Lignin, structural model

Terashima, N., Atalla, R. H., Ralph, S. A., Landucci, L. L., Lapierre, C., and Monties, B., 1996, New preparations of lignin polymer models under conditions that approximate cell well lignification I. Synthesis of novel lignin polymer models and their structural characterization by 13C NMR., Holzforsch. 49 521-527. 

We have also confirmed our previous results on the effect of methoxylation of phenolic hydroxyl groups within lignin. On the basis of our model studies, we suggest that the most likely explanation for this is that triplet carbonyl groups are quenched statically by hydroxyl groups within the lignin structure on timescales less than 20 ns thus reducing the amount of transient detected in our laser photolysis experiments. 

Little work has been carried out so far to characterize the lignin structures present in various types of high yield pulps. Model compound experiments have... 

Limitations in the use of spectral data arise because of the complex nature of lignin and the difficulty in relating UV absorption data to lignin structure. Also, the precision of the results obtained with wood sections is somewhat lower than that obtained when measuring the UV spectra of model compounds in solution. 

Acidic condition. Acidic hydroxymethylation occurs mainly at the C2 or C6 position of aromatic nuclei which may be phenolic or etherified units. It is used in the preparation of wood adhesives. The influence of lignin structure on reactivity and performance of the resulting resin product is still not entirely understood, as discussed by Nimz [3951. Van der Klashorst [396-398] reported the acidic condensation of alkali lignin and lignin model compounds with formaldehyde. Initial hydroxymethylation was faster with syringyl units... 

Figure 7.43. SIMS analysis of lignin, the second most abundant biopolymer in nature, following cellulose. Shown is the phenylpropane subunits and a structural model of softwood Ugnin (top). The secondary-ion mass spectra of pine (softwood) and beech (hardwood) milled wood Ugnin (MWL, a solvent-extracted form of Ugnin from beech wood) are also shown (bottom). Reproduced with permission from Saito, K. Kato, T. Tsuji, Y. Fukushima, TL. Biomacromolecules 2005, 6,678. Copyright 2005 American Chemical Society.

Figure 1.- Structural model for a modem lignin from gymnosperm (modified from Adler, 34). The numbering convention is shown for a typical structural unit of lignin. Reproduced with permission from reference 34. Copyright 1990 Elsevier Science Ltd.—UK.

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