Deded Sarip Nawawi

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.

Analysis of Lignin Aromatic Structure in Wood Based on the IR Spectrum

Abstract A total of 17 softwoods and 48 hardwoods were analyzed by IR spectroscopy to examine if syringyl ratio (syringyl/(syringyl+guaiacyl)) calculated from nitrobenzene oxidation products can be precisely expressed by area ratios of characteristic peaks of lignin in IR spectrum. Area ratio of two peaks is referred to as that of two wavenumber domains, represented by “wavenumber 1/ wavenumber 2.” Examined peak area ratios were 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/(855+815). Among these ratios, log(1595/1509) and log(1275/1220) showed significant linear relationship with the syringyl ratios with a correlation coefficient of 0.98 for all 65 woods. These two ratios could also be used to distinguish all the hardwoods from the softwoods.

Relationships between Hemicellulose Composition and Lignin Structure in Woods

The composition and absolute amount of neutral sugars were determined for 48 hardwood species (including 17 hardwoods of genera Acacia, 14 hardwoods of genera Eucalyptus, and 17 hardwoods of other genera) and 14 softwood species by alditol-acetate method, and their relationships to the syringyl ratio (syringyl/(syringyl+guaiacyl)) of lignin, which was determined by nitrobenzene oxidation, was investigated. In the hardwood species, an increase in the syringy ratio of lignin correlated with a tendency toward increased xylose/glucose, rhamnose/glucose, and arabinose/glucose ratios. However, the absolute amount of glucose in hardwood was maintained in a small range (0.4–0.5 g in 1 g sample), independent of changes in the syringyl ratio. In the softwood species, with increasing lignin content, the mannose/glucose ratio decreased, but the absolute amount of glucose remained almost constant. In both hardwood and softwood species, a strong correlation was suggested between lignin, indicated by higher syringy ratio, and hemicellulose, indicated by higher xylan/mannan ratio.

Characteristics of guaiacyl-syringyl lignin in reaction wood in the gymnosperm Gnetum gnemon L.

Abstract Gnetum gnemon L. is a unique gymnosperm species showing angiosperm-like features in terms of its morphology and chemical composition of the cell wall. Xylan is the main hemicellulose component, and its lignin is primarily composed of syringyl (S) and guaiacyl (G) units and small amounts of p-hydroxyphenyl (H) units. In the present study, in addition to branch, root, bark, and leaf samples, the reaction wood (RW) taken from the leaning stem of G. gnemon, was investigated mainly by alkaline nitrobenzene oxidation, ozonation and NMR spectroscopy. The leaning stem was wider on the lower side of the wood stem (lsW) than on the upper side (usW), similar to the case for compression wood (CW) in gymnosperms. The usW contained lignin with a higher S/G ratio, and β-O-4 structure had a higher erythro/threo ratio, while both ratios decreased around the periphery of the stem towards the lsW. The lignin content was higher towards the lsW. Overall, the lignin composition in the RW of this tree was similar to that in the tension wood of angiosperms. The H-units were minor components in the lignin, but the content was higher towards the lsW, which resembles the distribution of the H-units in a gymnosperm CW.

Characteristic of β-O-4 structures in different reaction wood lignins of Eusideroxylon zwageri T. et B. and four other woody species

Abstract Lignin analyses were performed on the reaction woods of five tropical wood species. The reaction woods of these five species and that of Gnetum gnemon L. (previously reported) were categorized into three types based on eccentric thickening growth and p-hydroxyphenyl/guaiacyl/syringyl (H/G/S) ratios: compression wood (CW) containing GH-lignin observed in gymnosperms (GH-lignin-CW), tension wood (TW) containing GS-lignin observed in angiosperms (GS-lignin-TW), and reaction wood that resembles CW and contains GS-lignin (GS-lignin-CW). GS-lignin-CW is an unusual type that was found in the angiosperm Eusideroxylon zwageri and in the gymnosperm G. gnemon. The erythro/threo ratio of the β-O-4 structures and the S/G ratio were higher on the upper side (usW) of the leaning wood stem or branch, and both ratios decreased along the periphery of the stem toward the lower side (lsW). Except for a difference in thickening growth, these distribution patterns were similar to the GS-lignin-TW patterns for Melia azedarach L. and Avicennia sp. Reaction wood of Paraserianthes falcataria (L.) Nielsen was also classified as a GS-lignin-TW, but this was lacking a clear distribution pattern. In contrast, the GH-lignin-CW of the usW of Pinus merkusii Jungh. et de Vriese had a low erythro/threo ratio, which increased toward the lsW along with increasing lignin contents and H/G ratios.