454 research outputs found
Solid-State fermentation of Lentinus edodes: a new and efficient approach to chitosan production
No full textMetalloporphyrins immobilized on motmorillonite as biomimetic catalysts in the oxidation of lignin model compounds
No full textBiomimetic catalysts such as metalloporphyrins, which can yield highly oxidized metallo-oxo species, have been used as lignin peroxidase models. However, natural porphyrins are unstable under catalytic oxidation conditions due to their self-destruction or to the formation of inactive μ-oxo complexes. An alternative approach to the preparation of robust catalysts consists in the immobilization of metalloporphyrins on supports that mimic the polypeptide envelope, which protects the catalytic center of natural enzymes. We report here the use of manganese meso-tetrakis(tetramethylpyridinio) porphyrin pentaacetate immobilized on the smectite clay montmorillonite as a suprabiotic catalyst for the oxidation of lignin model compounds. © 2003 Elsevier B.V. All rights reserved
Mechanistic insights on the laccase-catalysed modification of technical lignins. A new solution for an old issue
No full textA strategy to understand the chemistry of the changes
occurring on kraft and Organosolv lignins during their
laccase-catalysed oxidation has been devised in this work.
This approach has been based on two steps: (a) fractionation,
and (b) enzymatic oxidation. The laccase-oxidised technical
lignins as well as their low molecular weight compounds
(LMWC) derivatives have been fully characterised via 31P
NMR, GPC, and GC-MS. From one side, LMWC formation
has been rationalised. From the other side, the variation in
the molecular weight of lignins after the enzymatic treatment
coupled with the decrease in the content of the various
hydroxylated moieties has suggested
polymerising/depolymerising activity for the enzyme
depending on the nature of the treated substrate. For both
technical lignins a more recalcitrant fraction to the action of
laccase has been identified, and the overall chemical
transformations occurring during the laccase-catalysed have
been identified
A novel and efficient catalytic epoxidation of olefins and monoterpenes with microencapsulated Lewis base adducts of methyltrioxorhenium
No full textThe reactivity of methyltrioxorhenium in the epoxidation of olefins can be tuned by the presence of Lewis bases as ligands of the metal center. Unfortunately, a large excess of ligand is usually required to obtain high yields and selectivities mainly because of the fluxional behaviour that these compounds show in solution. We describe here the microencapsulation technique that can resolve this problem. Microencapsulated Lewis base adducts of methyltrioxorhenium with nitrogen containing ligands are highly efficient and selective catalysts for the epoxidation of several olefins and monoterpenes with hydrogen peroxide even in the case of the most sensitive substrates. These systems show the advantages of the ligand accelerated catalysis and the benefits of heterogeneous compounds. They can be easily recovered from the reaction mixture and used for more transformations. (C) 2004 Elsevier Ltd. All rights reserved
A novel and efficient catalytic epoxidation of monoterpenes by homogeneous and heterogeneous methyltrioxorhenium in ionic liquids
No full textA convenient and efficient synthesis of monoterpene epoxides by application of methyltrioxorhenium and heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium and microencapsulated polystyrene/methyltrioxorhenium catalytic systems in ionic liquids is described here. It was found that even highly sensitive terpenic epoxides were obtained in excellent yields. Environmentally friendly, easily available and low cost (UHP) urea hydrogen peroxide adduct was used as the primary oxidant. Catalysts were stable systems for at least four recycling oxidations. Experimental results showed that the reactions performed in ionic liquids were more selective and efficient than the ones performed in molecular solvents. (c) 2009 Elsevier B.V. All rights reserved
Photodegradation of lignin: The role of singlet oxygen
No full textThe photochemical irradiation of some phenoxyacetophenone derivatives in
the presence of oxygen by using visible light did not produce any
decomposition product. In the presence of singlet oxygen, sensitized by
using Bengal Rose, decomposition products were obtained. The products
obtained were similar to those obtained by direct beta-C-O cleavage on
the substrate. In this case, the observed behavior can be explained
assuming an attack of singlet oxygen on a phenoxy part of the molecule
Nanoparticles for Adsorption and Photocatalytic Degradation of Methylene Blue in Water
No full textThe full use of biomass plays a central role in transition to a circular bioeconomy. Unlike non-biobased adsorbents, which are criticized for high production costs and the generation of secondary pollutants, lignin nanoparticles (LNPs) are a cost-effective and environmentally benign alternative for water treatment. In this study, LNPs were demonstrated for the first time as multifunctional materials for the adsorption and UV-light driven photocatalytic degradation of methylene blue dye (MB) in water
The immobilized porphyrin-mediator system Mn(TMePyP)/clay/HBT (clay-PMS): A lignin peroxidase biomimetic catalyst in the oxidation of lignin and lignin model compounds
No full textA biomimetic system for lignin peroxidase (LiP) was designed by using a cationic porphyrin, [Mn(TMePyP)OAc5], supported on the smectitic clay montraorillonite [Mn(TMePyP)/clay]. The natural role of the polypeptidic pocket of UP was mimicked by the clay. The possibility to use low-molecular-weight redox mediators as active readily diffusible oxidizing species has been investigated. This assembly - a sort of "synthetic enzyme" - can be defined as an immobilized porphyrin-mediator system (clay-PMS). The clay-PMS was found to be a stable, recyclable, and efficient catalyst for the environmentally friendly H2O2-catalyzed oxidation of different lignins and representative lignin model compounds. The clay-PMS showed a higher reactivity than Mn(TMePyP)/clay alone due to an effective role of the redox mediator on the oxidation. (C)Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004
Elucidation of lignin structure by quantitative 2D NMR
No full textQuick quantitative HSQC (QQ-HSQC) was applied to quantitative evaluation of different inter-unit linkages in an array of milled softwood and hardwood and technical lignins by using the guaiacyl C2 and syringyl C2-C6 signals as internal standards. The results were found to be highly reproducible and comparable with earlier literature reports. The advantage of QQ-HSQC NMR analysis of lignin is contemporary detection and quantification of lignin inter-unit linkages with a direct, non-destructive method requiring short acquisition times. Quick quantitative HSQC (QQ-HSQC) NMR was applied to the quantitative evaluation of different inter-unit linkages in lignins (see figure) by using the guaiacyl C2 and syringyl C2-C6 signals as internal standards. The advantage of QQ-HSQC NMR analysis of lignin is the detection and quantification of lignin inter-unit linkages by a direct, non-destructive method with short acquisition times. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
A novel and efficient synthesis of tocopheryl quinones by homogeneous and heterogeneous methyltrioxorhenium/hydrogen peroxide catalytic systems
No full textA convenient and efficient application of heterogeneous poly(4-vinylpyridine), poly(4-vinyl-pyridine N-oxide), and polystyrene/ methylrhenium trioxide systems for the selective oxidation of tocopherols and tocopherol derivatives to the corresponding ortho- and para-tocopherylquinones is described. Environment friendly, easily available, and low-cost hydrogen peroxide (H2O2) was used as the oxygen atom donor. The antiviral activity of the newly synthesized tocopherylquinones and their parent tocopherols against influenza A virus is also reported. On the basis of the biological assay, the activity of tocopherols against influenza virus is higher than that showed by the corresponding tocopherylquinones, thus suggesting, for the first time, a drawback effect of the oxidative metabolism on the antiviral activity of these compounds. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA
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