1. PSE 406 - Lecture 71 Wood Chemistry PSE 406 Lecture 7 - Hemicelluloses

2. PSE 406 - Lecture 72 Class Agenda lGeneral Information lComponents »Sugars »Acetyl/Methyl Groups lNomenclature/Classification lXylans lMannans

3. PSE 406 - Lecture 73 General Information lCell wall supporting components l27-30% of wood »~27% softwoods »~30% hardwoods »~30% agricultural biomass lShort branched polymers »50-300 DP lIn wood they are not crystalline »Very accessible to chemicals »Very reactive

4. PSE 406 - Lecture 74 Major Components Hexoses Pentoses

5. PSE 406 - Lecture 75 Other Components Hexuronic Acids: Minor Constituents

6. PSE 406 - Lecture 76 Acetyl and Methyl Groups lHemicellulose sugars can also contain methoxyl or acetyl groups. The percentage of these groups varies significantly between different hemicelluloses. Notes

7. PSE 406 - Lecture 77 Nomenclature lNamed after components in linear backbone »Xylans (1-4 linked xylose chain) »glucomannans (1-4 glucose/mannose backbone) lBranching noted in first part of the name »gluco, arabino, o-acetyl lBranching linkage is also included »1  2, 1  6, or -O- lIn structural drawings, abbreviations for the components are used: Glc  = glucopyranose Notes

8. PSE 406 - Lecture 78 Hemicellulose Classifications lSoftwood Hemicelluloses »Galactoglucomannan (Mannans)-main »Arabinoglucuronoxylan (Xylans) »Arabinogalactan »Pectins lHardwood Hemicelluloses »Glucuronxylan (Xylans)-main »Glucomannan

9. PSE 406 - Lecture 79 Softwood Xylans l10-15% of wood lMajor xylan: » Arabino-4-O-methylglucuronoxylan 1  4 linked  -D-xylopyranose linked backbone Arabinose furanose ring attached 1  3  to about 1 in every 10 xylose units 2/10 xylose 1  2  linked to 4-O-methylglucuronic acid lDP ~ 120

10. PSE 406 - Lecture 710 Softwood Xylans  4-  -D-Xly  -1  4-  -D-Xly  -1  4-  -D-Xly  -1  4-  -D-Xly  4-  -D-Xly   4-O-Me-  -D-Glc         -L-Araf  1 3 1 4 2

11. PSE 406 - Lecture 711 Xylan Reducing End -  -Xly  -1  4--  -D-Xly  3-  -L-Rha  -1  2-  -D-Gal  A-1  4-D-Xly  lXylans have a very unusual reducing end which makes them mostly stable to alkaline degradation reactions. As you can see, there is a rhamnose molecule attached 1  2 to a galacturonic acid in the backbone. Notes

12. PSE 406 - Lecture 712 Hardwood Xylans l15-30% of wood lMajor xylan: » O-acetyl-4-O-methylglucurono-  D-xylan »Also called glucuronoxylan 1  4 linked  -D-xylopyranose linked backbone lMost xylose (7/10) are actylated at C2 or C3 1/10 xylose 1   linked to 4-O-methylglucuronic acid lDP~ 150-200

13. PSE 406 - Lecture 713 Hardwood Xylans  4 -  - D - Xly  -1  4 -  - D - Xly  -1  4 -  - D - Xly  -1  4 -  - D - Xly    R  R = Acetyl 4 - O - Me -  - D - Glc    

14. PSE 406 - Lecture 714 Hardwood Mannans l3-5% of Hardwoods lSimple unbranched polymer lDP ~ 70 lContains 1 to 2 parts Mannose per 1 part Glucose Linkage 1  4   4-  -D-Glc  -1  4-  -D-Man  -1  4-  -D-Glc  -1  4-  -D-Man  -1  4-  -D-Man 

15. PSE 406 - Lecture 715 Softwood Mannans-Water Soluble lGalactoglucomannans l5-10% of wood lDP 100-150 Glucose/Mannose backbone linked 1  4  »Mannose/Glucose = 3/1 lGalactose side chain »Galactose/Glucose = 1/1 »Galactose 1  6  lAcetyl Groups 1 per every 3~4 backbone units - on C2 or C3

16. PSE 406 - Lecture 716 Softwood Mannans-Alkali Soluble lGalactoglucomannans (glucomannans) l10-15% of wood lDP 100-150 Glucose/Mannose backbone linked 1  4  »Mannose/Glucose = 4/1 lGalactose side chain »Galactose/Glucose = 0.1/1 »Galactose 1  6  lAcetyl Groups 1 per every 3~4 backbone units - on C2 or C3 Notes

17. PSE 406 - Lecture 717 Softwood Mannans  4-  -D-Glc  -1  4-  -D-Man  -1  4-  -D-Man  -1  4-  -D-Man  -1  2,3  Acetyl 6   -D-Gal  1 l Alkali soluble mannans are similar in structure except there is much less branching (i.e. less galactose groups) Water Soluble Structure