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PubMed2004

Study of the lignin model compound supramolecular structure by combination of near-field scanning optical microscopy and atomic force microscopy.

In this paper, we present a nanoscale study of the supramolecular structure of the dehydrogenate polymer (ZL-DHP) lignin model compound. The combination of near-field scanning optical microscopy (NSOM or SNOM) and atomic force microscopy (AFM) has been utilized to explore physicochemical properties of the lignin model compound on a scale ranging from individual macromolecules to globular supramolecular assemblies. By utilizing NSOM in transmission mode, the optical inhomogeneity in the lignin supramolecular structure has been observed for the first time. In particular, the transmission-mode NSOM images reveal a combination of hollow and layered supramolecular globular structure in the lignin model compound. Through the paired use of TappingMode and pulsed-mode AFM, we have also confirmed the existence of regions with different rheological properties on the single lignin model compound supramolecular assembly.

Alcohols↗
PubMedDate not supplied

Lignification in poplar plantlets fed with deuterium-labelled lignin precursors.

Lignification was investigated in wild-type (WT) and in transgenic poplar plantlets with a reduced caffeic acid O-methyl-transferase (COMT) activity. Coniferin and syringin, deuterated at their methoxyl, were incorporated into the culture medium of microcuttings. The gas chromatography-mass spectrometry (GC-MS) analysis of the thioacidolysis guaiacyl (G) and syringyl (S) lignin-derived monomers revealed that COMT deficiency altered stem lignification. GC-MS analysis proved that the deuterated precursors were incorporated into root lignins and, to a lower extent, in stem lignins without major effect on growth and lignification. Deuterium from coniferin was recovered in G and S lignin units, whereas deuterium from syringin was only found in S units, which further establishes that the conversion of G to S lignin precursors may occur at the level of p-OH cinnamyl alcohols.

Cinnamates↗
PubMedDate not supplied

The regulation from guaiacyl to syringyl lignin in the differentiating xylem of Robinia pseudoacacia.

13C- and deuterium (D)-labeled ferulic acid and sinapic acid ([8-(13)C, 3-OCD3]-ferulic acid and [8-(13)C, 3,5-OCD3]-sinapic acid) were administered to robinia (Robinia pseudoacacia L.) shoots. To estimate the distribution of the label from administrated ferulic or sinapic acid, continuous 50-microm-thick tangential sections cut from the cambium of robinia were subjected to lignin chemical analysis by the DFRC method. Labeled ferulic acid was incorporated into guaiacyl and syringyl lignin. The incorporation of labeled ferulic acid into syringyl units was observed only in the later stage of lignification. Labeled sinapic acid was incorporated into syringyl lignin in the early stage and the later stage of lignification. In general, syringyl lignin was deposited in the later stage of cell wall lignification. Thus, the incorporation of sinapic acid to syringyl lignin in the early stage of lignification was abnormal. Taken together, the aromatic ring-modifying reactions (the conversion from guaiacyl to syringyl moiety, including the hydroxylation and methylation) were more important for the regulation of the sinapyl alcohol biosynthesis than the reducing reactions (the reduction of acids to alcohols) in the differentiating xylem.

Lignin↗
PubMedDate not supplied

Lignin-polymer blends: evaluation of compatibility by image analysis.

This paper opens onto a general discussion on the development of new polymeric materials obtained from lignin blends. The aim is (i) to look for good polymer candidates to obtain a good compatibility with lignins (that is among semi polar polymers), and (ii) to look for good lignin candidates to obtain a good compatibility with polymers showing extreme behaviours (very polar, e.g. starch, or apolar, e.g. polypropylene). The compatibility is simply assessed through the blend morphology, as studied by visible microscopy. The morphology of the blends obtained from semi polar polymers is very sensitive to the variation of the solubility parameters. In a low range of polymer solubility parameters (delta delta = 1 cal cm(-3)), both heterogeneous and homogeneous systems are obtained. These blends could be easily improved by a careful choice in the polymer structure (particularly in the family of biodegradable polyesters); it could be possible also to take advantage of lignin variability to improve the compatibility. Only low molecular weight lignins are compatible with apolar and very polar matrixes. These compounds induce interesting specific properties, and original methods have to be looked for in order to improve their production.

Lignin↗
PubMed2005

Single, binary and multi-component adsorption of copper and cadmium from aqueous solutions on Kraft lignin--a biosorbent.

A new biosorbent for removing toxic metal ions from water/industrial wastewater has been investigated using by-product lignin from paper production. Lignin was extracted from black liquor waste, characterized and utilized for the removal of copper and cadmium from aqueous solutions in single, binary and multi-component systems. Adsorption studies were conducted at different temperatures, lignin particle sizes, pHs and solid to liquid ratios. All the studies were conducted by a batch method to determine equilibrium and kinetic parameters. The Langmuir and Freundlich isotherm models were applied. The Langmuir model fits best the equilibrium isotherm data. The maximum lignin adsorption capacities at 25 degrees C were 87.05 mg/g (1.37 mmol/g) and 137.14 mg/g (1.22 mmol/g) for Cu(II) and Cd(II), respectively. Adsorption of Cu2+ (68.63 mg/g at 10 degrees C and 94.68 mg/g at 40 degrees C) and Cd2+ (59.58 mg/g at 10 degrees C and 175.36 mg/g at 40 degrees C) increased with an increase in temperature. Copper and cadmium adsorption followed pseudo-second order rate kinetics. From kinetic studies, various rate and thermodynamic parameters such as effective diffusion coefficients, activation energy, and activation entropy were evaluated. Adsorption occurs through a particle diffusion mechanism at temperatures 10 and 25 degrees C while at 40 degrees C it occurs through a film diffusion mechanism. The sorption capacity of black liquor lignin is higher than many other adsorbents/carbons/biosorbents utilized for the removal of Cu(II) and Cd(II) from water/wastewater in single and multi-component systems.

Adsorption↗
PubMed2005

Light promotes the synthesis of lignin through the production of H2O2 mediated by diamine oxidases in soybean hypocotyls.

In order to analyze the relationship between polyamine oxidative degradation induced by light and the Lignin synthesis in cell walls, the activities of diamine oxidases and peroxidase, the contents of H2O2 and lignin, and the growth of hypocotyls in soybean [Glycine max (Linn.) Merr.] grown under tight or in darkness were investigated. In comparison with the dark treatment, light irradiation significantly inhibited the growth of soybean hypocotyls and promoted the activities of diamine oxidases and peroxidase as well as the accumulation of H2O2 and lignin. Treatments with the different concentrations of diamine oxidase inhibitors (2-hydroxyethylhydrazine and aminoguanidine) under the light condition inhibited diamine oxidase activity, and decreased the contents of H2O2 and lignin. The results provide evidence for the hypothesis that light irradiation could promote the accumulation of H2O2 and lignin in cell walls by activating polyamine oxidative degradation mediated by diamine oxidases.

Amine Oxidase (Copper-Containing)↗
PubMed2006

Lignin composition in cambial tissues of poplar.

The cambial tissues of a Populus balsamifera, Balsam poplar clone were studied during a growth season. The Klason and acid-soluble lignin contents were determined as well as the carbohydrate monomer distribution and the protein content. Both the phloem and the xylem sides of the cambial region were examined. The samples were analyzed by thioacidolysis and structures of dimeric products were determined by mass spectrometry after desulphuration. Chemical analysis of samples during the growth season was combined with microscopy of embedded specimens that showed the state of cell differentiation at the time of sampling. In spring and early summer, growth is very rapid and the intention was to collect tissue in which exclusively the middle lamella/primary cell wall had begun to lignify. The Klason lignin, protein content and carbohydrate monomer distribution showed that all the specimens from the cambial tissues sampled during a growth season contained predominantly middle lamella and primary walls; except for the developing xylem sampled in August where the carbohydrate composition showed that secondary walls were present. Thioacidolysis showed that the lignin from the cambial tissues had more condensed structures than the lignin from the reference balsam poplar clone wood. More guaiacyl than syringyl units were detected and mass spectrometry showed that the cambial tissues contained more lignin structures with end-groups than the reference sample. These results suggest that lignification in the cambial layer and early developing xylem may take place predominantly in a bulk fashion during the summer.

Lignin↗
PubMed2004

Biomarker signature in tropical wetland: lignin phenol vegetation index (LPVI) and its implications for reconstructing the paleoenvironment.

Organic matter of a peat core (3.60 m, 7428 years BP) collected from Rawa Danau, west Java, Indonesia, was analyzed to evaluate the early diagenetic fates of lignin in a tropical wetland and to reconstruct past vegetation and climate changes. Vertical profiles of (Ad/Al)v, (Ad/Al)s, and lambda(8) show that the lignin composition is well preserved in a sub-aqueous environment under reducing conditions. The sedimentary terrigenous plant material at Rawa Danau is comprised predominantly of angiosperm wood. For this kind of tropical, diverse, and dynamic ecosystem, a new vegetation change index called lignin phenol vegetation index (LPVI): LPVI is defined using the lignin phenol composition. This index can sensitively detect terrestrial vegetation changes as well as environmental conditions forcing such changes. The LPVI of the Rawa Danau peat core provides better resolution than other lignin parameters used previously, and reveals four major vegetation change events since the mid-late Holocene. In comparison to other geochemical data (i.e. elemental carbon, isotopes, and hydrocarbons), the LPVI is more sensitive and is able to trace even minor vegetation and climate changes and thus could improve biogeochemical interpretations of peat records.

Biomarkers↗
PubMed2002

Modification phenomena of solid-state lignin caused by electron-abstracting oxidative systems.

Oxidative treatments of wood pulp lignin by one-electron-abstracting enzymatic or chemical systems result in modification phenomena which are not fully described in terms of those known from lignin model compound studies. The generation of, e.g., long-lived radicals necessitates nondestructive spectroscopic analysis of the lignin polymer for a proper characterization of these. The present work exposes a complexity of spectroscopic modification phenomena, which has not previously been realized. This is achieved by a laccase-mediator system, where the mediator is an aromatic low-molecular-weight compound, which mediates the electron abstraction between the lignin and the enzyme laccase. It is demonstrated that the modification generated exhibits qualitatively different temporal phases. The mechanisms are partly explained in terms of Marcus electron transfer theory, and it is suggested that these may play a role in the in vivo synthesis and degradation of lignin.

Benzothiazoles↗
PubMed2001

Analysis of alkali-lignin in a paper mill effluent decolourised with two Streptomyces strains by gas chromatography-mass spectrometry after cupric oxide degradation.

Alkali-lignin samples obtained from an untreated paper mill effluent and from the effluent decolourised by the strains Streptomyces avermitilis CECT 3339 and Streptomyces scabies UAH 51 were analysed by gas chromatography-mass spectrometry (GC-MS) after cupric oxide degradation. The analysis of the depolymerisation products of the alkali-lignin from the decolourised effluents showed a strain specific modification of the aromatic moiety of the alkali-lignin. Moreover, both strains were able to breakdown the aryl-alkyl ether linkages between the cinnamic acids and the lignin. Finally, GC-MS analysis showed that both strains oxidised the alkali-lignin regardless of its initial degree of oxidation.

Alkalies↗
PubMed2001

Caffeoyl coenzyme A O-methyltransferase and lignin biosynthesis.

Lignin, a complex phenylpropanoid compound, is polymerized from the monolignols p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. These three monolignols differ only by the 3- and 5-methoxyl groups. Therefore, enzymatic reactions controlling the methylations of the 3- and 5-hydroxyls of monolignol precursors are critical to determine the lignin composition. Recent biochemical and transgenic studies have indicated that the methylation pathways in monolignol biosynthesis are much more complicated than we have previously envisioned. It has been demonstrated that caffeoyl CoA O-methyltransferase plays an essential role in the synthesis of guaiacyl lignin units as well as in the supply of substrates for the synthesis of syringyl lignin units. Caffeic acid O-methyltransferase has been found to essentially control the biosynthesis of syringyl lignin units. These new findings have greatly enriched our knowledge on the methylation pathways in monolignol biosynthesis.

Lignin↗
PubMed2001

beta-fluoro-coniferyl alcohol does not inhibit lignin biosynthesis in suspension cultures of Picea abies (L.) Karst.

A fluorinated analogue of coniferyl alcohol has been reported to be a specific inhibitor of oxidases involved in the biosynthesis of lignin. The Z isomer of beta-fluoro-coniferyl alcohol was synthesized and used for the preparation of dehydrogenation polymers (DHPs) and was also tested on lignin producing suspension cultures of spruce (Picea abies (L.) Karst.). The growth of the cells or the production of lignin by the suspension cultures was not significantly affected by the addition of fluoroconiferyl alcohol. This analogue did not form polymers quite as easily as did coniferyl alcohol in oxidation with hydrogen peroxide and horseradish peroxidase. In both cases the beta-fluoroconiferyl alcohol became incorporated in the polymeric product. We were unable to detect any specific inhibition of peroxidase activity, which is at variance with earlier reports of pronounced inhibition of lignin biosynthesis in poplar plantlets by fluoroconiferin, a potential inhibitor of oxidases involved in lignin biosynthesis.

Culture Media↗
PubMed2000

Is cellobiose dehydrogenase from Phanerochaete chrysosporium a lignin degrading enzyme?

Cellobiose dehydrogenase (CDH) is an extracellular redox enzyme of ping-pong type, i.e. it has separate oxidative and reductive half reactions. Several wood degrading fungi produce CDH, but the biological function of the enzyme is not known with certainty. It can, however, indirectly generate hydroxyl radicals by reducing Fe(3+) to Fe(2+) and O2 to H2O2. Hydroxyl radicals are then generated by a Fenton type reaction and they can react with various wood compounds, including lignin. In this work we study the effect of CDH on a non-phenolic lignin model compound (3,4-dimethoxyphenyl glycol). The results indicate that CDH can affect lignins in three important ways. (1) It breaks beta-ethers; (2) it demethoxylates aromatic structures in lignins; (3) it introduces hydroxyl groups in non-phenolic lignins. The gamma-irradiated model compound gave a similar pattern of products as the CDH treated model compound, when the samples were analyzed by HPLC, suggesting that hydroxyl radicals are the active component of the CDH system.

Carbohydrate Dehydrogenases↗
PubMed2001

Topographical characterization and surface force spectroscopy of the photochemical lignin model compound.

By combining the results from atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), herein we investigate properties of photochemical lignin model compounds. We provide evidence that photochemical lignin forms random, probably non-functional structures. The topography of such structures is explored using ESEM. Non-functionality of such structures is proved by AFM and atomic force spectroscopy experiments wherein the photochemical lignin functionalized tip is approached to the substrate covered with photochemical lignin. There was no evidence of existence of any kind of host-guest interaction during the approach/retraction experiments. These results provide evidence for our previously stated hypothesis that photochemical lignin polymerization may be one of the degrading effects of UV radiation to the plant cell.

Dimerization↗
PubMed1998

Electrochemical analysis of the interactions of laccase mediators with lignin model compounds.

The mechanism of oxidation of lignin by laccase and mediator has been investigated by cyclic voltammetry and bulk electrolysis. Electrochemical properties and reactivities of the two mediators 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) and 1-hydroxybenzotriazole (HBT) were studied and their intermediates responsible for lignin oxidation were characterized. ABTS was oxidized first to the cation radical (ABTS+.) and then to the dication (ABTS2+). The two oxidized species are relatively stable and electrochemically reversible, with formal redox potentials (E0' vs Ag/AgCl) of 472 mV for ABTS/ABTS+. and 885 mV for ABTS+./ABTS2+. The dication was shown to be the intermediate responsible for the oxidation of the non-phenolic lignin model compound veratryl alcohol, whereas the cation radical reacted only with phenolic structures in lignin. Cyclic voltammetry of HBT shows only one oxidation peak at 878 mV, but unlike ABTS, the oxidized intermediate was not stable and decayed rapidly. The radical intermediate of HBT was shown to catalyze the oxidation of veratryl alcohol to veratraldehyde. The kinetics of homogeneous redox catalysis of mediators and veratryl alcohol were estimated. ABTS-mediated lignin oxidation at the redox potential of laccase (585 mV) was shown to be possible, but at a very slow rate, as previously reported for laccase and mediator.

Benzothiazoles↗
PubMed2003

The effect of lignin and sugars to the aerobic decomposition of solid wastes.

A series of experimental runs were conducted from 1995 to 1999 in Madison (WI, USA) with the goal to investigate the biodegradation process of seven (7) solid waste components and mixtures of them under near optimal aerobic conditions. It was shown that substrates with high initial lignin contents or high initial HWSM contents were observed to have relatively low and high degradation extents, respectively. Two linear equations were derived that correlate degradation extent (as indicated by the volatile solids reduction) to initial lignin and initial HWSM contents separately. The lignin equation was compared to a similar equation previously developed for anaerobic environments by Chandler et al. (Predicting methane fermentation biodegradability. In: Biotechnology and Bioengineering Symposium No. 10 (1980) New York: John Wiley & Sons). With comparison to the Chandler formula, lignin was found to be less inhibitory to the overall substrate decomposition in aerobic environments compared to anaerobic ones. Cellulose loss contributed to a higher than 50% to the overall dry mass loss for all substrates studied. In addition, the cellulose to lignin (C/L) ratio appeared to be a relatively accurate compost maturity indicator, since it reduced to a value less than 0.5 for most substrates that had reached their degradation extent.

Bacteria, Aerobic↗
PubMed1998

Structural modifications induced during biodegradation of wheat lignin by Lentinula edodes.

The structural modifications occurring during wheat straw lignin biodegradation were evaluated by the concerted use of 31P-, 1H- and 2D homo- and heteronuclear NMR spectroscopies. Straw lignin was found to be oxidatively degraded via stereoselective side-chain oxidation as evidenced by a lower erythro/threo ratio. Significantly lower amounts of phenolic hydroxy and methoxy groups in the decayed lignin may be indicative that its structure after the fungal treatment contained a lower amount of aromatic units. In addition an increase in carboxylic acids content, that cannot be explained only on the basis of side-chain oxidation reactions, was also apparent. This evidence, coupled with pertinent data collected during this effort, suggests the occurrence of aromatic ring cleavage reactions. In fact the oxidative degradation of lignin model compounds by fungi has been reported to occur via the 3-oxoadipate pathway which is known to cause aromatic ring cleavage with the formation of aliphatic chains. The presence of aliphatic moieties in the decayed lignin was confirmed by detailed 1H- and 2D NMR spectroscopic analyses.

Biodegradation, Environmental↗
PubMedDate not supplied

Identifying the characteristic secondary ions of lignin polymer using ToF-SIMS.

The chemical structure of lignin, a complex, irregular polymer of phenylpropane units that occurs in plant cell walls, was investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The positive ToF-SIMS spectra of lignin isolated from pine and beech wood showed prominent secondary ions possessing guaiacyl (at m/z 137 and 151) or syringyl (at m/z 167 and 181) rings, which are the basic building units of lignin polymer. This shows that ToF-SIMS is a useful tool for lignin structural analysis. The peaks at m/z 137 and 167 were assigned as the C6-C1 ion, and the peaks at m/z 151 and 181 may be double-component, the C6-C1 ion and the C6-C2 ion. We confirmed the characteristic guaiacyl ions using a synthetic lignin model compound, dehydrogenation polymer (DHP), which was formed by polymerizing of unlabeled and deuterium-labeled coniferyl alcohols. The formation mechanism of the main secondary ions was deduced by labeling specific positions of coniferyl alcohols with a stable isotope to study the relationship between chemical structure and secondary ion formation in ToF-SIMS.

Deuterium↗