Oxidative Degradation Of Lignin Research Articles

Effects of natural weathering on aged wood from historic wooden building: diagnosis of the oxidative degradation

Historic wooden buildings located outdoors are exposed to natural weathering conditions for extended periods of time, causing deterioration of wood properties by sunlight, oxygen, and other environmental factors. Current diagnostic procedures are limited to macroscopic inspection. In this interdisciplinary study, several aged samples from Yingxian Wooden Pagoda (ca. 1056 AD) were analyzed. Their micro-morphology and changes in chemical composition were investigated using less invasive multi-chemical techniques. The aim is to elucidate the oxidative degradation and its deterioration mechanism of the wood, which is essential in identifying the key factors responsible for natural weathering and devising strategies to counteract the surface deterioration. All aged wood samples had varying degrees of decay and lignin content was decreased in most of them. The high ratio of oxygen/carbon elements evidenced the occurrence of chemical reactions. In particular, the increasing ratio of oxygenated carbon/unoxygenated carbon indicates potential oxidation reactions. Overall, for the aged wood of historic wood building under warm-dry natural conditions, their deterioration occurred through the oxidative degradation of lignin. These unique results are useful in developing effective repair and restoration measures to conserve wooden components in historic buildings.

A review of lignin hydrogen peroxide oxidation chemistry with emphasis on aromatic aldehydes and acids

Abstract This review discusses the main factors that govern the oxidation processes of lignins into aromatic aldehydes and acids using hydrogen peroxide. Aromatic aldehydes and acids are produced in the oxidative degradation of lignin whereas mono and dicarboxylic acids are the main products. The stability of hydrogen peroxide under the reaction conditions is an important factor that needs to be addressed for selectively improving the yield of aromatic aldehydes. Hydrogen peroxide in the presence of heavy metal ions readily decomposes, leading to minor degradation of lignin. This degradation results in quinones which are highly reactive towards peroxide. Under these reaction conditions, the pH of the reaction medium defines the reaction mechanism and the product distribution. Under acidic conditions, hydrogen peroxide reacts electrophilically with electron rich aromatic and olefinic structures at comparatively higher temperatures. In contrast, under alkaline conditions it reacts nucleophilically with electron deficient carbonyl and conjugated carbonyl structures in lignin. The reaction pattern in the oxidation of lignin usually involves cleavage of the aromatic ring, the aliphatic side chain or other linkages which will be discussed in this review.

Biochemical Markers of Contact with the Organic Pollutants of Urban Atmosphere in the Leaves of Woody Plants

Changes caused by contact with typical organic pollutants of urban atmosphere (formaldehyde, benzaldehyde, hydroperoxides) in the chemical composition of the leaves and shoots of woody plants are investigated. A decrease in quinic acid content and an increase in shikimic acid content were detected in the young shoots of Picea obovata Ledeb. and Picea pungens Engelm.. Investigation of changes in the chemical composition of shoots in contact with pollutants under laboratory conditions revealed that the contact with formaldehyde and hydroperoxide affects the biochemical cycle of quinic acid. High concentration of gaseous formaldehyde was found to cause an increase in the content of lactic acid in the leaves of Padus maackii (Rupr.) Kom.. In the leaves of Tilia cordata Mill. and Syringa josikaea Jacq. fil., high formaldehyde concentration caused a decrease in glycolic acid content and an increase in oxalic acid content, while after the contact with gaseous benzaldehyde this compound was detected in the leaves in rather high concentration, Analysis of the ligneous parts of plants from the territories with heavy air pollution revealed increased content of syringaldehyde, which may be a consequence of the oxidative degradation of lignin under the action of atmospheric pollutants.

Oxidized Lignin Depolymerization using Formate Ionic Liquid as Catalyst and Solvent

AbstractLignin has been widely studied as a sustainable source of renewable materials, particularly aromatic feedstock chemicals, which are in great and increasing need in the world. Lignin oxidation and depolymerization presents a promising approach to functionalized phenolic products. In this work, a novel oxidative degradation of lignin using a formate ionic liquid was investigated resulting in ethyl acetate soluble and also water‐soluble depolymerized lignin products. The β‐O‐4 bonds in lignin were oxidized and then depolymerized by a recyclable ionic liquid, 2‐hydroxy ethylammonium formate. 2‐Hydroxy ethylammonium formate, which could dissolve lignin acting as a solvent, was found to also catalyze the depolymerization of the oxidized lignin. The lignin depolymerization products were characterized.

Highly selective generation of vanillin by anodic degradation of lignin: a combined approach of electrochemistry and product isolation by adsorption.

The oxidative degradation of lignin into a variety of valuable products has been under investigation since the first half of the last century. Especially, the chance to claim this cheap, abundant and renewable source for the production of the important aroma chemical vanillin (1) was one of the major driving forces of lignin research. So far most of the developed methods fail in technical application since no viable concept for work-up is included. This work represents a combined approach of electrochemical conversion of Kraft lignin and product recovery by adsorption on a strongly basic anion exchange resin. Electrolysis conditions are optimized regarding reaction temperatures below 100 °C allowing operation of aqueous electrolytes in simple experimental set-up. Employing ion exchange resins gives rise to a selective removal of low molecular weight phenols from the strongly alkaline electrolyte without acidification and precipitation of remaining lignin. The latter represents a significant advantage compared with conventional work-up protocols of lignin solutions.

Lignin-degrading peroxidases in Polyporales: an evolutionary survey based on 10 sequenced genomes

The genomes of three representative Polyporales (Bjerkandera adusta, Phlebia brevispora and a member of the Ganoderma lucidum complex) were sequenced to expand our knowledge on the diversity of ligninolytic and related peroxidase genes in this Basidiomycota order that includes most wood-rotting fungi. The survey was completed by analyzing the heme-peroxidase genes in the already available genomes of seven more Polyporales species representing the antrodia, gelatoporia, core polyporoid and phlebioid clades. The study confirms the absence of ligninolytic peroxidase genes from the manganese peroxidase (MnP), lignin peroxidase (LiP) and versatile peroxidase (VP) families, in the brown-rot fungal genomes (all of them from the antrodia clade), which include only a limited number of predicted low redox-potential generic peroxidase (GP) genes. When members of the heme-thiolate peroxidase (HTP) and dye-decolorizing peroxidase (DyP) superfamilies (up to a total of 64 genes) also are considered, the newly sequenced B. adusta appears as the Polyporales species with the highest number of peroxidase genes due to the high expansion of both the ligninolytic peroxidase and DyP (super)families. The evolutionary relationships of the 111 genes for class-II peroxidases (from the GP, MnP, VP, LiP families) in the 10 Polyporales genomes is discussed including the existence of different MnP subfamilies and of a large and homogeneous LiP cluster, while different VPs mainly cluster with short MnPs. Finally, ancestral state reconstructions showed that a putative MnP gene, derived from a primitive GP that incorporated the Mn(II)-oxidation site, is the precursor of all the class-II ligninolytic peroxidases. Incorporation of an exposed tryptophan residue involved in oxidative degradation of lignin in a short MnP apparently resulted in evolution of the first VP. One of these ancient VPs might have lost the Mn(II)-oxidation site being at the origin of all the LiP enzymes, which are found only in species of the order Polyporales.

Epoxy ceriporic acid produced by selective lignin-degrading fungus Ceriporiopsis subvermispora

Ceriporiopsis subvermispora is a selective white rot basidiomycete which degrades lignin in wood at a distance far from enzymes. Low molecular mass metabolites play a central role in the oxidative degradation of lignin. To understand the unique wood-decaying mechanism, we surveyed the oxidized derivatives of ceriporic acids (alk(en)ylitaconic acids) produced by C. subvermispora using high-resolution liquid chromatography multiple-stage mass spectrometry (HR-LC/MSn). The analysis of the precursor and product ions from the extract suggested that an epoxidized derivative of ceriporic acid is produced by the fungus. To identify the new metabolite, an authentic compound of ceriporic acid epoxide was synthesized in vitro by reacting (R)-3-[(Z)-hexadec-7-enyl]-itaconic acid (ceriporic acid C) with m-chloroperbenzoic acid. The precursor and product ions from the natural metabolite and authentic epoxide were identical and distinguishable from those of hydroxy and hydroperoxy derivatives after reduction with NaBD4. Feeding experiments with [U-13C]-glucose, 99% and the subsequent analyses of the first and second generation product ions demonstrated that the oxidized ceriporic acid was (R)-3-(7,8-epoxy-hexadecyl)-itaconic acid. To our knowledge, this study is the first to report that natural alkylitaconic acid bears an epoxy group on its side chain.

Pretreatment of hybrid poplar by aqueous ammonia

Enzymatic hydrolysis of hybrid poplar treated by ammonia recycle percolation (ARP) was studied applying cellulase enzyme supplemented with additional xylanase or pectinase. The effect of xylanase addition was much more significant than pectinase addition. Conversion of ARP-treated hybrid poplar to ethanol was carried out by simultaneous saccharification and fermentation (SSF) and SS and cofermentation (SSCF). The maximum ethanol yield observed from the SSCF experiment was 78% of theoretical maximum based on the total carbohydrate (glucan + xylan). The same feedstock was also treated by soaking in aqueous ammonia (SAA), a batch pretreatment process with lower severity than ARP. The test results indicated that relatively high severity is required to attain acceptable level of digestibility of hybrid poplar. In order to lower the severity of the pretreatment, addition of H(2)O(2) was attempted in the SAA. Addition of H(2)O(2) significantly enhanced delignification of hybrid poplar due to its oxidative degradation of lignin. Several different H(2)O(2) feeding schemes and different temperature profiles were attempted in operation of the SAA to investigate the effects of H(2)O(2) on degradation of lignin and carbohydrates in hybrid poplar. More than 60% of lignin in hybrid poplar was removed with stepwise-increase of temperature (60-120 degrees C after 4h of reaction). Increase of carbohydrate degradation was also observed under this condition.

Methyltrioxorhenium: a new catalyst for the activation of hydrogen peroxide to the oxidation of lignin and lignin model compounds

The oxidative degradation of lignin under totally chlorine free conditions is one of the most relevant targets for the design of environmental friendly pulping and bleaching industrial processes. Methyltrioxorhenium was found a powerful and promising catalyst for the oxidation of both phenolic and non-phenolic lignin model compounds by use of hydrogen peroxide as primary oxidant. Three different technical lignins, hydrolytic sugar cane lignin (SCL), red spruce kraft lignin (RSL) and a hardwood organosolvent lignin (OSL), that are representative examples of widely diffused para-hydroxyphenyl–guaiacyl, guaiacyl and guaiacyl–syringyl lignins, were also extensively degraded under similar experimental conditions.

FORMATION AND INVOLVEMENT OF RADICALS IN OXYGEN DELIGNIFICATION STUDIED BY THE AUTOXIDATION OF LIGNIN AND CARBOHYDRATE MODEL COMPOUNDS

The formation of superoxide and hydroxyl radicals under the conditions of oxygen bleaching and their involvement in the oxidative degradation of lignin and carbohydrate structures have been demonstrated using simple model compounds. It was found that: 1. The first step of autoxidation is a one-electron transfer process yielding a substrate radical and superoxide. Direct coupling between these species in the initial solvent cage is of minor importance. 2. Hydroxyl radicals are formed by a superoxide driven Fenton reaction with a pH-maximum in the range 11–11.5. 3. Of the heavy metal salts investigated CuSO4 and MnSO4 facilitate both the degradation of phenolic substrates and the formation of hydroxyl radicals, whereas FeSO4 has no significant effect. 4. Striking mechanistic analogies between the autoxidative degradation of lignin and carbohydrate model compounds determine the fundamental selectivity of the process, while formation of hydroxyl radicals determine the conditional selectivity imposed on oxygen delignification processes.

The chemistry of chromated copper arsenate II. Preservative-wood interactions

The reactions which cause chromated copper arsenate preservative to fix strongly into wood are reviewed. A number of the mechanisms proposed in the literature appear chemically implausible. A new model is advanced in which the final fixation products are dominated by chromium (III) arsenate, chromium (III) hydroxide, and copper (II)- wood carboxylate complexes. Carboxylate groups should be generated in large numbers in the reduction of chromium (VI) by primary alcohol groups in lignin and carbohydrate fractions, or in the oxidative degradation of lignin. The model is supported by a recent X-ray absorption fine structure analysis.

Sources and Transformations of Organic Matter in Surface Soils and Sediments from a Tidal Estuary (North Inlet, South Carolina, USA)

Surface soil and sediment samples collected along a forest-brackish marsh-salt marsh transect in a southeastern U.S. estuary were separated into three different fractions (sand, macro-organic matter, and humus) based on size and density. Elemental, stable carbon isotope, and lignin analyses of these samples reveal important contrasts in the quantity, composition, and sources of organic matter, between forest and marsh sites. Elevated nitrogen contents in humus samples suggest nitrogen incorporation during humification is most extensive in forest soils relative to the marsh sites. The lignin compositions of the macro-organic and humus samples reflect the predominant type of vegetation at each site. Lignin phenol ratios indicate that woody and nonwoody litter from, gymnosperm and angiosperms trees (pines and oaks) is the major source of vascular plant-derived organic matter in the forest site and that angiosperm, grasses (Juncus andSpartina) are the major sources of lignin at the marsh sites. The phenol distributions also reveal that oxidative degradation of lignin is most extensive in the forest and brackish marsh zones whereas little lignin decay occurs in the salt marsh samples. In forest soils, most organic matter originates from highly altered forest vegetation while at the brackish marsh site organic matter is a mixture of degradedJuncus materials and microbial/algal remains. Organic matter in the salt marsh appears to be composed of a more complex mixture of sources, including degradedSpartina detritus as well as algal and microbial inputs. Microbial methane oxidation appears to be an important process and a source of13C depleted organic carbon in subsurface sediments at this site.

Biobleaching of Pulp with Dioxygen in the Laccase-Mediator System. Part 1. Kinetics of Delignification

SummaryKinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects of variable factors on the delignification were studied. The delignification was conducted in acetate buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage of 10 UCorioluslaccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The amounts of dioxygen consumed per removal of one C9-unit equivalent of residual lignin is rather high, 1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed by alkaline extraction (E), (LMS-E)4, decreased kappa number of a pine kraft-AQ pulp from 21.8 to less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.

Oxidative cracking of precipitated hardwood lignin by hydrogen peroxide.

Precipitated hard-wood lignin (PHL) is a major byproduct in the biomass-to-ethanol process. Oxidative cracking of PHL by hydrogen peroxide in aqueous medium was investigated as a means to produce potentially useful chemicals. The cracking reaction takes place at moderate temperatures (80-160 degrees C), giving mono- and dicarboxylic acids as the main products. The yields of these products are in the range of 30-50% of initial lignin. The reaction mechanism and the product distribution are dependent upon the reaction conditions, especially the pH. The reaction under strong alkaline condition proceeds well even at low reaction temperatures (80-90 degrees C). Under acidic conditions, higher temperatures (130-160 degrees C) are required to attain the same degrees of cracking. The reaction patterns of the oxidative cracking reaction involve the cleavage of lignin ring, aryl ether bond, or other linkages within lignin. By using the findings of this investigation and those of previous work, we have illustrated the reaction pathways for degradation of PHL under alkaline and acidic conditions. Aldehydes and aromatic acids are intermediate products in the oxidative degradation of lignin. However, they were produced only in trace amounts owing to rapid degradation induced by hydrogen peroxide.

Catalytic Mechanism of Cu2+and Fe3+in Alkaline O2Oxidation of Lignin

Abstract The catalytic mechanisms of Cu2+ and Fe3+ in the alkaline oxidation of lignin are discussed. Best aldehyde yields were obtained by using Cu2+ and Fe3+ as catalysts. Without these two ions present or in the absence of one or other of them, yields were lower. It is clear that Cu2+ and Fe3+ significantly influence the reactions. Cu2+, acting as the electron acceptor, accelerates the formation of the phenoxy radical, thus speeding up the radical reaction. In order to interpret the effect of Fe3+ on oxidative degradation of lignin and formation of aldehydes, formation of an intermediate, O2-Fe3+-lignin complex and its catalytic mechanism have been proposed.