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.

Naturally p-Hydroxybenzoylated Lignins in Palms

“…It is revealed that there are syn-and anti-isomers of the normal β-ether units (Figs. 2f-g and 3d-e), with anti-isomers predominating because of the S-rich nature of the lignin, as already well established [68][69][70][71][72]. It is equally clear that p-hydroxybenzoates acylate both of the β-ether isomers (Figs.…”

Wood Based Lignin Reactions Important to the Biorefinery and Pulp and Paper Industries

“…While softwood lignin appears to vary little among species (Sarkanen et al 1967;Akiyama et al 2005;Creighton et al 1944;Leopold and Malmstrom 1952;Bland et al 1950;Tower and Gibbs 1953), there is increasing evidence that the structure of hardwood lignin varies greatly from one species to another. Monolignol-forming lignin structures are of major importance when discussing lignin reactivity under either acidic or alkaline conditions.…”

“…While guaiacyl lignin (G) was found in vessels and cell corners, syringyl-guaiacyl lignin (S) was found in the secondary wall of fibers and rays, in which the S/G ratio varied from species to species among hardwoods. More recent studies demonstrated that the S/G ratio varies not only among different species (Akiyama et al 2005;Pinto et al 2005), but also among species of the same genus (Gonzalez-Vila et al 1999;Bose et al 2009), and among clones of the same species (Guerra et al 2009). A correlation has been established between the structural form of the β-O-4 structures found in lignin and the S/G ratio, indicating that the syringyl/guaiacyl composition is the key factor governing the proportion of erythro and threo forms of β-O-4 structure in hardwood lignin (Santos et al 2012c).…”

Quantitative Examination of Pre-Extraction Treatment on the Determination of Lignin Content in Leaves

“…1, the yield of NPs is plotted against apparent lignin content. All the values from leaves were found to be lower than those of 21 wood species (data from Akiyama et al (2005)), indicating that NP yield on the basis of apparent lignin content was extremely low even after various pre-extraction treatments. Acid-soluble lignin will be overestimated if non-lignin contents give absorbance at 205 nm.…”

“…The lignin basis yield of nitrobenzene oxidation products (NPs) varies depending on the lignin structure. Usually, lignin basis yield of NPs from softwood lignin is 26 to 39% and that from hardwood lignin is 32 to 59% (Akiyama et al 2005). On the other hand, Jin et al (2003) reported that the yield of NPs from wood leaves is extremely lower (2% for gingko) than wood lignin's value (Jin et al 2003).…”