- Catalytic spectrophotometric determination of molybdenum
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A highly selective, sensitive, and simple catalytic method for the determination of molybdenum in natural and waste waters was developed. It is based on the catalytic effect of Mo(VI) on the oxidation of 2-aminophenol with H2O2. The reaction is monitored spectrophotometrically by tracing the oxidation product at 430 nm after 10 min of mixing the reagents. Addition of 800 μg·cm-3 EDTA conferred high selectivity; however, interfering effects of Au(III), Cr(III), Cr(VI), and Fe(III) had to be eliminated by a reduction and co-precipitation procedure with SnCl2 and Al(OH)3. Mo(VI) shows a linear calibration graph up to 11.0 ng·cm-3; the detection limit, based on the 3Sb-criterion, is 0.10 ng·cm-3. The unique selectivity and sensitivity of the new method allowed its direct application to the determination of Mo(VI) in natural and waste waters.
- Mohamed,Ahmed,El-Shahat
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- A supramolecular-hydrogel-encapsulated hemin as an artificial enzyme to mimic peroxidase
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(Figure Presented) Faking it: The use of a supramolecular hydrogel as the structural component of artificial enzymes provides a new and useful approach to the development of biomimetic catalysts. In toluene, hemin chloride encapsulated in such a hydrogel achieves about 60% nascent catalytic activity of horseradish peroxidase. Additionally, the activity of hemin in the hydrogel is 387.1 times greater than that of free hemin.
- Wang, Qigang,Yang, Zhimou,Zhang, Xieqiu,Xiao, Xudong,Chang, Chi K.,Xu, Bing
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- 2-Amino-phenoxazine-3-one attenuates glucose-induced augmentation of embryonic form of myosin heavy chain, endothelin-1 and plasminogen activator inhibitor-1 in human umbilical vein endothelial cells
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The aim of this study was to investigate the changes in mRNA level of embryonic form of myosin heavy chain (SMemb), endothelin-1 (ET-1) and plasminogen activator inhibitor-1 (PAI-1), which are considered to be involved in the angiogenesis and atherosclerosis in diabetic blood vessels, in human umbilical vein endothelial cells (HUVECs) caused by high ambient glucose, and the effects of 2-aminophenoxazine-3-one (Phx-3), which was produced by the reaction of bovine hemoglobin with o-aminophenol, on them. The mRNA level of SMemb, ET-1 and PAI-1 and the level of SMemb protein were extensively upregulated in HUVECs treated with high concentration of glucose (15 mM), compared with those in the cells with normal concentration of glucose (5 mM). The migration activity of HUVECs evaluated by the cell migration assay was accelerated by 15 mM glucose. When 10 μM Phx-3, at the concentration of which the proliferation of HUVECs was not affected, was administered to HUVECs with 15 mM glucose, the mRNA level of SMemb, ET-1 and PAI-1 and the level of SMemb protein were significantly downregulated to the normal levels in the cells. However, when 10 μM Phx-3 was administered to HUVECs with 5 mM of glucose, the mRNA level of SMemb, ET-1 and PAI-1 and the level of SMemb protein were not affected. The migration activity of HUVECs, which was accelerated by high glucose, was reversed by 10 μM Phx-3. The present results suggest that Phx-3 may be a drug to prevent the high glucose-associated endothelial damage, vascular angiogenesis in diabetic patients, by inhibiting the expression of angiogenic factors, such as SMemb, ET-1 and PAI-1, in the endothelial cells.
- Fukuda, Gen,Yoshitake, Noriko,Khan, Zia Ali,Kanazawa, Masao,Notoya, Yoko,Che, Xiao-Fang,Akiyama, Shin-Ichi,Tomoda, Akio,Chakrabarti, Subrata,Odawara, Masato
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- Mechanistic studies of the tyrosinase-catalyzed oxidative cyclocondensation of 2-aminophenol to 2-aminophenoxazin-3-one
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Abstract Tyrosinase (EC 1.14.18.1) catalyzes the monophenolase and diphenolase reaction associated with vertebrate pigmentation and fruit/vegetable browning. Tyrosinase is an oxygen-dependent, dicopper enzyme that has three states: Emet, Eoxy, and Edeoxy. The diphenolase activity can be carried out by both the met and the oxy states of the enzyme while neither mono- nor diphenolase activity results from the deoxy state. In this study, the oxidative cyclocondensation of 2-aminophenol (OAP) to the corresponding 2-aminophenoxazin-3-one (APX) by mushroom tyrosinase was investigated. Using a combination of various steady- and pre-steady state methodologies, we have investigated the kinetic and chemical mechanism of this reaction. The kcat for OAP is 75 ± 2 s-1, KMOAP = 1.8 ± 0.2 mM, KMO2 = 25 ± 4 μM with substrates binding in a steady-state preferred fashion. Stopped flow and global analysis support a model where OAP preferentially binds to the oxy form over the met (k7 蠑 k1). For the met form, His269 and His61 are the proposed bases, while the oxy form uses the copper-peroxide and His61 for the sequential deprotonation of anilinic and phenolic hydrogens. Solvent KIEs show proton transfer to be increasingly rate limiting for kcat/KMOAP as [O2] → 0 μM (1.38 ± 0.06) decreasing to 0.83 ± 0.03 as [O2] → ∞ reflecting a partially rate limiting μ-OH bond cleavage (Emet) and formation (Eoxy) following protonation in the transition state. The coupling and cyclization reactions of o-quinone imine and OAP pass through a phenyliminocyclohexadione intermediate to APX, forming at a rate of 6.91 ± 0.03 μM-1s-1 and 2.59E-2 ± 5.31E-4 s-1. Differences in reactivity attributed to the anilinic moiety of OAP with o-diphenols are discussed.
- Washington, Courtney,Maxwell, Jamere,Stevenson, Joenathan,Malone, Gregory,Lowe, Edward W.,Zhang, Qiang,Wang, Guangdi,McIntyre, Neil R.
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- Square planar versus square pyramidal copper(II) complexes containing N3O moiety: Synthesis, structural characterization, kinetic and catalytic mimicking activity
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In quest of copper complexes having [CuN3O] cores, [Cu(phen)(L–Val)(H2O)]NO3 (1) and [Cu(bpy)(L–Val)]ClO4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). Complex 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structures of 1 and 2 have supramolecular networks formed via inter- and intra-molecular hydrogen bonding interactions. The kinetics and mechanism of ligand substitution of 1 and 2 by thiourea (TU) were studied in detail and showed a biphasic process in which an initial fast reaction is followed by a slower one. The activation parameters for the fast reaction: ΔH# = 68 ± 4 and 73 ± 5 kJ mol?1, ΔS# = 43 ± 10 and 54 ± 9 J K?1 mol?1 for 1 and 2, respectively, supports a dissociative substitution mechanism. Whereas for the slow reaction: ΔH# = 33 ± 6 and 43 ± 3 kJ mol?1, ΔS# = ?77 ± 10 and ?56 ± 9 J K?1 mol?1 for 1 and 2, respectively, support an associative substitution mechanism. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthase. The model complexes 1 and 2 show catecholase activity of Kcat = 10.9 × 103 and 11.4 × 103 h?1 and phenoxazinone synthase activity of Kcat = 2.1 × 103 and 4.3 × 103 h?1, respectively. Compared to the enzyme itself (Kcat = 8.3 h?1), the model complexes 1 and 2 are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase.
- Shaban, Shaban Y.,Ramadan, Abd El-Motaleb M.,Ibrahim, Mohamed M.,Elshami, Fawzya I.,van Eldik, Rudi
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- Catalytic oxidation of 2-aminophenol to questiomycin A by dioxygen in the presence of cobaloxime derivatives. Free radical intermediates
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The multistep oxidative dehydrogenation of 2-amino-phenol to Questiomycin A, catalyzed by cobaloxime(II) derivatives, involves ESR-detectable 2-aminophenoxyl type free radical intermediate.
- Simandi,Barna,Korecz,Rockenbauer
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- Inactivation path during the copper (II) catalyzed synthesis of Questiomycin A from oxidation of 2-aminophenol
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The catalytic oxidation of 2-aminophenol (OAP) to 2-amino-3H-phenoxazin-3- one (APX, Questiomycin A) was the object of numerous studies partly due to antimicrobial properties of Questiomycin A and mostly because it can be used as a model for the synthesis of the naturally occurring antineoplastic agent Actinomycin D. Several copper complexes were used as dioxygen and/or substrates activators in order to mimic the activity of phenoxazinone synthase, but the reported assays failed to provide reasonable mechanistic features in media compatible with natural conditions. The main purposes of our work were to use simple copper salts to perform oxidation of OAP in oxygenated aqueous solutions and to develop a reaction scheme able to explain the low yields in APX along with the operational inactivation of the catalyst. A 11-step kinetic model able to describe the inactivation of copper(II) catalyst during oxidation of OAP to APX in oxygenated solutions was developed, and the rate constants for both catalytic and non-catalytic branch were estimated either experimentally or using a computing program for detailed kinetic simulation. It was demonstrated that the inactivation path can be assigned to formation of the stable bis(o-iminosemiquinonato)copper(II) complex, a compound reported as a moderate antimicrobial agent.
- Olmazu, Cǎtǎlina,Puiu, Mihaela,Babaligea, Irina,Rǎducan, Adina,Oancea, Dumitru
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- Nuclearity: Versus oxidation state in the catalytic efficiency of MnII/III azo Schiff base complexes: Computational study on supramolecular interactions and phenoxazinone synthase-like activity
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A novel mononuclear Mn(iii) complex, [MnIII(L1)Cl(H2O)]·H2O (1), and a tetranuclear Zn(ii)-Mn(ii) complex, [{ZnII2(L2)2Cl2}MnII2(μ1,1-N3)2(H2O)2]·2H2O (2), have been synthesized involving azo Schiff base ligands, viz. H2L1 = (E)-6,6′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxy-4-((E)-p-tolyldiazenyl)phenol) and H2L2 = (E)-6,6′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxy-4-((E)-p-tolyldiazenyl)phenol), respectively. The solid-state structures were determined by single crystal X-ray crystallography. In complex 1, the Mn(iii) centre adopts slightly distorted octahedral geometry, while in complex 2 the Mn(ii) centre residing in the outer core of the ligand adopts a distorted pentagonal bipyramidal geometry. In complex 1, the chloride ion simply acts as a terminal coligand, while in complex 2, azide ions bind the metal centres in an end-on bridging fashion to produce a tetranuclear complex. The phenoxazinone synthase-like activity of both complexes has been examined and a detailed investigation of the structure-property correlation has been performed. Whereas the mononuclear complex 1 exhibits significant phenoxazinone activity, complex 2 is almost inactive, although in both complexes labile sites are available at manganese centres for substrate binding. The present work therefore highlights the importance of higher oxidation states of manganese over nuclearity for the development of better in vitro catalysts. In addition, extensive efforts have been made to visualize and quantify all supramolecular interactions present in 1 and 2.
- Banerjee, Saikat,Brand?o, Paula,Bauzá, Antonio,Frontera, Antonio,Barceló-Oliver, Miquel,Panja, Anangamohan,Saha, Amrita
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- Bis-benzimidazole diamide iron(III) complexes as mimics of phenoxazinone synthase
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New Bis Benzimidazole diamide ligands-N,N′-Bis(2- Methylbenzimidazolyl) pyridinediamide [GBPA = L1] and N-Picolylated-N,N′- Bis(2-Methylbenzimidazolyl) hexandiamide [Pic-GBHA = L2] have been synthesized and utilized to prepare Fe(III) complexes. The X-ray structure of the ligand L2 crystallizes in the monoclinic space group P21/n. The complexes were suitable as catalyst for the oxidation of 2-aminophenol (OAPH) to 2-aminophenoxazine-3-one (APX) (phenoxazinone synthase activity) with dioxygen at ambient temperature. Kinetic measurements revealed dependence on the substrate concentration with respect to the corresponding catalyst. The results show that the oxidation of OAP is not dependent upon E1/2 values of the respective complexes.
- Bakshi, Ruchi,Kumar, Ravinder,Mathur, Pavan
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- Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols
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Abstract Enzymatic reactions have inspired many chemists to design small molecule mimics that would perform the function of the enzymes in aqueous and or non-aqueous medium. Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two multi-copper enzymes in nature, which has led to model complexes of Mn, Fe, Co, Ni, Cu. Based on our earlier work in this area we have probed the commercially available metal acetates of the above metals to establish a trend in reactivity for catalytic conversions similar to those of the two enzymes. The results show that Mn is the best 3d transition metal for similar catalysis. MnII acetate was found to convert 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butylquinone (DTBQ) with a kcat of 1.3(1) × 103 h-1and for o-aminophenol (OAP) to 2-aminophenoxazinone (APX) conversion the kcat = 111(2) h-1, demonstrating efficient CO and PHS like activity. Kinetic studies show that DTBC oxidation follows a first order kinetics with respect to the substrate for each of those metal(II) acetates with activity order of Mn >> Co > Cu > Fe ≥ Ni. Through mechanistic investigation we found that the reactive oxygen species detected during the oxidation of DTBC is mostly hydroxyl radical for Mn, Fe and Co whereas Cu and Ni generate H2O2.
- Dey, Suman Kr.,Mukherjee, Arindam
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- The first alternating MnII-MnIII 1D chain: Structure, magnetic properties and catalytic oxidase activities
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An unprecedented one-dimensional mixed-valence chain, [{MnIII(L)2}{MnII(bpy)2}(ClO4)(H2O)0.5]∞ (H2L = N-salicylidene-l-alanine and bpy = 2,2′-bipyridine), h
- Ganguly, Sayantan,Kar, Paramita,Chakraborty, Maharudra,Ghosh, Ashutosh
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- Towards the rational biosynthesis of substituted phenazines and phenoxazinones by laccases
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Laccases are multi-copper oxidases that oxidise a wide range of substrates including phenol and aniline derivatives, which could be further involved in coupling reactions leading to the formation of dimeric and trimeric structures. This paper describes the enzyme-mediated dimerisation of several ortho and meta,para-disubstituted aromatic amines into phenazine ("head-to-tail" dimers) and phenoxazinone chromophores. The redox properties of substituted aromatic amines were studied by cyclic voltammetry and the kinetic constants of CotA and Trametes versicolor laccases were measured for selected aromatic amines. The structure of novel enzymatically synthesised phenazine and phenoxazinone dyes using CotA laccase was assessed by NMR and MS. Overall our data show that this enzymatic green process is an efficient alternative to the classic chemical oxidation of aromatic amines and phenols, with an impact on the broad field of applications of these heterocyclic compounds. the Partner Organisations 2014.
- Sousa, Ana Catarina,Oliveira, M. Conceicao,Martins, Ligia O.,Robalo, M. Paula
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- Mn(III) and Cu(II) complexes of 1-((3-(dimethylamino)propylimino)methyl) naphthalen-2-ol): Synthesis, characterization, catecholase and phenoxazinone synthase activity and DFT-TDDFT study
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Two new complexes, [MnL2](ClO4) (1) and [CuL2] (2) (where LH?=?(E)-1-((3-(dimethylamino)propylimino)methyl)naphthalen-2-ol), have been synthesized and characterized by spectroscopic techniques and their molecular structures are established by single-crystal X-ray diffraction study. Complex 1 adopts an octahedral geometry around the central manganese atom which is in?+?3 oxidation state, whereas in complex 2, the Cu+2 ion preferred a square pyramidal environment around it through the ligand donor atoms. Both complexes were tested for catecholase and phenoxazinone synthase activity. Complex 1 catalyzes the oxidation of 3,5-ditertiary-butyl catechol with a kcat value of 6.8424?×?102?h?1 in acetonitrile whereas the same for complex 2 is 3.7485?×?102?h?1 in methanol. Phenoxazinone synthase activity was shown only by complex 2 having kcat?=?74.225?h?1. Structures of both the title complexes have been optimized by means of DFT calculations. Experimental electronic spectra of the complexes have been corroborated by TDDFT analysis. Electrochemical investigations by means of cyclic voltammetry have been carried out to study the electron transfer processes in the complexes.
- Sengupta, Swaraj,Naath Mongal, Binitendra,Das, Suman,Panda, Tarun K.,Mandal, Tarun K.,Fleck, Michel,Chattopadhyay, Shyamal K.,Naskar, Subhendu
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- Tri- and hexa-nuclear NiII-MnII complexes of a N2O2 donor unsymmetrical ligand: Synthesis, structures, magnetic properties and catalytic oxidase activities
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A new mononuclear Ni(ii) complex, [NiL] (1) of an unsymmetrically dicondensed N2O2 donor ligand, H2L (where H2L = N-α-methylsalicylidene-N′-salicylidene-1,3-propanediamine), has been synthesized. Complex 1, on r
- Mahapatra, Prithwish,Drew, Michael G. B.,Ghosh, Ashutosh
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- Designing a biomimetic catalyst for phenoxazinone synthase activity using a mesoporous Schiff base copper complex with a novel double-helix morphology
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The condensation reaction of 3-aminopropyltrimethoxysilane with o-hydroxyacetophenone and subsequent complexation with Cu(CH3COO)2·H2O afforded a Schiff base copper complex with a silane moiety. Covalent functionalisation of MCM-41 with the Schiff base copper complex yielded a heterogenised copper complex which mimics the "CuN2O2" coordination site that resembles the galactose oxidase enzyme. The synthesized materials were characterized by UV-DRS, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) studies along with high resolution transmission electron microscopy (HR-TEM) to confirm successful functionalisation. Low-angle X-ray diffraction (LA-XRD) and nitrogen sorption analyses not only revealed the conservation of the textural properties of the support but also the permeability of the copper Schiff base complex into the channel system despite simultaneous decreases in surface area, pore volume and pore size. Electron paramagnetic resonance (EPR) studies confirmed the presence of copper Schiff base in MCM-41 even after dimerisation with o-aminophenol. The catalytic reaction was carried out with tert-butyl hydroperoxide (TBHP) and aqueous peroxide for MCM-41 and heterogenised copper complex under the mild reaction conditions.
- Muthusami, Rubiga,Moorthy, Malathy,Irena, Kostova,Govindaraj, Anbarasu,Manickam, Chozhanathmisra,Rangappan, Rajavel
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- Kinetics and mechanism of the cobaloxime(II)-catalysed oxidation of 2-aminophenol by dioxygen. A phenoxazinone synthase model involving free-radical intermediates
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Cobaloxime(II) derivatives catalysed the oxidative dehydrogenation of 2-aminophenol (ap) to 2-amino-3H-phenoxazin-3-one by dioxygen under ambient conditions. The 2-aminophenoxyl radical (ap?) and a cobalt-bound dimeric radical have been detected as intermediates. The kinetics was followed by monitoring dioxygen uptake. The cobaloxime(II) concentration is very low during the reaction as evidenced by ESR spectroscopy. According to the proposed mechanism, in the rate-determining step superoxocobaloxime abstracts an H atom from ap via a hydrogen-bonded intermediate, affording the ap? radical. In the steady state cobaloxime(III) predominates and the active catalyst is generated in low concentration via its reduction by the ap? radical. The system studied serves as a model of phenoxazinone synthase and calls attention to the possible involvement of radical intermediates in the enzymatic reaction.
- Simandi, Laszlo I.,Barna, Terez,Nemeth, Sandor
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- Methylene bridge regulated geometrical preferences of ligands in cobalt(iii) coordination chemistry and phenoxazinone synthase mimicking activity
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Two new azide bound cobalt(iii) complexes, [Co(L1)(N 3)3] (fac-1) and [Co(L2)(N3) 3] (mer-2), where L1 is bis(2-pyridylmethyl)amine and L2 is (2-pyridylmethyl)(2-pyridylethyl)amine, derived from tridentate reduced Schiff-base ligands have been reported. Interestingly, a methylene bridge regulated preferential coordination mode of ligands is noticed in their crystal structures: it is found in a facial arrangement in fac-1 and has a meridional disposition in mer-2. Both complexes show phenoxazinone synthase-like activity and the role of the structural factor on the catalytic activity is also explored. Moreover, the easily reducible cobalt(iii) center in mer-2 favors the oxidation of o-aminophenol. The ESI-MS positive spectra together with UV-vis spectroscopy clearly suggest the formation of a catalyst-substrate adduct by substitution of the coordinated azide ions in the catalytic cycle. This journal is the Partner Organisations 2014.
- Panja, Anangamohan,Shyamal, Milan,Saha, Amrita,Mandal, Tarun Kanti
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- Synthesis and spectroscopic characterization of a photo-stable tetrazinc(II)–Schiff base cluster: A rare case of ligand centric phenoxazinone synthase activity
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Herein, the synthesis, structural characterization and catalytic activity of a novel tetranuclear zinc(II)–Schiff base complex, [Zn4(L)2(μ3-OCH3)2(CH3OH)2]·2CH3OH (1),
- Garai, Mamoni,Das, Ajit,Joshi, Mayank,Paul, Suvendu,Shit, Madhusudan,Choudhury, Angshuman Roy,Biswas, Bhaskar
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- Heterogeneous Manganese-Catalyzed Oxidase C?H/C?O Cyclization to Access Pharmaceutically Active Compounds
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Heterogeneous manganese-catalyzed C?H oxidative couplings were accomplished to gain access to pharmaceutically relevant 2-aminophenoxazin-3-ones and to diaminophenazine and purpurogallin moieties in excellent yields. The user-friendly K-OMS-2 oxidase strategy proved to be more versatile and robust than enzymatic catalysts-based procedures allowing a wider substrate scope and being effectively reusable as proven by leaching measurements and XRD analyses.
- Ferlin, Francesco,Marini, Alberto,Ascani, Nicola,Ackermann, Lutz,Lanari, Daniela,Vaccaro, Luigi
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- Manganese(III) acetate mediated catalytic oxidation of substituted dioxolene and phenols
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Manganese(III) acetate is found to be an efficient catalyst to perform oxidation of 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butylbenzoquinone (DTBQ) and 2-aminophenol (OAP) to 2-aminophenoxazinone (APX). The k cat values are 1.72(2) × 103 and 2.8(2) × 102 h-1 for the formation of DTBQ and APX, respectively. The turnover number of APX formation is highest among the synthetic mimics. ESI-MS studies of DTBC oxidation suggest formation of a MnIV intermediate. Manganese(III) acetate is also capable of oxidative CC bond coupling in sterically hindered phenols to form biaryls in 65-94% yield.
- Dey, Suman Kr,Mukherjee, Arindam
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- Influence of the first and second coordination spheres on the diverse phenoxazinone synthase activity of cobalt complexes derived from a tetradentate Schiff base ligand
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This paper describes syntheses and structural characterization of four new cobalt(iii) compounds (1-4) derived from a N3O donor Schiff base ligand, a condensation product of N,N-dimethyldipropylenetriamine and o-vanillin, and their catalytic activity relating to the function of phenoxazinone synthase. X-ray crystallography reveals that the Schiff base can coordinate the metal centre either in a tetradentate fashion through the monoanionic deprotonated form using all four donor sites (in 1 and 2) or in a tridentate fashion using the zwitterionic form of the Schiff base ligand, leaving the quaternary amine nitrogen free from coordination (in 3). The monoanionic deprotonated ligand can also bind the metal centre in a tridentate fashion where the pendent tertiary amine nitrogen is engaged in intramolecular hydrogen bonding in 4. Moreover, the triamine part of the Schiff base ligand can bind a metal centre both facially and meridionally. Therefore, all these versatilities associated with this triamine make it appealing for the development of coordination chemistry with diverse structures. All complexes are active functional models for phenoxazinone synthase, and as expected the availability of labile sites at the first coordination sphere for the substrate, o-aminophenol, binding is responsible for higher catalytic activity in 1 and 2. The importance of a proton abstraction site at the second coordination sphere behind the facile oxidation of the substrate is also explored (reactivity of 3vs.4). The remarkable finding from the mass spectral study discloses several important intermediates, and thereby provides significant information relating to the mechanistic pathway of the functioning phenoxazinone synthase activity of the synthetic models.
- Panja, Anangamohan,Jana, Narayan Ch.,Brand?o, Paula
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- Ni(II) Complex of N2O3 Donor Unsymmetrical Ligand and Its Use for the Synthesis of NiII-MnII Complexes of Diverse Nuclearity: Structures, Magnetic Properties, and Catalytic Oxidase Activities
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A new mononuclear Ni(II) complex [NiL] (1) of an unsymmetrically dicondensed N2O3 donor ligand, H2L (N-α-methylsalicylidene-N′-3-methoxysalicylidene-1,3-propanediamine), has been synthesized. Complex 1 on reaction with Mn(ClO4)2·6H2O and NaN3 in different molar ratios yielded three novel heterometallic NiII-MnII complexes, [(NiL)2Mn(N3)](ClO4) (2), [(NiL)2Mn2(N3)2(μ1,1-N3)2(CH3OH)2] (3), and [{(NiL)2Mn}2(μ1,3-N3)(H2O)]·(CH3OH),(ClO4)3 (4). The single crystal structure analyses show a trinuclear NiII2MnII structure for complex 2 and a tetranuclear NiII2MnII2 structure where two dinuclear NiIIMnII units are connected via μ1,1-azido and phenoxido bridges for complex 3. Complex 4 possesses a hexanuclear structure where two trinuclear NiII2MnII units are connected via a μ1,3-azido bridge. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 3 and 4 are antiferromagnetically coupled with the exchange coupling constants (J) of -4.97, -0.14, -0.55 cm-1 for 3 and -3.94 cm-1 for 4. All complexes 2-4 show biomimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers (Kcat) are 768, 1985, and 2309 h-1 for complexes 2-4, respectively, whereas for phenoxazinone synthase like activity, the turnover numbers are 3240, 3360, and 13 248 h-1 for complexes 2-4, respectively. This difference in catalytic efficiencies is attributed to the variations in structures of the complexes and formation of active NiII-MnII species in solution during catalysis. The mass spectral analyses suggest the probable intermediate formation and cyclic voltammetry measurement suggest the reduction of Ni(II) to Ni(I) during catalytic reaction. The very high catalytic efficiencies for aerial dioxygen activation of all these heterometallic complexes as well as the highest activity of 4 is attributed to the coordinatively unsaturated penta-coordinated geometry or hexa-coordinated geometry with a solvent water molecule around Mn(II).
- Mahapatra, Prithwish,Drew, Michael G. B.,Ghosh, Ashutosh
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- Vibrational spectra of 1,2-benzenedithiol, 2-aminothiophenol and 2-aminophenol and their SER spectra
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The Raman and infra-red spectra of 1,2-benzenedithiol, 2-aminothiophenol and 2-aminophenol are reported and assignments of fundamental modes are proposed.The Surface-Enhanced Raman Spectra (SRES) of these three ortho-disubstituted benzenes and 2-aminophenoxazone on gold and silver colloids are recorded.
- Griffith, William P.,Koh, Tse Yuen
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- Oxidation of 2-aminophenol with molecular oxygen and hydrogen peroxide catalyzed by water soluble metalloporphyrins
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5,10,15,20-Tetrakis-(p-sulfonatophenyl)porphinatocobalt(II) and 5,10,15,20-tetrakis-(p-sulfonatophenyl)porphinatomanganese(III) chloride have been used as catalysts for the oxidative coupling of 2-aminophenol to 2-aminophenoxazine-3-one with molecular oxygen and hydrogen peroxide. The effects of pH and concentration of catalysts, hydrogen peroxide and oxygen on the oxidation reaction and yield of 2-aminophenoxazine-3-one have been studied. The oxidation of 2-aminophenol with molecular oxygen catalyzed by cobalt(II) tetra(4-sulfophenyl)porphyrin involves a hydrogen atom abstraction from 2-aminophenol by cobalt(II) superoxo species. UV-vis analysis indicated that oxomanganese(IV) is the active species in the oxidation of 2-aminophenol with hydrogen peroxide and manganese(III)tetra(4-sulfophenyl)porphyrin.
- El-Khalafy, Sahar H.,Hassanein
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- Valence-Tautomerism-Driven Aromatic Nucleophilic Substitution in Cobalt-Bound Tetrabromocatecholate Ligands – Influence of Positive Charge at the Ligand Backbone on Phenoxazinone Synthase Activity
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The mononuclear CoIII complex [Co(Br3Cat-py)2(py)2]Cl·8H2O (1, py = pyridine, Br3pyCatH2 = 3,5,6-tribromo-4-pyridiniumcatechol) was synthesized through the reaction of CoCl2·6H2O with tetrabromocatechol in the presence of an excess of pyridine at elevated temperature. The solid-state structure was determined by X-ray crystallography, which disclosed the valence-tautomerism-induced aromatic nucleophilic substitution of the tetrabromocatecholate ligands by pyridine. A cyclic voltammetry study revealed the redox flexibility of both the transition-metal centre and the coordinated redox-active ligand in this complex. Moreover, 1 exhibits moderately strong catalytic activity and mimics the function of phenoxazinone synthase. A detailed kinetic study disclosed that the extra positive charges at the ligand backbone resulting from the substitution of the Br atoms by pyridyl groups could play an anchoring role for the stabilization of the complex–substrate intermediate. This process resembles those in biological systems, in which the extraordinary catalytic activities of metalloenzymes in various biochemical processes are associated with substrate recognition and the stabilization of the reactive intermediates through diverse supramolecular forces. DFT calculations at the M06-2X/6-31+G* level of theory were used to support the mechanistic aspects related to both the redox-driven aromatic nucleophilic substitution and the biomimetic catalysis.
- Panja, Anangamohan,Frontera, Antonio
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- Selective coordination of multidentate ligands in manganese(II) complexes: Syntheses, structures and phenoxazinone synthase mimicking activity
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The present report describes the syntheses, structures and catalytic activity mimicking the function of phenoxazinone synthase of four new mononuclear manganese(II) complexes, [Mn(L1)Cl2] (1), [Mn(L2)Cl2] (2), [Mn(L3)Cl2] (3) and [Mn(L4)Cl2]·H2O (4), derived from the multidentate ligands L1-L4, which are the 1:2 condensation products of triamines (or tetraamine) and 2-pyridinecarboxaldehyde (or 6-methyl-2-pyridinecarboxaldehyde). X-ray crystallography reveals the preferential coordination ability of all the ligands (cyclic isomers over the acyclic analogues) to a common metal center (Mn2+) and in one case (2) methanol addition across the -CN- bond. All the complexes show moderate phenoxazinone synthase activity and the experimental data suggest that a correlation can be drawn between E1/2 and Vmax of the complexes, namely the lower the E1/2 value the higher the catalytic activity. The effect of methyl substitution on the pyridine ring (in 3) on the matrix parameters and on the phenoxazinone synthase activity is also noticeable. The ESI-MS positive spectrum of a mixture of a representative complex (1 or 4) and o-aminophenol shows a peak corresponding to [Mn(L)(OAP)]+ (OAPH = o-aminophenol), suggesting that the catalytic activity proceeds through the formation of a stable complex-substrate intermediate.
- Panja, Anangamohan
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- Simple cyclodextrin aldehydes as excellent artificial oxidases
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Cyclodextrin based oxidases, with a ketone as functional group are well known as good artificial enzyme mimics (Fenger et al. Org Biomol Chem 7:933-943; Marinescu and Bols Angew Chem Int Ed 45:4590-4593; Bjerre et al. Eur J Org Chem 704-710; Marinescu et al. J Am Chem Soc 127:17578-17579). We here report a series of modified cyclodextrins, having aldehydes as functional groups. The aldehyde based artificial enzymes have, in most cases, better catalysis than the ketones, because of their powerful covalent binding of hydrogen peroxide. Among the modified cyclodextrins studied are mono and di aldehydes on the 6 positions, with or without methylated hydroxyl groups. The aldehyde functionality was also introduced close to the secondary side, by attaching ethoxy-2-al or propoxy-3-al to the 2 position. The modified cyclodextrins showed excellent enzymatic activity towards oxidation of different aminophenols, and 4-methoxy benzyl alcohol with hydrogen peroxide as a stoichiometric oxidant. Rate enhancements up to 4,600 were achieved for oxidation of 4-methoxy benzyl alcohol, where as oxidation of amines gave rate enhancements up to 3,400. The artificial oxidases catalyses oxidations under enzymatic conditions (water, pH 7, 25 °C), following Michaelis-Menten kinetics. To confirm the enzyme activity, inhibition studies with sodium naphthalene-2-sulfonate were carried out. These studies showed competitive inhibition of the enzymes, verifying the cyclodextrins enzyme like character.
- Fenger, Thomas Hauch,Bols, Mikael
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- Synthesis, structure, catechol oxidase and phenoxazinone synthase mimicking activity of a manganese(III) Schiff base complex [Mn(HL)2(CH3OH)2][Mn(HL)2(N3)2]
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An ionic coordination complex of manganese(III), [Mn(HL)2(CH3OH)2][Mn(HL)2(N3)2] (where H2L = 1-(5-hydroxy-3-oxapentyliminomethyl)-3-ethoxyphenol), has been synthesized. Elementa
- Sarkar, Nandita,Harms, Klaus,Chattopadhyay, Shouvik
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- Visible-light-mediated synthesis of substituted phenazine and phenoxazinone using eosin y as a photoredox catalyst
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This paper describes an efficient, sustainable, one-step procedure for synthesizing substituted phenazines and phenoxazinones from commercially available ortho-substituted aromatic amines with very good yield (≥80%) in water. The procedure uses eosin Y (EY) as a photoredox catalyst at room temperature (RT). The highly reactive o-quinone-diimine or o-quinone-imine intermediate was characterized by the HR-MS technique.
- Dhar, Basab Bijayi,Dhara, Ashish Kumar,Maity, Sayantan
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- Metal ionic size directed complexation in manganese(II) coordination chemistry: Efficient candidates showing phenoxazinone synthase mimicking activity
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The present report describes the syntheses and structural characterizations of two new mononuclear manganese(II) complexes, [Mn(L1)Cl 2]·2MeOH (1) and [Mn(L2)Cl2] (2), in which L1 and L2 are tetradentate ligands. Although the previous studies described that ligand L1 exclusively binds the metal centers (Fe2+, Ni2+ and Zn2+) in the acyclic isomeric form (Schiff dibasic) of the ligand, in the present investigation it selectively binds Mn2+ ion in its cyclic (hexahydropyrimidine) analogue during the complexation reaction as evidenced by X-ray crystallography. The structure of 2 is quite interesting as it shows that one arm of the Schiff dibasic form of the ligand has been hydrolyzed, suggesting that these types of ligands with the Schiff dibasic form are incapable of yielding the stable manganese(II) complexes. The metal ionic size directed hydrolysis of one arm of the ligand has been confirmed by IR spectral studies. Both the complexes are reactive towards the oxidation of o-aminophenol (OAPH), and their relative catalytic efficiencies can be clearly explained by considering the steric contribution from the ligands and the electrochemical responses of the metal center. From the experimental data, a nice correlation, wherein the lower the E1/2 value the higher the catalytic activity, can be drawn between E1/2 and Vmax of the complexes. The kinetics study exhibited a deuterium kinetic isotope effect in the catalytic oxidative coupling of two moles of OAPH by O2 as evidenced by the 1.6 times rate retardation in the deuterated solvent, suggesting hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo species. the Partner Organisations 2014.
- Panja, Anangamohan
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- Catalase, catecholase and phenoxazinone synthase-like activities of homodinuclear co(II), ni(II), cu(II) and zn(II) complexes including oxime group
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Homodinuclear (1) Co(II), (2) Ni(II), (3) Cu(II) and (4) Zn(II) metal complexes containing oxime group were tested for their catalase, catecholase and phenoxazinone synthase-like activity by volumetric and spectrophotometric procedures. Catalase-like acti
- G?rgülü, Güven?,Dede, Bülent
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- 5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II) supported on ion exchange resin as reusable and effective catalyst for the oxidative coupling of 2-aminophenol to 2-aminophenoxazine-3-one
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5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrinatocobalt(II) supported on Amberlite ion exchange resin showed good catalytic activity as heterogeneous catalyst for the biomimetic oxidative coupling of 2-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX). The reaction rate was found to fit a Michaelis-Menten kinetic model for saturation of catalyst site with increasing OAP concentration. Recycling of the Co(II)TPPS-resin system showed no loss of activity after six successive runs.
- Hassanein,El-Khalafy,Shendy
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- Kinetics and mechanism of the ferroxime(II)-catalysed biomimetic oxidation of 2-aminophenol by dioxygen. A functional phenoxazinone synthase model
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[Fe(Hdmg)2(MeIm)2] (1), referred to as ferroxime(II), is the precursor of a selective catalyst for the oxidative dehydrogenation of 2-aminophenol (Hap) to 2-amino-3H-phenoxazine-3-one (apx) by dioxygen under ambient conditions. The superoxoferroxime(III) species has been detected by ES-MS, and a 4-substituted 2-aminophenoxyl free radical by the ESR technique. The kinetics of the reaction was followed spectrophotometrically and by monitoring dioxygen uptake at constant pressure. According to the proposed mechanism, solvolysis of 1 is followed by O2 binding to afford a superoxoferroxime, which abstracts an H-atom from Hap in the rate-determining step via an H-bonded intermediate, generating the free radical. This is supported by the observed primary deuterium kinetic isotope effect of 2.63. The system studied is a functional phenoxazinone synthase model.
- Simandi, Tatiana M.,Simandi, Laszlo I.,Gyor, Miklos,Rockenbauer, Antal,Goemoery, Agnes
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- Observation of novel oxygen?oxygen interaction in supramolecular assembly of cobalt(iii) Schiff base complexes: a combined experimental and computational study
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Two mononuclear cobalt(iii) Schiff base complexes with azide [Co(L)(N3)(L′)] (1) and [Co(L)(N3)(L″)] (2) {where HL = 1-((2-(diethylamino)ethylimino)methyl)naphthalene-2-ol, HL′ = 2-hydroxy-1-naphthaldehyde and HL″ = acetylacetone} have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy and single crystal X-ray diffraction studies. Both complexes show mononuclear structures with azide as terminal coligand. Structural features have been examined in detail that reveal the formation of interesting supramolecular networks generated through non-covalent forces including hydrogen bonding, C-H?H-C and C-H/π interactions. These interactions have been studied energetically by means of theoretical DFT calculations. We have also analyzed the unexpected O?O interactions observed in one complex between the oxygen atoms of the coordinated aldehyde groups using several computational tools, including Bader's "atoms-in-molecules" (AIM) and natural bond orbital (NBO) analyses.
- Das, Mithun,Ghosh, Biswa Nath,Bauzá, Antonio,Rissanen, Kari,Frontera, Antonio,Chattopadhyay, Shouvik
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- Feed-back action of nitrite in the oxidation of nitrophenols by bicarbonate-activated peroxide system
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In this study it was found that the nitrite anion greatly increases the oxidation rate of the substituted phenols by the bicarbonate-activated peroxide (BAP) system at ambient temperature. This feed-back effect was investigated in the BAP oxidation of 2-amino-4-nitrophenol and 4-nitrophenol, where the kinetic analysis showed that the rate determining step was the elimination of a nitro group as nitrite. Complementary oxidation experiments with 2-aminophenol in BAP system, performed in the presence/absence of sodium nitrite confirmed the catalytic role of this anion. High concentrations of nitrite/BAP prevented formation of polymeric species and favoured the degradation to aliphatic fragments such as 3-oxobutanoic and acetic acid. Indirect evidence suggested in-situ generation of reactive oxygen species (ROS), other than hydroxyl, peroxyl and carbonate radicals, during the nitrite/BAP oxidation. Formation of additional ROS - peroxynitrite and nitrosoperoxycarbonate - may account the synergistic action of nitrite/BAP system. The estimated value of the apparent rate constant of the autocatalytic step for 2-amino-4-nitrophenol (kapp = (4.97 ± 0.19) × 103 M-3 s-1) demonstrates that fast degradation of this oxidation-resistant phenolic dye is feasible even in ambient conditions. These findings can be exploited for developing clean, cost-effective methods for the removal of phenolic dyes as alternative to current advanced oxidation processes.
- Puiu, Mihaela,Galaon, Toma,Bondil?, Luiza,R?ducan, Adina,Oancea, Dumitru
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- The first example of a centro-symmetrical bis(imido)-bridged dinuclear cobalt(iii) complex: Synthesis via oxidative dehydrogenation and phenoxazinone synthase activity
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A bis(imido)-bridged dinuclear cobalt(iii) complex, [Co2(amp) 2(μ-imp)2Cl2]Cl2·2H 2O (1) [amp = 2-aminomethylpyridine; imp = 2-iminomethylpyridine anion], was synthesized by the reaction of cobalt(ii) chloride with 2-aminomethylpyridine in the presence of alkaline hydrogen peroxide at room temperature. X-ray crystallography reveals that both the metal centres in the molecule are related to each other through an inversion centre, and the geometry of each of the CoIII ions is a distorted octahedral structure having a CoN5Cl coordination environment. The most important feature of the structure is the modification of half of the coordinated amines by the oxidative dehydrogenation process which involves double bridging in the complex cation. To the best of our knowledge, this is the first example of a bis(imido)-bridged dinuclear cobalt(iii) complex derived from metal-assisted oxidative dehydrogenation of the coordinated primary amine ligand. Complex 1 was found to be an excellent functional model for the phenoxazinone synthase, catalyzing the oxidative coupling of 2-aminophenol to the corresponding 2-aminophenoxazinone chromophore in dioxygen saturated methanol. The detailed kinetic investigations reveal that the phenoxazinone chromophore is produced via a potential complex-substrate intermediate.
- Panja, Anangamohan,Guionneau, Philippe
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- Catalytic aspects of a copper(II) complex: biological oxidase to oxygenase activity
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Abstract: A coper(II) complex, [Cu(dpa) 2(OAc)](ClO 4) (1) [dpa =2 , 2 ′-dipyridylamine; OAc = acetate], has been synthesized and crystallographically characterized. X-ray structure analysis revealed that this mononuclear Cu(II) complex crystallizes as a rare class of hexa coordination geometry named bicapped square pyramidal geometry with P2 1/ c space group. This copper complex displays excellent catalytic efficiency, k cat/ K M(h - 1) = 6.17 × 10 5 towards the oxidative coupling of 2-aminophenol (2-AP) to aminophenoxazin-3-one. Further, upon stoichiometric addition of copper(II) complex to 3,5-DTBC in presence of molecular oxygen in ethanol medium, the copper complex affords predominantly extradiol cleavage products along with a small amount of benzoquinone and a trace amount of intradiol cleavage products at a rate, k obs= 1.09 × 10 - 3min - 1, which provide substantial evidence for the oxygen activation mechanism. This paper presents a novel addition of a copper(II) complex having the potential to mimic the active site of phenoxazinone synthase and catechol dioxygenase enzymes with significant catalytic efficiency. Graphical Abstract : SYNOPSIS The mononuclear copper complex having unusual hexa coordination geometry exhibits significant catalytic efficiency, k cat/ K M(h - 1) = 6.17 × 10 5 towards oxidation of 2-aminophenol which predominantly produced extradiol cleavage products at a rate, k obs= 1.09 × 10 - 3min - 1 upon addition of 3,5-DTBC in presence of molecular oxygen. [Figure not available: see fulltext.].
- Chowdhury, Biswajit,Maji, Milan,Biswas, Bhaskar
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- Catalytic activation of dioxygen to hydroxyl radical and efficient oxidation of o-aminophenol by cobalt(II) ions in bicarbonate aqueous solution
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Increasing attention has been paid to the activation of the ideal oxidant O2 to reactive oxygen species for environmental pollutants transformation and complete degradation. In this work, the oxidation of o-aminophenol (OAP), a poor biodegradable intermediate, by simple Co 2+ ions in HCO3- aqueous solution with O 2 under ambient conditions was investigated. The results reveal that OAP is efficiently transformed to a less harmful compound 2-aminophenoxazine-3- one (APZ) by the Co2+-HCO3- system. HCO 3- is necessary for the reaction by promoting the protonation of the two-electron reduction species of O2 to produce H2O2. The metal-bound hydroxyl radical ( ?OH) generated from the intermediacy of H2O 2 contributes to APZ formation. Based on the analysis of electron spin resonance spin-trapping technologies, radical scavenging measurements and kinetics of APZ formation under different conditions, a possible pathway for ?OH radical formation and APZ production is proposed. This study can provide new insight on the mechanism of the molecular oxygen activation by simple metal complexes and their application on pollutant removal under mil reaction conditions.
- Li, Xiaoxia,Shi, Wei,Cheng, Qiang,Huang, Lianghua,Wei, Mingyu,Cheng, Long,Zeng, Qingfu,Xu, Aihua
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- Mononuclear cobalt(III) and iron(II) complexes with diimine ligands: Synthesis, structure, DNA binding and cleavage activities, and oxidation of 2-aminophenol
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Mononuclear cobalt(III) and iron(II) complexes with diimine ligands were synthesized and characterized by elemental analyses, spectroscopic and electrochemical techniques. Single crystal X-ray diffraction studies revealed that the metal ions in both complexes are situated in distorted octahedral environments comprised of six nitrogen atoms from three diimine ligands. Interaction of the complexes with calf thymus DNA was investigated through UV-Vis and fluorescence spectroscopic methods and viscosity measurements. These results suggest that both complexes preferably interact with CT-DNA through the grove binding mode. Moreover, both complexes are capable of promoting DNA cleavage in the presence of suitable activating agent(s). The nuclease activity is strongly suggested to be oxidative, possibly due to the involvement of a diffusible hydroxyl radical mechanism. Furthermore, the cobalt(III) complex has been found to be an excellent oxidant for oxidative coupling of 2-aminophenol to the phenoxazinone chromophore under aerobic conditions.
- Panja, Anangamohan
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- Ternary complexes containing Copper(II), L-Valinate and α, ?-bipyridyl or 1,10-phenanthroline: Synthesis, characterization, ligand substitution and oxidase biomimetic catalytic activity studies
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Ternary copper(II) complexes with the molecular formulae of [CuIILL′]X or [CuIILL′X]; L =L-Valinate; L′ = α, ?-bipyridyl or 1,10 - phenanthroline and X is Clˉ, Brˉ, NO3ˉ, AcOˉ, ?SO4 2? or ClO4ˉ were synthesized. Elemental and thermal analysis in addition to electrochemical (molar conductance and cyclic voltammetry), magnetic moment measurements as well spectral (FT-IR, UV–Vis and ESR) techniques were used to characterize the complexes. The spectroscopic results suggested square pyramidal and square planar geometries for the five- and four-coordinate complexes respectively. Powder X-ray diffraction spectral data along with the structure solution program Expo 2014 has been used for structural elucidation of the sulfato complexes 1 and 5. Stopped follow technique was employed to study the substitution of the nonelectrolytic coordinately counter anion ligand by using thiourea (TU) as a function of nucleophile and a biphasic process is proposed. An initial fast reaction is followed by a slower one and the initial one was found to be counter ion dependent. Bio-mimicking the multicopper oxidase enzyme such as catechol oxidase and phenoxazinone synthase is a further goal of the present study. Catalytic examinations displayed that the present complexes are promising candidates as functional mimic of the examined enzymes and the probable mechanistic catalytic sequences are discussed.
- Ramadan,Shaban,Ibrahim,El-Shami,Al-Harbi
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- Exclusive selectivity of multidentate ligands independent on the oxidation state of cobalt: Influence of steric hindrance on dioxygen binding and phenoxazinone synthase activity
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The present report describes the syntheses, characterizations, crystal structures and study of the phenoxazinone synthase activity of two peroxo-bridged dicobalt(iii) complexes, [Co2(L1) 2(μ-O2)](ClO4)4·2CH 3CN (1) and [Co2(L2)2(μ-O 2)](ClO4)4 (2), and three mononuclear cobalt(ii) complexes, [Co(L3)(CH3CN)](ClO 4)2 (3), [Co(L4)(H2O)](ClO 4)2 (4) and [Co(L5)(H2O)](ClO 4)2 (5), derived from the pentadentate ligands L 1-L5, which are the 1:2 condensation products of triamines and 2-acetylpyridine or 2-pyridinecarboxaldehyde (6-methyl-2- pyridinecarboxaldehyde). X-ray crystallography reveals exclusive selectivity of the acyclic Schiff dibasic form of the ligands over the heterocyclic analogues, and this selectivity is found to be insensitive to the oxidation state of cobalt. Other first row transition metals have been characterized in either form of the ligands in their complexes but it is specific for cobalt established in the present study. The pronounced effect of the methyl substitutions is observed from their crystal structures; substitution at imine-C does not have any significant influence on the peroxo-bridging but substitution at sixth position of pyridyl ring prevents the formation of peroxo-bridging, and both the steric and electronic factors play vital roles on such chemical diversity. All the complexes show the phenoxazinone synthase mimicking activity and the comparative catalytic activity has been explored. Although electrochemical behaviors of all the complexes are very similar, their relative catalytic activity mimicking the function of phenoxazinone synthase arises from the electronic and steric factors of the methyl substitution. This journal is the Partner Organisations 2014.
- Panja, Anangamohan
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- Synthesis and structure of a cobalt(III) complex containing pendant Schiff base ligand: Exploration of its catechol oxidase and phenoxazinone synthase like activity
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A new cobalt(III) complex, [Co(L-κ-N,N,O)(L-κ-N,O)(NCS)]·0.5H2O, with a pendant Schiff base {HL = 2((2-morpholinoethylimino)methyl)-6-ethoxyphenol} has been synthesized and characterized by elemental and several spectral analyses. Single crystal X-ray diffraction studies confirmed its structure. Extended supra-molecular assemblies were generated in the complex through weak noncovalent interactions. The complex was found to exhibit catechol oxidase and phenoxazinone synthase mimicking activity.
- Ghosh, Kousik,Drew, Michael G.B.,Chattopadhyay, Shouvik
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- Porphyrin cobalt(III) "Nitrene radical" reactivity; Hydrogen atom transfer from Ortho-YH substituents to the nitrene moiety of cobalt-bound aryl nitrene intermediates (Y = O, NH)
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In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier.
- Goswami, Monalisa,Rebreyend, Christophe,De Bruin, Bas
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- Structurally characterized mononuclear Mn(II) complex: Functional model for catecholase and phenoxazinone synthase activities
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Structurally characterized [Mn(L)2(OH2)2] (1) [L?=?3-methoxy-4-hydroxy benzaldehyde] with C2/c space group and distorted octahedral molecular geometry is found to show catecholase as well as phenoxazinone synthase activities in MeOH at room temperature. Each of the reactions with 1 as catalyst is found to be of first order with turn over numbers 5.98?×?102 and 3.15?×?102?h?1, respectively. Catalyst-substrate adduct as intermediate is trapped by mass spectrometry for both the activities.
- Kumar, Sarat Chandra,Ghosh, Ayon Kanti,Chen, Jhy-Der,Ghosh, Rajarshi
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- Subtle Structural Changes in (CuIIL)2MnII Complexes To Induce Heterometallic Cooperative Catalytic Oxidase Activities on Phenolic Substrates (H2L = Salen Type Unsymmetrical Schiff Base)
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A new Cu(II) complex of an asymmetrically dicondensed Schiff base (H2L = N-(2-hydroxyacetophenylidene)-N′-salicylidene-1,3-propanediamine) derived from 1,3-propanediamine, salicylaldehyde, and o-hydroxyacetophenone has been synthesized. Using this complex, [CuL] (1), as a metalloligand, two new trinuclear Cu-Mn complexes, [(CuL)2Mn(N3)(H2O)](ClO4)·H2O (2) and [(CuL)2Mn(NCS)2] (3), have been prepared. Single-crystal structural analyses reveal that complexes 2 and 3 both have the same bent trinuclear {(CuL)2Mn}2+ structural unit in which two terminal bidentate square-planar (CuL) units are chelated to the central octahedral Mn(II) ion. This structural similarity is also evident from the variable-temperature magnetic susceptibility measurements, which suggest that compounds 2 and 3 are both antiferromagnetically coupled with comparable exchange coupling constants (?21.8 and ?22.3 cm-1, respectively). The only difference between 2 and 3 lies in the coordination around the central Mn(II) ion; in 3, two SCN- groups are coordinated to the Mn(II), leaving a neutral complex, but in 2, one N3- group and one H2O molecule are coordinated to give a positively charged species. The presence of such a labile H2O coligand makes 2 catalytically active in mimicking two well-known polynuclear copper proteins, catecholase and phenoxazinone synthase. The turnover numbers (kcat) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 1118 and 6581 h-1, respectively, values which reflect the facility of the heterometallic catalyst in terms of both efficiency and catalytic promiscuity for aerial dioxygen activation. The mechanisms of these biomimetic oxidase reactions are proposed for the first time involving any heterometallic catalyst on the basis of mass spectral analysis, EPR spectroscopy, and cyclic voltammetry. The evidence of the intermediates indicates possible heterometallic cooperative activity where the substrates bind to a Mn(II) center and Cu(II) plays the role of an electron carrier for transformation of the phenolic substrates to their respective products with the reduction of aerial dioxygen.
- Mahapatra, Prithwish,Ghosh, Soumavo,Giri, Sanjib,Rane, Vinayak,Kadam, Ramakant,Drew, Michael G. B.,Ghosh, Ashutosh
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- Waste minimized synthesis of pharmaceutically active compounds: Via heterogeneous manganese catalysed C-H oxidation in flow
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Herein, we present our results on the development of a continuous flow protocol enabling the waste minimised synthesis of relevant pharmaceuticals and natural compounds. Heterogeneous manganese catalytic systems have been used in combination with molecular oxygen to promote the C-H oxidative coupling of 2-aminophenols, benzenetriols and o-phenylenediamines to access a variety of 2-aminophenoxazin-3-ones (2a-i) and related diaminophenazines (2j-k) and purpurogallin (2l) with minimal metal contamination. Making use of safe and green cyclopentyl methyl ether (CPME), this methodology allowed a fast synthesis of fully decorated molecular entities, preserving the stability of the heterogeneous catalyst which showed minimal metal leaching, with minimal waste production (low E-factor).
- Ferlin, Francesco,Luque Navarro, Pilar María,Gu, Yanlong,Lanari, Daniela,Vaccaro, Luigi
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- Temperature and pH Effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution
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The kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin- 3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows rst order kinetics according to the rate law - d[OAP]/dt = k'[OAP]. The experimental data, within the pH range 4-9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH = 9.85 within the range 25-50 °C and the corresponding activation energy was evaluated.
- Oancea, Dumitru,Puiu, Mihaela
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- Simple and efficient syntheses of 2-hydroxy-3H-phenoxazin-3-ones by aerobic oxidative cross-cyclocondensation in water
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A novel, simple and versatile synthetic approach that utilized natural renewable low-toxic gallic acid as an organocatalyst was developed for efficient aerobic oxidative cross-cyclocondensations of equimolar 2-aminophenols and 2-hydroxylphenols to afford various 2-hydroxy-phenoxazin-3-ones with moderate to high isolated yields at room temperature in water.
- Li, Wenhao,Duan, Wenxue,Tang, Qingxuan,Li, Zhan-Ting,Yang, Guanyu
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supporting information
p. 1136 - 1139
(2021/02/26)
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- Acyl Derivatives of Eudesmanolides To Boost their Bioactivity: An Explanation of Behavior in the Cell Membrane Using a Molecular Dynamics Approach
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Semisynthetic analogs of natural products provide an important approach to obtain safer and more active drugs and they can also have enhanced physicochemical properties such as persistence, cross-membrane processes and bioactivity. Acyl derivatives of different natural product families, from sesquiterpene lactones to benzoxazinoids, have been synthesized and tested in our laboratories. These compounds were evaluated against tumoral and nontumoral cell lines to identify selective derivatives with a reduced negative impact upon application. The mode of action of these compounds was analyzed by anti-caspase-3 assays and molecular dynamics simulations with cell membrane re-creation were also carried out. Aryl derivatives of eudesmanolide stand out from the other compounds and are better than current anticancer drugs such as etoposide in terms of selectivity and activity. Computational studies provide evidence that lipophilicity plays a key role and the 4-fluorobenzoyl derivative can pass easily through the cell membrane.
- Mejías, Francisco J. R.,Durán, Alexandra G.,Zorrilla, Jesús G.,Varela, Rosa M.,Molinillo, José M. G.,Valdivia, Manuel M.,Macías, Francisco A.
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p. 1297 - 1307
(2021/02/09)
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- TEMPO-catalyzed electrochemical dehydrogenative cyclocondensation of: O -aminophenols: Synthesis of aminophenoxazinones as antiproliferative agents
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The aminophenoxazinone core is widely prevalent in natural products, dyes and pharmaceutical molecules. We report here a TEMPO-catalyzed electrosynthetic method allowing the dehydrogenative cyclocondensation of o-aminophenols. This mild and sustainable method proceeds in the absence of stoichiometric oxidants and uses an easily available organo-electrocatalyst to access pharmaceutically valuable 2-aminophenoxazinones. Mechanistic studies indicate that the electrochemically generated TEMPO+ enables the oxidative radical homo-dimerization of o-aminophenols. The application of electrosynthesis provides an approach for the synthesis of pseudo-aminophenoxazinone alkaloids with improved structural diversification and bioactivities. This journal is
- Cai, Yun-Rui,Ji, Su-Hui,Ma, Zhi-Yuan,Shonhe, Chantale,Zhou, Jianmin
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supporting information
p. 8566 - 8570
(2021/11/17)
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- Phenoxazinone synthase-like catalytic activity of novel mono- And tetranuclear copper(ii) complexes with 2-benzylaminoethanol
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Three novel coordination compounds, [Cu(ca)2(Hbae)2] (1), [Cu(va)2(Hbae)2] (2) and [Cu4(va)4(bae)4]·H2O (3), have been prepared by self-assembly reactions of copper(ii) chloride (1 and 2) or tetrafluoroborate (3) and CH3OH (1 and 3) or CH3CN (2) solution of 2-benzylaminoethanol (Hbae) and cinnamic (Hca, 1) or valeric (Hva, 2 and 3) acid. Crystallographic analysis revealed that both 1 and 2 have mononuclear crystal structures, wherein the complex molecules are H-bonded forming extended supramolecular chains. The tetranuclear structure of 3 is based on the {Cu4(μ3-O)4} core, wherein the metal atoms are bound together by μ3 oxygen bridges from 2-benzylaminoethanol forming an overall cubane-like configuration. The strong hydrogen bonding in 1-3 leads to the joining of the neighbouring molecules into 1D chains. Concentration-dependent ESI-MS studies disclosed the equilibria between di-, tri- and tetranuclear species in solutions of 1-3. All three compounds act as catalysts for the aerobic oxidation of o-aminophenol to the phenoxazinone chromophore (phenoxazinone synthase-like activity), with the maximum reaction rates of 4.0 × 10-7, 2.5 × 10-7 and 2.1 × 10-7 M s-1 for 1, 2 and 3, respectively, supported by the quantitative yield of the product after 24 h. The dependence of the reaction rates on catalyst concentrations is evidence of reaction orders higher than one relative to the catalyst. Kinetic and ESI-MS data allowed us to assume that the tetranuclear species, originating from 1, 2 and 3 in solution, possess considerably higher activity than the species of lower nuclearity. Mechanistic and isotopic 18O-labelling experiments suggested that o-aminophenol coordinates to CuII species with the formation of reactive intermediates, while the oxygen from 18O2 is not incorporated into the phenoxazinone chromophore.
- Bondarenko, Olena E.,Nesterov, Dmytro S.,Nesterova, Oksana V.,Pombeiro, Armando J. L.
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p. 4710 - 4724
(2020/04/27)
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- Facile synthesis of a new Cu(ii) complex with an unsymmetrical ligand and its use as an O3 donor metalloligand in the synthesis of Cu(ii)-Mn(ii) complexes: Structures, magnetic properties, and catalytic oxidase activities
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A new, facile Cu(ii) template method has been employed for the unsymmetrical dicondensation of 1,2-ethylenediamine with salicylaldehyde and o-vanillin. The mononuclear complex, [CuL] (1), thus obtained, has been used as an O3 donor metalloligand for the synthesis of four new Cu(ii)-Mn(ii) complexes, [(CuL)MnCl2] (2), [(CuL)Mn(NO3)2(CH3OH)]n (3), {[(CuL)Mn(benz)(H2O)]2·(CuL)2(ClO4)2} (4) and [(CuL)Mn(benz)Cl]2 (5) (where benz = benzoate). Single-crystal structural analyses reveal that 2 is a dinuclear complex while complex 3 is polymeric with a repeating dinuclear [(CuL)Mn(NO3)2(CH3OH)] unit, linked via the nitrate ion. Both 4 and 5 are discrete tetranuclear complexes, where the dinuclear units [(CuL)Mn(benz)(H2O)] and [(CuL)Mn(benz)Cl] are connected by double benzoate and double chloride bridges, respectively. In complex 4, two monomeric [CuL] units are cocrystallized with the tetranuclear complex. An important difference in the structure of 4 from the other three complexes is that one solvent water molecule is coordinated to each Mn(ii) ion, which makes complex 4 catalytically very active towards mimicking catecholase and phenoxazinone synthase-like oxidation reactions. The turnover numbers (kcat) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 399 h-1 and 230 h-1, respectively. The evidence of the intermediate species in the mass spectra indicates possible heterometallic cooperation where the Mn(ii) center helps in substrate binding and Cu(ii) participates in the oxidation reactions with molecular oxygen. Cyclic voltammetry measurements suggest the reduction of Cu(ii) to Cu(i) during the catalytic process. Temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 2-5 are antiferromagnetically coupled with the exchange coupling constants (J) of J = -13.5 cm-1 and J = -13.5 cm-1 for 2 and 3, respectively, J1 = -12.6 cm-1 and J2 = -1.20 cm-1 for complex 4 and J1 = -13.24 cm-1 and J2 = 0.36 cm-1 for complex 5 as is expected from the Cu-O-Mn bridging angles.
- Dutta, Sabarni,Mayans, Júlia,Ghosh, Ashutosh
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p. 1276 - 1291
(2020/02/13)
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- Method for generating 2-aminophenoloxazine-3-ketone compound by catalyzing oxidation of molecular oxygen in water phase
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The invention provides a method for generating a 2-aminophenoloxazine-3-ketone compound by catalyzing oxidation of molecular oxygen in a water phase. According to the method, gallic acid is used as acatalyst, metal salts are used as a co-catalyst, and an o-aminophenol compound carries out reactions in a water phase in an oxygen or air environment in the presence of an alkali to generate the 2-aminophenoloxazine-3-ketone compound. The reaction is carried out in a water phase, and other organic solvents do not need to be added. The catalyst is simple, high in catalytic activity and high in reaction efficiency; and the method is simple in synthesis process, less in waste and environment-friendly, and has a wide industrial application prospect.
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Paragraph 0028-0030
(2020/06/16)
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- M[TPP]Cl (M = Fe or Mn)-Catalyzed Oxidative Amination of Phenols by Primary and Secondary Anilines
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Iron- and manganese-catalyzed para-selective oxidative amination of (4-R)phenols by primary and secondary anilines was developed. Depending on the identity of the R group, the products of this efficient reaction are either benzoquinone anils (C-N coupling) that are produced via a sequential oxidative amination/dehydrogenation (R = H), oxidative amination/elimination (R = OMe) steps, or N,O-biaryl compounds (C-C coupling) that are formed when R = alkyl through an oxidative amination/[3,3]-sigmatropic rearrangement (quinamine rearrangement) process.
- Pappo, Doron,Vershinin, Vlada
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supporting information
(2020/03/03)
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- A copper(II)-Schiff base complex: Synthesis, structural characterization and catalytic oxidative coupling of 2-aminophenol
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This present study reports the synthesis, X-ray structural analysis, supramolecular architectures and oxidative coupling of 2- A minophenol of a copper(II)-Schiff base complex, [Cu(L)](H2O) (1) containing a previously reported Schiff base, H2L = 2,2?-((1,2-phenylenebis(azanylylidene))bis(methanylylidene))diphenol. Crystal structure analysis reveals that Cu(II) centre adopts a square planar coordination geometry with R-3 space group. Investigation on self-assembled crystalline architecture displays that the aqua molecule in crystal lattice involves in significant intermolecular H-bonding to lead the formation of water mediated dimeric unit of Cu(II) complex. Noteworthy ??a?? interactions are operative strongly among the centroids of ligands to assemble Cu(II) complex in a zigzag 1D chain. The red highlighted spots in Hirshfeld surface suggests the active involvement of C-HaO, O-HaO types H-bonding and ??a?? interactions. The catalytic aspects of Cu(II) complex has been evaluated towards oxidative dimerization of 2-aminophenol (2-AP) in methanol and found high catalytic efficiency, kcat/KM (h-1) as 2.14×105. Mass spectrometry studies of the Cu(II) complex with 2-AP ensures that the course of catalysis undergoes through enzyme-substrate adduct formation in solution phase.
- Mahato, Shreya,Biswas, Bhaskar
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p. 849 - 856
(2020/12/05)
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- Biomimetic catalytic activity and structural diversity of cobalt complexes with N3O-donor Schiff base ligand
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This report describes the syntheses and structural characterizations of four new cobalt(III) compounds (1–4) derived from a tetradentate Schiff base ligand and their catalytic oxidation of different o-aminophenols in aerobic condition. X-ray crystal struc
- Jana, Narayan Ch.,Patra, Moumita,Brand?o, Paula,Panja, Anangamohan
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supporting information
p. 163 - 172
(2019/03/19)
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- Mixed azido/phenoxido bridged trinuclear Cu(ii) complexes of Mannich bases: Synthesis, structures, magnetic properties and catalytic oxidase activities
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Three similar Mannich base ligands viz. N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N′,N′-dimethyl-1,3-diaminopropane (H2L1), N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N′,N′-dimethyl-1,2-diaminoethane (H2L2) and N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N′,N′-diethyl-1,2-diaminoethane (H2L3) upon reaction with Cu(CH3COO)2·H2O produced dinuclear complexes [Cu2L21-3]. The reaction of each of these isolated dimeric species with Cu(ClO4)2·6H2O and NaN3 resulted in three new trinuclear complexes, [(CuL1)2(μ1,1-N3)2Cu(H2O)]·CH3OH (1), [(CuL2)2(μ1,1-N3)2Cu(H2O)]·CH3OH (2) and [(CuL3)2(μ1,1-N3)2Cu(H2O)]·2CH3OH (3), respectively. The complexes (1-3) have been characterized by elemental analysis and single crystal X-ray diffraction. In all three complexes, the central Cu(ii) ion is coordinated by two terminal [CuL] units through a phenoxido and an azido bridge. These are the first trinuclear Cu(ii) complexes of this type of Mannich base ligands. Magnetic susceptibility measurements showed intramolecular antiferromagnetic interactions with J = ;64.42, ;9.60 and ;4.54 cm;1 for 1, 2 and 3, respectively. All three complexes exhibited catecholase-like and phenoxazinone synthase-like activities towards the aerobic oxidation of 3,5-di-tert-butylcatechol and o-aminophenol, respectively. The turnover numbers (kcat) for the aerobic oxidation of 3,5-di-tert-butylcatechol are 568.8, 542.1 and 500.4 h;1 and those of o-aminophenol are 125.83, 118.9 and 114.7 h;1 for complexes 1-3, respectively. The X-band EPR spectroscopy and estimation of the produced hydrogen peroxide indicated that the aerobic oxidation of 3,5-di-tert-butylcatechol proceeded through the formation of a semiquinonate radical. The mechanism of phenoxazinone synthase-like activities is also proposed for trinuclear Cu(ii) catalysts with the help of mass spectral analysis.
- Das, Avijit,Bhattacharya, Kisholoy,Das, Lakshmi Kanta,Giri, Sanjib,Ghosh, Ashutosh
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supporting information
p. 9385 - 9399
(2018/07/29)
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- Crystal structure and bio-catalytic potential of oxovanadium(IV) Schiff base complexes derived from 2-hydroxy-4-(prop-2-yn-1-yloxy)benzaldehyde and alicyclic/aromatic diamines
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Syntheses, structures, electronic properties and bio-catalytic activities of oxovanadium(IV) complexes [VOL1,VOL2] containing N,O-donor Schiff base ligands (L1 = 2,2′-{cyclohexane-1,2-diylbis[nitrilo(E)methylylidene]}bis[5-(prop-2-yn-1-yloxy)phenol] and L2 = 2,2′-{1,2-phenylenebis[nitrilo(E)methylylidene]}bis[5-(prop-2-yn-1-yloxy)phenol]) are presented. The single crystal XRD analyses show distorted square pyramidal based geometry for VOL1 and VOL2. The structure and electronic properties of the complexes were analyzed using DFT and TD-DFT calculations. The topological analysis of the electron density was carried out to analyze the bonding nature in the complexes. The bio-relevant catalytic activities (catecholase, phenoxazinone synthase and haloperoxidases) of the complexes have been investigated. The X-band EPR studies show that the oxidation of 3,5-DTBC and 2-aminophenol catalyzed by VOL1 and VOL2 are due to the formation of ligand-centered radical pathway. DFT studies support the ligand-centered radical formation in the reduced metal complexes with significant elongation of the imine bond length.
- Balakrishnan, Chithiraivel,Neelakantan
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supporting information
p. 503 - 514
(2017/10/23)
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- Phenoxazinone synthase activity of two iron(III) complexes comprising the same Schiff base ligand: Biomimetic functional model and mechanistic investigation
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A new 4,4′-bipyridine (4,4′-byp) mediated 1D- polymeric FeIII complex (complex 1) of Schiff base ligand H2L, a 1:2 condensation product of 1,2-diaminopropane and salicylaldehyde, has been synthesized. Complex 1 is structurally characterized by single crystal X-ray diffraction. A phenoxo bridged dinuclear FeIII complex (complex 2) of analogous ligand has been synthesized also. Dioxygen activation in terms of Phenoxazinone synthase activity using o-aminophenol (OAPH) as a model substrate catalyzed by both the complexes are thoroughly investigated here. ESI-MS spectral study reveals that polynuclear complex 1 dissociates into mononuclear units while dissolve in methanol during catalytic study. The kinetic study illustrates that both the complexes have well competence towards o-aminophenol oxidation where dinuclear FeIII species demonstrate higher activity than mononuclear intermediate species. Important finding from the mass spectral and electrochemical study provide significant information of the mechanistic pathway of the functioning phenoxazinone synthase like activity of synthesized iron complexes.
- Chatterjee, Sourav,Sukul, Dipankar,Banerjee, Priyabrata,Adhikary, Jaydeep
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p. 105 - 112
(2018/02/14)
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- Synthesis, structural and magnetic characterizations of a dinuclear copper(II) complex with an (N,S,O) donor ligand: Catecholase and phenoxazinone synthase activities
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A new dinuclear Cu(II) complex (1) was synthesized and crystallographically characterized. Each of the Cu(II) centres has penta coordination and been found to adopt square pyramidal geometry. Variable temperature magnetic measurements showed that there is weak ferromagnetic interaction between the Cu(II) centres in 1. 1 shows catecholase as well as phenoxazinone synthase activities in different solvents. The turn over numbers for the catecholase activity were 4.02 × 103 h?1 (MeOH) and 9.57 × 103 h?1 (MeCN), and that of phenoxazinone synthase activity were 1.065 × 103 h?1 (MeOH), 2.13 × 102 h?1 (MeCN) and 2.844 × 103 h?1 (DCM).
- Ghosh, Ayon Kanti,Ali, Anzar,Singh, Yogesh,Purohit, Chandra Shekhar,Ghosh, Rajarshi
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supporting information
p. 156 - 163
(2018/02/20)
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- Estimating the energy of noncovalent interactions in a dioxovanadium(V) Schiff base complex: Exploration of its phenoxazinone synthase like activity
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A mononuclear dioxovanadium(V) Schiff base complex, [VO2(L)] {HL = 2-((diethylamino)ethyliminomethyl)-4-bromophenol} has been synthesized and characterized. The importance of noncovalent interactions in the solid state of the complex has been s
- Thakur, Snehasish,Sarkar, Nandita,Drew, Michael G.B.,Bauzá, Antonio,Frontera, Antonio,Chattopadhyay, Shouvik
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- Two mononuclear cobalt(III) complexes exhibiting phenoxazinone synthase activity
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Two mononuclear cobalt(III) complexes, namely [LCo(tmtp)(H2O)]ClO4?MeOH (1) (tmtp = tri(m-tolyl)phosphine) and [LCo(PPh3)(H2O)]PF6 (2), have been prepared from a polydentate ligand, N,N′-bis(3-methoxy
- Mahato, Mamata,Van Hecke, Kristof,Nayek, Hari Pada
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- Influence of anions and solvents on distinct coordination chemistry of cobalt and effect of coordination spheres on the biomimetic oxidation of o-aminophenols
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The present work reports the synthesis and structural characterizations of five new cobalt complexes (1–5) resulting from a N3O donor ligand, a Schiff base condensation product of N,N-dimethyldipropylenetriamine and 3-ethoxysalicylaldehyde, and their catalytic activity for the aerobic oxidation of various substrates, namely o-aminophenols and catechol. X-ray structural studies reveal that the Schiff base ligand can bind the metal centre either in the tetradentate fashion using all the available donor sites of the monoanionic deprotonated form (in 2 and 3) or in the tridentate fashion using the zwitterionic form of the Schiff base ligand with pendent quaternary amine nitrogen (in 1 and 4). Additionally, the monoanionic deprotonated ligand can bind the metal centre in the tridentate fashion (in 4 and 5) where the pendent tertiary amine nitrogen is involved in the intramolecular hydrogen bonding. All these adaptabilities associated with this triamine make it appealing candidate for exploration of the coordination chemistry with diverse structures. All complexes except compound 1 are efficient functional models for phenoxazinone synthase, and as expected the availability of labile sites at the first coordination sphere for the substrate, o-aminophenol, binding is the governing factor for higher catalytic activity in 2 and 3. Requisite of the hydrogen bond acceptor centre as well as proton abstraction centre at the second coordination sphere behind the facile oxidation of the substrate were also explored (reactivity of 1 versus 4 and 5). Moreover, the broader catalytic ability of these complexes was examined with substituted aminophenol and catechol as substrates, and the results were assembled and analysed. Furthermore, emphasis was given to get insight into the mechanistic pathway of functioning phenoxazinone synthase activity, well supported by the mass spectral study.
- Panja, Anangamohan,Jana, Narayan Ch.,Brand?o, Paula
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- Synthesis and characterization of three hetero-dinuclear complexes with CuO2M cores (M?=?Na, Hg): Exploration of their phenoxazinone synthase mimicking activity
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Three new hetero-dinuclear complexes, [CuL1Na(NCS)]·0.5H2O (1), [CuL1Na(OClO3)]·0.25H2O (2) and [CuL2HgCl2] (3) {where H2L1 = N,N′-bis(3-ethoxysalicylidene)
- Roy, Sourav,Drew, Michael G.B.,Chattopadhyay, Shouvik
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supporting information
p. 28 - 34
(2018/05/25)
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- One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities
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Two new cobalt(iii) tetrazolato complexes [Co(L1)(PTZ)(N3)] (1) and [Co(L2)(PTZ)(N3)] (2) {where H2L1 = 2((3-(methylamino)propylimino)methyl)-6-methoxyphenol, H2L2 = 2
- Ghosh, Kousik,Banerjee, Abhisek,Bauzá, Antonio,Frontera, Antonio,Chattopadhyay, Shouvik
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p. 28216 - 28237
(2018/08/16)
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- Synthesis and structural characterization of a cobalt(III) complex with an (N,S,O) donor Schiff base ligand: Catechol oxidase and phenoxazinone synthase activities
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A mononuclear Co(III) complex [CoL2]Cl (1) [HL = (E)-2-((3-(2-hydroxyethylthio)propylimino)methyl)phenol] was synthesized and its X-ray crystallographic characterization revealed a distorted octahedral geometry around the metal centre. 1 shows catechol oxidase as well as phenoxazinone synthase activities in different solvents. The turn over numbers for the catechol oxidase activity were 1.18 × 102 h?1 in MeOH and 1.80 × 103 h?1 in MeCN, and that of phenoxazinone synthase activity were 9.72 × 103 h?1 in MeOH.
- Ghosh, Ayon Kanti,Purohit, Chandra Shekhar,Ghosh, Rajarshi
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p. 194 - 201
(2018/09/10)
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- Rare azido and hydroxido bridged tetranuclear Co(ii) complexes of a polynucleating Mannich base ligand with a defect dicubane core: structures, magnetism and phenoxazinone synthase like activity
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Three novel tetranuclear cobalt(ii) complexes [Co4L2(μ1,1,1-N3)2(N3)2] (1), [Co4L2(μ3-OH)2(NCS)2]·4CH3CN (2) and [Co4L2(μ3-OH)2(NCSe)2]·2CH3CN (3) have been synthesized on reacting a Mannich base ligand, N,N′-dimethyl-N,N′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine (H2L), with cobalt(ii) acetate tetrahydrate in the presence of azide, thiocyanate and selenocynate salts, respectively. Single crystal X-ray structural analyses showed that these discrete tetranuclear Co(ii) complexes possess defect dicubane cores with μ1,1,1-N3 (for 1) and μ3-OH bridges (for 2 and 3). Magnetic susceptibility measurements showed prominent intramolecular ferromagnetic interactions for 1 (J1/kB = ?19 K, J2/kB = 38 K) and dominant antiferromagnetic interactions for 2 and 3 (J1/kB = 4.7 K, J2/kB = ?34 K for 2 and J1/kB = 4.4 K, J2/kB = ?12 K for 3). All three complexes (1-3) exhibited phenoxazinone synthase-like catalytic activity towards the aerobic oxidation of o-aminophenol. The turn over numbers (Kcat) for the aerobic oxidation of o-aminophenol were calculated to be 500.4, 508.9 and 511.2 h?1 for complexes 1-3, respectively. The mechanism of phenoxazinone synthase-like catalytic activity has also been proposed for these tetranuclear Co(ii) catalysts with the help of mass spectral analysis.
- Das, Avijit,Goswami, Soumyabrata,Ghosh, Ashutosh
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supporting information
p. 19377 - 19389
(2018/12/13)
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- Two new manganese(III) complexes with salicylaldimine Schiff bases: Synthesis, structure, self-assembly and phenoxazinone synthase mimicking activity
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Two new mononuclear manganese(III) complexes, [Mn(L1)2]ClO4(1) and [Mn(L2)(NCS)(H2O)]·DMSO (2), where HL1?=?3-(N,N-dimethylamino)propyliminomethyl-6-ethoxyphenol, H2L2
- Sarkar, Nandita,Das, Mithun,Chattopadhyay, Shouvik
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- Synthesis, characterization and phenoxazinone synthase mimicking activity of cobalt(III) Schiff base complexes
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Three new mononuclear cobalt(III) complexes, [Co(L1)2]ClO4·2H2O (1) {HL1?=?2((2(2-hydroxyethylamino)ethylimino)methyl)-6-methoxyphenol}, [Co(L2)(acna)(N3)] (2) {HL2?=?
- Ghosh, Kousik,Harms, Klaus,Chattopadhyay, Shouvik
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p. 162 - 175
(2016/12/16)
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- Mixed valence trinuclear cobalt (II/III) complexes: Synthesis, structural characterization and phenoxazinone synthase activity
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Three new mixed valence trinuclear Co(II/III) compounds [Co3L2(μ2-C6H5CO2?)2(CH3CN)2](ClO4?)2·(CH3CN)3 (1) [Co3LR2(μ2-C6H5CO2?)2(C6H5CO2?)2]·(CH3CN)2 (2) and [Co3LR2(μ2-C6H5CH[dbnd]CH–CO2?)2(C6H5CH[dbnd]CH–CO2?)2]·((CH3)2CO)2 (3) have been synthesized by reacting the di-Schiff base ligand [H2L] or its reduced analog [H2LR] (where H2L?=?N,N′-bis(salicylidene)-1,3-propanediamine) and (H2LR?=?N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium benzoate or sodium cinnamate. The complexes have been characterized by IR, UV–Vis and single crystal X-ray diffraction analyses. All the complexes are linear trinuclear species [CoIII–CoII–CoIII] in which two terminal octahedral CoIIIN2O2 cores coordinate to the central octahedral CoII ion through μ2-phenoxido oxygen atom and the bridging carboxylato ions. In addition, the complexes (2 and 3) derived from reduced Schiff base ligand have, rather unusually, a terminally coordinated carboxylato ion to CoIII, which is acetonitrile molecule in case of complex (1) with unreduced ligand. Complex 2 has been found to be an excellent functional model for the phenoxazinone synthase activity, in the aerial oxidation of 2-aminophenol to the corresponding 2-aminophenoxazine-3-one chromophore in acetonitrile solvent medium. Detailed kinetic data analysis of this oxidation reaction reveals a fairly high phenoxazinone synthase activity of 2 with kcat?=?153.60?h?1.
- Hazari, Alokesh,Das, Avijit,Mahapatra, Prithwish,Ghosh, Ashutosh
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- Importance of C-H?π interactions in stabilizing the: Syn / anti arrangement of pendant alkoxy side arms in two manganese(IV) Schiff base complexes: Exploration of catechol oxidase and phenoxazinone synthase like actIVities
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Two new octahedral manganese(iv) complexes [Mn(HL1)(L1)(NCS)]n (1) and [Mn(HL2)2(OH)Cl] (2) [where H2L1 = 1-(5-hydroxy-3-oxapentyliminomethyl)-3-ethoxyphenol and H2L2 = 1-(5-hydroxy-3-oxapentyliminomethyl)-4-chlorophenol] have been prepared and characterized. Unconventional C-H?π(SCN) interactions play a key role in stabilizing the unexpected syn arrangement of the ligand pending arms in 1, whereas conventional C-H?π(phe) interactions favour the anti arrangements in 2. The energetic features of these interactions have been studied by DFT calculations and characterized using Bader's theory of atoms in molecules in both complexes. Both complexes exhibit catechol oxidase and phenoxazinone synthase like activities.
- Sarkar, Nandita,Harms, Klaus,Frontera, Antonio,Chattopadhyay, Shouvik
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p. 8053 - 8065
(2017/08/14)
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- Synthesis, crystal structure, catecholase and phenoxazinone synthase activities of a mononuclear cobalt(III) complex containing in situ formed tridentate N-donor Schiff base
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Synthesis and structural characterization of a mononuclear cobalt(III) Schiff base complex is reported. It crystallizes with monoclinic crystal system with P21/n space group with a = 9.9793(4) ?, b = 28.2907(12) ? and c = 13.1233(6) ?, and β = 97.532(3)°. The compound is active to catecholase and phenoxazinone synthase activities in MeOH, and MeOH and MeCN solvents, respectively at room temperature. Each of the reactions was found to be of first order with reaction rate 8.08 × 10?3 min?1 (MeOH) for the catecholase activity and 1.05 × 10?3 min?1 (MeOH) and 3.82 × 10?3 min?1 (MeCN) for the phenoxazinone synthase activity. The turn over numbers for the catecholase activity is 5.02 × 103 h?1 (MeOH) and for the phenoxazinone synthase activity is 4.59 × 103 h?1 (MeOH) and 5.12 × 103 h?1 (MeCN). Substrate-catalyst adduct was tried to be trapped in each case using mass spectrometry.
- Maji, Ashis Kumar,Chatterjee, Arnab,Khan, Sumitava,Ghosh, Barindra Kumar,Ghosh, Rajarshi
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p. 821 - 827
(2017/06/23)
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- Variations of structures and phenoxazinone synthase-like activity of the complexes based on (CuII)2MnII node and dicyanamide spacer
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Three new heterometallic Cu(II)?Mn(II) complexes, [((CuL)2Mn)2(μ1,5-N(CN)2)(CH3CN)2](ClO4)3 (1), [(CuL)2Mn(N(CN)2)2]·(H2O) (2), and [(CuL)2Mn-(μ1,5-N(CN)2)2]n (3), have been synthesized using a Cu(II)metalloligand of an asymmetrically dicondensed Schiff base ligand (where H2L = N-α-methylsalicylidene-N′-salicylidene-1,3-propanediamine). Complex 1 was formed when the ratio of [CuL]/Mn(ClO4)2/NaN(CN)2 was 2:1:1, whereas complexes 2 and 3 were obtained with a 2:1:2 ratio of the same reactants on varying the reaction conditions. Single-crystal structural analyses reveal that complex 1 possesses a hexanuclear structure in which two (CuII)2MnII units are connected by one μ1,5-N(CN)2? bridge, 2 is a discrete trinuclear species with two terminally coordinated N(CN)2? ions to the Mn(II), whereas complex 3 is a polymeric form of 2 with μ1,5-N(CN)2? bridges between Cu(II) and Mn(II) centers. The thermal variations of dc magnetic susceptibilities suggest that all three complexes (1?3) are antiferromagnetically coupled with comparable exchange coupling constants (?25.4, ?22.8, and ?22.0 cm?1, respectively) which are expected from the Cu?O?Mn angles. All the complexes show biomemitic phenoxazinone synthase-like activity for the aerial oxidation of o-aminophenol to amino phenoxazinone. The turnover numbers (kcat) for the process are 4966, 2021, and 1107 h?1 for complexes 1?3 respectively. The mass spectral evidence on intermediates suggests that the cooperative activity of the two different metal ions, i.e., coordination of substrate to Mn(II) and shuttling of oxidation state of Cu between I and II, is possibly operative in the oxidation process. The highest catalytic activity of 1 is attributed to the presence of one coordinating solvent molecule to Mn(II).
- Mahapatra, Prithwish,Drew, Michael G. B.,Ghosh, Ashutosh
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p. 6809 - 6820
(2018/05/29)
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- Valence tautomerism induced nucleophilic ipso substitution in a coordinated tetrabromocatecholate ligand and diverse catalytic activity mimicking the function of phenoxazinone synthase
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Two new manganese(III) complexes, [pyH][Mn(Br4Cat)2(py)] (1) and [Mn(Br4Cat)(Br3pyCat)(py)2] (2), where py is pyridine, Br4CatH2 is tetrabromocatechol and Br3pyCatH2 is 3,5,6-tribromo-4-pyridiniumcatechol, derived from redox 'noninnocent' bromo-substituted catecholate ligands are reported. Both complexes were characterized by various spectroscopic techniques in addition to the single crystal X-ray crystallography, and the electrochemical behavior of these complexes was investigated by cyclic voltammetry. Variable temperature UV-vis spectral studies for complex 1 reveal an unprecedented observation in which a dramatic increase of the ligand-to-metal charge transfer band at 592 nm associated with concomitant change in color of the solution from olive-green to dark-green is noticed with increase in temperature. This unprecedented spectral feature is consistent with the formation of a new species 2 in which valence tautomerism induced aromatic nucleophilic substitution of a tetrabromocatecholate ligand by pyridine is observed. DFT calculations have been used to rationalize this unexpected result. To the best of our knowledge, the nucleophilic aromatic substitution of tetrabromosemiquinone by pyridine to generate this pyridinium-containing catecholate ligand is the first example of valence tautomerism induced nucleophilic ipso substitution by a nitrogen containing ligand. Although the electrochemical behavior of both complexes is similar, the probable role of a positive charge on the ligand backbone has been discussed in order to justify the significantly higher catalytic activity of complex 2 over complex 1.
- Panja, Anangamohan,Jana, Narayan Ch.,Patra, Moumita,Brand?o, Paula,Moore, Curtis E.,Eichhorn, David M.,Frontera, Antonio
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- Three mononuclear octahedral cobalt(III) complexes with salicylaldimine Schiff bases: Synthesis, characterization, phenoxazinone synthase mimicking activity and DFT study on supramolecular interactions
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Three mononuclear facial cobalt(III) complexes, [Co(L)2]ClO4 (1), [Co(L)(bzan)(N3)] (2) and [Co(L)(bzan)(NCS)] (3), {HL = 2-(3-(dimethylamino)propyliminomethyl)-6-ethoxyphenol and Hbzan = 1-benzoylacetone} were prepared an
- Ghosh, Kousik,Roy, Sumit,Ghosh, Anindya,Banerjee, Abhisek,Bauzá, Antonio,Frontera, Antonio,Chattopadhyay, Shouvik
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