- Enzymatic cleavage of lignin β-O-4 aryl ether bonds via net internal hydrogen transfer
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The current greening of chemical production processes going along with a rising interest for the utilization of biogenic feedstocks recently revived the research to find new ways for the degradation of the complex lignin-backbone by means of biocatalysis and combined chemo-enzymatic catalysis. Lignin, which accumulates in 50 million t/a, is regarded as a potential substitute for phenolic and other aromatic, oil-based chemicals in the upcoming post oil age. The cleavage of the β-O-4-aryl ether linkage is the most favoured, since it accounts for approximately 50% of all ether linkages in lignin. This enzymatic cleavage was proposed to be a part of the lignin catabolism in the proteobacterium Sphingobium sp. SYK6. Three enzymes, LigD, a Cα-dehydrogenase, LigF, a β-etherase and LigG, a glutathione lyase, are supposed to be involved in lignin degradation. We cloned and recombinantly expressed these genes in E. coli and determined their pH and temperature optima on the lignin model substrate 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) -1,3-propanediol 1. Using an NAD+ dependent glutathione reductase from Allochromatium vinosum (AVR) we established an efficient way to regenerate the co-substrates NAD+ and glutathione allowing for a self-sufficient balanced enzymatic cascade with net internal hydrogen transfer (hydrogen borrowing). We showed the capability of this enzyme system to release lignin monomers from complex lignin structures coming from differently prepared real lignin substrates. This novel enzyme system could become a useful tool to release lignin monomers from complex lignin structures.
- Reiter, Jochen,Strittmatter, Harald,Wiemann, Lars O.,Schieder, Doris,Sieber, Volker
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- Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks for Visible-Light Photoredox Catalytic Degradation of Lignin β-O-4 Models
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We report a facile approach to fine tune the redox potentials of π-conjugated porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers (CzCPs) exhibit a wide range of redox potentials that are comparable to common transition-metal complexes and are used in the stepwise photocatalytic degradation of lignin β-O-4 models. With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency for the oxidation of benzylic β-O-4 alcohols, while the highly reductive CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of β-O-4 ketones. CzCPs also exhibit excellent stability and recyclability and represent a class of promising heterogeneous photocatalysts for the production of fine chemicals from sustainable lignocellulosic biomass.
- Luo, Jian,Zhang, Xiang,Lu, Jingzhi,Zhang, Jian
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p. 5062 - 5070
(2017/08/17)
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- Method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from lignin beta-O-4 linkage dimer model compound
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The invention provides a method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from a lignin beta-O-4 linkage dimer model compound. The content of beta-O-4 linkages in all linkages of lignin is highest and about 40-60%, so research of the beta-O-4 linkage lignin model compound plays an important role in research of the structure of lignin and the reaction mechanism of lignin in reaction. The method is simple, reaction conditions are mild, the yield is high, and the production period is short.
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- Aerobic Oxidation of Olefins and Lignin Model Compounds Using Photogenerated Phthalimide-N-oxyl Radical
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A metal-free protocol to generate phthalimide-N-oxyl (PINO) radicals from N-hydroxyphthalimide (NHPI) via a photoinduced proton-coupled electron transfer process is reported. Using donor-substituted aromatic ketones, such as 4,4′-bis(diphenylamino)benzophenone (DPA-BP), PINO radicals are efficiently produced and subsequently utilized to functionalize olefins to afford a new class of alkyl hydroperoxides. The DPA-BP/NHPI/O2 photocatalytic system exhibits high efficiency toward the aerobic oxidation of β-O-4 lignin models.
- Luo, Jian,Zhang, Jian
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p. 9131 - 9137
(2016/10/17)
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- SELECTIVE C-O BOND CLEAVAGE OF OXIDIZED LIGNIN AND LIGNIN-TYPE MATERIALS INTO SIMPLE AROMATIC COMPOUNDS
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A method to cleave C-C and C-0 bonds in β-Ο-4 linkages in lignin or lignin sub-units is described. The method includes oxidizing at least a portion of secondary benzylic alcohol groups in β-Ο-4 linkages in the lignin or lignin sub-unit to corresponding ketones and then leaving C-0 or C-C bonds in the oxidized lignin or lignin sub-unit by reacting it with an organic carboxylic acid, a salt of an organic carboxylic acids, and/or an ester of an organic carboxylic acids. The method may utilize a metal or metal-containing reagent or proceed without the metal or metal-containing reagent.
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- Selective aerobic benzylic alcohol oxidation of lignin model compounds: Route to aryl ketones
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A mild and chemoselective oxidation of the α-alcohol in β-O-4'-ethanoaryl and β-O-4'-glycerolaryl ethers has been developed. The benzylic alcohols were selectively dehydrogenated to the corresponding ketones in 60-93-% yield. A one-pot selective route to aryl ethyl ketones was performed. The catalytic system comprises recyclable heterogeneous palladium, mild reaction conditions, green solvents, and oxygen in air as oxidant. Catalytic amounts of a coordinating polyol were found pivotal for an efficient aerobic oxidation. The ligninator: A mild and chemoselective oxidation of the α-alcohol in β-O-4' lignin model compounds is developed. The benzylic alcohols are selectively dehydrogenated to the corresponding ketones in 60-93-% yield. A one-pot selective route to aryl ethyl ketones is performed. The catalytic system comprises recyclable heterogeneous palladium, mild reaction conditions, green solvents, and oxygen in air as oxidant.
- Dawange, Monali,Galkin, Maxim V.,Samec, Joseph S. M.
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p. 401 - 404
(2015/03/04)
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- SELECTIVE AEROBIC ALCOHOL OXIDATION METHOD FOR CONVERSION OF LIGNIN INTO SIMPLE AROMATIC COMPOUNDS
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Described is a method to oxidize lignin or lignin sub-units. The method includes oxidation of secondary benzylic alcohol in the lignin or lignin sub-unit to a corresponding ketone in the presence of unprotected primarily aliphatic alcohol in the lignin or lignin sub-unit. The optimal catalyst system consists of HNO3 in combination with another Br?nsted acid, in the absence of a metal-containing catalyst, thereby yielding a selectively oxidized lignin or lignin sub-unit. The method may be carried out in the presence or absence of additional reagents including TEMPO and TEMPO derivatives.
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Paragraph 0050; 0076; 0077; 0078; 0091; 0092
(2014/09/03)
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- Chemoselective metal-free aerobic alcohol oxidation in lignin
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An efficient organocatalytic method for chemoselective aerobic oxidation of secondary benzylic alcohols within lignin model compounds has been identified. Extension to selective oxidation in natural lignins has also been demonstrated. The optimal catalyst system consists of 4-acetamido-TEMPO (5 mol %; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) in combination with HNO3 and HCl (10 mol % each). Preliminary studies highlight the prospect of combining this method with a subsequent oxidation step to achieve C-C bond cleavage.
- Rahimi, Alireza,Azarpira, Ali,Kim, Hoon,Ralph, John,Stahl, Shannon S.
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supporting information
p. 6415 - 6418
(2013/06/05)
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- Hydrogenolysis of lignosulfonate into phenols over heterogeneous nickel catalysts
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We report a strategy for the catalytic conversion of lignosulfonate into phenols over heterogeneous nickel catalysts. Aryl-alkyl bonds (C-O-C) and hydroxyl groups (-OH) are hydrogenated to phenols and alkanes, respectively, without disturbing the arenes. The catalyst is based on a naturally abundant element, and is recyclable and reusable. The Royal Society of Chemistry 2012.
- Song, Qi,Wang, Feng,Xu, Jie
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p. 7019 - 7021
(2012/08/14)
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- Co(salen)/SBA-15 catalysed oxidation of a β-O-4 phenolic dimer under microwave irradiation
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The microwave-assisted oxidative degradation of a lignin model phenolic dimer [1-(4-hydroxy-3-methoxyphenoxy)-2-(2-methoxyphenoxy)-propane-1,3-diol, 1] catalysed by Co(salen)/SBA-15 is reported. The investigated model compound 1 was prepared through a multistep synthesis and characterized by 1H, 13C NMR, and GC-MS studies. The catalyst was prepared by immobilizing [N,N′-bis(salicylidene)ethane-1,2-diaminato]Cobalt(II), Co(salen) complex onto the periodic mesopore channels of siliceous SBA-15. The activity of the Co(salen)/SBA-15 was investigated in the oxidation of 1 in the presence of hydrogen peroxide as oxidant, both under microwave irradiation and conventional heating. The phenolic dimer was selectively oxidized to 2-methoxy phenol with very high TON under microwave activation conditions. Comparatively, reactions run under conventional heating led to oligomerisation of the dimer and resulted in a mixture of products.
- Badamali, Sushanta K.,Luque, Rafael,Clark, James H.,Breeden, Simon W.
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p. 993 - 995
(2012/02/14)
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- Low molecular weight lignin suppresses activation of NF-κB and HIV-1 promoter
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Human immunodeficiency virus type 1 (HIV-1) is a cytopathic retrovirus and the primary etiological agent of acquired immunodeficiency syndrome (AIDS) and related disorders. In cells chronically infected with HIV-1, nuclear factor-κB (NF-κB) activation by external stimuli such as tumor necrosis factor α (TNFα) augments replication of HIV-1. NF-κB involves in many diseases such as inflammation, cancer, and Crohn's disease. In this paper, we exhibit that (i) HIV-1gene expression was inhibited by lignin, (ii) fraction of small molecular mass in HBS lignin (less than 0.5 kDa) had stronger inhibitory effects than large molecular mass (more than 1.3 kDa), (iii) lignin also inhibited activation of NF-κB induced by TNFα, (iv) among six lignin dimer-like compounds, compound 6 containing β-5 bond has more potent inhibitory activity than compounds 1, 2, 3, 4 and 5, which contain β-1, β-O-4, 5-5, or β-β structural units. These results suggested that small molecules of lignin inhibit HIV-1 replication through suppression of HIV-1 transcription from LTR including activation via NF-κB. Low molecular lignin may be a beneficial material or drug leads as a new class for AIDS and NF-κB-related diseases.
- Mitsuhashi, Shinya,Kishimoto, Takao,Uraki, Yasumitsu,Okamoto, Takashi,Ubukata, Makoto
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p. 2645 - 2650
(2008/12/21)
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- 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
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A biomimetic system for lignin peroxidase (LiP) was designed by using a cationic porphyrin, [Mn(TMePyP)OAc5], supported on the smectitic clay montmorillonite [Mn(TMe-PyP)/clay]. The natural role of the polypeptidic pocket of LiP 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. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Crestini, Claudia,Pastorini, Alessandra,Tagliatesta, Pietro
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p. 4477 - 4483
(2007/10/03)
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- Singlet oxygen in the photodegradation of lignin models
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The photochemical oxidation of lignin models in the presence of singlet oxygen was studied. The treatment of the non-phenolic β-O-4 aryl ether derivatives 6, 7, and 8 in the presence of both oxygen and Rose Bengal gave products deriving from a formal β-C-O cleavage formation. By this way. the derivatives 12, 13, and 15 were obtained. The photochemical oxidation of the phenolic β-O-4 aryl ether 9 gave the same type of product confirming that, in this case, the presence of the carbonyl group is not indispensable to have the cleavage reaction. The use of the model compound 10 showed that, when the phenoxy part of the molecule shows a lower reactivity towards singlet oxygen, the oxidation of the phenol moiety to hydroquinone call occur. The photochemical behaviour of these model compounds can be rationalised from a reaction of singlet oxygen with the phenoxy part of the molecule.
- Crestini, Claudia,D'Auria, Maurizio
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p. 7877 - 7888
(2007/10/03)
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