Guaiacyl structures

Thioacidolysis of extractive-free softwood meal or softwood MWL essentially leads to the guaiacyl structures listed in Table 6 4 2 and referred to previously in the section on thioacidolysis of hardwood lignins When subjected to thioacidolysis, compression wood additionally gives rise to significant amounts of p-hydroxyphenyl QC-, monomeric compounds (Lapierre et al 1987)... 

Preferential alteration of syringyl lignin is not surprising in soils or oxidized peats because fungi would be present and are known to selectively degrade syringyl versus guaiacyl structural units (17, 41). This pattern could... 

The chemical structure of lignin is quite complex. In softwood, coniferyl alcohol will yield the guaiacyl structure (G, Figure 6.7). 

Many grasses have mostly guaiacyl structures. Which monomer forms the guaiacyl lignin structure ... 

Akiyama, T. Goto, H. Nawawi, D. S. Syafii, W. Matsumoto, Y. Meshitsuka, G. Erythro/threo ratio of P-O-4-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. Holzforschung 2005, 59, 276-281. 

Fig. 2.2 A. Chemical structure of the three types of lignin monomer units H, p-hydroxyphenyl- G, guaiacyl and S, syringyl. Note the methyl groups (boxed) in the methoxy moieties of the G and S monomers. B. Pie chart showing the proportions of pine xylem ESTs that putatively encode enzymes of Ci metabolism, glycolysis, and the TCA cycle.

Figure 1. Removal of 3H at position 5 of the guaiacyl ring of coniferyl alcohol (I) by formation of ring substituted structures (V, VI, VII) during dehydrogenative polymerization.

Condensed Structures in p-Hydroxyphenyl-Guaiacyl Type DHP. It has been difficult to determine the exact amount of p-hydroxyphenylpropane units in lignin. This can best be illustrated by an example nitrobenzene oxidation of a DHP prepared by the Zutropfverfahren method from a mixture of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, gave no detectable p-hydroxybenzaldehyde on alkaline nitrobenzene oxidation... 

In our analysis of the chemical structures which are active tur-inducers (41) it was found that the compounds fell into four groups (1) acetophenones and related structures, (2) monolignols, (3) hydroxycinnamic acids and their esters, and (4) chalcone derivatives (Fig. 1). Each compound had either a guaiacyl or a syringyl nucleus, and with the exception of the monolignols, possessed a carbonyl group. Most were of common occurrence in vascular plants. 

M.W.L. contains free phenolic (guaiacyl) hydroxy groups in about every third unit kraft lignin contains about twice as much. In addition, probably about every 15th unit of kraft lignin has a catechol ring structure 2,13). 

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