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PubMedDate not supplied

Lignin esters for use in unsaturated thermosets: lignin modification and solubility modeling.

Kraft lignins from hardwood and softwood were esterified with several anhydrides to alter their solubility behavior in nonpolar solvents, such as styrene-containing thermoset resins. The esterification reaction was facile, it reduced the amount of waste products, and can be readily scaled up. Increasing the carbon chain length on the ester group improved the solubility of kraft lignin in nonpolar solvents, with butyrated lignin being completely soluble in styrene. Esterification with unsaturated groups such as methacrylic anhydride, improved the solubility to a lesser extent than the saturated analogues. The solubility behavior of the modified lignin was described using the Flory-Huggins solubility theory, combined with the predictive method of Hoy. The main goal to obtain a styrene soluble kraft lignin that could be used in unsaturated polyesters and vinyl esters was achieved with fully butyrated kraft lignin and a butyrated/methacrylated kraft lignin. The solubility of the latter is governed by the butyrate/methacrylate ratio. The reaction rate constants for the butyration and methacrylation reactions were also determined and the aromatic hydroxyl groups were found to be consistently three times more reactive than the aliphatic ones.

Chromatography, Gel↗

PubMed2006

Organosolv ethanol lignin from hybrid poplar as a radical scavenger: relationship between lignin structure, extraction conditions, and antioxidant activity.

Twenty-one organosolv ethanol lignin samples were prepared from hybrid poplar (Populus nigra xP. maximowiczii) under varied conditions with an experimental matrix designed using response surface methodology (RSM). The lignin preparations were evaluated as potential antioxidants. Results indicated that the lignins with more phenolic hydroxyl groups, less aliphatic hydroxyl groups, low molecular weight, and narrow polydispersity showed high antioxidant activity. Processing conditions affected the functional groups and molecular weight of the extracted organosolv ethanol lignins, and consequently influenced the antioxidant activity of the lignins. In general, the lignins prepared at elevated temperature, longer reaction time, increased catalyst, and diluted ethanol showed high antioxidant activity. Regression models were developed to enable the quantitative prediction of lignin characteristics and antioxidant activity based on the processing conditions.

Acetylation↗

PubMed2001

Downregulation of caffeic acid 3-O-methyltransferase and caffeoyl CoA 3-O-methyltransferase in transgenic alfalfa. impacts on lignin structure and implications for the biosynthesis of G and S lignin.

Transgenic alfalfa plants were generated harboring caffeic acid 3-O-methyltransferase (COMT) and caffeoyl CoA 3-O-methyltransferase (CCOMT) cDNA sequences under control of the bean phenylalanine ammonia-lyase PAL2 promoter. Strong downregulation of COMT resulted in decreased lignin content, a reduction in total guaiacyl (G) lignin units, a near total loss of syringyl (S) units in monomeric and dimeric lignin degradation products, and appearance of low levels of 5-hydroxy guaiacyl units and a novel dimer. No soluble monolignol precursors accumulated. In contrast, strong downregulation of CCOMT led to reduced lignin levels, a reduction in G units without reduction in S units, and increases in beta-5 linked dimers of G units. Accumulation of soluble caffeic acid beta-d-glucoside occurred only in CCOMT downregulated plants. The results suggest that CCOMT does not significantly contribute to the 3-O-methylation step in S lignin biosynthesis in alfalfa and that there is redundancy with respect to the 3-O-methylation reaction of G lignin biosynthesis. COMT is unlikely to catalyze the in vivo methylation of caffeic acid during lignin biosynthesis.

Base Sequence↗

PubMed1994

Degradability of chlorine-free bleachery effluent lignins by two fungi: effects on lignin subunit type and on polymer molecular weight.

A bleachery effluent from a sulfite process pulp mill, which was extracted with alkali and treated with oxygen and hydrogen peroxide (EOP), was treated with two fungi, Trametes versicolor and Stagonospora gigaspora. Trametes versicolor did not cause any depolymerization or degradation of effluent lignins but increased the amount of chromophores, whereas S. gigaspora depolymerized the EOP lignins and caused a substantial reduction in aromatic compounds. For both fungal treatments, CuO oxidation caused a decrease in the yield of the aldehydes within the vanillyl and p-hydroxy phenol families, which was faster than the rates of decrease in the yields of the corresponding acids and ketones. However, only S. gigaspora caused changes in the pattern of the 11 characteristic lignin phenols produced by CuO oxidation, reflecting a preferential metabolism of some phenolic precursors. This fungus decreased the yield of total vanillyl phenols (V), which contributed the bulk of the 11 lignin oxidation products, from 93% initially to 59%. As a consequence, coumaryl (C), syringyl (S), and p-hydroxy phenols (P) became relatively enriched to 1.2, 6.5, and 33%, respectively. The stability of EOP-lignin constituent subunits is S > P > C > V. The two fungi differed significantly in their level of enzyme activities. In effluent-free medium, the ratio of laccase to peroxidase was higher for T. versicolor than for S. gigaspora. The presence of EOP-lignins significantly increased this ratio. No lignin peroxidase was detected but manganese peroxidase and laccase were detected during degradation activities.

Basidiomycota↗

PubMed1983

Lignin Degradation by Streptomyces viridosporus: Isolation and Characterization of a New Polymeric Lignin Degradation Intermediate.

A new, quantitatively significant intermediate formed during lignin degradation by Streptomyces viridosporus T7A was isolated and characterized. In Streptomyces-inoculated cultures, the intermediate, an acid-precipitable, polyphenolic, polymeric lignin (APPL), accumulated in the growth medium. The APPL was a water-soluble polymer probably consisting of a heterogeneous mixture of molecular weight components of >/=20,000. APPLs were precipitable from culture filtrates after they had been acidified to pH <3 to 5. Noninoculated controls yielded little APPL, but supernatant solutions from inoculated cultures produced quantities of APPL that correlated with the biodegradability of the lignocellulose type. Maximal recovery of APPL was obtained from corn lignocellulose, reaching 30% of the initial lignin present in the substrate. APPLs contained small amounts of carbohydrate, organic nitrogen, and inorganic materials. The lignin origin of APPLs was confirmed by chemical analyses, which included acidolysis, permanganate oxidation, elemental analyses, functional group analyses, nuclear magnetic resonance spectroscopy, and C isotopic techniques. Analyses of APPLs from corn lignocelluloses showed that S. viridosporus-degraded APPLs were lignin derived but significantly different in structure from APPLs derived from uninoculated controls or from a standard corn milled-wood lignin. Degraded APPLs were enriched in phenolic hydroxyl groups and, to a small extent, in carboxyl groups. Degradative changes appeared to be largely oxidative and were thought to involve substantial cleavage of p-hydroxy ether linkages and methoxyl groups in the lignin.

Journal Article↗

PubMed1978

Screening for lignin degrading bacteria by means of 14C-labelled lignins.

Several Nocardia and Pseudomonas spp., as well as some unidentified bacteria, isolated from lake water containing high loads of waste lignin, were tested for their capacity to release 14CO2 from specifically 14C-labelled dehydropolymer of coniferyl alcohol (DHP) or corn stalk lignins. The bacteria were selected according to their ability to degrade phenolic compounds. However, only some of them could release significant amounts of 14CO2 from the labelled lignin. The tested Nocardia spp. were more active than the Pseudomonas spp. and the unidentified bacteria. The most active strains belonged to N. autotrophica. These strains released CO2 significantly from the methoxyl group and transformed the other carbons from the phenylpropane skeleton of lignin also into CO2. Other less demethylating strains also released little CO2 from the other carbons of the lignin molecule. From corn stalk materials which were specifically labelled in the lignin part, only small amounts of labelled CO2 were released.

Biodegradation, Environmental↗

PubMed1996

A fungal metabolite mediates degradation of non-phenolic lignin structures and synthetic lignin by laccase.

Lignin peroxidase is generally considered to be a primary catalyst for oxidative depolymerization of lignin by white-rot fungi. However, some white-rot fungi lack lignin peroxidase. Instead, many produce laccase, even though the redox potentials of known laccases are too low to directly oxidize the non-phenolic components of lignin. Pycnoporus cinnabarinus is one example of a laccase-producing fungus that degrades lignin very efficiently. To overcome the redox potential barrier, P. cinnabarinus produces a metabolite, 3-hydroxyanthranilate that can mediate the oxidation of how non-phenolic substrates by laccase. This is the first description of how laccase might function in a biological system for the complete depolymerization of lignin.

Benzyl Alcohols↗

PubMed1999

Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins.

The biomimetic oxidation of 5-5' condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is reported. The oxidative efficiency of manganese and iron meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride (TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl porphyrin chloride (TSPPMnCl) and manganese meso-tetra(N-methylpyridinio)porphyrin pentaacetate (TPyMePMn(CH3COO)5) was compared on the basis of the oxidation extent of the models tested. Manganese porphyrins were found more effective in degrading lignin substructures than iron ones. Among them the cationic TPyMePMn (CH3COO)5, never used before in lignin oxidation, showed to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. The use of quantitative 31P NMR allowed the focusing on the occurrence of different degradative pathways depending on the catalyst used. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and carboxylic acids. Noteworthy, no significant condensation reactions occurred during manganese porphyrins catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins a substantial increase of condensed substructures was detected.

Anions↗

PubMed2003

NMR analysis of lignins in CAD-deficient plants. Part 1. Incorporation of hydroxycinnamaldehydes and hydroxybenzaldehydes into lignins.

Peroxidase/H2O2-mediated radical coupling of 4-hydroxycinnamaldehydes produces 8-O-4-, 8-5-, and 8-8-coupled dehydrodimers as has been documented earlier, as well as the 5-5-coupled dehydrodimer. The 8-5-dehydrodimer is however produced kinetically in its cyclic phenylcoumaran form at neutral pH. Synthetic polymers produced from mixtures of hydroxycinnamaldehydes and normal monolignols provide the next level of complexity. Spectral data from dimers, oligomers, and synthetic polymers have allowed a more substantive assignment of aldehyde components in lignins isolated from a CAD-deficient pine mutant and an antisense-CAD-downregulated transgenic tobacco. CAD-deficient pine lignin shows enhanced levels of the typical benzaldehyde and cinnamaldehyde end-groups, along with evidence for two types of 8-O-4-coupled coniferaldehyde units. The CAD-downregulated tobacco also has higher levels of hydroxycinnamaldehyde and hydroxybenzaldehyde (mainly syringaldehyde) incorporation, but the analogous two types of 8-O-4-coupled products are the dominant features. 8-8-Coupled units are also clearly evident. There is clear evidence for coupling of hydroxycinnamaldehydes to each other and then incorporation into the lignin, as well as for the incorporation of hydroxycinnamaldehyde monomers into the growing lignin polymer. Coniferaldehyde and sinapaldehyde (as well as vanillin and syringaldehyde) co-polymerize with the traditional monolignols into lignins and do so at enhanced levels when CAD-deficiency has an impact on the normal monolignol production. The implication is that, particularly in angiosperms, the aldehydes behave like the traditional monolignols and should probably be regarded as authentic lignin monomers in normal and CAD-deficient plants.

Alcohol Oxidoreductases↗

PubMed1999

Direct interaction of lignin and lignin peroxidase from Phanerochaete chrysosporium.

Binding properties of lignin peroxidase (LiP) from the basidiomycete Phanerochaete chrysosporium against a synthetic lignin (dehydrogenated polymerizate, DHP) were studied with a resonant mirror biosensor. Among several ligninolytic enzymes, only LiP specifically binds to DHP. Kinetic analysis revealed that the binding was reversible, and that the dissociation equilibrium constant was 330 microM. The LiP-DHP interaction was controlled by the ionization group with a pKa of 5.3, strongly suggesting that a specific amino acid residue plays a role in lignin binding. A one-electron transfer from DHP to oxidized intermediates LiP compounds I and II (LiPI and LiPII) was characterized by using a stopped-flow technique, showing that binding interactions of DHP with LiPI and LiPII led to saturation kinetics. The dissociation equilibrium constants for LiPI-DHP and LiPII-DHP interactions were calculated to be 350 and 250 microM, and the first-order rate constants for electron transfer from DHP to LiPI and to LiPII were calculated to be 46 and 16 s-1, respectively. These kinetic and spectral studies strongly suggest that LiP is capable of oxidizing lignin directly at the protein surface by a long-range electron transfer process. A close look at the crystal structure suggested that LiP possesses His-239 as a possible lignin-binding site on the surface, which is linked to Asp-238. This Asp residue is hydrogen-bonded to the proximal His-176. This His-Asp...proximal-His motif would be a possible electron transfer route to oxidize polymeric lignin.

Amino Acid Sequence↗

PubMed2006

Detailed analysis of modifications in lignin after treatment with cultures screened for lignin depolymerizing agents.

Termites, beetles, and other arthropods can digest living and decaying wood plus other lignocellulosic plant litter. Microbial sources like other wood-eating insect guts and wastewater treatment sludge were screened for lignin depolymerization. Near infrared spectroscopy and atomic force microscopy (AFM) along with high-performance liquid chromatography (HPLC), were used to track changes in functional groups, size, shape, and molecular weight of lignin molecules during incubations. Odontotaenius disjunctus (Betsy beetle) guts dissected whole or separately as midgut, foregut, and hindgut, consumed corn stover but did not show lignin depolymerization. The sludge-treated lignin did show some reduction in molecular weight on the HPLC, particle size (350-650 nm initially to 135-220 nm by day 30) and articles per field on AFM. pH and the presence of nutrients had a substantial effect on the extent of depolymerization. Cultures in lignin and nutrients showed higher growth than cultures with lignin only. Colony characteristics within the beetle gut and the sludge were also evaluated.

Animals↗

PubMed1999

Lignin and Mn peroxidase-catalyzed oxidation of phenolic lignin oligomers.

The oxidation of phenolic oligomers by lignin and manganese peroxidases was studied by transient-state kinetic methods. The reactivity of peroxidase intermediates compound I and compound II was studied with the phenol guaiacol along with a beta-O-4 phenolic dimer, trimer, and tetramer. Compound I of both peroxidases is much more reactive than compound II. The rate constants for these substrates with Mn peroxidase compound I range from 1.0 x 10(5) M-1 s-1 for guaiacol to 1.1 x 10(3) M-1 s-1 for the tetramer. Reactivity is much higher with lignin peroxidase compound I with rate constants ranging from 1.2 x 10(6) M-1s-1 for guaiacol to 3.6 x 10(5) M-1 s-1 for the tetramer. Rate constants with compound II are much lower with Mn peroxidase exhibiting very little reactivity. The rate constants dramatically decreased with both peroxidases as the size of the substrate increased. The extent of the decrease was much more dramatic with Mn peroxidase, leading us to conclude that, despite its ability to oxidize phenols, Mn2+ is the only physiologically significant substrate. The rate decrease associated with increasing substrate size was more gradual with lignin peroxidase. These data indicate that whereas Mn peroxidase cannot efficiently directly oxidize the lignin polymer, lignin peroxidase is well suited for direct oxidation of polymeric lignin.

Catalysis↗

PubMed1994

Fungal degradation of recalcitrant nonphenolic lignin structures without lignin peroxidase.

Lignin peroxidases (LiPs) are likely catalysts of ligninolysis in many white-rot fungi, because they have the unusual ability to depolymerize the major, recalcitrant, non-phenolic structures of lignin. Some white-rot fungi have been reported to lack LiP when grown on defined medium, but it is not clear whether they exhibit full ligninolytic competence under these conditions. To address this problem, we compared the abilities of a known LiP producer, Phanerochaete chrysosporium, with those of a reported nonproducer, Ceriporiopsis subvermispora, to degrade a synthetic lignin with normal phenolic content, a lignin with all phenolic units blocked, and a dimer, 1-(4-ethoxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol, that represents the major nonphenolic structure in lignin. P. chrysosporium mineralized all three models rapidly in defined medium, but C. subvermispora showed appreciable activity only toward the more labile phenolic compound under these conditions. However, in wood, its natural environment, C. subvermispora mineralized all of the models as rapidly as P. chrysosporium did. Defined media therefore fail to elicit a key component of the ligninolytic system in C. subvermispora. A double-labeling experiment with the dimeric model showed that a LiP-dependent pathway was responsible for at least half of dimer mineralization in wood by P. chrysosporium but was responsible for no more than 6-7% of mineralization by C. subvermispora in wood. Therefore, C. subvermispora has mechanisms for degradation of nonphenolic lignin that are as efficient as those in P. chrysosporium but that do not depend on LiP.

Journal Article↗

PubMed2000

Photocatalytic degradation of lignin and lignin models, using titanium dioxide: the role of the hydroxyl radical.

The role of hydroxyl radicals on the degradation of lignins during a cellulosic pulp bleaching process including a photocatalytic stage, was assessed using peroxyformic acid lignins EL1 and REL1 and two phenolic niphenyl lignin models 1 and 2. The irradiations were performed in the absence of photocatalyst TiO2 and H2O2 (condition a), in the presence of TiO2 (condition b) and in the presence of H2O2 (condition c). The experiments were conducted in alkaline (pH approximately 11) aqueous ethanol solutions with oxygen bubbling. The relative phenolic content of the irradiated solutions, which is indicative of the involvement of hydroxyl radicals, was determined by ionization absorption spectroscopy. The results obtained show that the catalyzed reaction involves both degradation of the phenolate groups by electron transfer and hydroxylation of the lignin aromatic structure. Benzyl alcohol structural elements in sodium borohydride reduced lignin REL1 and compound 2 were also found as good trapping agents for the hydroxyl radicals. The degradation of EL1 was studied by measuring its fluorescence emission by comparison to the fluorescence of compound 2. The emission spectra indicate that some biphenyl phenolate anions in EL1 are reacting under UV/visible irradiation and some others, probably polyphenolic chromophores emitting less fluorescence, are formed.

Catalysis↗

PubMed1995

Lignin oxidation by laccase isozymes from Trametes versicolor and role of the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) in kraft lignin depolymerization.

Two laccase isozymes (I and II) produced by the white-rot fungus Trametes versicolor were purified, and their reactivities towards various substrates and lignins were studied. The N-terminal amino acid sequences of these enzymes were determined and compared to other known laccase sequences. Laccase II showed a very high sequence similarity to a laccase which was previously reported to depolymerize lignin. The reactivities of the two isozymes on most of the substrates tested were similar, but there were some differences in the oxidation rate of polymeric substrates. We found that the two laccases produced similar qualitative effects on kraft lignin and residual lignin in kraft pulp, with no evidence of a marked preference for depolymerization by either enzyme. However, the presence of the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) prevented and reversed the polymerization of kraft lignin by either laccase. The delignification of hardwood and softwood kraft pulps with the two isozymes and the mediator was compared; either laccase was able to reduce the kappa number of pulp, but only in the presence of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate).

Amino Acid Sequence↗

PubMed2003

Ultra violet resonance Raman spectroscopy in lignin analysis: determination of characteristic vibrations of p-hydroxyphenyl, guaiacyl, and syringyl lignin structures.

Raman spectroscopy of wood and lignin samples is preferably carried out in the near-infrared region because lignin produces an intense laser-induced fluorescence background at visible excitation wavelengths. However, excitation of aromatic and conjugated lignin structures with deep ultra violet (UV) light gives resonance-enhanced Raman signals while the overlapping fluorescence is eliminated. In this study, ultra violet resonance Raman (UVRR) spectroscopy was used to define characteristic vibration bands of model compounds of p-hydroxyphenyl, guaiacyl, and syringyl lignin structures at three excitation wavelengths (229, 244, and 257 nm). The intensities of each band, relative to the intensity of the aromatic vibration band at 1600 cm-1, were defined and the most suitable excitation wavelength was suggested for each structure. p-Hydroxyphenyl structures showed intensive characteristic bands at 1217-1214 and 1179-1167 cm-1 with excitation at 244 nm, whereas the bands of guaiacyl structures were more intensive with 257 nm excitation. Most intensive characteristic bands of guaiacyl structures were found at 1289-1279, 1187-1185, 1158-1155, and 791-704 cm-1. Syringyl structures had almost identical spectra with 244 and 257 nm excitations with characteristic bands at 1514-1506, 1333-1330, and 981-962 cm-1. The characteristic bands of the three structural units were also found from the compression wood, softwood, and hardwood samples, indicating that UVRR spectroscopy can be applied for the determination of chemical structures of lignin.

Lignin↗

PubMed1991

Modification of a colorimetric analysis for lignin and its use in studying the inhibitory effects of lignin on forage digestion by ruminal microorganisms.

The colorimetric acetyl bromide soluble lignin (ABSL) procedure was modified to use for analyzing intact alfalfa and its cell wall fractions for both lignin and total phenolic substances. A purified lignin extracted from alfalfa (native lignin) was used as a standard. Soluble phenolic compounds present in alfalfa did not inhibit cellulose digestion in vitro, because cell wall fractions had the same or slightly lower cellulose digestibility values than did the intact forage (intact forage = 46.5%; Morrison's cell walls = 46.4%; NDF = 42.6%; ADF = 48.7%). Disappearance of ABSL from the solid digesta was very high for intact alfalfa (48.5%), presumably reflecting either solubilization or utilization of the phenolics. However, very little ABSL was detected in the liquid fraction, suggesting that the soluble phenolic substances possibly were metabolized or modified by ruminal microorganisms. On the other hand, little, if any, of the ABSL present in the cell wall fractions disappeared after 48 h of fermentation. These data emphasize the resistance of core lignin to microbial degradation in short-term anaerobic fermentations.

Animals↗

PubMed1977

Microbial decomposition of synthetic C-labeled lignins in nature: lignin biodegradation in a variety of natural materials.

Lignin biodegradation in a variety of natural materials was examined using specifically labeled synthetic C-lignins. Natural materials included soils, sediments, silage, steer bedding, and rumen contents. Both aerobic and anaerobic incubations were used. No C-labeled lignin biodegradation to labeled gaseous products under anaerobic conditions was observed. Aerobic C-labeled lignin mineralization varied with respect to type of natural material used, site, soil type and horizon, and temperature. The greatest observed degradation occurred in a soil from Yellowstone National Park and amounted to over 42% conversion of total radioactivity to CO(2) during 78 days of incubation. Amounts of C-labeled lignin mineralization in Wisconsin soils and sediments were significantly correlated with organic carbon, organic nitrogen, nitrate nitrogen, exchangeable calcium, and exchangeable potassium.

Journal Article↗