Β-guaiacyl Ether Research Articles

Theoretical Elucidation of β-O-4 Bond Cleavage of Lignin Model Compound Promoted by Sulfonic Acid-Functionalized Ionic Liquid.

While the depolymerization of lignin to chemicals catalyzed by ionic liquids has attracted significant attention, the relevant molecular mechanism, especially the cleavage of specific bonds related to efficient depolymerization, still needs to be deeply understood for the complexity of this natural aromatic polymer. This work presents a detailed understanding of the cleavage of the most abundant β-O-4 bond in the model system, guaiacylglycerol β-guaiacyl ether, by a Brønsted acidic IL (1-methyl-3-(propyl-3-sulfonate) imidazolium bisulfate ([C3SO3Hmim][HSO4]) using density functional theory calculation and molecular dynamics simulation. It has been found that [C3SO3Hmim][HSO4] generates zwitterion/H2SO4 via proton transfer with an energy barrier of 0.38 kcal/mol, which plays a dominant role in the lignin depolymerization process. Subsequently, the reaction can be carried out via three potential pathways, including (1) the dehydration of α-C-OH, (2) dehydration of γ-C-OH, and (3) the protonation of β-O. The electrophilic attack of H2SO4 and the hydrogen-bonding interaction between GG and zwitterion are the two most important factors to promote the depolymerization reaction. In all steps, the dehydration of α-C-OH route is computed to be favored for the experiment. The relatively higher energy barrier for β-O-4 bond dissociation among these reaction steps is attributed to the hindrance of the self-assembled clusters of GG in the mixed system. Further, the dense distribution of H13([C3SO3Hmim]) surrounding O21(GG), indicated by sharp peaks in RDFs, reveals that -SO3H in cations plays a substantial role in solvating lignin. Hopefully, this work will demonstrate new insights into lignin depolymerization by functionalized ILs in biomass conversion chemistry.

Two distinct enzymatic approaches for coupling fatty acids onto lignocellulosic materials

Two enzyme based strategies for hydrophobic functionalization of lignocellulose materials were developed and mechanistically compared using sinapic acid and the dimer syringylglycerol β-guaiacyl ether as models respresenting (hardwood) lignin substructures for coupling fatty acid esters. Coupling of lipase/hydrogen peroxide treated methyl linoleate to sinapic acid indeed resulted in a 1:1 coupling product with an m/z peak at 575.5 measured with HPLC–MS. Using laccase for coupling, oligo/polymerization of sinapic acid seems to prevent a coupling-reaction to methyl linoleate. However, methyl linoleate was successfully coupled by laccase 1:1 onto syringylglycerol β-guaiacyl ether through the ether bond at position four. The efficient enzyme mediated incorporation of fatty acid esters as hydrophobic molecules were further confirmed when triglycerides were used to treat veneers resulting in a water contact angle increase from 58.3° to 93.5°. Thus, this study demonstrates for the first time that both (laccase mediator and lipase-hydrogen peroxide) systems can act as promising strategies for introducing fatty acid esters in wood leading to increased hydrophobization.

Phenolic mediators enhance the manganese peroxidase catalyzed oxidation of recalcitrant lignin model compounds and synthetic lignin

Fungal oxidative enzymes, such as peroxidases and laccases, are the key catalysts in lignin biodegradation in vivo, and consequently provide an important source for industrial ligninolytic biocatalysts. Recently, it has been shown that some syringyl-type phenolics have potential as industrial co-oxidants or mediators, in laccase-catalyzed modification of lignocellulosic material. We have now studied the effect of such mediators with ligninolytic peroxidases on oxidation of the most recalcitrant lignin model compounds. We found that they are able to enhance the manganese peroxidase (MnP) catalyzed oxidation reactions of small non-phenolic compounds, veratryl alcohol and veratrylglycerol β-guaiacyl ether (adlerol), which are not usually oxidized by manganese peroxidases alone. In these experiments we compared two peroxidases from white-rot fungi, MnP from Phlebia sp. Nf b19 and versatile peroxidase (VP) from Bjerkandera adusta under two oxidation conditions: (i) the Mn(III) initiated mediated oxidation by syringyl compounds and (ii) the system involving MnP-dependent lipid peroxidation, both with production of (hydrogen) peroxides in situ to maintain the peroxidase catalytic cycle. It was found that both peroxidases produced α-carbonyl oxidation product of veratryl alcohol in clearly higher yields in reactions mediated by phenoxy radicals than in lipid-peroxyl radical system. The oxidation of adlerol, on the other hand, was more efficient in lipid-peroxidation-system. VP was more efficient than MnP in the oxidation of veratryl alcohol and showed its lignin peroxidase type activity in the reaction conditions indicated by some cleavage of Cα–Cβ-bond of adlerol. Finally, the mediator assisted oxidation conditions were applied in the oxidation of synthetic lignin (DHP) and the structural analysis of the oxidized polymers showed clear modifications in the polymer outcome, e.g. the oxidation resulted in reduced amount of aliphatic hydroxyls indicated by 31P NMR.

Reactivity of long chain alkylamines to lignin moieties: Implications on hydrophobicity of lignocellulose materials

Enzymatic processes provide new perspectives for modification of lignocellulose materials. In the current study, laccase catalyzed coupling of long chain alkylamines to lignin model molecules and lignocellulose was investigated. Up to two molecules of dodecylamine (DA) and dihexylamine (DHA) were successfully coupled with lignin monomers (guaiacol, catechol and ferulic acid) while coupling onto complex lignin model compounds (syringylglycerol β-guaiacyl ether, guaiacylglycerol β-guaiacyl ether and dibenzodioxocin) yielded 1:1 coupling products. Surface analysis of beech veneers enzymatically grafted with DA showed an increase in nitrogen content of 3.18% compared to 0.71% in laccase only treated controls while the O/C ratio decreased from 0.52 to 0.46. Concomitantly the grafting of DHA or DA onto beech veneers resulted in a 53.8% and 84.2% increase in hydrophobicity, respectively when compared to simple adsorption. Therefore, laccase-mediated grafting of long chain alkylamines onto lignocellulose materials can be potentially exploited for improving their hydrophobicity.

Study of the substrate specificities of the extracellular lignin peroxidases of the wood-destroying fungusPleurotus ostreatus

The substrate specificities of two forms of purified extracellular lignin peroxidase isolated from a total enzyme preparation of the fungus Pleurotus ostreatus — LGP-1 and LGP-II — have been determined. The substrate specificities of the isoenzymes differ considerably: LGP-I preferentially destroys model compounds of lignin — the β-guaiacyl ether of I-veratrylpropanol, coniferyl alcohol, and pyrocatechol, while LGP-II is most specific in relation to veratryl alcohol, veratrylpropane-1,3-diol, and vanillyl alcohol. Both forms partially oxidize syringaldazine and ABTS. The isoenzymes possess peroxidase and oxidase properties simultaneously, since veratryl, vanillyl, and coniferyl alcohols were oxidized by both forms of the enzyme only in the presence of H2O2, which confirms their peroxidase natures. At the same time, ABTS, syringaldazine, pyrocatechol, and o -phenylenediamine were also oxidized by the lignin peroxidase in the absence of H2O2, which confirms their oxidase function. The isoenzymes also possess Mn-peroxidase activity in relation to NADH. Since almost all substrates were oxidized by the enzymes only in the presence of hydrogen peroxide, they cannot be assigned to the class of oxidases. On the other hand, the LGP ofP. ostreatus is not Mn-dependent, since the presence of manganese ions had no effect whatever on the oxidation of aromatic substrates by the enzyme. Moreover, both forms of the enzyme oxidized veratryl alcohol — a specific substrate for ligninases, which permits the extracellular isoenzymes of P. ostreatus, LGP-I and LGP-II, to be assigned to the class of ligninases.

Reactions of Metal Ion Complexes with Lignin Model Compounds, Part II. Fe(TSPC) Catalyzed Formation of Oxidized Products in the Absence of Oxygen

Abstract The water soluble phthalocyanine complex trisodium tetra-4-sulfonatophthalocyanineiron(III) (Fe(TSPc)) was found to be an effective catalyst for the cleavage of the β-ether bonds in the phenolic lignin model compounds guaiacylglycol β-guaiacyl ether (1) and guaiacylglycerol β-guaiacyl ether (11). The products of these reactions were very different from those formed in the corresponding reactions catalyzed by anthraquinone (AQ) or Co(SPP).1–4 In particular, they gave large quantities of oxidized products, even though the reactions were performed in the absence of oxygen or other added oxidant. Mechanisms have been proposed for the oxidation reactions involving 1 and 11. In both cases the first step involves one electron oxidation of the lignin model compound by the catalyst. The radical derived from 1 then undergoes further one electron oxidation and deprotonation to give 4′-hydroxy-3′-methoxy-l-(2″-methoxyphenoxy)acetophenone (8) whereas that derived from 11 undergoes Cα-Cβ bond cleavage to give ...

Reactions of Metal Ion Complexes with Lignin Model Compounds, Part III. Rh(TSPP) Catalyzed Formation of Guaiacol from β-Aryl Ethers in Exceptionally High Yield

Abstract Trisodium meso-tetra-4-sulfonatophenylporphinerhodium(III) (Rh(SPP)) was found to be a very effective catalyst for cleaving the β-aryl ether bonds of the lignin model compounds guaiacylglycol β-guaiacyl ether (1) and guaiacylglycerol β-guaiacyl ether (11). In both cases very large amounts of guaiacol (2) were formed regardless of whether the reducing sugar glucose was present or not. With the substituted phenylethane model 1 the other major product was acetovanillone (5); with the substituted phenylpropane model 11 considerable amounts of vanillin (4) were formed. The products obtained with the rhodium catalyst were very different to those formed in the Co(SPP) or anthraquinone (AQ) catalyzed reactions. They were, however, similar to those obtained with Fe(TSPc), although the rhodium catalyst was much more active and formed guaiacol at a much faster rate. In addition to these reactions, the rhodium complex also catalyzes the partial demethylation of the 3, 4-dimethoxyphenyl model compound 10. Mec...

Reactions of Metal Ion Complexes with Lignin Model Compounds Part I. Co(TSPP) as a Single Electron Transfer Catalyst and Implications for the Mechanism of AQ Pulping

Abstract Cleavage of the β-aryl ether bonds of the lignin model compounds guaiacylglycol β-guaiacyl ether (1) and guaiacylglycerol β-guaiacyl ether (11) to form guaiacol was found to be catalyzed by the water soluble porphyrin complex trisodium meso-tetra-4-sulfonatophenvlporphinecobalt(III), (Co(TSPP)). The resulting product distributions were remarkably similar to those obtained for the anthraquinone (AQ) catalyzed reactions under the same conditions. Studies of the reactions of CofTSPP) with proposed intermediate compounds indicate that the major route to guaiacol formation involves reaction of the reduced catalyst, CoII(TSPP), with the quinone methides 9 and 13 which are derived from the phenolic model compounds 1 and 11 respectively. It is proposed that the mechanisms of these reactions involve single electron transfer to the quinone methide as the first step. The implications of this proposal for the AQ catalyzed reactions of 1 are discussed.

Quantitative use of model compound information: Monte Carlo simulation of the reactions of complex macromolecules

A Monte Carlo simulation of complex depolymerization reactions was developed. Transition probabilities derived through analysis of simple prototype reaction sequences were used to test reactive sites in a polymer. This stochastic approach allowed facile accounting of the often confounding effects of unequal reactivity, nearest-neighbor substituents, and oligomer molecular weight distributions. The simulation was applied to the depolymerization of a model lignin, poly(veratryl β-guaiacyl ether)

アルカリメタノール蒸解 ＩＶ リグニンおよび炭水化物の挙動に関するモデル実験

In the earlier report13, 6) of this series, it was shown that pulp yield by alkali-methanol cooking is 25% higher than that by kraft cooking and both pulps are similar in sheet strength. It was also elucidated that the rapid delignification during alkali-methanol cooking is due to the prevention of condensation through methylation of active benzylalcohol groups in lignin molecule. Recovery of methanol in spent liquor was also discussed2) .The present paper is concerned with the behaviors of lignin and carbohydrate during alkalimethanol cooking. Model experiments were carried out by the use of guaiacylglycerol-β-guaiacyl ether as a lignin model substance, and by the use of hydrocellulose and cellobiose as carbohydrate model substances. Each model substance was cooked in alkali-methanol [(40 g NaOH+400 g MeOH) /l ] and soda [40 g NaOH/l] cooking liquors under various cooking conditions. Results obtained are as follows : a) The yield of guaiacyl produced by the clavage of β-ether linkage of guaiacylglycerol β-guaiacyl ether was lower in alkali-methanol cooking than in soda cooking (Table 1). It is noteworthy that the kraft-like rapid delignification can be attained in alkali methanol cooking, although the rate of, β-ether cleavage is slower than soda cooking.b) Guaiacylglycerol-β-guaiacyl ether was methylated at the α-position of side chain. A methylated compound was isolated and identified by mass spectrum and 13C-NMR of it (Fig. 13). The mechanism of methylation was discussed by the analysis of 13C-NMR and assumed to follow the SN 2 (Fig. 4).c) Residual hydrocellulose after alkali-methanol cooking was 12% higher than soda cooking (Table 2). Corresponding to this result, the yield of gluco-isosaccharinic acid produced by peeling-off reaction was lower in alkali-methanol cooking than in soda cooking.d) Residual cellobiose depends on the concentration of methanol in alkali-methanol cooking liquor (Fig. 5). It was shown that the higher the concentration of methanol, the more the residual cellobiose.e) It can be concluded from the above-mentioned results that the peeling-off reaction was suppressed in alkali-methanol cooking. This may suggest that the isomerization rate of a glucose end group to a fructose end group is slower in alkali-methanol cooking liquor than in soda cooking liquor.

The formation of lignin and its biochemical degradation

The mechanism of the biogenesis of lignin has intrigued lignin chemists ever since the discovery of this complex material. The process of lignification is the transformation in certain plants whereby the aromatic lignin polymer is synthesized, ultimately from CO 2, probably by way of intermediates related to carbohydrates. Lignification is but one illustration of the more general phenomenon of aromatization, i.e. the conversion by living cells of non-aromatic precursors into compounds containing benzenoid-type rings. Fundamentally, an understanding of the biogenesis of lignin centers on knowing the enzymic pathway by which this highly polymeric aromatic compound is formed from substances pre-existing in the plant. A comprehensive solution to this problem requires consideration of two basic assumptions: First, the complex material must have its ultimate origin in certain relatively simpler units; and second, the biogenesis of lignin must involve the functioning of not one enzyme system but, rather, of several different systems, each exerting its influence in its substrate in an organized and integrated sequence, with the sum total of the reactions giving rise to a product, lignin, which is required for the existence of the mature plant. Thus, in such a biosynthetie study, both the precursors of the final product and the energetics of the reactions involved must be considered. To elucidate the mechanism of the enzymic degradation of softwood lignin by white-rot fungi, studies were conducted of the chemical properties of isolated pine and spruce lignins after decay by Polyporus versicolor, Polyporus hirsutus, Poria subacida J247 and N199, Fomes fomentarius, Fomes annosus, and Trametes pini. Determinations of the intermediate products formed from these lignins by the action of the fungi were also carried out. Products thus derived from lignin were coniferaldehyde, p-hydroxycinnamic acid, guaiacylglycerol and guaiacylglycerol-β-coniferyl ether. The results indicate the presence of the guaiacylglycerol-β-coniferyl ether unit in the lignins of pine and spruce woods. To understand the metabolism of lignin degradation products by white-rot fungi, investigations were carried out on the enzymic conversion by Polyporus versicolor and Fomes fomentarius of certain aromatic compounds structurally related to softwood lignin. Products derived in this way were vanillic acid, vanillin and dehydrodivanillin from ferulic acid and 4-hydroxy-3-methoxyphenylpyruvic acid; vanillic acid, vanillin, dehydrodivanillin and ferulic acid from coniferaldehyde and coniferyl alcohol; vanillic acid, vanillin, dehydrodivanillin and 4-droxy-3-methoxyphenylpyruvic acid from guaiacylglycerol and its β-guaiacyl ether. It is therefore suggested that 4-hydroxy-3-methoxyphenylpyruvic acid is an intermediate in the fugal decomposition of the guaiacylglycerol-β-coniferyl ether units present in softwood lignin, and that the enol form of this acid is converted to vanillic acid and vanillin. Coniferaldehyde and ferulic acid, obtained from lignin, were also converted to vanillic acid via vanillin.

Investigations on lignins and lignification: XXVIII. The degradation by Polyporus versicolor and Fomes fomentarius of aromatic compounds structurally related to softwood lignin

To gain an understanding of the metabolism of lignin degradation products by white-rot fungi, a study was made of the enzymic conversion by Polyporus versicolor and Fomes fomentarius of certain aromatic compounds structurally related to softwood lignin. Products derived in this way were vanillic acid, vanillin, and dehydrodivanillin, from ferulic acid and 4-hydroxy-3-methoxyphenylpyruvic acid; vanillic acid, vanillin, dehydrodivanillin, and ferulic acid, from coniferaldehyde and coniferyl alcohol; vanillic acid, vanillin, dehydrodivanillin and 4-hydroxy-3-methoxyphenylpyruvic acid, from guaiacylglycerol and its β-guaiacyl ether. It is therefore suggested that 4-hydroxy-3-methoxyphenylpyruvic acid is an intermediate in the fungal decomposition of the guaiacylglycerol-β-coniferyl ether units present in softwood lignin, and that the enol form of this acid is converted to vanillic acid and vanillin. Coniferaldehyde and ferulic acid, obtained from lignin, were also converted to vanillic acid via vanillin.

Action of nitric acid on the ?-guaiacyl ether of ?-veratryl-glycerol

1. The action of nitric acid on a model of lignin, β-guaiacyl ether of α-veratryl-glycerol, was studied. 2. Nitration of the β-guaiacyl ether of α-veratryl-glycerol with nitric acid in CCl4 yielded the β-nitroguaiacyl ether of α-6-nitroveratryl-glycerol [1-(6-nitro-3,4-dimethoxyphenyl)-1-hydroxy-2-(nitro-2-methoxyphenoxy)-3-propanol]. 3. The glycerol side chain of the dimer was unchanged during nitration under the conditions described.