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Wood Chemistry PSE 406

Wood Chemistry PSE 406. Lecture 9 Lignin Biosynthesis. Class Agenda Lignin I. Basic Lignin Biosynthesis Nomenclature Methoxyl Groups Phenoxy Radical Formation Radical Coupling. Lignin-introduction. Phenolic Polymer - the glue that holds the fibers together

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Wood Chemistry PSE 406

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  1. Wood ChemistryPSE 406 Lecture 9 Lignin Biosynthesis PSE 406 Lecture 9

  2. Class AgendaLignin I • Basic Lignin Biosynthesis • Nomenclature • Methoxyl Groups • Phenoxy Radical Formation • Radical Coupling PSE 406 Lecture 9

  3. Lignin-introduction • Phenolic Polymer - the glue that holds the fibers together • Increase the mechanical strength properties of plants • Present in higher plants in vascular tissues (liquid transport and mechanical strength) • Distribution in the cell wall and parts of tree differs • Mechanical barrier against pathogens • Polydisperse (Large and Small Polymers) • 3 Dimensional Networks - Branched Polymer PSE 406 Lecture 9

  4. Lignin distribution PSE 406 Lecture 9

  5. Lignin Biosynthesis I PSE 406 Lecture 9

  6. Lignin Biosynthesis II PSE 406 Lecture 9

  7. Lignin BiosynthesisNomenclature Side Chain } Phenylpropane Unit C9 Common Names PSE 406 Lecture 9

  8. Lignin StructureMethoxyl Content PSE 406 Lecture 9

  9. Lignin BiosynthesisNomenclature • Once incorporated into lignin, the ring structures of the precursors are given these names. PSE 406 Lecture 9

  10. Lignin BiosynthesisEnzymatic Formation of Phenoxy Radical • The initial step in the polymerization of lignin is an enzymatic directed one electron abstraction forming a phenoxy radical. PSE 406 Lecture 9

  11. Lignin BiosynthesisResonance Forms of Phenoxy Radical • The phenoxy radical is only one of several resonance structures. • This figure shows a second resonance structure with the free radical on the 5 carbon of the ring. PSE 406 Lecture 9

  12. Lignin BiosynthesisResonance Forms of Phenoxy Radical PSE 406 Lecture 9

  13. Lignin Coupling-O-4 PSE 406 Lecture 9

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