar ratio of 2:1. These complexes also catalyzed the disproportionation of hydrogen peroxide. Analysis of the K-edge of Cu using XAFS spectroscopy indicated that when treated with Cu, the Cu was bound to polygalacturonic acid (on the cell wall), and once inside the cell, Cu may complex with the reduced glutathione (GSH) (in the cell). When the cell is treated with IM and Cu simultaneously, IM–Cu may be the primary complex formed. Once Cu combines with IM, it is difficult for it to interact with the cell wall. In addition, using scanning transmission soft X-ray microscopy, it was found that Cu could induce changes in the distribution of the essential trace element Fe, whereas IM–Cu cannot. This finding demonstrates the importance of interactions between heavy metals and organic contaminants, which are able to mediate the toxicity of heavy metals and should be considered in future risk assessments.

Synthesis, structure and catalase activity of three new manganese(III) complexes with a N,N,O donor Schiff-base ligand

Three new Mn(III) complexes [Mn(L)(L′)(N3)] (1), [Mn(L)(L′)(Cl)] (2) and {[Mn(L)(L′)(H2O)](ClO4)}2 (3) (where, HL=2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol and HL′=o-hydroxyacetophenone) have been synthesized and characterized by UV–Vis and IR spectroscopy and single-crystal X-ray diffraction analyses. All of the three monomeric complexes show six-coordinate octahedral geometry around the Mn(III) center and are bonded to the deprotonated tridentate ligand L together with the deprotonated bidentate ligand L′ and a labile monodentate donor i.e. azide in 1, chloride in 2 and water in 3, respectively. All of the complexes catalyze the disproportionation of hydrogen peroxide into water and dioxygen i.e. they possess catalase activity. The turnover numbers of the complexes follow the order: 3>1>2.

Synthesis, crystal structure, and catalytic properties of 2,2’-bipyridyl-dicyano-palladium(II)

In the solvothermal condition, a Pd(II) complex with a in situ synthesis ligand, [Pd(2,2’-bipy)2(CN)2] (1) was obtained and characterized by elemental analysis, IR, UV, TG, and powder X-ray analysis. The single crystal X-ray analysis showed that the title complex is different from the reported 2,2’-bipyridyl-dicyanopalladium(II) (2) in crystal system and structural parameters. The catalytic investigation for the reactions of the disproportionation of hydrogen peroxide and oxidation of sulfide showed that the complex 1 is an active homogeneous catalyst in the presence of imidazole and 2-sulfobenzoic acid, respectively.

A novel single-site manganese(ii) complex of a pyridine derivative as a catalase mimetic for disproportionation of H2O2 in water

A novel single site Mn(II) complex was successfully synthesized and tested in the aqueous disproportionation of hydrogen peroxide. The complex was found to be stable (HR-XAS) and exhibits catalase-like activity in neutral pH. Theoretical calculations suggested a reaction mechanism involving two complexes, changes in metal oxidation state and proton shuttling.

A facile and scalable synthesis of qinghaosu (artemisinin)

A very simple and efficient approach for the conversion of dihydro-artemisinic acid into artemisinin is developed, featuring use of a molybdate induced disproportionation of hydrogen peroxide to generate singlet oxygen. The whole synthesis was completed by stirring at ambient temperature without need for any special equipments.

The Outer-Coordination Sphere: Incorporating Amino Acids and Peptides as Ligands for Homogeneous Catalysts to Mimic Enzyme Function

Great progress has been achieved in the field of homogeneous transition metal-based catalysis; however, as a general rule these solution-based catalysts are still easily outperformed by their analogous enzyme counterparts, in terms of both rates and selectivity. This includes structural mimics of enzymatic active sites. This observation suggests that the features of the enzyme beyond the active site, i.e., the outer-coordination sphere, are important for enzymes' exceptional function. Directly mimicking the outer-coordination sphere requires the incorporation of amino acids and peptides as ligands for homogeneous catalysts. This effort has been attempted for many homogeneous catalysts which span the manifold of catalytic reactions including hydrogenation, hydroformylation, hydrogen production, oxygen activation, dioxygen transport, electron transfer, disproportionation of the superoxide anion radical, acylation, phosphorylation, esterification, ester hydrolysis, and hydrogen peroxide disproportionation. How much of the outer-coordination sphere to include in molecular catalysts and the preferential structural conformation of the appended section are long-standing questions. Synthetically incorporating an amino acid- or peptide-based outer-coordination sphere requires care to avoid unwanted side reactions with the large number of functional groups. Catalysis with amino acid or peptide containing catalysts requires careful consideration of solvent and pH to promote solubility, stabilize structure, optimize catalysis, and avoid catalyst degradation. This article reviews the current capability of synthesizing and characterizing this often challenging but very promising category of metal-based catalysts.

Synthesis, Characterization, Electrochemical Behavior, and Biological Studies of 1-p-Diphenylmethane-2-hydroxyimino-2-(arylamino)-1-ethanone Copper(II) and Ruthenium(III) Complexes

New copper and ruthenium mononuclear complexes of the type [ML2(H2O)X] [X = H2O for M = Cu(II) and X = Cl for M = Ru(III)] have been prepared from 1-p-diphenyl- methane-2-hydroxyimino-2-(4-chloroanilino)-1-ethanone (HL1) and 1-p-diphenylmethane-2-hydroxyimino-2-(4-toluidino)-1-etha- none (HL2). The complexes were characterized by elemental analyses, magnetic susceptibility, molar conductance, IR, thermal analysis, and cyclic voltammetry. Stoichiometric and spectral results of the metal complexes indicated that the metal:ligand ratios in the complexes were found to be 1:2 and the ligands behave as a bidentate ligand forming neutral metal chelates through the carbonyl and oxime oxygen. The electrochemical behavior of the ligands and their complexes were obtained by cyclic voltammetry. The interaction between these complexes with DNA has also been investigated by agarose gel electrophoresis. The copper(II) complexes (3 and 4) with H2O2 as a co-oxidant exhibited strongest cleaving activity. Moreover, catalytic activities of the complexes for the disproportionation of hydrogen peroxide were also investigated in the presence of imidazole.

Cyano‐Bridged ‘Oximato’ Complexes: Synthesis, Structure, and Catalase‐Like Activities

AbstractThe reaction of the ‘oximato’‐ligand precursor A (Fig. 1) and metal salts with KCN gave two mononuclear complexes [ML(CN)(H2O)n](ClO4) (1 and 2; L={N‐(hydroxy‐κO)‐α‐oxo‐N′‐[(pyridin‐2‐yl‐κN)methyl[1,1′‐biphenyl]‐4‐ethanimidamidato‐κN′}; M=CoII (1), CuII (2); n=2 for CoII, n=0 for CuII; Figs. 2 and 3). The new cyano‐bridged pentanuclear ‘oximato’ complexes [{ML(H2O)n(NC)}4M1(H2O)x](ClO4)2 (3–6) and trinuclear complexes [{ML(H2O)n(NC)}2M1L](ClO4) (7–10) ([M1=MnII, CuII; x=2 for MnII, x=0 for CuII] were synthesized from mononuclear complexes and characterized by elemental analyses, magnetic susceptibility, molar conductance, and IR and thermal analysis. The four [ML(CN)(H2O)n]+ moieties are connected by a metal(II) ion in the pentanuclear complexe 3–6, each one involving four cyano bridging ligands (Fig. 4). The central metal ion displays a square‐planar or octahedral geometry, with the cyano bridging ligands forming the equatorial plane. The axial positions are occupied by two aqua ligands in the case of the central Mn‐atom. The two [ML(CN)(H2O)n]+ moieties and an ‘oximato’ ligand are connected by a metal(II) ion in the trinuclear complexes 7–10, each one involving two cyano bridging ligands (Fig. 5). The central metal ions display a distorted square‐pyramidal geometry, with two cyano bridging ligands and the donor atoms of the tridentate ‘oximato’ ligand. Moreover catalytic activities of the complexes for the disproportionation of hydrogen peroxide (H2O2) were also investigated in the presence of 1H‐imidazole. The synthesized homopolynuclear CuII complexes 6 and 10 displayed eficiency in disproportion reactions of H2O2 producing H2O and dioxygen thus showing catalase‐like activity.

Catalase-like activity of the polyoxovanadate anion [MnIVV13O38]7−: a mechanistic study

The anion [MnIVV13O38]7−, 1, in aqueous acetate buffer catalyses the disproportionation of hydrogen peroxide into oxygen and water (TON > 200) by a MnIV/II cycle, which operates via quick formation of diperoxovanadate at the surface of 1.

Direct evidence for the role of imidazole in disproportionation of hydrogen peroxide by a mononuclear manganese salen complex

It has long been known that imidazole can enhance the catalytic activity of catalase model compounds; however, the role of imidazole is still not well understood. In an attempt to elucidate the role of imidazole in promoting the disproportionation of hydrogen peroxide by model compounds, four mononuclear manganese salen (Mn-Salen) complexes with and without axial imidazole ligands were synthesized and characterized by single-crystal X-ray diffraction, UV–vis spectroscopy, electrochemical and HPLC measurements. By comparing the Mn-Salen compounds with and without imidazole ligands, we demonstrated that the activity enhancement of imidazole originated from coordination of imidazole to the manganese center when less than one equivalent of imidazole was present, and from assisted deprotonation of the substrate when excess imidazole was present. These results provide direct evidence for the mechanism of activity enhancement of imidazole in the catalysis of enzyme model compounds.

ChemInform Abstract: The Importance of Developing Metal Complexes with Pronounced Catalase‐Like Activity.

AbstractReview: 56 refs.

Properties and antioxidant activity of water-soluble iron catalysts with Schiff base ligands. Comparison with their manganese counterparts

Three new iron complexes Na2(Fe(5-SO3-salpn)(H2O)2)OH⋅4H2O (1⋅4H2O), Na2(Fe(5-SO3- salpnOH)(H2O)2)Cl⋅7H2O (2⋅7H2O) and Na2(Fe2(5-SO3-salpentO)(µ-OAc)(µ- (OH)(H2O)2)OH⋅3H2O (3⋅3H2O), where 5-SO3-salpn = 1,3-bis(5-SO3-salicylidenamino)propane, 5-SO3-salpnOH = 1,3-bis(5-SO3-salicylidenamino)propan-2-ol and 5-SO3-sapentOH = 1,5-bis(5- SO3-salicylidenamino)pentan-3-ol, have been obtained and characterized. The ligands tune the redox potential of 1 and 2 within the range required for superoxide dismutase activity, with 2 being less reactive as a result of the formation of an inactive dimer. Complex 3 looses acetate and converts into a µ-oxo-Fe2 species responsible for its catalase activity. The more negative reduction potentials of 1 - 3 and their lower stability result in rates of superoxide and peroxide disproportionation 10- to 100-times slower than those of the Mn counterparts.