Structure of Lignin

Apart from that, in contrast to other biopotymers, which consist of a single intermonomeric linkage, the tight physical binding and chemical linkages between lignin and cell wall polysaccharides practically prevent its isolation in unaltered form. This also makes 

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Fig. 12. Tentative structure of lignin according to Adler together with typical solid state NMR signals of its carbon atoms...

Akiyama, T. Magara, K. Matsumoto, Y. Meshitsuka, G. Ishizu, A. Lundquist, K. Proof of the presence of racemic forms of arylglycerol-p-aryl ether structure in lignin studies on the stereo structure of lignin by ozonation. J. Wood Sci. 2000, 46, 414-4-15. 

Matsumoto, Y. Ishizu, A. Nakano, J. Studies on chemical structure of lignin by ozonation. Holzforschung 1986, 40, 81-85. 

Figure 16. Structure of lignin polymer formed in anaerobic solvent.

Although many suggestions have been advanced for the structure of lignin (15), establishment of a valid constitutional formula for this substance is still far from realized. It was considered (67) that the building stones of lignin are linked together by a methylene dioxv bridge... 

These complications proved to be the greatest deterrents to identification of the structure of lignin. Without knowledge of the make-up of lignin, it is clear that little promise could be expected from empirical studies directed at finding useful applications for it. In view of this situation, there has been a great intensification in fundamental research on the structure and properties of lignin in the hope that a better scientific foundation could be laid for future applied research. 

Figure 22.1 Representative structure of lignin. (Source Kirk-Othmer s Encyclopedia of Chemical Technology, 4" ed., John Wiley Sons, 1991-1998. Reprinted by permission of John Wiley Sons, Inc.)...

An Improved Radiotracer Method for Studying Formation and Structure of Lignin... 

For some time now, it has been proposed that the structural variations observed in DHP s are caused by the mode of polymerization, with bulk polymerization containing more condensed units than end-wise polymerization (32,33). However, in these experiments, DHP s prepared under the same conditions gave different D.S. values depending upon the pH at which the reaction took place. This result suggests that the molecular structure of lignin in the cell wall can also be controlled by factors other than the mode of polymerization. 

Figure 1. Structures of lignin model compounds used in this study.

Present views on the structure of lignin are still largely speculative and in particular little is known of the non-aromatic parts of the molecules. 

We now wish to report our results on isolating lignin-derived dimers by alkaline hydrogenation and to propose mechanisms for their formation. In addition, we will present some information on the (NMR) spectra of these and related compounds this technique has been useful for analyzing the structure of lignin degradation products and related synthetic materials. 

Evtuguin, D. V., and Amada, F. M. L., 2003, Application of electrospray ionization mass spectrometry to the elucidation of the primary structure of lignin, Macromol. Biosci. 3 339-343. 

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