Lignin polymerization

Lignin polymerization is a natural process initiated by the enzymatic oxidation of hydroxycinnamyl alcohols such as /)-coumaryl (CM), coniferyl (CF), and sinapyl alcohols (SN), which are known as monolignols (Scheme 2.20).60... 

SCHEME 2.20 Hydroxycinnamyl alcohols involved in lignin polymerization. 

SCHEME 2.21 Two possible reaction mechanisms for the initiation step of the lignin polymerization, investigated at PCM-B3LYP/6-311G(2df,p)//B3LYP/6-31G(d,p) level of theory. 

Russell, W. R. Forrester, A. R. Chesson, A. Burkitt, M. J. Oxidative coupling during lignin polymerization is determined by unpaired electron delocalization within parent phenylpropanoid radicals. Arch. Biochem. Biophys. 1996, 332, 357-366. 

In summary, lignin polymerization is carefully controlled and occurs in different parts of the cell wall at different times utilizing specific monolignols with the assembly template for seeding polymerization being the hemicelluloses (or proteins) already adsorbed on the microfibrils - and the lignin molecule takes its stractural form from that template. 

Several of these papers [105-107] along with a discussion of archival reports on the application of computational methods to lignin polymerization are summarized in a review article by Durbeej et al. [108],... 

Lignin polymerization is initiated by an oxidative enzymatic dehydrogenation of monoUgnols [6], which form Uve different resonance structures [16] shown in Fig. 2. This leads to a large number of probable coupUng reactions, yielding a disordered polymer. 

The first step of lignin polymerization is the generation of free radicals and recombination to form a dimer. Draw the possible reactions for coniferyl alcohol. 

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