1,354,085 research outputs found
Enzymatic activation of lignin leads to an unexpected copolymerization with carbohydrates
No full textChemo-enzymatically induced copolymerization of phenolics with acrylate compounds
No full textInitiation of copolymerization of lignin-like phenolic and acrylic compounds by the phenoloxidase laccase (EC 1.10.3.2) and a peroxide species (t-butylhydroperoxide, t-BHP) was compared to a Fenton-like system (ferrous ion, t-BHP). Initially, the relative activity of laccase towards different phenolic compounds and the optimum pH of some characteristic phenolics were determined. The polymer yield and the average molecular weight ((M) over bar (w)) of chemo-enzymatically produced polymers were dependent both on the type of each phenolic tested and on the phenol/monomer ratio. Furthermore, the success of copolymerization of the phenolics was dependent both on their redox potential and on the type of acrylic monomer applied. The extent of phenol incorporation into the polymer chain was enhanced by the presence of laccase in the reaction mixture and was significantly higher than in polymerization initiated by a Fenton-like reaction
Chemo-enzymatically induced copolymerization of phenolics with acrylate compounds
No full textInitiation of copolymerization of lignin-like phenolic and acrylic compounds by the phenoloxidase laccase (EC 1.10.3.2) and a peroxide species (t-butylhydroperoxide, t-BHP) was compared to a Fenton-like system (ferrous ion, t-BHP). Initially, the relative activity of laccase towards different phenolic compounds and the optimum pH of some characteristic phenolics were determined. The polymer yield and the average molecular weight ((M) over bar (w)) of chemo-enzymatically produced polymers were dependent both on the type of each phenolic tested and on the phenol/monomer ratio. Furthermore, the success of copolymerization of the phenolics was dependent both on their redox potential and on the type of acrylic monomer applied. The extent of phenol incorporation into the polymer chain was enhanced by the presence of laccase in the reaction mixture and was significantly higher than in polymerization initiated by a Fenton-like reaction
Chemoenzymatical grafting of acrylamide onto lignin
No full textLaccase (E.C.1.10.3.2.) from white-rot basidiomycete Trametes versicolor and dioxane peroxides were essential in the copolymerization of acrylamide and a derivative with lignin in a dioxane-H2O (7:3) mixture. Both a solubility test and an elemental analysis of the eluted and separated fractions provided evidence of grafting. Gel permeation chromatography on Sephadex G-100 showed that the side chain and the lignin backbone migrate as one unit through the column. Copolymers obtained were characterized by UV-VIS-spectroscopy as well as FT-IR, and C-13-CPMAS-NMR spectroscopy. Freeze-dried copolymers of lignin and acrylamide appeared as homogeneous fibril-like particulate. The mechanism of the enzymatical grafting is discussed. (C) 2000 Elsevier Science B.V. All rights reserved
Chemo-enzymatic synthesis and characterization of graft copolymers from lignin and acrylic compounds
No full textChemo-enzymatic initiation of graft copolymerization of acrylic compounds onto different technical lignosulfonates (LS) was compared to a Fenton-like system (ferrous ion, t-BHP). The enzyme tested was a phenoloxidase laccase (EC 1.10.3.2) from the white rot basidomycete Trametes versicolor. Most applied lignins were successfully grafted, resulting in a polymer yield of more than 90%. The effect of initiator concentration and the lignin/monomer ratio on the yield and (M) over bar(w) of enzymatically grafted polymers were studied. The homopolymer proportion in the enzymatically produced grafts of Ca-LS and acrylic acid was 5 to 6x lower than those initiated by the Fenton-like reagent; no such differences were observed for Na-LS. (C) 2000 Elsevier Science Inc. All rights reserved
Modification of lignin for the production of new compounded materials
No full textThe cell walls of woody plants are compound ed materials made by in situ polymerization of a polyphenolic matrix (lignin) into a web of fibers (cellulose), a process that is catalysed by polyphenoloxidases (laccases) or peroxidases. The first attempt to transform the basic strategy of this natural process for use in human craftsmanship was the ancient lacquer method. The sap of the lacquer tree (Rhus verniciflua) contains large amounts of a phenol (urushiol), a polysaccharide and the enzyme laccase. This oil-in-water emulsion solidifies in the presence of oxygen. The Chinese began using this phenomenon for the production of highly creative artwork more than 6,000 years ago. It was the first example of an isolated enzyme being used as a catalyst to create an artificial plastic compound. In order to apply this process to the production of products on an industrial scale, an inexpensive phenol must be used, which is transferred by an enzyme to active radicals that react with different components to form a compounded material. At present, the following approaches have been studied: (1) In situ polymerization of lignin for the production of particle boards. Adhesive cure is based on the oxidative polymerization of lignin using phenoloxidases (laccase) as radical donors. This lignin-based bio-adhesive can be applied under conventional pressing conditions. The resulting particle boards meet German performance standards. By this process, 80% of the petrochemical binders in the wood-composite industry can be replaced by materials from renewable resources. (2) Enzymatic copolymerization of lignin and alkenes. In the presence of organic hydroperoxides, laccase catalyses the reaction between lignin and olefins. Derailed studies on the reaction between lignin and acrylate monomers showed that chemo-enzymatic copolymerization offers the possibility to produce defined lignin-acrylate copolymers. The system allows control of the molecular weights of the products in a way that has not been possible with chemical catalysts. This is a novel attempt to enzymatically induce grafting of polymeric side chains onto the lignin backbone, and it enables the utilization of lignin as part of new engineering materials. (3) Enzymatic activation of the middle-lamella lignin of wood fibers for the production of wood composites. The incubation of wood fibers with a phenol oxidizing enzyme results in oxidative activation of the lignin crust on the fiber surface. When such fibers are pressed together, boards are obtained which meet the German standards for medium-density fiber boards (MDF). The fibers are bound together in a way that comes close to that by which wood fibers are bound together in naturally grown wood. This process will, for the first time, yield wood composites that are produced solely from naturally grown products without any addition of resins
The influence of laccase on the chemo-enzymatic synthesis of lignin graft-copolymers
No full textThe mechanism unterlying the chemo-enzymatic graft copolymerization of lignin with acrylic compounds was studied. When lignin sulfonate (LS) was incubated with the phenoloxidase laccase in the presence of a peroxide species (t-butylhydroperoxide, i.e. t-BHP), the decrease of the phenolic groups was significantly higher than when LS was incubated with laccase or t-BHP, separately. The enzymatic oxidation of the phenolic groups did lead to the formation of quinones however, the number of quinone groups formed in LS in the presence of t-BHP? was not significantly higher than in its absence. Still, a certain proportion of the quinones formed in the presence of t-BHP appeared to be further oxidized resulting in an opening of the aromatic rings. In addition, the rate of LS polymerization, i.e. its increase in (M) over bar (w) instigated by laccase, was significantly reduced in the presence of t-BHP even though the activity of laccase was only slightly affected by the peroxide. Incubation of LS with laccase prior to the grafting reaction resulted in a significant increase of die spin concentration as detected in the EPR spectra. In spite of a high steady state concentration of radicals, the generation rate of these radicals in pre-incubated LS was lower than in unpretreated LS. Thus, the polymer yields obtained with pre-incubated LS were lower than those obtained with unpretreated LS. (C) 2002 Elsevier Science Inc. All rights reserved
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