Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LIGNIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMedDate not supplied

Isolation of residual lignin from softwood kraft pulp. Advantages of the acetic acid acidolysis method.

Lignin in kraft pulp was extracted by enzymatic hydrolysis of the carbohydrates, acidolysis with dioxane-water-HCl (conventional method), and acidolysis with acetic acid-water-ZnCl2. The latter method was shown to extract lignin with a better yield than for conventional acidolysis and with a much lower content in impurities than for enzymatic hydrolysis. It was confirmed by 13C NMR analysis of the lignin samples that conventional hydrolysis modified the lignin polymer, causing the cleavage of some aryl-ether linkages. The cleavage was also observed on a model compound submitted to the same extraction conditions. In that respect, the acetic acid-water-ZnCl2 method was less damaging and consequently more suitable for analytical purposes.

Acetic Acid↗
PubMed1988

Manganese, Mn-dependent peroxidases, and the biodegradation of lignin.

Manganese and Mn-dependent peroxidases have been implicated in the enzymatic degradation of lignin. However, the specific role of manganese is uncertain. We report here the novel observation that in the absence of enzyme, suitably chelated Mn3+ is a ligninolytic agent capable of oxidizing veratryl alcohol, lignin model compounds, and lignin. We also demonstrate the unexpected effect of reducing agents which stimulate the oxidations by Mn3+. The stimulation is apparently through the production of a reduced oxygen species likely to be superoxide. These observations provide a fresh insight into the process of lignin biodegradation.

Basidiomycota↗
PubMed1999

Aromatic ring cleavage of a non-phenolic beta-O-4 lignin model dimer by laccase of Trametes versicolor in the presence of 1-hydroxybenzotriazole.

The novel cleavage products, 2,3-dihydroxy-1-(4-ethoxy-3-methoxyphenyl)-1-formyloxypropane (II) and 1-(4-ethoxy-3-methoxyphenyl)-1,2,3-trihydroxypropane-2,3-cyclic carbonate (III) were identified as products of a non-phenolic beta-O-4 lignin model dimer, 1,3-dihydroxy-2-(2,6-dimethoxylphenoxy)-1-(4-ethoxy-3-methoxypheny l)propane (I), by a Trametes versicolor laccase in the presence of 1-hydroxybenzotriazole (1-HBT). An isotopic experiment with a 13C-labeled lignin model dimer, 1,3-dihydroxy-2-(2,6-[U-ring-13C] dimethoxyphenoxy)-1-(4-ethoxy-3-methoxyphenyl)propane (I-13C) indicated that the formyl and carbonate carbons of products II and III were derived from the beta-phenoxy group of beta-O-4 lignin model dimer I as aromatic ring cleavage fragments. These results show that the laccase-1-HBT couple could catalyze the aromatic ring cleavage of non-phenolic beta-O-4 lignin model dimer in addition to the beta-ether cleavage, Calpha-Cbeta cleavage, and Calpha-oxidation.

Basidiomycota↗
PubMed1999

Peroxyl radicals are potential agents of lignin biodegradation.

Past work has shown that the extracellular manganese-dependent peroxidases (MnPs) of ligninolytic fungi degrade the principal non-phenolic structures of lignin when they peroxidize unsaturated fatty acids. This reaction is likely to be relevant to ligninolysis in sound wood, where enzymes cannot penetrate, only if it employs a small, diffusible lipid radical as the proximal oxidant of lignin. Here we show that a non-phenolic beta-O-4-linked lignin model dimer was oxidized to products indicative of hydrogen abstraction and electron transfer by three different peroxyl radical-generating systems: (a) MnP/Mn(II)/linoleic acid, (b) arachidonic acid in which peroxidation was initiated by a small amount of H(2)O(2)/Fe(II), and (c) the thermolysis in air of either 4,4'-azobis(4-cyanovaleric acid) or 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Some quantitative differences in the product distributions were found, but these were attributable to the presence of electron-withdrawing substituents on the peroxyl radicals derived from azo precursors. Our results introduce a new hypothesis: that biogenic peroxyl radicals may be agents of lignin biodegradation.

Aspergillus↗
PubMed2003

A lignin-specific peroxidase in tobacco whose antisense suppression leads to vascular tissue modification.

A tobacco peroxidase isoenzyme (TP60) was down-regulated in tobacco using an antisense strategy, this affording transformants with lignin reductions of up to 40-50% of wild type (control) plants. Significantly, both guaiacyl and syringyl levels decreased in essentially a linear manner with the reductions in lignin amounts, as determined by both thioacidolysis and nitrobenzene oxidative analyses. These data provisionally suggest that a feedback mechanism is operative in lignifying cells, which prevents build-up of monolignols should oxidative capacity for their subsequent metabolism be reduced. Prior to this study, the only known rate-limiting processes in the monolignol/lignin pathways involved that of Phe supply and the relative activities of cinnamate-4-hydroxylase/p-coumarate-3-hydroxylase, respectively. These transformants thus provide an additional experimental means in which to further dissect and delineate the factors involved in monolignol targeting to precise regions in the cell wall, and of subsequent lignin assembly. Interestingly, the lignin down-regulated tobacco phenotypes displayed no readily observable differences in overall growth and development profiles, although the vascular apparatus was modified.

Amino Acid Sequence↗
PubMed1997

Extractibility of structural carbohydrates and lignin deposition in maturing alfalfa internodes.

In the present study, we have performed chemical investigations of the stem cell walls during internode maturation in order to study the growth dynamics of alfalfa and the deposition of the main cell wall components (polysaccharides and lignins). Internode cell walls were analysed by chemical fractionation using a mild delignification step aiming at sequential removal of polysaccharides and lignins. Delignification facilitated the subsequent removal of the xylose-rich polysaccharides by NaOH extraction as previously shown. This trend was more pronounced in the case of older internodes which have a larger proportion of secondary tissues containing syringyl type lignins in contrast to younger ones which are mainly composed of primary tissues containing guaiacyl type lignins and pectin rich cell walls.

Carbohydrates↗
PubMed2000

Extent of incorporation of hydroxycinnamaldehydes into lignin in cinnamyl alcohol dehydrogenase-downregulated plants.

Down-regulation of cinnamyl alcohol dehydrogenase leads to an accumulation of cinnamaldehydes available for incorporation into the developing lignin polymer. Using electron spin resonance spectroscopy we have demonstrated that the parent radical of 4-hydroxy-3-methoxycinnamaldehyde is generated by peroxidase catalysed oxidation. The extent of radical generation is similar to that of 4-hydroxy-3-methoxycinnamyl alcohol and is increased by further aromatic methoxylation. From the distribution of the electron-spin density, it was predicted that the regiochemistry of 4-hydroxy-3-methoxycinnamaldehyde coupling would be similar to that of the corresponding alcohol, with the possibility of a higher degree of 8-O-4 linkages occurring. These predictions were confirmed by polymerisation studies, which also showed that after radical coupling the alpha,beta-enone structure was regenerated. This suggests that, although the cross-linking and physical properties of cinnamaldeyde rich lignins differ from that of normal lignins, cinnamaldehydes are incorporated into the lignin polymer under the same controlling factors as the cinnamyl alcohols.

Alcohol Oxidoreductases↗
PubMed2000

Degradation of nonphenolic lignin by the laccase/1-hydroxybenzotriazole system.

Phenolic and nonphenolic (permethylated) synthetic [14C]lignins were depolymerized by Trametes villosa laccase in the presence of a radical mediator, 1-hydroxybenzotriazole (HOBT). Gel permeation chromatography of the treated lignins showed that approximately 10% of their substructures were cleaved. The system also cleaved a beta-O-4-linked model compound, 1-(4-ethoxy-3-methoxy-ring-[14C]phenyl)-2-(2-methoxyphenoxy)-propane- 1,3-diol, and a beta-1-linked model, 1, 2-bis-(3-methoxy-4-[14C]methoxyphenyl)-propane-1,3-diol, that represent nonphenolic substructures in lignin. High performance liquid chromatography of products from the oxidized models showed that they were produced in sufficient yields to account for the ability of laccase/HOBT to depolymerize nonphenolic lignin.

Dimerization↗
PubMed2000

Investigation of aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process.

In efforts to apply a polymer-based aqueous biphasic system (ABS) extraction to the paper pulping process, the study of the distribution of various lignin and cellulosic fractions in ABS and the effects of temperature on system composition and solute partitioning have been investigated. The partitioning of three lignin species (Indulin AT, Indulin C, and Reax 85A) have been studied in ABS prepared from stock solutions of 40% (w/w) poly(ethylene glycol) (PEG)-2000 and increasing concentrations of K2CO3, (NH4)2SO4, and NaOH. The partitioning of these lignins is affected by the free energy of hydration of the salt forming the ABS, the tie line length, and the dissociation of the sulfonic acid and hydroxyl groups of the distributed solutes. The partitioning of fibrous cellulose and diethylaminoethyl cellulose have been studied in 40% (w/w) PEG-2000-(NH4)2SO4 ABS. The hydrophilic nature of these species is important in terms of their phase preference when designing a polymer-based aqueous biphasic extraction process for use in a paper pulping process. Both cellulosic samples do not dissolve, but rather report to the salt-rich phase of an ABS. In both chemical pulping and Organosolv pulping, temperatures in excess of 120 degrees C are needed to solubilize the lignin from the cellulose fraction of wood. To study the effects of temperature on the phase diagram and solute partitioning, phthalic acid and NH499TcO4 (as system probes) have been partitioned in 40% (w/w) PEG-2000-(NH4)2SO4 ABS at known tie line lengths as a function of temperature. Temperature does not appear to affect the partitioning results beyond the expected increase in phase divergence as temperature is increased. The PEG-2000 polymer itself appears to be stable to chemical pulping conditions.

Cellulose↗
PubMed2000

Photo- and radiation chemical induced degradation of lignin model compounds.

The basic mechanistic aspects of the photo- and radiation chemistry of lignin model compounds (LMCs) are discussed with respect to important processes related to lignin degradation. Several reactions occur after direct irradiation, photosensitized or radiation chemically induced oxidation of LMCs. Direct irradiation studies on LMCs have provided supportive evidence for the involvement of hydrogen abstraction reactions from phenols, beta-cleavage of substituted alpha-aryloxyacetophenones and cleavage of ketyl radicals (formed by photoreduction of aromatic ketones or hydrogen abstraction from arylglycerol beta-aryl ethers) in the photoyellowing of lignin rich pulps. Photosensitized and radiation chemically induced generation of reactive oxygen species and their reaction with LMCs are reviewed. The side-chain reactivity of LMC radical cations, generated by radiation chemical means, is also discussed in relation with the enzymatic degradation of lignin.

Free Radicals↗
PubMed1999

Regiochemical control of monolignol radical coupling: a new paradigm for lignin and lignan biosynthesis.

BACKGROUND: Although the lignins and lignans, both monolignol-derived coupling products, account for nearly 30% of the organic carbon circulating in the biosphere, the biosynthetic mechanism of their formation has been poorly understood. The prevailing view has been that lignins and lignans are produced by random free-radical polymerization and coupling, respectively. This view is challenged, mechanistically, by the recent discovery of dirigent proteins that precisely determine both the regiochemical and stereoselective outcome of monolignol radical coupling. RESULTS: To understand further the regulation and control of monolignol coupling, leading to both lignan and lignin formation, we sought to clone the first genes encoding dirigent proteins from several species. The encoding genes, described here, have no sequence homology with any other protein of known function. When expressed in a heterologous system, the recombinant protein was able to confer strict regiochemical and stereochemical control on monolignol free-radical coupling. The expression in plants of dirigent proteins and proposed dirigent protein arrays in developing xylem and in other lignified tissues indicates roles for these proteins in both lignan formation and lignification. CONCLUSIONS: The first understanding of regiochemical and stereochemical control of monolignol coupling in lignan biosynthesis has been established via the participation of a new class of dirigent proteins. Immunological studies have also implicated the involvement of potential corresponding arrays of dirigent protein sites in controlling lignin biopolymer assembly.

Amino Acid Sequence↗
PubMed2002

Rewriting the lignin roadmap.

Considerable interest in lignin biosynthesis has been fueled by the many roles that lignin plays in development and in resistance to biotic and abiotic stress, as well as its importance to industry and agriculture. Although the pathway leading to the lignin polymer has been studied for decades, new insights into the enzymes of the pathway have required a complete re-evaluation of how we think lignin precursors are synthesized. Although free hydroxycinnamic acids have long been thought to be key intermediates, it has become apparent that many of the hydroxylation and methylation steps in the pathway occur instead at the level of hydroxycinnamic acid esters, and their corresponding aldehydes and alcohols.

Caffeic Acids↗
PubMed2003

Production of wood-decay enzymes, mass loss and lignin solubilization in wood by tropical Xylariaceae.

Tropical xylariaceous taxa in the genera Biscognauxia, Hypoxylon and Xylaria were evaluated for their ability to produce wood-decay enzymes and effect mass loss and lignin solubilization in angiosperm and gymnosperm wood. All xylariaceous taxa were capable of cellulose and xylan hydrolysis, but few produced enzymes involved in lignin breakdown. Xylariaceous fungi were incapable of causing mass loss in gymnosperm wood, but several caused significant mass loss in angiosperm wood during a six month in vitro exposure. Mass loss values obtained were low at approx. 20% of those obtained for basidiomycetes. Lignin was solubilized at similar rates to mass loss by Hypoxylon and Xylaria species, resulting in indices of lignin solubilization between 0.88 and 1.11, which were similar to those obtained for white-rot basidiomycetes and higher than those previously reported for any other xylariaceous fungi.

Ascomycota↗
PubMedDate not supplied

Lignin incorporation combined with electron-beam irradiation improves the surface water resistance of starch films.

We investigated the potential of an electron-beam post-treatment to tailor the properties of 70/30 and 80/20 wt. extruded starch-lignin films. The effect of a 400 kGy radiation on films differing essentially by the kind of lignins incorporated (lignosulfonates/alkali lignins) was assessed both at the macroscopic and the molecular levels. Changes in the polymer molecular structure were studied by IR spectroscopy, by thioacidolysis as well as by model compound experiments. Electron beam-irradiation at 400 kGy, a rather high dose for processing natural polymers, alters to some extent the mechanical resistance of the starch-based materials. However this treatment substantially reduces the hydrophilic surface properties of the films, while not harming their biodegradability. Involved in radical cross-coupling reactions, lignin phenolic compounds are likely to play a primary role in the formation of a hydrophobic condensed network. This study suggests that lower irradiation doses might yield biomaterials with improved usage properties.

Electrons↗
PubMedDate not supplied

Hydrogen bonding in lignin: a Fourier transform infrared model compound study.

Hydrogen bonding plays an important role in the thermal and mechanical properties of biopolymers. To investigate hydrogen bond formation in lignin, an abundant natural polymer found in plants, Fourier transform infrared (FTIR) analysis of various lignin model compounds was performed. Four monomeric model compounds and one dimeric model compound were studied under various conditions. FTIR analysis revealed aliphatic hydroxyl groups form stronger hydrogen bonds than phenolic hydroxyl groups. Further, the dimeric biphenyl-type structure formed significantly stronger intermolecular hydrogen bonds as compared to the other monomeric model compounds. Results from the model compound studies were used to explain the observed complex hydrogen-bonding system present in both softwood and hardwood technical lignins. Together with chemical analysis, we discuss the difference in hydrogen bonding between hardwood and softwood lignin and the observed differences in the glass transition temperature.

Biopolymers↗
PubMed2002

Heavy metal uptake by lignin: comparison of biotic ligand models with an ion-exchange process.

Metal uptake by kraft lignin, hereafter referred to as lignin, occurs by displacement of protons or bound metals with equilibrium constants K(ex)H and K(ex), respectively. Values calculated for wide ranges of initial concentrations are reasonably constant, thereby demonstrating the validity of these displacement processes and proving that uptake in these systems is not simple adsorption. It was found that the stoichiometry for Sr and Cd uptake by Ca-loaded lignin is 1 mol of metal for 1 mol of Ca released. This observation for metals of very different binding strengths is difficult to rationalize with the biotic ligand model as generally applied but is in complete agreement with an ion-exchange process. Binding strengths to lignin, which contains only oxygen ligands, follow the order Pb > Cu > Zn > Cd > Ca (strongest to weakest). For proton displacement, only more tightly bound metals such as Pb, Cu, Zn, and Cd can compete with protons for anion-binding sites at low pH, but at high pH, uptake of Ca, Sr, and Li can occur. An observed logarithmic decrease of K(ex)H with pH can be explained by having only weaker acids available for proton displacement under more basic conditions. The advantages and disadvantages of using adsorption and biotic ligand models for an ion-exchange process are discussed.

Adsorption↗
PubMed2004

Effect of cellulose/hemicellulose and lignin on the bioavailability of toluene sorbed to waste paper.

Paper constitutes about 38% of municipal solid waste, much of which is disposed of in landfills. Sorption to such lignocellulosic materials may limit the bioavailability of organic contaminants in landfills. The objective of this study was to identify the effect of individual biopolymers in paper on toluene sorption and bioavailability by subjecting fresh and anaerobically degraded office paper and newsprint to enzymatic hydrolysis and acid hydrolysis. Enzymatic degradation of cellulose and hemicellulose had no effect on toluene bioavailability. In contrast, acid-insoluble lignin controlled toluene sorption and bioavailability for both fresh and degraded newsprint. Acid-insoluble lignin could explain only 54% of the toluene sorption capacity of degraded office paper however, suggesting that crude protein and/or lipophilic organic matter were also important sorbent phases. Toluene sorbed to degraded office paper was also less bioavailable than toluene sorbed to an equivalent mass of lignin extracted from this sorbent. The latter result suggests that a fraction of toluene sorbed to degraded office paper may have been sequestered by lipophilic organic matter. The sorption and bioavailability data indicate that the preferential decomposition of cellulose and hemicellulose relative to lignin in landfills should not decrease the overall toluene sorption capacity of paperwaste or increase the bioavailability of sorbed toluene.

Adsorption↗
PubMed2006

Pesticide sorption and desorption by lignin described by an intraparticle diffusion model.

Lignin was used as a model compound for soil organic matter to gain insight into the mechanisms that control the kinetics of pesticide sorption and desorption. Hydrolytic lignin was immobilized in a matrix of alginate gel, and sorption-desorption experiments were undertaken with isoproturon. Sorption increased with time and was close to equilibrium after 14 days. Desorption was measured after sorption for different time intervals and for a number of successive desorption steps of different lengths. The results showed strong differences between the sorption and desorption isotherms. The ratio of sorbed to dissolved pesticide approached and even exceeded the equilibrium ratio, depending on the number of desorption steps and the length of each equilibration period. A numerical diffusion model was developed to describe radial diffusion into the lignin particles in combination with Freundlich sorption inside the particles. Key model parameters were adjusted to fit the sorption data, and the same parameters were then used to predict stepwise desorption. Desorption was well described by the model, which suggests that sorption and desorption were driven by the same mechanism and occurred at the same rate. The observed difference between the sorption and desorption isotherms could be fully explained by the nonattainment of equilibrium due to slow diffusion into and out of the lignin particles.

Adsorption↗