Xn:Harmful;
88-75-5Relevant articles and documents
Selective Nitration of Phenol
Pervez, Humayun,Rees, Lilias,Suckling, Colin J.
, p. 512 - 513 (1985)
Activated nitro derivatives of pyridinium salts have been shown to mediate in the highly selective ortho nitration of phenol in high yield.
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Menke
, p. 270 (1925)
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Improving the properties of β-galactosidase from Aspergillus oryzae via encapsulation in aggregated silica nanoparticles
Wu, Zhuofu,Wang, Zhi,Guan, Buyuan,Wang, Xue,Zhang, Ye,Xiao, Yu,Zhi, Bo,Liu, Yunling,Li, Zhengqiang,Huo, Qisheng
, p. 3793 - 3797 (2013)
In this study, a new immobilization method was exploited to encapsulate β-galactosidase (β-gal) from Aspergillus oryzae using aggregated core-shell silica nanoparticles as a matrix. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the material encapsulated β-gal. Compared to the free β-gal, the encapsulated β-gal shows a broader pH tolerance and thermal stability. Furthermore, the encapsulated β-gal shows better storage stability over 30 days. After nine cycles of hydrolytic reaction, the encapsulated β-gal still maintains 94.2% of its initial activity, which indicates that the β-gal exhibits excellent reusability after encapsulation.
Role of lysine ε-amino groups of β-lactoglobulin on its activating effect of Kluyveromyces lactis β-galactosidase
Del Moral-Ramirez, Elizabeth,Dominguez-Ramirez, Lenin,Cruz-Guerrero, Alma E.,Rodriguez-Serrano, Gabriela M.,Garcia-Garibay, Mariano,Gomez-Ruiz, Lorena,Jimenez-Guzman, Judith
, p. 5859 - 5863 (2008)
Native β-lactoglobulin binds and increases the activity of Kluyveromyces lactis β-galactosidase. Construction of a three-dimensional (3D) model of β-lactoglobulin showed that lysine residues 15, 47, 69, and 138 are the most exposed ones, thus the ones more likely to interact with β-galactosidase. Molecular docking estimated the interaction energies of amino acid residues with either lactose or succinic anhydride, showing that Lys138 is the most likely to react with both. Affinity chromatography demonstrated that succinylated β-lactoglobulin diminished its ability to bind to the enzyme. Furthermore, when activity was measured in the presence of succinylated β-lactoglobulin, its activating effect was lost. Since succinylation specifically blocks Lys ε-amino groups, their loss very likely causes the disappearance of the activating effect. Results show that the activating effect of β-lactoglobulin on β-galactosidase activity is due to the interaction between both proteins and that this interaction is very likely to occur through the Lys ε-amino groups of β-lactoglobulin.
β-galactosidase from Lactobacillus plantarum WCFS1: Biochemical characterization and formation of prebiotic galacto-oligosaccharides
Iqbal, Sanaullah,Nguyen, Thu-Ha,Nguyen, Tien Thanh,Maischberger, Thomas,Haltrich, Dietmar
, p. 1408 - 1416 (2010)
Recombinant β-galactosidase from Lactobacillus plantarum WCFS1, homologously over-expressed in L. plantarum, was purified to apparent homogeneity using p-aminobenzyl 1-thio-β-D-galactopyranoside affinity chromatography and subsequently characterized. The enzyme is a heterodimer of the LacLMfamily type, consisting of a small subunit of 35 kDa and a large subunit of 72 kDa. The optimum pH for hydrolysis of its preferred substrates o-nitrophenyl-β-D-galactopyranoside (oNPG) and lactose is 7.5 and 7.0, and optimum temperature for these reactions is 55 and 60 °C, respectively. The enzyme is most stable in the pH range of 6.5-8.0. The Km, k cat and kcat/Km values for oNPG and lactose are 0.9 mM, 92 s-1, 130 mM-1 s-1 and 29 mM, 98 s-1, 3.3 mM-1 s-1, respectively. The L. plantarum β-galactosidase possesses a high transgalactosylation activity and was used for the synthesis of prebiotic galacto-oligosaccharides (GOS). The resulting GOS mixture was analyzed in detail, and major components were identified by using high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) as well as capillary electrophoresis. The maximal GOS yield was 41% (w/w) of total sugars at 85% lactose conversion (600 mM initial lactose concentration). The enzyme showed a strong preference for the formation of β-(1→6) linkages in its transgalactosylation mode, while β-(1→3)-linked products were formed to a lesser extent, comprising ～80% and 9%, respectively, of the newly formed glycosidic linkages in the oligosaccharide mixture at maximum GOS formation. The main individual products formed were β-DGalp-( 1→6)-D-Lac, accounting for 34% of total GOS, and β-D-Galp-(1→6)-D-Glc, making up 29% of total GOS.
Immobilization of β-Galactosidases on Magnetic Nanocellulose: Textural, Morphological, Magnetic, and Catalytic Properties
Gennari, Adriano,Mobayed, Francielle H.,Da Rolt Nervis, Brenda,Benvenutti, Edilson V.,Nicolodi, Sabrina,Da Silveira, Nádya Pesce,Volpato, Giandra,Volken De Souza, Claucia F.
, (2019)
We describe a process for obtaining nanocrystalline cellulose (NC) by either acidic (H-NC) or alkaline treatment (OH-NC) of microcrystalline cellulose, which was subsequently bonded to magnetic nanoparticles (H-NC-MNP and OH-NC-MNP) and used as support for the immobilization of Aspergillus oryzae (H-NC-MNP-Ao and OH-NC-MNP-Ao) and Kluyveromyces lactis (H-NC-MNP-Kl and OH-NC-MNP-Kl) β-galactosidases. The mean size of magnetic nanocellulose particles was approximately 75 nm. All derivatives reached saturation magnetizations of 7-18 emu/g, with a coercivity of approximately 4 kOe. Derivatives could be applied in batch hydrolysis of lactose either in permeate or in cheese whey for 30× and it reached hydrolysis higher than 50%. Furthermore, using a continuous process in a column packed-bed reactor, the derivative OH-NC-MNP-Ao had capacity to hydrolyze over 50% of the lactose present in milk or whey after 24 h of reaction. Fungal β-galactosidases immobilized on magnetic nanocellulose can be applied in lactose hydrolysis using batch or continuous processes.
Selective ortho hydroxylation of nitrobenzene with molecular oxygen catalyzed by the H5PV2Mo10O40 polyoxometalate
Khenkin, Alexander M.,Weiner, Lev,Neumann, Ronny
, p. 9988 - 9989 (2005)
Nitrobenzene was regioselectively oxidized to 2-nitrophenol with oxygen in a reaction catalyzed by the H5PV2Mo10O40 polyoxometalate. The reaction was first order in oxygen and catalyst. 15N NMR showed the interaction between nitrobenzene and the polyoxometalate. Use of labeled 18O2, H218O, a competitive kinetic isotope experiment, and use of phenyl-tert-butylnitrone as a spin-trap and identification by EPR provided evidence for formation of a radical intermediate involving a selective intramolecular interaction at the ortho position due to formation of a H5PV2Mo10O40-nitrobenzene complex. Copyright
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Chaney,Wolfrom
, p. 2998 (1961)
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Mechanism of the dimerization of enzymes upon adsorption on silicate adsorbents using the example of lysozyme and β-galactosidase
Chukhrai,Pilipenko,Ovsyannikov,Atyaksheva,Knyazeva,Ivanova
, p. 1986 - 1992 (2010)
It is shown by the kinetic analysis of lysozyme and β-galactosidase adsorption on silochrome, silica gel, and mesoporous silica that the adsorption follows a two-stage scheme, including reversible pre-adsorption and the irreversible binding of dimmers. The corresponding rate constants of adsorption, desorption, and dimerization were calculated. It was found that β-galoctosidase adsorbed on silica gel and mesoporous silica retained 20% of its activity, while β-galoctosidase adsorbed on silochrome retained more than 30% of its activity.
Characterization of a heterodimeric GH2 β-galactosidase from lactobacillus sakei Lb790 and formation of prebiotic galacto-oligosaccharides
Iqbal, Sanaullah,Nguyen, Thu-Ha,Nguyen, Hoang Anh,Nguyen, Tien Thanh,Maischberger, Thomas,Kittl, Roman,Haltrich, Dietmar
, p. 3803 - 3811 (2011)
The lacLM genes from Lactobacillus sakei Lb790, encoding a heterodimeric β-galactosidase that belongs to glycoside hydrolase family GH2, were cloned and heterologously expressed in Escherichia coli. Subsequently, the recombinant β-galactosidase LacLM was purified to apparent homogeneity and characterized. The enzyme is a β-galactosidase with narrow substrate specificity because o-nitrophenyl-β-d-galactopyranoside (oNPG) was efficiently hydrolyzed, whereas various structurally related oNP analogues were not. The Km and kcat values for oNPG and lactose were 0.6 mM and 180 s-1 and 20 mM and 43 s-1, respectively. The enzyme is inhibited competitively by its two end-products d-galactose and d-glucose (Ki values of 180 and 475 mM, respectively). As judged by the ratio of the inhibition constant to the Michaelis constant, K i/Km, this inhibition is only very moderate and much less pronounced than for other microbial β-galactosidases. β-Galactosidase from L. sakei possesses high transgalactosylation activity and was used for the synthesis of galacto-oligosaccharides (GalOS), employing lactose at a concentration of 215 g/L. The maximum GalOS yield was 41% (w/w) of total sugars at 77% lactose conversion and contained mainly non-lactose disaccharides, trisaccharides, and tetrasaccharides with approximately 38, 57, and 5% of total GalOS formed, respectively. The enzyme showed a strong preference for the formation of β-(1→6)-linked transgalactosylation products, whereas β-(1→3)-linked compounds were formed to a lesser extent and β-(1→4)-linked reaction products could not be detected.
Radical-anion coupling through reagent design: hydroxylation of aryl halides
Chechik, Victor,Greener, Andrew J.,James, Michael J.,Oca?a, Ivan,Owens-Ward, Will,Smith, George,Ubysz, Patrycja,Whitwood, Adrian C.
, p. 14641 - 14646 (2021/11/17)
The design and development of an oxime-based hydroxylation reagent, which can chemoselectively convert aryl halides (X = F, Cl, Br, I) into phenols under operationally simple, transition-metal-free conditions is described. Key to the success of this approach was the identification of a reducing oxime anion which can interact and couple with open-shell aryl radicals. Experimental and computational studies support the proposed radical-nucleophilic substitution chain mechanism.
Photocatalytic synthesis of phenols mediated by visible light using KI as catalyst
Huiqin, Wei,Wu, Mei
supporting information, (2021/11/30)
A transition-metal-free hydroxylation of iodoarenes to afford substituted phenols is described. The reaction is promoted by KI under white LED light irradiation and uses atmospheric oxygen as oxidant. By the use of triethylamine as base and solvent, the corresponding phenols are obtained in moderate to good yields. Mechanistic studies suggest that KI and catalysis synergistically promote the cleavage of C-I bond to form free aryl radicals.
