1916-59-2Relevant articles and documents
Catalytic spectrophotometric determination of molybdenum
Mohamed,Ahmed,El-Shahat
, p. 31 - 40 (2002)
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.
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Nogami,T. et al.
, p. 3709 - 3714 (1975)
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Mechanistic studies of the tyrosinase-catalyzed oxidative cyclocondensation of 2-aminophenol to 2-aminophenoxazin-3-one
Washington, Courtney,Maxwell, Jamere,Stevenson, Joenathan,Malone, Gregory,Lowe, Edward W.,Zhang, Qiang,Wang, Guangdi,McIntyre, Neil R.
, p. 24 - 34 (2015)
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.
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Schlunegger et al.
, p. 1383,1388 (1976)
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Inactivation path during the copper (II) catalyzed synthesis of Questiomycin A from oxidation of 2-aminophenol
Olmazu, Cǎtǎlina,Puiu, Mihaela,Babaligea, Irina,Rǎducan, Adina,Oancea, Dumitru
, p. 74 - 80 (2012)
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.
Bis-benzimidazole diamide iron(III) complexes as mimics of phenoxazinone synthase
Bakshi, Ruchi,Kumar, Ravinder,Mathur, Pavan
, p. 140 - 145 (2012)
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.
The first alternating MnII-MnIII 1D chain: Structure, magnetic properties and catalytic oxidase activities
Ganguly, Sayantan,Kar, Paramita,Chakraborty, Maharudra,Ghosh, Ashutosh
, p. 9517 - 9529 (2018)
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
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
Sengupta, Swaraj,Naath Mongal, Binitendra,Das, Suman,Panda, Tarun K.,Mandal, Tarun K.,Fleck, Michel,Chattopadhyay, Shyamal K.,Naskar, Subhendu
, p. 1214 - 1233 (2018)
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.
Designing a biomimetic catalyst for phenoxazinone synthase activity using a mesoporous Schiff base copper complex with a novel double-helix morphology
Muthusami, Rubiga,Moorthy, Malathy,Irena, Kostova,Govindaraj, Anbarasu,Manickam, Chozhanathmisra,Rangappan, Rajavel
, p. 18608 - 18620 (2018)
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.
Methylene bridge regulated geometrical preferences of ligands in cobalt(iii) coordination chemistry and phenoxazinone synthase mimicking activity
Panja, Anangamohan,Shyamal, Milan,Saha, Amrita,Mandal, Tarun Kanti
, p. 5443 - 5452 (2014)
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.
Heterogeneous Manganese-Catalyzed Oxidase C?H/C?O Cyclization to Access Pharmaceutically Active Compounds
Ferlin, Francesco,Marini, Alberto,Ascani, Nicola,Ackermann, Lutz,Lanari, Daniela,Vaccaro, Luigi
, p. 449 - 454 (2020)
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.
Influence of the first and second coordination spheres on the diverse phenoxazinone synthase activity of cobalt complexes derived from a tetradentate Schiff base ligand
Panja, Anangamohan,Jana, Narayan Ch.,Brand?o, Paula
, p. 9784 - 9795 (2017)
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.
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
Mahapatra, Prithwish,Drew, Michael G. B.,Ghosh, Ashutosh
, p. 8338 - 8353 (2018)
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).
Oxidation of 2-aminophenol with molecular oxygen and hydrogen peroxide catalyzed by water soluble metalloporphyrins
El-Khalafy, Sahar H.,Hassanein
, p. 148 - 152 (2012)
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.
Selective coordination of multidentate ligands in manganese(II) complexes: Syntheses, structures and phenoxazinone synthase mimicking activity
Panja, Anangamohan
, p. 258 - 268 (2014)
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.
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]
Sarkar, Nandita,Harms, Klaus,Chattopadhyay, Shouvik
, p. 198 - 207 (2018)
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
Metal ionic size directed complexation in manganese(II) coordination chemistry: Efficient candidates showing phenoxazinone synthase mimicking activity
Panja, Anangamohan
, p. 37085 - 37094 (2014)
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.
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
Hassanein,El-Khalafy,Shendy
, p. 125 - 128 (2013)
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.
Observation of novel oxygen?oxygen interaction in supramolecular assembly of cobalt(iii) Schiff base complexes: a combined experimental and computational study
Das, Mithun,Ghosh, Biswa Nath,Bauzá, Antonio,Rissanen, Kari,Frontera, Antonio,Chattopadhyay, Shouvik
, p. 73028 - 73039 (2015)
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.
The first example of a centro-symmetrical bis(imido)-bridged dinuclear cobalt(iii) complex: Synthesis via oxidative dehydrogenation and phenoxazinone synthase activity
Panja, Anangamohan,Guionneau, Philippe
, p. 5068 - 5075 (2013)
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.
Catalytic activation of dioxygen to hydroxyl radical and efficient oxidation of o-aminophenol by cobalt(II) ions in bicarbonate aqueous solution
Li, Xiaoxia,Shi, Wei,Cheng, Qiang,Huang, Lianghua,Wei, Mingyu,Cheng, Long,Zeng, Qingfu,Xu, Aihua
, p. 297 - 304 (2014)
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.
Ternary complexes containing Copper(II), L-Valinate and α, ?-bipyridyl or 1,10-phenanthroline: Synthesis, characterization, ligand substitution and oxidase biomimetic catalytic activity studies
Ramadan,Shaban,Ibrahim,El-Shami,Al-Harbi
, p. 360 - 376 (2019)
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.
Synthesis and structure of a cobalt(III) complex containing pendant Schiff base ligand: Exploration of its catechol oxidase and phenoxazinone synthase like activity
Ghosh, Kousik,Drew, Michael G.B.,Chattopadhyay, Shouvik
, p. 23 - 33 (2018)
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.
Structurally characterized mononuclear Mn(II) complex: Functional model for catecholase and phenoxazinone synthase activities
Kumar, Sarat Chandra,Ghosh, Ayon Kanti,Chen, Jhy-Der,Ghosh, Rajarshi
, p. 49 - 54 (2017)
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.
Waste minimized synthesis of pharmaceutically active compounds: Via heterogeneous manganese catalysed C-H oxidation in flow
Ferlin, Francesco,Luque Navarro, Pilar María,Gu, Yanlong,Lanari, Daniela,Vaccaro, Luigi
, p. 397 - 403 (2020)
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).
Simple and efficient syntheses of 2-hydroxy-3H-phenoxazin-3-ones by aerobic oxidative cross-cyclocondensation in water
Li, Wenhao,Duan, Wenxue,Tang, Qingxuan,Li, Zhan-Ting,Yang, Guanyu
supporting information, p. 1136 - 1139 (2021/02/26)
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.
TEMPO-catalyzed electrochemical dehydrogenative cyclocondensation of: O -aminophenols: Synthesis of aminophenoxazinones as antiproliferative agents
Cai, Yun-Rui,Ji, Su-Hui,Ma, Zhi-Yuan,Shonhe, Chantale,Zhou, Jianmin
supporting information, p. 8566 - 8570 (2021/11/17)
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
