Linear structure of lignin :

structure of lignin

The two mre used until today, are those of FREUDENBERG and ADLER. These models which present an irregular polymer, probably three-dimensional, discocert the very many biologists and biochemists who are interested in the processes of lignification of the plants which is however of first importance in the comprehension of the biological processes governing their cycle of life.

Lignine selon Freudenberg
Lignins according to Freudenberg (1968)

Lignine selon Adler
Lignins according to Adler (1977)

Thus, so today one knows perfectly the enzymes and the biosynthetic ways at the origin of lignification, nobody ventures himself to explain how lignin is built in the vegetable wall and which its true structure is.

Two assumptions are to be considered according to whether we would be in presence :

  • Of a completely random process of biosynthesis leading to an irregular polymer which would be single in the alive world.

  • Of an extraction modifying their structure and/or of an arroneous analysis of these structures.

It is the second assumption as I have just shown it with my colleague Professor J BANOUB which is the good one.

Indeed we realized by analyzing lignins of straws extracted by our process which it was enough in mass spectrometry to a very weak energy to ionization to split up the lignin macromolecules. The main part of the lignin analyses by mass spectrometry raised so far in the literature used methods much harder which did not bring information on the structure of polymer. It was thus necessary to reconstitute, starting from monomeric fragments, of hypothetical connections which led to models like those of FREUDENBERG or ADLER previously evoked.

Moreover brutal conditions of extraction during pulping support the recombinations which make that the extracted macromolecules have very high molecular masses and has nothing any more to see with native lignins.

The mass spectrometry analysis of our lignins combined several techniques by chemical ionization with atmospheric pressure (Apci-ms), tandem Ms-Ms and by laser desorption and detection in time of flight (Maldi-tof -ms). The details of the experimental practices and the structural analyses are reported in the paper published at the end of 2003 in the Journal of Mass Spectrometry, 38, 900-903, 2003.

That enabled us to conclude formally, for the first time, with a linear structure for lignin of straw visualized below.
 

Lignine selon Delmas et Banoun
Lignins according to Delmas and Banoub (2003)

These observations were confirmed thereafter with other types of vegetable matter and are the subject of four scientific articles to appear very soon.

Moreover of the analyses by NMR of the solid allowed to confirm the presence of a carboxylic function on final phenol, fundamental structural observation, ever brought back before us in the literature.
This fundamental scientific discoveries on the structure of lignin :

  • Scientific : allow to elimiminate stuctural uncertainty on a macromolecule which constitutes nearly 20 % of the terrestrial biomass and in the near future to improve the knowledge of the general structure of the plants. A group of international biochemists and biologists is in the course of constitution currently with this intention with our initiative.

  • Economic : to be able to regard our lignin as a pre polymer structurally definite, usable without modification in polyurethans and polyesters, at a price higher than pheno.