Gyosuke Meshitsuka

Erythro/threo ratio of β-O-4-5 structures as an important structural characteristic of lignin. Part 4: Variation in the erythro/threo ratio in softwood and hardwood lignins and its relation to syringyl/guaiacyl ratio

Abstract The proportion of erythro- and threo-forms of β-O-4-structures in lignin was elucidated by ozonation analysis of 21 wood species, and the relationship to the syringyl and guaiacyl composition was investigated. For all hardwood species, the erythro-form of β-O-4-structures predominated, although the extent varied widely, depending on wood species. In contrast, the proportion and amount of erythro- and threo-forms were very similar in all softwood species. The proportion of the erythro-form was greater in species with a higher methoxyl content in the lignin (correlation coefficient, R2=0.83). The S/V ratio (molar ratio of syringaldehyde and syringic acid to that of vanillin and vanillic acid) obtained by nitrobenzene oxidation was also strongly correlated with the proportion of the erythro-form (R2=0.99). Accordingly, the syringyl/guaiacyl ratio is closely related to the erythro/threo ratio. This stereochemical characteristic of β-O-4-structures is discussed in relation to the process of lignin formation.

Erythro/threo ratio of β-O -4 structures as an important structural characteristic of lignin. I: Improvement of ozonation method for the quantitative analysis of lignin side-chain structure

Ozonation as a quantitative tool to analyze the stereo structures of arylglycerol-β-aryl ether linkages was examined using wood meal, milled wood lignin, and a lignin model compound, 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (veratrylglycerol-β-guaiacyl ether, VG). The procedure was improved. When mild postreduction was conducted for ozonation products, the total yield of erythronic and threonic acids from this model compound was 74%, which is 15% higher than the yield without postreduction. A decrease in the recovery of these two acids under prolonged ozonation treatment was successfully suppressed by postreduction. Theerythro/threo ratio of VG determined by the ozonation method with postreduction is in good agreement with the ratio determined by1H-nuclear magnetic resonance. Excellent reproducibility of the yield was obtained by adopting a procedure that included trimethylsilylation of ammonium salts of ozonation products using a dimethylsulfoxide-hexamethyldisilazane-trimethylchlorosilane mixture and subjecting it to gas chromatography analysis. It was concluded that arylglycerol-β-aryl ether structures comprise at least 35% of the C3-C6 structure in birch wood meal, with anerythro/threo ratio of 2.8.

Ratio of erythro and threo forms of β-O-4 structures in tension wood lignin

Abstract The ratio of erythro and threo forms of β-O-4 structures in tension wood lignin was investigated by ozonation analysis of wood meal taken from various positions in the stem of yellow poplar ( Liriodendron tulipifera ). The proportion of the erythro form was higher in tension wood than in opposite wood, and the methoxyl group content showed a similar trend. The proportion of the erythro form and the methoxyl group content in the 7 positions in the stem lignin was correlated (correlation coefficient R =0.98), suggesting that the type of aromatic ring, syringyl or guaiacyl, is one of the factors which stereochemically controls the ratio of erythro and threo forms of β-O-4 structures during lignin formation.

A Two-Dimensional NMR Study of Birch Milled Wood Lignin

Abstract Chemical structures of underivatized and acetylated birch Milled Wood Lignins were investigated in solution by various two-dimensional NMR experiments such as COSY, HOHAHA, HMQC, and HMBC.

Structural characteristics of compound middle lamella lignin

Abstract One of the most important targets of current lignin chemistry is to visualize the inhomogeneities of lignin in the wood cell wall. The soft xylem fraction was separated from birch wood at the end of May, 1983. Cell walls of the soft xylem fraction were extremely thin and were mainly composed of compound middle lamella. Degradation products from the soft xylem by alkaline nitrobenzene oxidation and permanganate oxidation strongly indicated that compound middle lamella lignin in hardwood must be rich in guaiacyl units and highly condensed.

Reaction Selectivity of Active Oxygen Species in Oxygen-Alkali Bleaching

Abstract A non-phenolic lignin model compound, 3, 4-dimethoxybenzyl alcohol (veratryl alcohol, VA), and a carbohydrate model compound, methyl β-D-glucopyranoside (MGP), were subjected together to the reaction with active oxygen species which were generated by an oxygen-alkali oxidation of a phenolic compound, 2, 4, 6-trimethylphenol (TMPh), at different temperature or different pH. The reaction selectivity of active oxygen species between VA and MGP (ΔA/ΔMGP) under these conditions were examined. The rates of VA and MGP degradation were similar at 70 °C while the degradation of MGP was much faster than that of VA at 95 °C. This result indicates that active oxygen species produced at 70°C and at 95 °C are different. The degradation of MGP was greater and the reaction selectivity between VA and MGP was lower (undesirable for the carbohydrate protection) when the initial reaction pH was increased. These results clearly demonstrate that the reactivity of active oxygen species produced during oxygen bleaching ...

2D Nmr Study of Residual Lignin in Beech Kraft Pulp Combined with Selective Cleavage with Pivaloyl Iodide

ABSTRACT Structures of acetylated residual lignin obtained from unbleached beech kraft pulp were investigated by 2D NMR in combination with selective cleavage of non-phenolic α-alkyl ether bonds with pivaloyl iodide generated in situ from pivaloyl chloride / sodium iodide. β-O-4 and resinol structures still remained in this polymer lignin. Furthermore, carbohydrates were proved to be linked glycosidically to benzyl carbons of lignin. Possibly this inhibits complete delignification during kraft pulping.

Structure of small lignin fragments retained in water-soluble polysaccharides extracted from birch MWL isolation residue

To analyze the structural features of lignin in the vicinity of lignin–carbohydrate linkages, water-soluble lignin–carbohydrate complex (LCC) with low lignin content was prepared from residual birch wood meal after the extraction of milled wood lignin (MWL). The molecular weight distribution of lignin in this LCC appeared together with carbohydrate in the relatively high molecular weight region of the gel permeation chromatogram. This result was consistent with our previous results obtained for the same fraction of Japanese cedar (sugi); however, after treatment with polysaccharide-degrading enzyme, the molecular weight distribution of carbohydrate and that of lignin shifted significantly to the lower region. These results demonstrated that molecular size of this LCC is determined by carbohydrates while lignin is present as a minor fragment in this fraction. The syringyl/guaiacyl (S/V) ratio of this LCC was higher than other lignin fractions. Ozonation analysis implied that this LCC has a relatively high number of β-1 structures. It is likely that lignin that exists near lignin–carbohydrate linkages has more endwise-type features than other lignin fractions.

Studies on the Nature of Lignin - Carbohydrate Bonding

Abstract A lignin - carbohydrate complex (LCC) fraction which was initially extracted with dimethyl sulfoxide from birch residual wood meal after stepwise MWL extraction (total yield 28%), contained about 7% qalacturonic acid together with about 4% glucuronic acid. Although galacturonic acid residue is well known to be a component of hardwood xylan, it also suggests the possibility of the existence of pectic substance in this LCC fraction. The nature of galacturonic acid in this LCC fraction was characterized by means of two purified pectinases, endo-polygalacturonase and endo-pectin lyase. It was concluded that most of the carbohydrate in this LCC fraction, especially xylan, is combined with lignin through pectic substance.

Interference of Carbohydrates in the Determination of the Methoxyl Content of Lignin in Woody Samples

Abstract To evaluate the effect of the presence of carbohydrates on the determination of the methoxyl content of lignin, the mechanism of acid‐catalyzed reaction of lignin methoxyl groups with iodide ion to form methyl iodide was evaluated using carbohydrate and lignin model compounds. Not only the iodide concentration but also the acid concentration was found to significantly affect the rate of formation of methyl iodide. This fact and Hammett plots of the relative reaction rates observed for several model compounds suggest an SN2cA reaction mechanism for methyl iodide formation. Carbohydrates interfered with the rate of formation of methyl iodide, probably by acting as Lewis bases. Interestingly, the study also revealed that a certain amount of methyl iodide could arise from carbohydrates even when the carbohydrates did not contain methoxyl groups as potential precursors to methyl iodide. These sources of error were significant when methoxyl content was determined for samples with low lignin content.