Guaiacyl Structures Research Articles

Нитрозирование лигносульфонатов в условиях твердофазного катализа

Lignosulfonates are the most common commercial lignin-based product due to their unique properties. Various methods are known for modifying lignosulfonates and lignosulfonic acids. This article presents the results of the development of a new approach to the production of nitrosated lignosulfonic acids. The method is based on a reaction catalyzed by cation exchange resins in the H-form: KU-2-8 cation exchanger and wofatite. The influence of reagent consumption and reaction duration on the course of nitrosation has been studied. The dynamics of the proposed nitrosation practically coincides with the dynamics of a similar reaction using sulfuric acid by the known method. The optimal consumption of sodium nitrite equals 15 %, and the optimal consumption of cation exchanger equals 100 % by weight of lignosulfonates. During the nitrosation of lignosulfonates, significant changes in the electronic spectra occur in the region of 280...500 nm. Two overlapping absorption bands appear with maxima at 300 and 330 nm, as well as an intense absorption band at 430 nm, due to nitroso groups conjugated with the aromatic nuclei of phenylpropane units. To analyze the ionization spectra, they have been deconvoluted. The resulting spectra are well approximated by 5 Gaussians with an error of no more than 5 %. Two options for carrying out the nitrosation reaction of lignosulfonates have been proposed: under static and dynamic conditions. It has been established that under dynamic conditions, nitroso derivatives of lignosulfonic acids are formed that do not contain metal cations, and the pH of the resulting solutions does not exceed 1.4. The elemental compositions of the isolated initial and nitrosated lignosulfonic acids have been determined. The nitrogen content of lignosulfonic acids has increased from 0.32 (initial) to 2.17 % (nitrosated). In addition, under dynamic conditions, an additional stage of separating the cation exchanger from the reaction medium by filtration is not required. New bands have appeared in the IR spectrum of nitrosated lignosulfonic acids: at 1540 cm–1, which is due to the presence of nitroso groups, and a wide absorption band at 1700...1715 cm–1, which can be caused by vibrations of the carboxyl group or the quinone monooxime tautomeric form of the guaiacyl structures of lignosulfonic acids.

Contribution of Lignin from Different Bioresources to the Pollution Load

Lignin was extracted from eucalyptus, Pinus koraiensis, and bagasse (representatives for hardwood, softwood, and Gramineae, respectively) black liquors to quantitatively distinguish the pollution loads caused by lignin. The results indicated that the actual common chemical oxygen demand (CODCr) of lignin was lower than the theoretical CODCr with an actual oxidative ratio of approximately 85%. The results also showed that 1 kg of lignin from eucalyptus, P. koraiensis, and bagasse could produce CODCr pollution loads of 1.476 kg, 1.540 kg, and 1.561 kg, respectively, which revealed the large contribution of lignin to the pollution load. Through the elemental analysis, infrared spectroscopy, and nuclear magnetic resonance analysis in the hydrogen and carbon spectra of the different lignin, it was found that guaiacyl structures in the lignin units can lead to a better thermal stability for P. koraiensis. Compared with the P. koraiensis and bagasse lignins, the eucalyptus lignin had a higher elemental oxygen content and lower molecular weight with mainly syringyl structures, which resulted in a higher reaction activity.

Characterization of Residual Lignin Obtained by the Enzymatic Hydrolysis of Oil Palm Empty Fruit Bunch Pulps

Residual lignin present in alkali pulps prepared from oil palm (Elaeis guineensis) empty fruit bunch was isolated using an enzymatic method and characterized successfully by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). These pulps were prepared by soda-anthraquinone (AQ) and prehydrolysis (PH) soda-AQ cooking methods (pulp yields were 45.3 and 33.9%, respectively). Py-GC/MS of the residual lignin showed that two pyrolysis products which were indole and methylindole originating from the enzyme (contents 12 to 44%), in addition to eight pyrolysis products originating from syringyl (S) and guaiacyl (G) structure of lignin. Furthermore, palmitic acid was also detected in the residual lignin (contents 0.11 to 0.28%). The residual lignin was subjected to further purification by a cellobiose treatment method, and the quantity of enzyme present in the residual lignin was found to decrease after the treatment. Residual lignin in PH-soda-AQ pulp exhibited a higher S/G ratio (0.86 to 0.98) than that in soda-AQ pulp (0.76 to 0.97). This study showed that the contents of lignin (19 to 44%) and enzyme in enzymatically isolated lignin can be estimated by the Py-GC/MS method.

Py-GC/MS studies and principal component analysis to evaluate the impact of feedstock and temperature on the distribution of products during fast pyrolysis

This paper investigates the effect of pyrolysis temperature between 350 and 600°C on the distribution of pyrolytic products derived from Avicel, α-cellulose, Douglas Fir wood (softwood) and Hybrid Poplar wood (hardwood) by Py-GC/MS as a way to identify the best conditions for bio-oil production. The products were grouped in five families depending on their origin. The C1 family is formed by products of cellulose fragmentation reactions (glycoaldehyde, acetol, 1,2-ethanediol, monoacetate, butanedial). The products grouped in the C2 family (levoglucosan, levoglucosenone, 1,4:3,6-dianhydro-α-d-glucopyranose) are derived from cellulose depolymerization reactions. The molecules derived from hemicellulose (acetic acid, furfural, 2-furanmethanol) were grouped in the H family. The products derived from lignin were grouped in two families L1 (derived from p-hydroxyl phenol (H) and guaiacyl (G) structures) and L2 (derived from syringyl (S) structures). Principal components analysis was used to identify the main factors controlling the distribution of products. Our results show that the yield of most of the pyrolytic products can be explained in the five groups or families described above. Most of the C1 products derived from Avicel, α-cellulose and Douglas Fir fragmentation reactions increase in yield as the temperature increases. In the case of Hybrid Poplar these products reach a maximum at 400°C. CO2, 2-oxo methyl ester propanoic acid, 1,2-cyclopentanedione, 3-methyl, levoglucosenone, 1,4:3,6-dianhydro-α-d-glucopyranose, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, and most of the phenolic compounds show a response to temperature changes that is independent of the feedstock processed. As the temperature increased the yield of levoglucosenone (product of dehydration reactions) decreased for all the samples studied. Levoglucosan yield is however highly dependent on the feedstock used and, as such, its behavior with temperature changes is more difficult to predict. The maximum yield of the products derived from lignin (L1 and L2) was found between 400 and 450°C.

Investigation of structure of milled wood and dioxane lignins of Populus nigra and Cupressus sempervirens using the DFRC method

AbstractIn this study, derivatisation followed by reductive cleavage (DFRC) were used to investigate milled wood lignin (MWL) and dioxane lignin (DL) structures of Populus nigra and Cupressus sempervirens. After the DFRC reactions, the constituents obtained from these two kinds of lignin were recognised structurally using several chromatographic and spectral methods such as 13C NMR, GC-MS, and GPC. Comparative results showed that the dominant structural components of the two kinds of lignin are obtained from the cleavage of β-O-4 bonds. The main component of DL and MWL of P. nigra is 4-hydroxy-3,5-dimethoxy-1-phenyl-γ-hydroxypropene (syringyl structures). Also, some guaiacyl structures were observed. The dominant component identified in both lignins of C. sempervirens is 4-hydroxy-3-methoxy-1-phenyl-γ-hydroxypropene (guaiacyl structures). The cleavage method has a good performance for both P. nigra and C. sempervirens and the results obtained are in good agreement with previously published data.

Nitrobenzene oxidation of lignins from several plants of the family Gramineae

It was found based on results from alkaline nitrobenzene oxidation of natural and isolated dioxane lignins from several plants of the family Gramineae such as rice husks, rice straw, and corn and sorghum stems that the studied lignins consisted of three types of structural units with the predominance of guaiacyl structures.

Lignin oxidation mechanisms under oxygen delignification conditions. Part 2: Advanced methods for the detailed characterization of lignin oxidation mechanisms

AbstractAdvanced analysis methods have been developed to follow the reactions of lignin during alkaline oxygen delignification conditions more comprehensively than before. This aim was attained by monitoring both the lignin macromolecule and the dissolved reaction products. Softwood (SW) and hardwood (HW) kraft spent liquor lignins were studied as substrates under various reaction conditions. The decrease in the contents of different types of free phenolic hydroxyl groups and the concurrent formation of carboxylic acids was followed by31P NMR of the phosphitylated products. In addition, the formation of acidic degradation products with low molecular weight was determined by capillary zone electrophoresis (CE). This way, it was possible to distinguish the carboxylic acids bound to the lignin macromolecule from the cleaved reaction products, even if they partly co-precipitated during sample preparation. Peak deconvolution was applied to get information on syringyl type phenolic structures and on C(5) condensed guaiacyl structures in hardwood lignin. Pyrolysis-GC/MS was applied to provide additional information about the distribution of guaiacyl/syringyl/p-hydroxyphenyl (G/S/H) type lignin subunits, as well as changes in the phenylpropane side chain.

Chemical structure and pyrolysis response of beta-O-4 lignin model polymer

Hydroxyphenyl (H-type) and guaiacyl (G-type) lignin model polymers composed of the β–O–4 structure without g–hydroxymethyl groups were synthesized. The chemical structures of the H- and G-type lignin models were characterized by 1H- and 13C-NMR, as well as MALDI-TOF/MS. The pyrolysis response was analyzed by means of TG-DTG, Py-GC/MS, and a tube furnace technique. 1H-, 13C-NMR, and MALDI-TOF/MS showed that the lignin models were linear polymers. The polymers included the β–O–4 linkage, as in natural lignin. Pyrolytic products from H-type lignin model only possessed p-hydroxyphenyl structure without methoxyl groups, and the pyrolytic products from G-type lignin model only possessed guaiacyl structure with methoxyl groups. Pyrolysis products from H- and G- type lignin models were classified into char, gas, and liquid (bio-oil), and the gaseous products of two model compounds mainly consisted of H2, CO, CH4, CO2, and C2H4.

UV resonance Raman spectroscopic study of photodegradation of hardwood and softwood lignins by UV laser

Abstract The effect of laser irradiation (Ar+ ion laser, 244 nm) on photodegradation of lignin in silver birch and rubberwood as hardwoods and spruce and chir pine as softwoods has been investigated by UV resonance Raman spectroscopy (UVRRS). UVRR spectra showed degradation of aromatic structures accompanied by the formation of both ortho- and para-quinone structures as a result of photodegradation of wood surfaces. There was a rapid decrease in the intensities of all the lignin-associated bands accompanied by broadening of aromatic bands at 1602 cm-1 and in the region of 1500–1000 cm-1 due to formation of unsaturated structures arisen from lignin degradation. The rate of lignin degradation was observed by measuring the relative intensity of aromatic band at 1602 cm-1 during photodegradation. The rates of UV-degradation of hardwood and softwood surfaces were compared and it was found that hardwoods degrade at a faster rate than softwoods. The syringyl structures in hardwood lignin are more sensitive to photochemical degradation than guaiacyl structures. The rate of photodegradation increased with increasing intensity of the irradiated laser energy.

Structure of extracted lignins from oak heartwood (Quercus petraea Liebl., Q. Robur L.)

This paper presents a complete structural investigation into the main extracted lignin of Quercus robur and Q. petraea heartwood. Extensive 1H and 13C homo- and heteronuclear NMR were employed, particularly the TOCSY and HMQC techniques. Three major fractions represented the raw material: lignan, the most degradative form of lignin polymers, the ethanol-lignins which are very similar to the lignins obtained during ageing spirits on wood contact and finally the dioxan-lignin, almost similar to the in situ lignins. All these fractions were characterized as syringyl–guaiacyl structures with mainly β-O-4 and β–β linkages. S/G ratio was 1.1 and 2.7, for ethanol-lignin and dioxan-lignin, respectively. The lignan fraction required a second step of purification to obtain two lignans (60:40, w/w) prior to NMR investigation, in order to obtain preliminary structural information. To cite this article: N. Vivas et al., C. R. Chimie 9 (2006). Cet article présente une étude structurale complète des lignines extraites du bois de cœur de Quercus robur et Quercus petraea. La RMN 1H et 13C homo- et hétéronucléaire a été employée, et particulièrement les techniques TOCSY et HMQC. Trois fractions principales représentent la matière première : les lignanes, qui représentent la forme la plus dégradée des lignines polymères, les lignines-éthanol, qui sont similaires aux lignines obtenues durant le vieillissement des alcools en contact avec le bois, et finalement les lignines dioxane, similaires aux lignines in situ. Toutes ces fractions sont caractérisées comme des structures syringyl–guaïacyl avec principalement des liaisons β-O-4 et β-β. Le rapport S/G est de 1,1 et 2,7, respectivement pour la lignine éthanol et la lignine dioxane. La fraction lignane requiert une seconde étape de purification pour obtenir deux lignanes (60/40, w/w) avant l'analyse par RMN, dans le but d'obtenir des informations structurales préliminaires. Pour citer cet article : N. Vivas et al., C. R. Chimie 9 (2006).

Comparisons of chemical characteristic variations for photodegraded softwood and hardwood with/without polyurethane clear coatings

For better understanding of the differences between softwood and hardwood in the photodegradation process, hinoki ( Chamaecyparis sp.) and maple ( Acer sp.) were used in this study. The variations in chemical characteristics on their surfaces were analyzed by diffuse reflectance FTIR. The results revealed that in softwood lignin photodegradation, the phenolic hydrogen abstraction reacted faster than the β-aryl ether linkage cleavage. In addition, the guaiacyl structure in hardwood degraded faster than the syringyl unit. More nonconjugated carbonyl compounds were produced on the softwood surfaces than that on the hardwood surfaces. The cellulose crystallinity decreased to some extent in both the softwood and the hardwood. The protection effect of the hardwood surface by a polyurethane free film is better than that of the softwood surface. The guaiacyl unit was more degradable in the lightfastness test than the syringyl unit under the same filtering effect of the clear coatings.

Biosynthesis, molecular structure, and domain architecture of potato suberin: a (13)C NMR study using isotopically labeled precursors.

Although suberin in potato wound periderm is known to be a polyester containing long-chain fatty acids and phenolics embedded within the cell wall, many aspects of its molecular structure and polymer-polymer connectivities remain elusive. The present work combines biosynthetic incorporation of site-specifically (13)C-enriched acetates and phenylalanines with one- and two-dimensional solid-state (13)C NMR spectroscopic methods to monitor the developing suberin polymer. Exogenous acetate is found to be incorporated preferentially at the carboxyl end of the aliphatic carbon chains, suggesting addition during the later elongation steps of fatty acid synthesis. Carboxyl-labeled phenylalanine precursors provide evidence for the concurrent development of phenolic esters and of monolignols typical of lignin. Experiments with ring-labeled phenylalanine precursors demonstrate a predominance of sinapyl and guaiacyl structures among suberin's phenolic moieties. Finally, the analysis of spin-exchange (solid-state NOESY) NMR experiments in ring-labeled suberin indicates distances of no more than 0.5 nm between pairs of phenolic and oxymethine carbons, which are attributed to the aromatic-aliphatic polyester and the cell wall polysaccharide matrix, respectively. These results offer direct and detailed molecular information regarding the insoluble intermediates of suberin biosynthesis, indicate probable covalent linkages between moieties of its polyester and polysaccharide domains, and yield a clearer overall picture of this agriculturally important protective material.

Characterization of Organic Matter in Soils by Thermochemolysis Using Tetramethylammonium Hydroxide (TMAH)

Tetramethylammonium hydroxide (TMAH) thermochemolysis–gas chromatography/mass spectrometry (GC/MS) was employed to study the chemical structure of soil organic matter sampled from a soil plot in which corn (Zea mays L.) was farmed continuously for 15 yr. The chromatograms exhibited peaks related to compounds derived from lignin, fatty acid methyl esters (FAMEs), non‐lignin aromatic structures, and heterocyclic N compounds. The dominant lignin‐derived peaks in the TMAH thermochemolysis–GC/MS chromatograms were mainly derivatives of p‐hydroxyphenyl and guaiacyl structures, suggesting a non‐woody (grass) lignin type. With depth, the ratio of syringyl to guaiacyl compounds (S/G) decreased, suggesting a preferential degradation of the syringyl units by microorganisms. Fatty acid methyl esters of varying C‐chain length (C7 to C27) were identified in the soil chromatograms. Both TMAH–GC/MS and 13C‐NMR (nuclear magnetic resonance) data suggested a relative increase of long‐chain fatty acids with soil depth (or degree of humification), suggesting a refractory nature for these compounds. The heterocyclic N compounds yielded from the TMAH thermochemolysis were mainly pyrroles, pyridines, and pyrazoles. In addition, low levels of methylated amino acids (phenylalanine, leucine, and valine) were detected. The presence of the amino acids in the bottom layer of the soil suggests a preservation mechanism. The changes identified in the chemical components provide clues as to the nature of the humification processes in the soil profile and also yield information on the nature of the sources of soil organic matter.

Brightness Reversion of Mechanical Pulps Part XIII: Photoinduced Degradation of Lignin on Cellulose Matrix

An acidic dioxane extraction procedure was employed to isolate lignin from softwood bleached chemithermomechanical pulp (BCTMP). The isolated lignin was characterized spectroscopically and applied on cellulose test sheets. The treated cellulose test sheets were shown to exhibit photoyellowing properties comparable to those of BCTMP. The photolyzed lignin was re-isolated and characterized using spectroscopic techniques. UV-VIS and FT-IR studies implied elimination of the guaiacyl structure of lignin and the formation of carboxyl and/or unconjugated carbonyl groups during the photoyellowing process. The steady-state emission intensity of the excited states of guaiacyl structures decreased with increasing photolysis time, suggesting the formation of quinones during photolysis. NMR spectroscopic analysis of the photolyzed lignin indicated that the formyl, methoxyl, and uncondensed phenolics decreased in concentration as the irradiation proceeds. In contrast, condensed lignin and carboxylic acids increased as photolysis time was increased. These results are explained within the mechanism of lignin photodegradation.

Oxidative Degradation of Alkali Wheat Straw Lignin by Fungal Lignin Peroxidase, Manganese Peroxidase and Laccase: A Comparative Study

Lignin peroxidase (LiP), manganese peroxidase (MnP) from Phanerochaete chrysosporium and laccase from Pleurotus eryngii were separately used to degrade alkali wheat straw lignin (AL). In order to characterize the catalytic action of the different enzymes, the chemical structure and the hydrodynamic properties of treated lignin were analyzed by thioacidolysis-gas chromatography and molecular size exclusion chromatography. The results confirmed that only LiP was able to degrade guaiacyl (G) and syringyl (S) structures in non-phenolic methylated lignins. However, provided that some phenolic terminal structures are present, MnP and laccase were able to degrade the non-phenolic part of the polymer linked by β-O-4 alkyl aryl ether bonds. This suggested that the oxidative reactions catalyzed in alkali straw lignin could progress through bond cleavages generating phenoxy radicals. The molecular size distribution of both thioacidolysis products and the oxidized polymer showed that AL underwent condensation side-reactions regardless of the enzymic treatment, but only LiP oxidation led to the increase in the hydrodynamic volume of the recovered lignin. This indicated that modification by enzymes of bonding patterns in lignin is not always associated with alterations in the spatial network of the polymer.

Fractionation Of Alcell® Lignin By Sequential Solvent Extraction

ABSTRACT A prototype solvolytic lignin has been fractionated into three fractions by successive extraction with organic solvents of increasing hydrogen-bonding capacity. A comparison between the fractions and the starting lignin has been made in terms of methoxyl group content, fractionation yields, molecular weight distribution, alkaline nitrobenzene oxidation, and 1H and13 C NMR spectroscopy. The fractionation procedure was found to isolate fractions having distinct group functionalities and molecular weight distributions. In particular, the heterogeneity of ALCELL® lignin is demonstrated from the data. A significant portion of this lignin, 27%, was found to be comprised of a very low molecular weight (Mw = 714 g/mol) fraction soluble in ether. This fraction had a lower polydispersity but a higher content of guaiacyl structures with saturated side chains than the higher molecular weight fractions.

The reaction of phloroglucinol in the presence of acid with lignin-containing materials

UV-visible diffuse reflectance spectrometry has been used to monitor the reaction of phloroglucinol (in the presence of hydrochloric acid) with high yield pulps. When papers made from such pulps are irradiated, coniferaldehyde residues are generated as judged by their reaction with phloroglucinol/HCl. Treatment of such papers with sodium borohydride reduces the coniferaldehyde residues and consequently no colour reaction with phloroglucinol/HCl is observed. Irradiation of these borohydride-reduced papers leads to the generation of coniferaldehyde entities as detected by phloroglucinol/HCl. Similar results were obtained using a thin section of abies wood. Irradiation of papers made from high yield pulps destroys coniferaldehyde residues on the one hand and generates them from other sources on the other hand. Examination of papers made from the morphological components of poplar showed that it is impossible to quantify the amount of lignin present by this colour test method. Thioacidolysis analysis of the fractions shows for all of them a higher proportion of syringyl than guaiacyl β-O-4 aryl ether linkages. In contrast, photocleavage of the β-O-4 aryl ether linkages is more important for the guaiacyl structures. This is in accordance with the observed higher sensitivity to UV light of softwood pulps compared with hardwood pulps. Also, the thioacidolysis experiments indicate that UV irradiation of the fractions maintains a stationary concentration of the coniferaldehyde structures.

Comparative study of lignins produced by the tea-plant and by tea-plant derived callus tissues

The main degradation products of lignin in the tea-plant stems and leaves are represented by vanillin, syringic aldehyde and syringic acid, along with many unidentified compounds absent in the degradation products of standard spruce lignin. In the stem lignin guaiacyl structures dominate (81.5%) and the leaf lignin is richer in syringyl structures (56.6%). Lignins of dark grown (heterotrophic) leaf- and stem-derived callus tissues consist of not only guaicyl and syringyl structures (vanillin, vanillic acid, syringic aldehyde, and syringic acid) but also of p-hydroxyphenyl structures ( p-hydroxybenzaldehyde and p-hydroxybenzoic acid). Lignins of light grown (photomixotrophic) callus tissues are represented by guaiacyl and syringyl structures (vanillin, and syringic acid) only. This means that tissue culture conditions contribute more to lignin composi tion than the origin of the callus tissue.

Electrohydraulic effect in water-plant heterodisperse systems I. Compositions of the solid residue and the aqueous phase

The electrohydraulic (EH) treatment of water-plant heterodisperse systems leads to the partial degradation of the main components of the plant materials: lignin, cellulose, and carbohydrates. The presence of p-hydroxyphenyl and guaiacyl structures has been established on the basis of the results of the GLC analysis of the ether-extracted phenolic products of plant materials subjected to EH treatment. It has been shown that part of the carbohydrates passes into the aqueous phase in the form of free monosaccharides: pentoses and hexoses.

Degradation of synthetic lignins and some lignin monomers by the yeastRhodotorula glutinis

Rhodotorula glutinis degraded variously(14)C-labelled synthetic lignins in the presence of 0.1% glucose as co-substrate. Side chain-labelled DHP was degraded the most. While this yeastutilized vanillate and forulate for growth, sinapate/syringate were poorly or not degraded. Gallate, protocatechuate and acetate also supported growth. [carboxy-(14)C]Syringate was rapidly converted to(14)CO2 by the yeast only in presence of glucose while [carboxy-(14)C]vanillate did not require any additional cosubstrate for mineralization. Ring-labelled vanillyl alcohol was also dagraded proving that the yeast could rapidly metabolize guaiacyl structures while syringyl structures required the presence of additional energy sources.