- SYNTHESIS AND SOLVATOCHROMIC AND ACID-BASE REACTIONS OF A BETAINE AND SALTS OF 4-N-PYRIDINIUMCATECHOL
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Oxidation of catechol by phenyliodosyldiacetate in the presence of pyridine gives 4-N-pyridiniumcatechol salts whose structures are confirmed by an independent synthesis from 2,2-dimethyl-5-aminobenzodioxole.The spectroscopically determined ionization constants for the 4-N-pyridiniumcatechol cation depend on the nature of the buffer cation solution (sodium, ammonium, tetraethylammonium).The large solvatochromic shift in the long wavelength absorption band of the betaine of 4-N-pyridinium-catechol followed the empirical scale of solvent polarity ENT.Introduction of the N-pyridinium group in position 4 increases the acidity of the catechol by 2.7 pK units, which is an almost identical effect to the introduction of a 4-nitro group.However, the solvatochromism for the anion of 4-nitrocatechol is insignificant.The compounds were characterized by their 1H NMR and IR spectra.
- Neiland, O. Ya.,Kraupsha, I. L.,Gudele, I. Ya.
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- Cooperative effects for CYP2E1 differ between styrene and its metabolites
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1. Cooperative interactions are frequently observed in the metabolism of drugs and pollutants by cytochrome P450s; nevertheless, the molecular determinants for cooperativity remain elusive. Previously, we demonstrated that steady-state styrene metabolism by CYP2E1 exhibits positive cooperativity. 2. We hypothesized that styrene metabolites have lower affinity than styrene toward CYP2E1 and limited ability to induce cooperative effects during metabolism. To test the hypothesis, we determined the potency and mechanism of inhibition for styrene and its metabolites toward oxidation of 4-nitrophenol using CYP2E1 Supersomes and human liver microsomes. 3. Styrene inhibited the reaction through a mixed cooperative mechanism with high affinity for the catalytic site (67μM) and lower affinity for the cooperative site (1100μM), while increasing substrate turnover at high concentrations. Styrene oxide and 4-vinylphenol possessed similar affinity for CYP2E1. Styrene oxide behaved cooperatively like styrene, but 4-vinylphenol decreased turnover at high concentrations. Styrene glycol was a very poor competitive inhibitor. Among all compounds, there was a positive correlation with binding and hydrophobicity. 4. Taken together, these findings for CYP2E1 further validate contributions of cooperative mechanisms to metabolic processes, demonstrate the role of molecular structure on those mechanisms and underscore the potential for heterotropic cooperative effects between different compounds.
- Hartman, Jessica H.,Boysen, Gunnar,Miller, Grover P.
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- Potentiometric determination of arylsulfatase activity using a novel nitrocatechol sulfate PVC membrane sensor
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A novel potentiometric assay method for arylsulfatase enzyme is described based on measuring the initial reaction rate of hydrolysis of 4-nitrocatechol sulfate (4-NCS) substrate under optimized conditions. A monitoring sensor incorporating a PVC membrane with a nickel(II) bathophenanthroline-4-NCS ion-pair complex as electroactive material and 2-nitrophenyl phenyl ether as solvent mediator is developed and characterized. The sensor exhibits fast and stable linear response for 8 × 10-3-7.5 × 10-6 M 4-NCS with an anionic slope of 58.5 ± 0.2 mV/decade over the pH range 3-6. The sensor is used to follow up the decrease in a fixed concentration of 4-NCS (2 × 10-4 M) as a function of arylsulfatase activity at pH 5.6 and 37 °C. A linear relationship between the initial rate of substrate hydrolysis and enzyme activity holds for 0.2-2.4 IU/mL (SD 2%). Activity measurement of arylsulfatase enzyme isolated from camel liver gives results that compare favorably well with data obtained using the standard spectrophotometric assay method. Significant advantages over many of the previously described spectroscopic methods are offered by the proposed potentiometric technique.
- Hassan, Saad S. M.,Marzouk,Abdel-Fattah,Shouckry
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- Nitrocatechols versus nitrocatecholamines as novel competitive inhibitors of neuronal nitric oxide synthase: Lack of the aminoethyl side chain determines loss of tetrahydrobiopterin-antagonizing properties
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6-Nitrocatecholamines were recently described as novel neuronal nitric oxide synthase inhibitors competing with both L-arginine and tetrahydrobiopterin (BH4). We report now that simple nitrocatechols are also competitive inhibitors, lacking however BH4-antagonizing properties. It is argued that 6-nitrocatecholamines interact with the L-arginine- and BH4-binding sites through the nitrocatechol and aminoethyl moieties, respectively.
- Palumbo, Anna,Napolitano, Alessandra,D'Ischia, Marco
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- Anthracene Substituted Co (II) and Cu (II) phthalocyanines; Preparations, Investigation of Catalytical and Electrochemical Behaviors
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An approach to investigation of catalytical behaviors of Co (II) and Cu (II) phthalocyanines is reported that is based on changing any parameter to effect these behaviors. Towards this end, new anthracene substituted Co (II) and Cu (II) phthalocyanines were prepared and characterized spectroscopic methods. New cobalt (II) and copper (II) phthalocyanines were used as catalyst for oxidation of different phenolic compounds (such as 2,3-dichlorophenol, 4-methoxyphenol, 4-nitrophenol, 2,3,6-trimethylphenol) with different oxidants. Then, electrochemical characterization of cobalt (II) and copper (II) phthallocyanines were determined by using cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Although copper (II) phthalocyanine showed similar Pc based electron transfer processes, cobalt (II) phthalocyanine showed metal and ligand based reduction reactions as expected.
- Saka, Ece Tugba,Biyiklioglu, Zekeriya,Caglar, Yasemin
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- Enhanced electrochemical degradation of 4-Nitrophenol molecules using novel Ti/TiO2-NiO electrodes
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Removal of 4-Nitrophenol (4-NP) compounds by the electrochemical degradation method using Ti/TiO2-NiO electrodes was successfully conducted. This study aims to study the activity of Ti/TiO2-NiO electrodes in the electrocatalytic degradation of 4-NP as organic compound pollutants. Ti/TiO2-NiO preparation was carried out by the wet impregnation technique, then TiO2-NiO composites were sprayed on the surface of Titanium electrodes. The electrode was characterized by X-Ray Diffraction (XRD), a Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Cyclic Voltammetry (CV). A Diffractogram XRD of TiO2-NiO composites showed a characteristic peak of TiO2-NiO at 2θ = 33°. Meanwhile, analysis of the SEM surface morphology showed that NiO with an average particle size of 22.07 μm can be attached to the surface of the Ti/TiO2 plate. Electrocatalytic degradation of 4-NP compounds was found to be optimum at pH 11 and 80 min electrolysis time with a rate constant of 0.0373 min?1. The electrochemical degradation exhibited the percentage of removing 4-NP rate of >95% with good electrode measurement stability.
- Fadillah, Ganjar,Saleh, Tawfik A.,Wahyuningsih, Sayekti
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- Nonmicrobial nitrophenol degradation via peroxygenase activity of dehaloperoxidase-hemoglobin from amphitrite ornata
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The marine hemoglobin dehaloperoxidase (DHP) from Amphitrite ornata was found to catalyze the H2O2-dependent oxidation of nitrophenols, an unprecedented nonmicrobial degradation pathway for nitrophenols by a hemoglobin. Using 4-nitrophenol (4-NP) as a representative substrate, the major monooxygenated product was 4-nitrocatechol (4-NC). Isotope labeling studies confirmed that the O atom incorporated was derived exclusively from H2O2, indicative of a peroxygenase mechanism for 4-NP oxidation. Accordingly, X-ray crystal structures of 4-NP (1.87 ?) and 4-NC (1.98 ?) bound to DHP revealed a binding site in close proximity to the heme cofactor. Peroxygenase activity could be initiated from either the ferric or oxyferrous states with equivalent substrate conversion and product distribution. The 4-NC product was itself a peroxidase substrate for DHP, leading to the secondary products 5-nitrobenzene-triol and hydroxy-5-nitro-1,2-benzoquinone. DHP was able to react with 2,4-dinitrophenol (2,4-DNP) but was unreactive against 2,4,6-trinitrophenol (2,4,6-TNP). pH dependence studies demonstrated increased reactivity at lower pH for both 4-NP and 2,4-DNP, suggestive of a pH effect that precludes the reaction with 2,4,6-TNP at or near physiological conditions. Stopped-flow UV-visible spectroscopic studies strongly implicate a role for Compound I in the mechanism of 4-NP oxidation. The results demonstrate that there may be a much larger number of nonmicrobial enzymes that are underrepresented when it comes to understanding the degradation of persistent organic pollutants such as nitrophenols in the environment.
- McCombs, Nikolette L.,D'Antonio, Jennifer,Barrios, David A.,Carey, Leiah M.,Ghiladi, Reza A.
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- Gas-phase IR cross-sections and single crystal structures data for atmospheric relevant nitrocatechols
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The gas-phase IR absorption cross sections for 3-nitrocatechol, 5-methyl-3-nitrocatechol, 4-nitrocatechol and 4-methyl-5-nitrocatechol were evaluated using the ESC-Q-UAIC (the environmental simulation chamber made of quartz from the “Alexandru Ioan Cuza” University of Iasi, Romania) photoreactor facilities. Specific infrared absorptions and integrated band intensities in the range of 650–4000 cm?1 were investigated by long path gas-phase FT-IR technique. Two different addition methods (solid and liquid transfer methods) of nitrocatechols into the reactor were employed in these investigations. All investigated nitrocatechols were synthesized and characterized by X-ray diffraction spectroscopy techniques beside traditional nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy in order to evaluate their structure-properties relationship in gas and solid phase. This study reports for the first time the gas-phase infrared cross sections and the X-ray diffraction analysis for (methyl) nitrocatechols.
- Arsene, Cecilia,Bejan, Iustinian-Gabriel,Olariu, Romeo-Iulian,Roman, Claudiu,Roman, Tiberiu
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- Solar-Powered Whole-Cell P450 Catalytic Platform for C-Hydroxylation Reactions
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Photobiocatalysis is a green platform for driving redox enzymatic reactions using solar energy, not needing high-cost cofactors and redox partners. Here, a visible light-driven whole-cell platform for human cytochrome P450 (CYP) photobiocatalysis was developed using natural flavins as a photosensitizer. Photoexcited flavins mediate NADPH/reductase-free, light-driven biocatalysis by human CYP2E1 both in vitro and in the whole-cell systems. In vitro tests demonstrated that the photobiocatalytic activity of CYP2E1 is dependent on the substrate type, the presence of catalase, and the acid type used as a sacificial electron donor. A protective effect of catalase was found against the inactivation of CYP2E1 heme by H2O2 and the direct transfer of photo-induced electrons to the heme iron not by peroxide shunt. Furthermore, the P450 photobiocatalysis in whole cells containing human CYPs 1A1, 1A2, 1B1, and 3A4 demonstrated the general applicability of the solar-powered, flavin-mediated P450 photobiocatalytic system.
- Le, Thien-Kim,Kim, Jinhyun,Anh Nguyen, Ngoc,Huong Ha Nguyen, Thi,Sun, Eun-Gene,Yee, Su-Min,Kang, Hyung-Sik,Yeom, Soo-Jin,Beum Park, Chan,Yun, Chul-Ho
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p. 3054 - 3058
(2021/06/21)
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- Regioselective chemoenzymatic syntheses of ferulate conjugates as chromogenic substrates for feruloyl esterases
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Generally, carbohydrate-active enzymes are studied using chromogenic substrates that provide quick and easy color-based detection of enzyme-mediated hydrolysis. For feruloyl esterases, commercially available chromogenic ferulate derivatives are both costly and limited in terms of their experimental application. In this study, we describe solutions for these two issues, using a chemoenzymatic approach to synthesize different ferulate compounds. The overall synthetic routes towards commercially available 5-bromo-4-chloro-3-indolyl and 4-nitrophenyl 5-O-feruloyl-α-l-arabinofuranosides were significantly shortened (from 7 or 8 to 4-6 steps), and the transesterification yields were enhanced (from 46 to 73% and from 47 to 86%, respectively). This was achieved using enzymatic (immobilized Lipozyme TL IM from Thermomyces lanuginosus) transesterification of unprotected vinyl ferulate to the primary hydroxy group of α‐l‐arabinofuranosides. Moreover, a novel feruloylated 4-nitrocatechol-1-yl-substituted butanetriol analog, containing a cleavable hydroxylated linker, was also synthesized in 32% overall yield in 3 steps (convergent synthesis). The latter route combined the regioselective functionalization of 4-nitrocatechol and enzymatic transferuloylation. The use of this strategy to characterize type A feruloyl esterase from Aspergillus Niger reveals the advantages of this substrate for the characterizations of feruloyl esterases.
- Gherbovet, Olga,Ferreira, Fernando,Clément, Apolline,Ragon, Mélanie,Durand, Julien,Bozonnet, Sophie,O'Donohue, Michael J.,Fauré, Régis
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p. 325 - 333
(2021/03/15)
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- Carbon nanotubes as catalysts for wet peroxide oxidation: The effect of surface chemistry
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Three magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (selectively N-doped), synthesized by catalytic chemical vapor deposition, were modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). Both treatments lead to higher specific surface areas. The acid treatment results in more acidic surfaces, with higher amounts of oxygenated species being introduced on N-doped surfaces. Heat-treated samples are less hydrophilic than those treated with nitric acid, heat treatment leading to neutral or basic surfaces, only N-quaternary and N-pyridinic species being found by XPS on N-doped surfaces. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L?1) at atmospheric pressure, T = 50 °C and pH = 3, using a catalyst load of 2.5 g L?1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. The high temperature treatment enhanced significantly the activity of the CNTs towards CWPO, evaluated in terms of 4-NP and total organic carbon conversion, due to the increased hydrophobicity of their surface. In particular, E30HT and E10A20HT were able to remove ca. 100% of 4-NP after 8 h of operation. On the other hand, by treating the CNTs with HNO3, the activity of the less hydrophilic samples decreased upon increasing the concentration of surface oxygen-containing functionalities, whilst the reactivity generated inside the opened nanotubes improved the activity of the highly hydrophilic A30 N.
- Martin-Martinez, Maria,Machado, Bruno F.,Serp, Philippe,Morales-Torres, Sergio,Silva, Adrián M.T.,Figueiredo, José L.,Faria, Joaquim L.,Gomes, Helder T.
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p. 332 - 340
(2019/03/17)
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- Dearomatization of Electron-Deficient Phenols to ortho-Quinones: Bidentate Nitrogen-Ligated Iodine(V) Reagents
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Despite their broad utility, the synthesis of ortho-quinones remains a significant challenge, in particular, access to electron-deficient derivatives remains an unsolved problem. Reported here is the first general method for the synthesis of electron-deficient ortho-quinones by direct oxidation of phenols. The reaction is enabled by a novel bidentate nitrogen-ligated iodine(V) reagent, a previously unexplored class of compounds which we have termed Bi(N)-HVIs. The reaction is extremely general and proceeds with excellent regioselectivity for the ortho over para isomer. Functionalization of the ortho-quinone products was examined, resulting in a facile one-pot synthesis of catechols, as well as the incorporation of a variety of heteroatom nucleophiles. This method represents the first synthetic application of Bi(N)-HVIs and demonstrates their potential as a platform for the further development of highly reactive, but also highly tunable, I(V) reagents.
- Xiao, Xiao,Greenwood, Nathaniel S.,Wengryniuk, Sarah E.
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p. 16181 - 16187
(2019/11/05)
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- Cleavage of Catechol Monoalkyl Ethers by Aluminum Triiodide-Dimethyl Sulfoxide
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Using eugenol and vanillin as model substrates, a practical method is developed for the cleavage o -hydroxyphenyl alkyl ethers. Aluminum oxide iodide (O=AlI), generated in situ from aluminum triiodide and dimethyl sulfoxide, is the reactive ether cleaving species. The method is applicable to catechol monoalkyl ethers as well as normal phenyl alkyl ethers for the removal of methyl, ethyl, isopropyl, and benzyl groups. A variety of functional groups such as alkenyl, allyl, amide, cyano, formyl, keto, nitro, and halogen are well tolerated under the optimum conditions. Partial hydrodebromination was observed during the demethylation of 4-bromoguaiacol, and was resolved using excess DMSO as an acid scavenger. This convenient and efficient procedure would be a practical tool for the preparation of catechols.
- Sang, Dayong,Tian, Juan,Tu, Xiaodong,He, Zhoujun,Yao, Ming
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p. 704 - 712
(2019/01/23)
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- Preparation, characterization of new Co(II) and Cu(II) phthalocyanines and their catalytic performances in aerobic oxidation of substituted phenols
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Substituted phenol pollutants are produced as by products of many industrial processes. Aerobic oxidations for their degradation in the context of effluent treatment or environmental remediation often lack selectivity. In this work Co(II) and Cu(II) phthalocyanines-catalyzed approach is described that converts substituted phenols into less harmfull products. New cobalt(II) and copper(II) phthalocyanine complexes are used as catalyst for degradation of substituted phenols with different oxidants. The oxidation process exhibits remarkable selectivity and conversion owing to the fact that Co(II) and Cu(II) phthalocyanines work with high performance.
- Saka, Ece Tugba
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- Ether bond cracking method of phenylalkyl ether
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The invention discloses an ether bond cracking method of phenylalkyl ether. The method comprises the following steps: performing ether bond breaking reaction on phenylalkyl ether at -20 to reflux temperature in the presence of aluminium triiodide and dimethyl sulfoxide, thereby generating phenol and derivatives thereof. The method disclosed by the invention is mild in condition, simple and convenient for operation, high in yield, and extensive in applicable phenylalkyl ether range.
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Paragraph 0146-0148
(2018/11/26)
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- Rapid photocatalytic degradation of nitrobenzene under the simultaneous illumination of UV and microwave radiation fields with a TiO2 ball catalyst
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To use the microwave/ML/TiO2 hybrid system as an advanced treatment of nitrobenzene (NB), a series of experiments were performed to examine the effects of microwave irradiation and auxiliary oxidants. The degradation of NB was carried out using different combinations of five-unit treatment techniques. The NB degradation rate increased with increasing microwave intensity. The circulation fluid velocity, concentration of H2O2, and the rate of O2 gas injection showed the highest rate of degradation under optimal conditions. A significant synergistic effect was observed when H2O2 addition was combined with the microwave/ML/TiO2 hybrid process.
- Jeong, Sangmin,Lee, Heon,Park, Hyunwoong,Jeon, Ki-Joon,Park, Young-Kwon,Jung, Sang-Chul
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- Sodium perborate/NaNO2/KHSO4-triggered synthesis and kinetics of nitration of aromatic compounds
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Sodium perborate (SPB) was used as efficient green catalyst for NaNO2/KHSO4-mediated nitration of aromatic compounds in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds was achieved under both conventional and solvent-free microwave conditions. Reaction times were comparatively shorter in the microwave-assisted than conventional reaction. The reaction kinetics for nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [Phenol], [NaNO2], and [SPB]. Reaction rates accelerated with introduction of electron-donating groups but retarded with electron-withdrawing groups. Kinetic results did not fit well quantitatively with Hammett’s equation. Observed deviations from linearity were addressed in terms of exalted Hammett’s constants (σˉ or σeff), para resonance interaction energy (ΔΔGp) parameter, and Yukawa–Tsuno parameter (r). This term provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive) in its transition state. The observed negative entropy of activation (?ΔS#) suggests greater solvation and/or cyclic transition state before yielding products.
- Rajanna,Muppidi, Suresh,Pasnoori, Srinivas,Saiprakash
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p. 6023 - 6038
(2018/09/21)
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- New Co(II) and Cu(II) Phthalocyanine Catalysts Reinforced by Long Alkyl Chains for the Degradation of Organic Pollutants
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Abstract: The need to develop sustainable, low-cost, earth abundant catalyst is becoming paramount for overcoming environmental problems. Toward this goal, new cobalt(II) and copper(II) phthalocyanine complexes used as catalyst for degradation of organic pollutants (such as 2,3-dichlorophenol, 4-methoxyphenol, 4-nitrophenol, 2,3,6-trimethylphenol) with different oxygen source. This catalytic system with these complexes showed high conversion rates for degradation of organic pollutants and could easily be recovered by recycling reactions. Graphical Abstract: [Figure not available: see fulltext.].
- Saka, Ece Tugba,?a?lar, Yasemin
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p. 1471 - 1477
(2017/05/17)
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- A phenyl alkyl ether ether linkage breaking method (by machine translation)
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The invention discloses a phenyl alkyl ether ether linkage breaking method, the method is: in the organic solvent, in the presence of a mineral acid and the aluminium triiodide scavenging agent under the conditions of, phenyl ether in the - 20 °C to reflux temperature lower ether linkage breaking reaction, generating phenol and its derivatives. The mild conditions, the operation is simple, and the yield is high, the applicable phenyl ether range is wide. (by machine translation)
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Paragraph 0110-0112
(2018/04/01)
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- Carbodiimides as Acid Scavengers in Aluminum Triiodide Induced Cleavage of Alkyl Aryl Ethers
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A practical procedure for the cleavage of alkyl aryl ethers containing labile functional groups has been developed using aluminum triiodide as the ether cleaving reagent. Carbodiimides, typically used as dehydration reagents for the coupling of amines and carboxylic acids to yield amide bonds, are found to be effective hydrogen iodide scavengers that prevent acid-labile groups from deterioration. The method is applicable to variant alkyl aryl ethers such as eugenol, vanillin, ortho -vanillin and methyl eugenol. Suitable substrates are not limited to alkyl o -hydroxyphenyl ethers.
- Sang, Dayong,Wang, Jiahui,Zheng, Yun,He, Jianyuan,Yuan, Caili,An, Qing,Tian, Juan
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p. 2721 - 2726
(2017/06/13)
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- Ether bond breakage method for phenylalkyl ethers
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The invention discloses an ether bond breakage method for phenylalkyl ethers. The method comprises the step: subjecting the phenylalkyl ethers to an ether bond breakage reaction at the temperature of -20 DEG C to reflux temperature in an organic solvent in the presence of aluminum triiodide and carbodiimide, so as to produce phenols and derivatives thereof. The method is moderate in conditions, simple and convenient in operation, high in yield and wide in applicable phenylalkyl ether range.
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Paragraph 0184-0186
(2017/07/19)
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- Polypeptides having peroxygenase activity and polynucleotides encoding same
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The present invention relates to isolated polypeptides having peroxygenase activity, and polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.
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Page/Page column 31
(2016/08/07)
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- Polypeptides having peroxygenase activity and polynucleotides encoding same
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The present invention relates to isolated polypeptides having peroxygenaseactivity, and polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.
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Page/Page column 32-33
(2016/08/29)
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- Identification and Structural Characterization of Three New Metabolites of Bupropion in Humans
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Bupropion is a widely used antidepressant and the recommended CYP2B6 probe drug. However, current understanding of bupropion elimination pathways is limited. Bupropion has three active circulating metabolites, OH-bupropion, threohydrobupropion, and erythrohydrobupropion, but together with bupropion these metabolites and their conjugates in urine represent only 23% of the dose, and the majority of the elimination pathways of bupropion result in uncharacterized metabolites. The aim of this study was to determine the structures of the uncharacterized bupropion metabolites using human clinical samples and in vitro incubations. Three new metabolites, 4′-OH-bupropion, erythro-4′-OH-hydrobupropion, and threo-4′-OH-hydrobupropion, were detected in human liver microsome incubations and were isolated from human urine. The structures of the metabolites were confirmed via comparison of UV absorbance, NMR spectra, and mass spectral data to those of the synthesized standards. In total, these metabolites represented 24% of the drug related material excreted in urine.
- Sager, Jennifer E.,Choiniere, John R.,Chang, Justine,Stephenson-Famy, Alyssa,Nelson, Wendel L.,Isoherranen, Nina
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supporting information
p. 791 - 796
(2016/08/24)
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- Photocatalytic activity of TiO2 supported SiO2-Al2O3 aerogels prepared from industrial fly ash
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A ternary composite of TiO2 and a SiO2-Al2O3 aerogel with good photocatalytic activity was prepared by a simple sol-gel method with TiO2 nanoparticles and SiO2-Al2O3 aerogels derived from industrial fly ash. The structural features of the TiO2/SiO2-Al2O3 aerogel composite were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, gas adsorption measurements and diffuse reflectance UV-visible spectroscopy. The optimal conditions for photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP), included an initial DNBP concentration of 0.167 mmol/L at pH = 4.86 with a catalyst concentration of 6 g/L, under visible light irradiation for 5 h. A plausible mechanism is proposed for the photocatalytic degradation of DNBP. Our composite showed higher photocatalytic activity for DNBP degradation than that of pure TiO2. This indicates that this material can serve as an efficient photocatalyst for degradation of hazardous organic pollutants in wastewater.
- Wang, Hui-Long,Qi, Hui-Ping,Wei, Xiao-Na,Liu, Xiao-Yu,Jiang, Wen-Feng
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p. 2025 - 2033
(2016/12/09)
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- Role of Nitrogen Doping on the Performance of Carbon Nanotube Catalysts: A Catalytic Wet Peroxide Oxidation Application
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Four magnetic carbon nanotube (CNT) samples (undoped, completely N-doped, and two selectively N-doped) were synthesized by chemical vapor deposition. The materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L?1). Relatively mild operating conditions were considered (atmospheric pressure, T=50 °C, pH 3), using a catalyst load of 2.5 g L?1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. N-doping was identified to influence considerably the CWPO performance of the materials. In particular, undoped CNTs, with a moderate hydrophobicity, favor the controllable and efficient decomposition of H2O2 into highly reactive hydroxyl radicals (HO.), thus showing high catalytic activity for 4-NP degradation. On the other hand, the completely N-doped catalyst, fully hydrophilic, favors a quick decomposition of H2O2 into nonreactive O2 and H2O species. The selectively N-doped amphiphilic catalysts, that is, hybrid structures containing undoped sections followed by N-doped ones, provided intermediate results, namely, a higher N content favored H2O2 decomposition towards nonreactive H2O and O2 species, whereas a lower N content resulted in the formation of HO., increasing 4-NP mineralization. Catalyst stability and reusability were also investigated by consecutive CWPO runs.
- Martin-Martinez, Maria,Ribeiro, Rui S.,Machado, Bruno F.,Serp, Philippe,Morales-Torres, Sergio,Silva, Adrián M. T.,Figueiredo, José L.,Faria, Joaquim L.,Gomes, Helder T.
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p. 2068 - 2078
(2016/07/07)
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- Effect of viscosity on photodegradation rates in complex secondary organic aerosol materials
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This work explores the effect of environmental conditions on the photodegradation rates of atmospherically relevant, photolabile, organic molecules embedded in a film of secondary organic material (SOM). Three types of SOM were studied: α-pinene/O3/
- Hinks, Mallory L.,Brady, Monica V.,Lignell, Hanna,Song, Mijung,Grayson, James W.,Bertram, Allan K.,Lin, Peng,Laskin, Alexander,Laskin, Julia,Nizkorodov, Sergey A.
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p. 8785 - 8793
(2016/04/09)
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- Tertiary Butyl Nitrite Triggered Nitration of Phenols: Solvent- and Structure-Dependent Kinetic Study
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Nitration of phenols with tertiary butyl nitrite (TBN) obeyed second-order kinetics with a first-order dependence on [TBN] and [phenol] under acid-free conditions. Reaction rates were significantly altered by a change in the dielectric constant and other physical properties of solvent. The rate of nitration increased with an increase in temperature (303-323 K) in different solvent media (acetonitrile, dichloroethane, CCl4, dimethyl formamide (DMF), and toluene). The rates of nitration (log k) could not fit into either Amis or Kirkwood plots [log k' vs. (1/D) or [(D - 1)/(2D + 1)], but the trends were better explained by the basic form of multivariate linear solvent energy relationships (MLSER) suggested by the Koppel and Palm approach on the one hand and the Kamlet and Taft approach on the other hand. These observations probably substantiate that cumulative contributions of basic solvent parameters (equilibrium as well as frictional solvent effects) and solvent-solute interactions for solvation of transition state during nitration of phenols. Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups. Accordingly, the reactivity of structurally different phenols was found to follow the following sequence: p-OH > p-MeO > p-Me > H > m-Me > p-Cl > p-Br > m-Cl > p-NO2 > m-OH. The results are interpreted by Hammett's theory of linear free energy relationship. The reaction constant (Hammett's ρ) is a measure of the sensitivity of the reaction toward the electronic effects of the substituent. The rho (ρ) values obtained from the present experiments are fairly large negative values (ρ CH3) versus σ? or, Es or combined Taft's relationship. However, Charton's MLRA of the log k with polar, resonance, steric, hydrophobicity, and molar refractivity showing a very good linear relationship was obtained. It is of interest to note that when log kexp values are correlated with log kcal a perfect linearity is obtained with a correlation coefficient of unity, indicating the consonance between experimental and calculated rate constants in the present work.
- Kumar, M. Satish,Rajanna,Venkateswarlu,Rao, K. Lakshman
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p. 171 - 196
(2016/04/09)
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- p-Hydroxyphenylacetate 3-Hydroxylase as a Biocatalyst for the Synthesis of Trihydroxyphenolic Acids
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Trihydroxyphenolic acids such as 3,4,5-trihydroxycinnamic acid (3,4,5-THCA) 4c and 2-(3,4,5-trihydroxyphenyl)acetic acid (3,4,5-THPA) 2c are strong antioxidants that are potentially useful as medicinal agents. Our results show that p-hydroxyphenylacetate (HPA) 3-hydroxylase (HPAH) from Acinetobacter baumannii can catalyze the syntheses of 3,4,5-THPA 2c and 3,4,5-THCA 4c from 4-HPA 2a and p-coumaric acid 4a, respectively. The wild-type HPAH can convert 4-HPA 2a completely into 3,4,5-THPA 2c within 100 min (total turnover number (TTN) of 100). However, the wild-type enzyme cannot efficiently synthesize 3,4,5-THCA 4c. To improve the efficiency, the oxygenase component of HPAH (C2) was rationally engineered in order to maximize the conversion of p-coumaric acid 4a to 3,4,5-THCA 4c. Results from site-directed mutagenesis studies showed that Y398S is significantly more effective than the wild-type enzyme for the synthesis of 3,4,5-THCA 4c; it can catalyze the complete bioconversion of p-coumaric acid 4a to 3,4,5-THCA 4c within 180 min (TTN ～ 23 at 180 min). The yield and stability of 3,4,5-THPA 2c and 3,4,5-THCA 4c were significantly improved in the presence of ascorbic acid. Thermostability studies showed that the wild-type C2 was very stable and remained active after incubation at 30, 35, and 40 °C for 24 h. Y398S was moderately stable because its activity was retained for 24 h at 30 °C and for 15 h at 35 °C. Transient kinetic studies using stopped-flow spectrophotometry indicated that the key improvement in the reaction of Y398S with p-coumaric acid 4a lies within the protein-ligand interaction. Y398S binds to p-coumaric acid 4a with higher affinity than the wild-type enzyme, resulting in a shift in equilibrium toward favoring the productive coupling path instead of the path leading to wasteful flavin oxidation.
- Dhammaraj, Taweesak,Phintha, Aisaraphon,Pinthong, Chatchadaporn,Medhanavyn, Dheeradhach,Tinikul, Ruchanok,Chenprakhon, Pirom,Sucharitakul, Jeerus,Vardhanabhuti, Nontima,Jiarpinitnun, Chutima,Chaiyen, Pimchai
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p. 4492 - 4502
(2015/08/18)
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- Degradation of p-nitrophenol using CuO/Al2O3 as a Fenton-like catalyst under microwave irradiation
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CuO/Al2O3 was synthesized successfully by the impregnation-deposition method and used as a heterogeneous catalyst in a microwave assisted Fenton-like process (MW/FL). The morphology and physico-chemical properties of the CuO/Al2O3 catalyst were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. The degradation of p-nitrophenol (PNP) was investigated by different processes, including microwave irradiation (MW) alone, hydrogen peroxide (H2O2) oxidation under microwave irradiation without the catalyst (MW/H2O2), a Fenton-like (FL) process, a MW/FL process and a thermally-assisted Fenton-like (TH/FL) process. The results showed that the CuO/Al2O3 catalyzed MW/FL could generate more hydroxyl radicals (OH) and remove PNP more effectively compared to other processes. The effects of initial pH, dosage of H2O2 and catalyst, microwave power and radiation time, and PNP concentration on the removal efficiency were also studied. The results showed that 93% removal efficiency of PNP was obtained within 6 min under optimized conditions. Moreover, the catalyst had a good stability and reusability, thus expanding the scope of non-iron based catalysts in the Fenton-like reactions.
- Pan, Weiqian,Zhang, Guangshan,Zheng, Tong,Wang, Peng
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p. 27043 - 27051
(2015/03/30)
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- H2O2 in WEB: a highly efficient catalyst system for the Dakin reaction
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Without using any transition metal catalyst, ligand, base, toxic or hazardous reagent, additives/promoters and organic solvent, green Dakin reactions have been successfully carried out by using H2O2 in a natural feedstock extract. The reaction proceeds in neat 'Water Extract of Banana' (WEB) at room temperature under aerobic conditions in very short reaction times and, therefore, it is an evergreen and environmentally sound alternative to the existing protocols for the Dakin reaction. In our system, the reaction was found to afford excellent yield for the desired product with different electron-withdrawing and electron-donating hydroxylated benzaldehydes.
- Saikia, Bishwajit,Borah, Parinita,Barua, Nabin Chandra
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supporting information
p. 4533 - 4536
(2015/09/15)
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- A new avenue to the Dakin reaction in H2O2-WERSA
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We have developed a novel protocol to realize the Dakin reaction in a more greener way. In fact, by the use of H2O2-WERSA, we can oxidize aromatic arylaldehydes to phenols at room temperature. It is remarkable that the catalytic system does not require activation or any toxic ligand, additive/promoter, transition metal catalyst, base, organic solvent and so on. A range of substituted hydroxylated benzaldehydes were screened to investigate the scope of this protocol.
- Saikia, Bishwajit,Borah, Parinita
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p. 105583 - 105586
(2015/12/30)
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- A general approach towards catechol and pyrogallol through ruthenium- and palladium-catalyzed C-H hydroxylation by weak coordination
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An efficient ruthenium(II)- and palladium(II)-catalyzed C-H hydroxylation of aryl carbamates has been developed for the facile synthesis of catechols and pyrogallols. The reaction demonstrates excellent reactivity, regio- and chemoselectivity, good functional group compatibility and high yields. The practicality of this method has been proved by a gram-scale synthesis.
- Yang, Xinglin,Sun, Yonghui,Chen, Zhang,Rao, Yu
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p. 1625 - 1630
(2014/06/09)
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- A 1H NMR study of the specificity of α-l- arabinofuranosidases on natural and unnatural substrates
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Background The detailed characterization of arabinoxylan-active enzymes, such as double-substituted xylan arabinofuranosidase activity, is still a challenging topic. Ad hoc chromogenic substrates are useful tools and can reveal subtle differences in enzymatic behavior. In this study, enzyme selectivity on natural substrates has been compared with enzyme selectivity towards aryl-glycosides. This has proven to be a suitable approach to understand how artificial substrates can be used to characterize arabinoxylan-active α-l-arabinofuranosidases (Abfs). Methods Real-time NMR using a range of artificial chromogenic, synthetic pseudo-natural and natural substrates was employed to determine the hydrolytic abilities and specificity of different Abfs. Results The way in which synthetic di-arabinofuranosylated substrates are hydrolyzed by Abfs mirrors the behavior of enzymes on natural arabinoxylo-oligosaccharide (AXOS). Family GH43 Abfs that are strictly specific for mono-substituted d-xylosyl moieties (AXH-m) do not hydrolyze synthetic di-arabinofuranosylated substrates, while those specific for di-substituted moieties (AXH-d) remove a single l-arabinofuranosyl (l-Araf) group. GH51 Abfs, which are supposedly AXH-m enzymes, can release l-Araf from disubstituted d-xylosyl moieties, when these are non-reducing terminal groups. Conclusions and general significance The present study reveals that although the activity of Abfs on artificial substrates can be quite different from that displayed on natural substrates, enzyme specificity is well conserved. This implies that carefully chosen artificial substrates bearing di-arabinofuranosyl d-xylosyl moieties are convenient tools to probe selectivity in new Abfs. Moreover, this study has further clarified the relative promiscuity of GH51 Abfs, which can apparently hydrolyze terminal disubstitutions in AXOS, albeit less efficiently than mono-substituted motifs.
- Borsenberger, Vinciane,Dornez, Emmie,Desrousseaux, Marie-Laure,Massou, Stéphane,Tenkanen, Maija,Courtin, Christophe M.,Dumon, Claire,O'Donohue, Michael J.,Fauré, Régis
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p. 3106 - 3114
(2014/09/17)
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- Catalytic phenol hydroxylation with dioxygen: Extension of the tyrosinase mechanism beyond the protein matrix
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A new catalyst (see structure) hydroxylates phenols with O2 via a stable side-on peroxide complex, which is similar to the active site of tyrosinase in terms of the ligand environment and its spectroscopic properties. The catalytic oxidation of phenols to quinones proceeds at room temperature in the presence of NEt3 and even non-native substrates can be oxidized catalytically. The reaction mechanism is analogous to that of the enzyme-catalyzed reaction. Copyright
- Hoffmann, Alexander,Citek, Cooper,Binder, Stephan,Goos, Arne,Ruebhausen, Michael,Troeppner, Oliver,Ivanovic-Burmazovic, Ivana,Wasinger, Erik C.,Stack, T. Daniel P.,Herres-Pawlis, Sonja
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supporting information
p. 5398 - 5401
(2013/06/27)
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- The formation of aryloxenium ion in the reaction of N-nitro-O-(4- nitrophenyl)hydroxylamine with strong acids
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The reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine (1) with conc. H2SO4 affords 4-nitropyrocatechol and that with conc. sulfonic acids (RSO3H where R = Me, CF3) affords 2-hydroxy-5-nitrophenyl-R-sulfonates in yields of 80-85%. These reactions are assumed to proceed through an intermediate (phenoxy)oxodiazonium ion [NO 2C6H4O-N=N=O]+, which eliminates the N2O molecule to form the aryloxenium ion [NO2C 6H4O]+. The latter reacts with acid anions at the ortho-carbon atom of the phenyl ring. The thermodynamical parameters of the elementary reactions resulting in the formation of the (phenoxy)oxodiazonium ion [NO2C6H4O-N=N=O]+ and aryloxenium ion [NO2C6H4O]+ were calculated in the B3LYP/6-311+G(d) study of the combined molecular system (nitrohydroxylamine 1 + [H3SO4]+). The reaction of nitrohydroxylamine 1 with aqueous solutions of strong acids (～70% H 2SO4, CF3SO3H) affords mainly 4-nitrophenol. It appears that the mechanism of this reaction does not involve the formation of the aryloxenium ion.
- Klenov, M. S.,Churakov, A. M.,Solkan, V. N.,Strelenko, Yu. A.,Tartakovsky, V. A.
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p. 2263 - 2274,12
(2020/08/31)
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- Physico-chemical properties of lutetium phthalocyanine complexes in solution and in solid polystyrene polymer fibers and their application in photoconversion of 4-nitrophenol
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The photophysical and photochemical behavior of two phthalocyanine complexes of lutetium peripherally substituted with tetraphenoxy and tetra-2-pyridiloxy groups were studied in solution and when dispersed in polystyrene polymer fiber. The phthalocyanines were found not to fluoresce significantly in solution and not at all within the fiber matrix as compared with standard unsubstituted zinc phthalocyanine. They showed very promising photoactivity in solution with high singlet oxygen quantum yields. Their photoactivity within the polymer fiber matrix was also demonstrated with the photoconversion of 4-nitrophenol, a water pollutant. The photodegradation process with both phthalocyanines follows first order kinetics similar to that observed for the zinc phthalocyanine and the photo-products were found to be hydroquinone, benzoquinone and 4-nitrocatechol.
- Zugle, Ruphino,Nyokong, Tebello
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scheme or table
p. 49 - 57
(2012/06/16)
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- Organocatalytic Dakin oxidation by nucleophilic flavin catalysts
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Flavin catalysts perform the first organocatalytic Dakin oxidation of electron-rich arylaldehydes to phenols under mild, basic conditions. Catechols are readily prepared, and the oxidation of 2-hydroxyacetophenone was achieved. Aerobic oxidation is displayed in the presence of Zn(0) as a reducing agent. This reactivity broadens the scope of biomimetic flavin catalysis in the realm of nucleophilic oxidations, providing a framework for mechanistic investigations for related oxidations, such as the Baeyer-Villiger oxidation and Weitz-Scheffer epoxidation.
- Chen, Shuai,Hossain, Mohammad S.,Foss, Frank W.
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supporting information; experimental part
p. 2806 - 2809
(2012/08/07)
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- Aerobic organocatalytic oxidation of aryl aldehydes: Flavin catalyst turnover by Hantzsch's ester
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The first Dakin oxidation fueled by molecular oxygen as the terminal oxidant is reported. Flavin and NAD(P)H coenzymes, from natural enzymatic redox systems, inspired the use of flavin organocatalysts and a Hantzsch ester to perform transition-metal-free, aerobic oxidations. Catechols and electron-rich phenols are achieved with as low as a 0.1 mol % catalyst loading, 1 equiv of Hantzsch ester, and O2 or air as the stoichiometric oxidant source.
- Chen, Shuai,Foss, Frank W.
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supporting information
p. 5150 - 5153,4
(2020/09/15)
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- A probable hydrogen-bonded meisenheimer complex: An unusually high S NAr reactivity of nitroaniline derivatives with hydroxide ion in aqueous media
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Observations show that nitroanilines exhibit an unusually high S NAr reactivity with OH- in aqueous media in reactions that produce nitrophenols. SNAr reaction of 4-nitroaniline (2a) in aqueous NaOH for 16 h yields 4-nitrophenol (4a) quantitatively, whereas a similar reaction of 4-nitrochlorobenzene (1a) gave 4a in 2% yield together with recovered 1a in 97%, suggesting that the leaving ability of the NH2 group far surpasses that of Cl under these conditions. An essential feature of SNAr reactions of nitroanilines is probably that the NH2 leaving group participates in a hydrogen-bonding interaction with H 2O. Density functional theory (DFT) calculations for a set of 4-nitroaniline, OH-, and H2O suggest a possible formation of a Meisenheimer complex stabilized by hydrogen-bonding interactions and a six-membered ring structure. The results obtained here contrast with conventional SNAr reactivity profiles in which nitroanilines are nearly unreactive with nucleophiles in organic solvents.
- Imoto, Mitsutaka,Matsui, Yasunori,Takeda, Motonori,Tamaki, Akihiro,Taniguchi, Hisaji,Mizuno, Kazuhiko,Ikeda, Hiroshi
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experimental part
p. 6356 - 6361
(2011/10/05)
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- Retrorsine, but not monocrotaline, is a mechanism-based inactivator of P450 3A4
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Retrorsine (RTS) and monocrotaline (MCT) cause severe toxicities via P450-mediated metabolic activation. The screening of mechanism-based inhibitors showed RTS inactivated 3A4 in the presence of NADPH. Unlike RTS, MCT failed to inhibit P450 3A4 and other enzymes tested. Further studies showed the loss of P450 3A4 activity occurred in a time- and concentration-dependent way, which was not recovered after dialysis. Dextromethorphan, a P450 3A4 substrate, protected the enzyme from the inactivation. Exogenous nucleophile glutathione (GSH) and reactive oxygen species scavengers catalase and superoxide dismutase did not protect P450 3A4 from the inactivation. GSH trapping experiments showed both P450 3A4 and 2C19 converted RTS and MCT to the corresponding electrophilic metabolites which could be trapped by GSH to form 7-GSH-DHP conjugate. We conclude that RTS and MCT are metabolically activated by P450 3A4 and 2C19, and that RTS, but not MCT, is a mechanism-based inactivator of P450 3A4.
- Dai, Jieyu,Zhang, Fan,Zheng, Jiang
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scheme or table
p. 49 - 56
(2010/11/18)
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- Synthesis of a new substrate for exo-galactofuranosidases, 2-hydroxy-4-nitrobenzene 1-yl β-d-galactofuranoside
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1,2,3,5,6-Penta-O-acetyl β-D-galactofuranose was synthesized by peracetylation of D-galactose in boiling pyridine followed by fractional crystallization. The first crops of crystals were 1,2,3,5,6-penta-O-acetyl β-D-galactopyranose, then mother liquor was concentrated and seeded with some crystals of 1,2,3,5,6-penta-O-acetyl β-D-galactofuranose. The crystalline mass obtained was recrystallized from ethanol. Optical rotation was a constant guide along the preparation of the furanosic precursor, due to the fact that only pentaacetate-β-furanose is levorotatory of the four D-galactose pentaacetate isomers. Bromination of penta-O-acetyl β-D-galactofuranose with hydrogen bromide produced the glycosylation donor, 1-bromo 1-deoxy 2,3,5,6-tetra-O-acetyl α-D-galactofuranose. The aglycon, 1,2-dihydroxy 4-nitrobenzene, was prepared by acidic hydrolysis of 2-hydroxy 5-nitrophenyl sulfate, synthesized at its turn by reacting 4-nitrophenol and potassium persulfate in a strongly alkaline solution conferred by potassium hydroxide. All intermediates and products were structurally characterized by chemical and physical methods.
- Iga, Dumitru Petru,Silvia,Nicolescu, Alina,Chira, Nicoleta-Aurelia
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experimental part
p. 357 - 363
(2011/08/03)
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- Photocatalytic oxidation of phenolic compounds by using a carbon nanotube-titanium dioxide composite catalyst
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A nanostructured multiwalled carbon nanotube (CNT) and titanium dioxide composite catalyst is prepared by a modified acid-catalyzed sol-gel method. Pure anatase TiO2 and the CNT-TiO2 composite are tested in the photocatalytic degradation of four para-substituted phenols: 4-chlorophenol, 4-aminophenol, 4-hydroxybenzoic acid and 4-nitrophenol. The effect of several operational parameters on the photoefficiency of the composite catalyst is studied by using 4-chlorophenol as model compound, namely catalyst loading, pH of the medium, hydrogen peroxide concentration, substrate concentration. A relationship between the Hammett constant of each para-substituted phenolic compound and its degradability by the photocatalysts is found. The effect of the carbon phase in the catalyst is ascribed to its photosensitizer action. A clear beneficial effect is observed for the degradation of 4-aminophenol and 4-chlorophenol. For the molecules with stronger electron-withdrawing (deactivating) groups, such as 4-hydroxybenzoic acid and 4-nitrophenol, no synergy effect is observed.
- Silva, Cláudia Gomes,Faria, Joaquim Luís
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experimental part
p. 609 - 618
(2011/12/02)
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- Enhanced mechanism of catalytic ozonation by ultrasound with orthogonal dual frequencies for the degradation of nitrobenzene in aqueous solution
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The experiments have been performed with a semi-continuous batch reactor to investigate the degradation efficiency of nitrobenzene in aqueous solution by ultrasound with the different orthogonal dual frequencies catalytic ozonation. The introduction of ultrasound can enhance the degradation efficiency of nitrobenzene compared to the results obtained from the processes of ozonation alone and ultrasound alone. The degradation of nitrobenzene is found to be zero-order in the two systems of ultrasound alone, and the reactions follow the pseudo-first-order kinetic model in the processes of ozone alone and ozone/ultrasound. The investigation confirms that the degradation of nitrobenzene follows the mechanism of hydroxyl radical (?OH) oxidation, and the enhancement function is even more pronounced in the presence of ultrasound with the greater difference between the orthogonal dual frequencies due to the obvious synergetic effect between ozone and ultrasound, which increases the utilization efficiency of ozone, and accelerates the initiation of ?OH and the formation of H2O2, resulting in the rapid formation of an increasing diversity of byproducts and the advancement degree of mineralization of total organic carbon (TOC). The oxidative byproducts have been, respectively identified in the different processes selected, including o, p, m-nitrophenols, phenol, malonic acid, 4-nitrocatechol, nitrate ion, maleic acid, oxalic acid, hydroquinone, p-quinone, 1,2,3-trihydroxy-5-nitrobenzene and acetic acid.
- Zhao, Lei,Ma, Jun,Zhai, Xuedong
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experimental part
p. 84 - 91
(2010/11/18)
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- Cationic and anionic surface binding sites on nanocrystalline zinc oxide: Surface influence on photoluminescence and photocatalysis
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To probe the influence of the surface on the overall nature of zinc oxide nanocrystals (ZnO NCs) this paper examines the effects of surface modifiers: cobalt Co(II) and trimethylsilanolate, on the properties of ZnO NCs. A clear relationship between the su
- Scott Bohle, D.,Spina, Carla J.
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supporting information; body text
p. 4397 - 4404
(2009/09/25)
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- Functional characterization of human and cynomolgus monkey cytochrome P450 2E1 enzymes
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Cytochrome P450 2E1 (CYP2E1) is an enzyme of major toxicological interest because it metabolizes various drugs, precarcinogens and solvents to reactive metabolites. In this study, human and cynomolgus monkey CYP2E1 cDNAs (humCYP2E1 and monCYP2E1, respectively) were cloned, and the corresponding proteins were heterologously expressed in yeast cells to identify the functions of primate CYP2E1s. The enzymatic properties of CYP2E1 proteins were characterized by kinetic analysis of chlorzoxazone 6-hydroxylation and 4-nitrophenol 2-hydroxylation. humCYP2E1 and monCYP2E1 enzymes showed 94.3% identity in their amino acid sequences. The functional CYP content in yeast cell microsomes expressing humCYP2E1 was 38.4 pmol/mg protein. The level of monCYP2E1 was 42.7% of that of humCYP2E1, although no significant differences were statistically observed. The Km values of microsomes from human livers and yeast cells expressing humCYP2E1 for CYP2E1-dependent oxidation were 822 and 627 μM for chlorzoxazone 6-hydroxylation, and 422 and 514 μM for 4-nitrophenol 2-hydroxylation, respectively. The Km values of microsomes from cynomolgus monkey livers and yeast cells expressing monCYP2E1 were not significantly different from those of humans in any enzyme source. Vmax and Vmax / Km values of human liver microsomes for CYP2E1-dependent oxidation were 909 pmol/min/mg protein and 1250 nl/min/mg protein for chlorzoxazone 6-hydroxylation, and 1250 pmol/min/mg protein and 2990 nl/min/mg protein for 4-nitrophenol 2-hydroxylation, respectively. The kinetic parameter values of cynomolgus monkey livers were comparable to or lower than those of human liver microsomes (49.5-102%). In yeast cell microsomes expressing humCYP2E1, Vmax and Vmax / Km values for CYP2E1-dependent oxidation on the basis of CYP holoprotein level were 170 pmol/min/pmol CYP and 272 nl/min/pmol CYP for chlorzoxazone 6-hydroxylation, and 139 pmol/min/pmol CYP and 277 nl/min/pmol CYP for 4-nitrophenol 2-hydroxylation, respectively, and the kinetic parameters of monCYP2E1 exhibited similar values. These findings suggest that human and cynomolgus monkey CYP2E1 enzymes have high homology in their amino acid sequences, and that their enzymatic properties are considerably similar. The information gained in this study should help with in vivo extrapolation and to assess the toxicity of xenobiotics.
- Hanioka, Nobumitsu,Yamamoto, Maki,Iwabu, Hiroyuki,Jinno, Hideto,Tanaka-Kagawa, Toshiko,Naito, Shinsaku,Shimizu, Takefumi,Masuda, Kazufumi,Katsu, Takashi,Narimatsu, Shizuo
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p. 1436 - 1445
(2008/02/13)
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- Group of anti-cancer compounds with specific structure and their production method
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Compounds containing a specific branched chain end terminal group, which is isopropyl, sec.-butyl, or tert.-butyl; a polar leading group; and long-chain aliphatic, non-cyclic, saturated or unsaturated, hydrocarbon group linking them; and having anti-cancer and immune boosting activity.
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Page/Page column 23-24
(2010/11/23)
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- Radiation-induced Degradation of Nitrobenzene in Aqueous Solutions
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Both the efficiency and pathways of nitrobenzene degradation induced by γ-ray irradiation were significantly influenced by the addition of reactive species scavengers. Experimental results showed that the degradation of nitrobenzene was more favorable und
- Feng, Shao-Hong,Zhang, Shu-Juan,Yu, Han-Qing,Li, Qian-Rong
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p. 718 - 719
(2007/10/03)
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- The reaction of peroxynitrite with organic molecules bearing a biologically important functionality. The multiplicity of reaction modes as exemplified by hydroxylation, nitration, nitrosation, dealkylation, oxygenation, and oxidative dimerization and cleavage
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The reactions of peroxynitrite with a variety of organic molecules which include a biologically important functionality have been examined to construct a simple model for the peroxynitrite-induced in vivo transformations as well as a chemical probe for the active species involved therein. Phenols were found to undergo hydroxylation, nitration, oxidative dimerization, and oxidation to cyclohexadienones and quinones. The ring nitration of catechol was confirmed for the first time in the in vitro reaction of peroxynitrite. Dealkylation and N-oxide formation were the major reaction modes observed for N,N-dimethyl-p-toluidine. 1,2-Phenylenediamine gave benzotriazole in high yield. The electron-deficient C-C double bond in 1,4-naphthoquinone underwent epoxidation, while the electron-rich C-C double bond in α-methylstyrene suffered oxidative cleavage to acetophenone. The activated double bond in trans-stilbene underwent oxidative cleavage and epoxidation in parallel to give benzaldehyde and trans-stilbene oxide as the major products. The triple bond in diphenylacetylene was simply oxygenated to form benzil, together with trace amounts of ring nitration products. 1-Phenylethanol, imidazole, 2′-deoxyadenosine, and 2′-deoxyguanosine were all quite slow to react, while uracil and cytosine were almost inert to peroxynitrite. The reaction modes exhibited by peroxynitrite are too widespread and complicated to explain the whole mechanistic pathway in terms of a single active species. All reaction modes observed for the peroxynitrite to date could be classified into five categories according to their types: i) electron transfer type, ii) O-electrophilic type, iii) N-electrophilic type, iv) O-nucleophilic type, and v) radical type. Some of these may compete under certain conditions. The active species involved in each of these types of reactions are as follows: i) NO+, NO2, and OH, ii) ONOOH, iii) ONOOH and NO+, iv) OOH- and ONOO-, and v) NO2 and OH.
- Nonoyama, Nobuaki,Oshima, Hiroshi,Shoda, Chizuru,Suzuki, Hitomi
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p. 2385 - 2395
(2007/10/03)
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- New fluorogenic substrate for the first continuous steroid sulfatase assay
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The screening for new inhibitors of steroid sulfatase requires an efficient test system. To overcome the shortcomings of the available discontinuous fluorimetric assay, several coumarin-type compounds were investigated as potential new substrates. 3,4-Benzocoumarin 7-O-sulfate was found to have appropriate substrate properties for the establishment of the first direct continuous assay of steroid sulfatase. (C) 2000 Elsevier Science Ltd. All rights reserved.
- Bilban, Melitta,Billich, Andreas,Auer, Manfred,Nussbaumer, Peter
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p. 967 - 969
(2007/10/03)
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- Complete destruction of p-Nitrophenol in aqueous medium by electro-fenton method
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An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxynitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease ofTOC values. A mineralization reaction mechanism is proposed. An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxynitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease of TOC values. A mineralization reaction mechanism is proposed. The destruction of p-nitrophenol by the electro-Fenton method was examined. The method is based on the oxidation of the substrate by hydroxyl radicals generated in situ in an electrochemically induced Fenton reaction. The progress of all reactions and product distribution were monitored by high-performance liquid chromatography and gas chromatography-mass spectrometry. Results showed that p-nitrophenol disappeared, as did the degradation products after reaching a maximum concentration. The rapid degradation of p-nitrophenol was accompanied by the appearance of aromatic intermediates, such as p-nitrocatechol and hydroquinone. The subsequent decrease in p-nitrocatechol was accompanied by an increase in 1,2,4-trihydroxybenzene, while the decrease in hydroquinone was accompanied by the production of benzoquinone. The mineralization mechanism is described. The variation in TOC values taken at different times during treatment showed their dependence on the charge passed or electrical energy consumed.
- Oturan,Peiroten,Chartrin,Acher
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p. 3474 - 3479
(2007/10/03)
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- Sonolysis of aqueous 4-nitrophenyl acetate - No evidence for hydrolysis induced by transient supercriticality
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The sonolysis of 4-nitrophenyl acetate in argon-saturated aqueous solution was studied at a frequency of 321 kHz. To examine the effect of OH radicals formed in the cavitational bubble and their reaction in the liquid phase with this substrate, a γ-radiolysis study was carried out as well. The OH radical adds preferentially in the ortho position to the ester function, thus forming 2-hydroxy-4-nitrophenyl acetate. Nitrite and acetate are generated as minor products by ipso addition at the nitro and acetate substituents. Upon sonolysis, pyrolytic products (increased yields of nitrite, nitrate, gaseous products) are also found. As 4-nitrophenol is not formed in the sonolysis of 4-nitrophenyl acetate, and as the acetate yield is largely accounted for by the OH-radical reactions occurring in the aqueous phase, the hydrolysis of 4-nitrophenyl acetate in the (transient) supercritical water layer inside the cavitational bubble can be ruled out as a pathway of its degradation.
- Tauber, Armin,Schuchmann, Heinz-Peter,Von Sonntag, Clemens
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p. 2198 - 2202
(2007/10/03)
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