- Role of laccase as an enzymatic pretreatment method to improve lignocellulosic saccharification
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The recalcitrant nature of lignocellulose, in particular due to the presence of lignin, is found to decrease the efficiency of cellulases during the saccharification of biomass. The efficient and cost effective removal of lignin is currently a critical bi
- Heap, Lucy,Green, Anthony,Brown, David,Van Dongen, Bart,Turner, Nicholas
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p. 2251 - 2259
(2014/07/22)
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- Alkoxyl- and carbon-centered radicals as primary agents for degrading non-phenolic lignin-substructure model compounds
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Lignin degradation by white-rot fungi proceeds via free radical reaction catalyzed by oxidative enzymes and metabolites. Basidiomycetes called selective white-rot fungi degrade both phenolic and non-phenolic lignin substructures without penetration of extracellular enzymes into the cell wall. Extracellular lipid peroxidation has been proposed as a possible ligninolytic mechanism, and radical species degrading the recalcitrant non-phenolic lignin substructures have been discussed. Reactions between the non-phenolic lignin model compounds and radicals produced from azo compounds in air have previously been analysed, and peroxyl radical (PR) is postulated to be responsible for lignin degradation (Kapich et al., FEBS Lett., 1999, 461, 115-119). However, because the thermolysis of azo compounds in air generates both a carbon-centred radical (CR) and a peroxyl radical (PR), we re-examined the reactivity of the three radicals alkoxyl radical (AR), CR and PR towards non-phenolic monomeric and dimeric lignin model compounds. The dimeric lignin model compound is degraded by CR produced by reaction of 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), which under N2 atmosphere cleaves the α-β bond in 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol to yield 4-ethoxy-3-methoxybenzaldehyde. However, it is not degraded by the PR produced by reaction of Ce4+/tert-BuOOH. In addition, it is degraded by AR produced by reaction of Ti3+/tert-BuOOH. PR and AR are generated in the presence and absence of veratryl alcohol, respectively. Rapid-flow ESR analysis of the radical species demonstrates that AR but not PR reacts with the lignin model compound. Thus, AR and CR are primary agents for the degradation of non-phenolic lignin substructures.
- Ohashi, Yasunori,Uno, Yukiko,Amirta, Rudianto,Watanebe, Takahito,Honda, Yoichi,Watanabe, Takashi
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p. 2481 - 2491
(2011/05/14)
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- Methyltrioxorhenium: A new catalyst for the activation of hydrogen peroxide to the oxidation of lignin and lignin model compounds
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The oxidative degradation of lignin under totally chlorine free conditions is one of the most relevant targets for the design of environmental friendly pulping and bleaching industrial processes. Methyltrioxorhenium was found a powerful and promising catalyst for the oxidation of both phenolic and non-phenolic lignin model compounds by use of hydrogen peroxide as primary oxidant. Three different technical lignins, hydrolytic sugar cane lignin (SCL), red spruce kraft lignin (RSL) and a hardwood organosolvent lignin (OSL), that are representative examples of widely diffused para-hydroxyphenyl-guaiacyl, guaiacyl and guaiacyl-syringyl lignins, were also extensively degraded under similar experimental conditions.
- Crestini, Claudia,Pro, Paola,Neri, Veronica,Saladino, Raffaele
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p. 2569 - 2578
(2007/10/03)
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- Evidence for Deuterium Retention in Products after Enzymatic C-C and Ether Bond Cleavages of Deuterated Lignin Model Compounds
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The mechanism of C-C and ether bond cleavages of Cα- or Cβ-deuterated β-O-4 and β-1 lignin substructure models and the vicinal diol compounds catalyzed by the enzyme system from Phanerochaete chrysosporium culture was investigated.The enzymatic oxidation of β-O-4 lignin model compounds in the presence of H2O2 and O2 yielded C6-Cα-derived benzaldehyde, and Cβ-Cγ-derived product together with the arylglycerol product.Likewise, the β-1 models and the diol compounds also underwent the C-C bond cleavage, yielding C6-Cα-derived benzaldehyde and the arylglycol product.The results demonstrated that the D-labels at Cα and Cβ of the substrates were retained in the products after the Cα-Cβ and ether bond cleavages.
- Habe, Tsuyoshi,Shimada, Mikio,Umezawa, Toshiaki,Higuchi, Takayoshi
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p. 3505 - 3510
(2007/10/02)
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- Metabolism of a Non-phenolic β-O-4 Lignin Substructure Model Compound by Coriolus versicolor
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A non-phenolic β-O-4 lignin substructure model, 4-ethoxy-3-methoxyphenylglycerol-β-syringaldehyde ether (I), was metabolized by a ligninolytic culture of Coriolus versicolor.Based on the identification of the metbaolic products (II-X1), the following reactions were found to occur in the culture; a) oxidation (III) and reduction (II) at the benzyl (Cα') position of the substrate (I), b) β-ether cleavage to give arylglycerols (IV, V), and c) Cα-Cβ cleavage of the arylglycerols and/or arylglycerol moiety of the substrate (I).In addition, β-deoxy diol (VI) and γ-formylglycerol (VII) were obtained as degradation products from substrate (I).
- Kawai, Shingo,Umezawa, Toshiaki,Higuchi, Takayoshi
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p. 2325 - 2330
(2007/10/02)
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