1916-59-2Relevant academic research and scientific papers
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.
A supramolecular-hydrogel-encapsulated hemin as an artificial enzyme to mimic peroxidase
Wang, Qigang,Yang, Zhimou,Zhang, Xieqiu,Xiao, Xudong,Chang, Chi K.,Xu, Bing
, p. 4285 - 4289 (2007)
(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.
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
Fukuda, Gen,Yoshitake, Noriko,Khan, Zia Ali,Kanazawa, Masao,Notoya, Yoko,Che, Xiao-Fang,Akiyama, Shin-Ichi,Tomoda, Akio,Chakrabarti, Subrata,Odawara, Masato
, p. 797 - 801 (2005)
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.
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.
Square planar versus square pyramidal copper(II) complexes containing N3O moiety: Synthesis, structural characterization, kinetic and catalytic mimicking activity
Shaban, Shaban Y.,Ramadan, Abd El-Motaleb M.,Ibrahim, Mohamed M.,Elshami, Fawzya I.,van Eldik, Rudi
, p. 608 - 616 (2019)
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.
Catalytic oxidation of 2-aminophenol to questiomycin A by dioxygen in the presence of cobaloxime derivatives. Free radical intermediates
Simandi,Barna,Korecz,Rockenbauer
, p. 717 - 720 (1993)
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.
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.
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
Banerjee, Saikat,Brand?o, Paula,Bauzá, Antonio,Frontera, Antonio,Barceló-Oliver, Miquel,Panja, Anangamohan,Saha, Amrita
, p. 11607 - 11618 (2017)
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.
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.
Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols
Dey, Suman Kr.,Mukherjee, Arindam
, p. 93 - 101 (2015)
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.
