26547-64-8Relevant articles and documents
Catalytic oxidation of para-substituted phenols with cobalt-Schiff base complexes/O2 - Selective conversion of syringyl and guaiacyl lignin models to benzoquinones
Cedeno, Diana,Bozell, Joseph J.
, p. 2380 - 2383 (2012)
Models of guaiacyl (G) and syringyl (S) subunits in lignin have been catalytically oxidized to their corresponding p-quinones in the presence of molecular oxygen. The oxidation of syringyl-like phenols readily occurred with 5-coordinate cobalt catalysts on which one of the ligands is a monodentate pyridine or imidazole base that coordinates axially to the metal. Formation of p-quinones with this system depends on the coordination of the axial base to the metal as influenced by its pKa and its size. The yield of p-quinones from guaiacyl models was markedly improved by the addition of a sterically hindered aliphatic nitrogen base that does not coordinate to the catalyst. A mechanism involving deprotonation of the phenol substrate by the bulky base is proposed.
Improved manganese-oxidizing activity of DypB, a peroxidase from a lignolytic bacterium
Singh, Rahul,Grigg, Jason C.,Qin, Wei,Kadla, John F.,Murphy, Michael E. P.,Eltis, Lindsay D.
, p. 700 - 706 (2013)
DypB, a dye-decolorizing peroxidase from the lignolytic soil bacterium Rhodococcus jostii RHA1, catalyzes the peroxide-dependent oxidation of divalent manganese (Mn2+), albeit less efficiently than fungal manganese peroxidases. Substitution of Asn246, a distal heme residue, with alanine increased the enzyme's apparent kcat and kcat/K m values for Mn2+ by 80- and 15-fold, respectively. A 2.2 A resolution X-ray crystal structure of the N246A variant revealed the Mn2+ to be bound within a pocket of acidic residues at the heme edge, reminiscent of the binding site in fungal manganese peroxidase and very different from that of another bacterial Mn2+-oxidizing peroxidase. The first coordination sphere was entirely composed of solvent, consistent with the variant's high Km for Mn2+ (17 ± 2 mM). N246A catalyzed the manganese-dependent transformation of hard wood kraft lignin and its solvent-extracted fractions. Two of the major degradation products were identified as 2,6-dimethoxybenzoquinone and 4-hydroxy-3,5-dimethoxybenzaldehyde, respectively. These results highlight the potential of bacterial enzymes as biocatalysts to transform lignin.
Steelink,Britton
, p. 2869 (1974)
Activated zeolites and heteropolyacids: An efficient catalysts for the synthesis of triacetoxyaromatic precursors of hydroxyquinones
Hadjila, Dokari,Mohamed, Hammadi
, p. 6112 - 6116 (2013)
The Thiele-Winter reaction is of interest for synthesis of triacetoxyaromatic precursors of hydroquinones. Liquid acid such as, chlorosulfonic acid and solid acids like heteropolyacids have an efficient catalyst can effectively replace sulfuric acid in acetoxylation reaction of quinones without use of organic solvent at room temperature.
Copper catalysts for selective c-c bond cleavage of b-o-4 lignin model compounds
Sedai, Baburam,Tom Baker
, p. 3563 - 3574 (2014)
The reactivity of homogeneous copper catalysts towards the selective C-C bond cleavage of both phenolic and non-phenolic arylglycerol b-aryl ether lignin model compounds has been explored. Several copper precursors, nitrogen ligands, and solvents were evaluated in order to optimize the catalyst system. Using the optimized catalyst system, copper(I) trifluoromethanesulfonate [CuACHTUNGTRENUNG(OTf)]/L/TEMPO (L=2,6-lutidine, TEMPO=2,2,6,6-tetramethyl-piperidin-1-yl-oxyl), aerobic oxidation of the non-phenolic b-O-4 lignin model compound proceeded with good selectivity for Ca-Cb bond cleavage, affording 3,5-dimethoxybenzaldehyde as the major product. Aerobic oxidation of the corresponding phenolic b-O-4 lignin model proceeded with different selectivity, affording 2,6-dimethoxybenzoquinone and a,b-unsaturated aldehyde products resulting from cleavage of the CaCaryl bond. At low catalyst concentrations, however, a change in selectivity was observed as oxidation of the benzylic secondary alcohol predominated with both substrates.
Molecular and biochemical characterization of a new thermostable bacterial laccase from Meiothermus ruber DSM 1279
Kalyani,Munk,Mikkelsen,Meyer
, p. 3910 - 3918 (2016)
A new laccase gene (mrlac) from Meiothermus ruber DSM 1279 was successfully overexpressed to produce a laccase (Mrlac) in soluble form in Escherichia coli during simultaneous overexpression of a chaperone protein (GroEL/ES). Without the GroEL/ES protein, the Mrlac overexpressed in E. coli constituted a huge amount of the total cellular protein, but the enzyme was localized in the insoluble fraction with no activity in the soluble fraction. Co-expression of the Mrlac with the E. coli GroEL/ES drastically improved proper folding and expression of active Mrlac in the soluble fraction. Spectroscopic analysis of the purified enzyme by UV/visible and electron paramagnetic resonance spectroscopy confirmed that the Mrlac was a multicopper oxidase. The Mrlac had a molecular weight of ～50 kDa and exhibited activity towards the canonical laccase substrates 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ), and 2,6-dimethoxyphenol (2,6-DMP). Kinetic constants Km and kcat were 27.3 μM and 325 min-1 on ABTS, 4.2 μM and 106 min-1 on SGZ, and 3.01 μM and 115 min-1 on 2,6-DMP, respectively. Maximal enzyme activity was achieved at 70°C with ABTS as substrate. In addition, Mrlac exhibited a half-life for deactivation at 70°C and 75°C of about 120 min and 67 min, respectively, indicating that the Mrlac is intrinsically thermostable. Finally, Mrlac was efficient in catalyzing the removal of 2,4-dichlorophene (DCP) in aqueous solution, a trait which makes the enzyme potentially useful for environmentally friendly applications.
Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
, p. 8591 - 8603 (2021/11/17)
Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
Polycarboxylated compounds and compositions containing same
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Page/Page column 17-22, (2021/06/09)
Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.
