1. Biomass Fundamentals Module 13: Lignin A capstone course for BioSUCCEED: Bioproducts Sustainability: a University Cooperative Center of Excellence in EDucation The USDA Higher Education Challenge Grants program gratefully acknowledged for support

2. This course would not be possible without support from: USDA Higher Education Challenge (HEC) Grants Program www.csrees.usda.gov/funding/rfas/hep_challenge.html

3. Lignin Anselme Payen 1838: Reacts wood with nitric acid and then sodium hydroxide. Remaining material he names Cellulose. Schulze 1857: Names dissolved material Lignin from the latin lignum meaning wood. Phenolic Polymer - The Glue that Holds the Fibers Together 3 Dimensional Crolinked Network Branched Polymer/Polydisperse (Large and Small Polymers)

4. Lignin Biosynthesis I

5. The Metabolic Pathways for the Biosynthesis of Wood Components hν

6. Shikimic Acid Pathway The Primary Metabolic Pathway for Lignin Shikimic Acid Pathway Occurs in all plants Leads to Lignin –Tannins and Extractives The whole pathway is enzymatically controlled

7. The 6 Carbon sugar is initially spit into 2 units CondensationCyclization Reduction of Carbonyl to OH Activation Using ATP- Install P at C5 Another PEP is used to extend the chain, P falls off as H 3 PO 4 Aromaticity is finally installed followed by Transamination (NH2)

8. Lignin Biosynthesis II The Cinnamate Pathway is a secondary metabolic pathway Specific to Woody Plants Creates the Lignin Precursors …the Lignin monomers Cinnamyl alcohols

9. Lignin Biosynthesis II CH 2

10. Dehydrogenative Polymerization of Lignin precursors Monolignols are NOT abundant in their free forms –exist as 4-O-  -D-glucosides Monolignol-glucosides Increase solubility - Facilitate transport Decrease toxicity

11. Lignin Nomenclature

12. Phenylpropane Unit C9 } Common Names Side Chain

13. Polymerization-Initiation Enzymatic Formation of Phenoxy Radical Peroxidases-H 2 O 2 systems cause proton abstraction from a given cinnamyl alcohol Creating a Phenoxy Radical

14. Lignin Polymerization Process 1Dehydrogenation - formation of phenoxy radicals 2Coupling - formation of oligolignols and quinone methide 3Addition of water, lignols, carbohydrates and acids - formation of  -hydroxyl group,  -O-4 linkages and lignin-carbohydrate complex

15. Lignin Polymerization Repetitive dehydrogenation of lignols, coupling and addition to quinone methide Lignol is a collective name for precursors and intermediate products of lignin during lignification. (Similar to saccharides) –Monolignol - precursors –Dilignol, triligonol, tetralignol, etc. –Oligolignol