Wood Chemistry Wood Chemistry PSE 406/Chem E 470 Lecture 8 Hemicellulose II PSE 406 - Lecture 8 1 Wood Chemistry Class Agenda Arabinogalactans Minor Species Glucans Galactans Pectins Starch Chitin PSE 406 - Lecture 8 2 Wood Chemistry
Arabinogalactan Minor hemicellulose except in Larch 10-20% of Larch 0.5-3% of other woods DP ~ 220 Backbone 13 -D-Galactopyranose units Branches: Nearly every galactose in backbone attached 16 to: -D-Galactopyranose -L-Arabinofuranose, -L-Arabinopyranose -D-Glucopyranosyluronic acid Text PSE 406 - Lecture 8 3 Wood Chemistry Arabinogalactan 1 -D-Gal 1 -D-Gal 1 -D-Gal
1 1 R -L-Araf 3 1 -D-Gal 6 1 -D-Gal 6 1 -D-Gal 6
3--D-Gal-1 3--D-Gal-1 3--D-Gal-1 3--D-Gal-1 3--D-Gal-1 6 6 6 6 6 1 -L-Ara R = galactopyranose or L-Arabinofuranose or D-glucopyranosyluronic acid PSE 406 - Lecture 8 4 Pectins Wood Chemistry Often described as water soluble extractives, not as hemicelluloses. Found in middle lamella and primary cell wall. Pectins is a class of several compounds Galactans (discussed on next slide) Galacturonans: Rhamnogalacturonan: 14 galacturonic acid backbone with rhamnose 1/8 units, sidechain of galcturonic units Arabinans 90% arabinose linked 15
Text PSE 406 - Lecture 8 5 Wood Chemistry Galactans Very minor component in normal and tension wood. Can be major (10%) component of compression wood. Galactan from Tamarack 200-300 14 galactopyranose backbone, 1/20 16 galacturonic acid Rhamnoarabinogalactan Sugar Maple Gal:Ara:Rha (1.7:1:0.2) Many other varieties PSE 406 - Lecture 8 6 Glucans Wood Chemistry
Glucans are very minor components in wood. The major representatives of this group are starch and callose. Starch Amylose:14 -D-Glucopyranose Amylopectin: 14 -D-Glucopyranose + 16 D Glucopyranose Callose 13 -D-Glucopyranose Text PSE 406 - Lecture 8 7 Callose Wood Chemistry Callose is found in very minor amounts in wood. Small granular hemicelluloses found in a few isolated locations. Polymer of 13 -D-Glucopyranose H OH H OH H H
O HO O HO O O H H O H OH H H PSE 406 - Lecture 8 OH H n 8 Wood Chemistry Starch in Plants Starch serves as an energy
reserve in plants. High concentrations of starch are found in seeds, bulbs, and tubers. Starch can be as high as 70-80% of certain tubers and seeds. Wood contains minor amounts of starch in the form of granules in living parenchyma cells. Typical amounts: 0.2-0.6% of total wood Sapwood >3% PSE 406 - Lecture 8 9 Wood Chemistry Chemical Composition of Starch Plants contain two types of starch, linear (helix) amyloses and branched amylopectins. The amounts of each of these starch types present is plant dependent. Typical amounts are 25% amylose, 75% amylopectin
Mutant species can have from 50-90% amylose PSE 406 - Lecture 8 10 Amylose Wood Chemistry 14 -D-Glucopyranose Because of the bonding, this molecule forms a helix It takes 6 gluopyranose units for each turn Addition of iodide to amylose results in a deep blue color. It is believed to be due to a complex of I5- within the polyglucoside spiral. Amylose is not water soluble H OH H O O H OH H HO H H OH
H O O H HO H H PSE 406 - Lecture 8 OH O n 11 Wood Chemistry Amylopectin 14 DGlucopyranose + 16 D Glucopyranose Amylopectin is a branched polymer Branching inhibits helix formation This starch is
therefore somewhat water (hot) soluble. H OH H O O H OH H HO H OH H H O O H HO H OH H OH H H
O O H O H HO H H OH H H HO H H PSE 406 - Lecture 8 O O OH O n 12 Wood Chemistry
Isolation of Starch From tubers (potato, tapioca, etc.) Wet tuber is ground fine. Hot water dissolves soluble fraction of tuber. Insoluble starch is separated from the liquid phase. Starch is dried. From corn The skin and the germ (oil containing portion) are mechanically removed from the kernel after soaking in water. Isolation of the starch is then similar to tubers. PSE 406 - Lecture 8 13 Wood Chemistry Chitin Cellulose type polymer found in insects and crustaceans; used in making the hard exoskeletons (~30%). Second or third most abundant biopolymer. Second most abundant if you study this kind of thing for a living.
Third most if you are a lignin chemist. PSE 406 - Lecture 8 14 Chitin Structure Wood Chemistry Chitin is an amino polysaccharide It is a linear polymer of 14 -D-Glucopyranose units just like cellulose The difference is that the hydroxyl group of C2 has been replaced by an amide group H3C H OH CO H H O O NH H HO
H O O HO H H NH OC H H H O OH CH3 n PSE 406 - Lecture 8 15
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