Wood Chemistry PSE 406

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Wood ChemistryPSE 406

• Lecture 15
• Stilbenes, Flavonoids, Condensed and Hydrolysable
  Tannins, other Miscellaneous Extractives and
  Inorganic Compounds

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Stilbenes

• Phenolic extractive found in the heartwood of
  softwoods
• Particularly prevalent in Pinus
• Most often 2 aromatic rings occasionally more
• Presence of double bond linkage
• Naturally present most often in trans form

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Flavonoids

• Serve many roles in plants
• Protection
• Coloration
• Other unique roles.

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FlavonoidsGeneral Structural Information

• Polyphenolic compounds found in softwoods and
  hardwoods
• Composed of diphenylpropane units C6-C3-C6
• Eight structural classifications
• Flavonoids differ through substitution on the
  rings
• Typically OH or OCH3 groups
• Typical to have OH on positions
• 5 and 7
• 3, 4 and 5
• Are also present as gylcosides

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Representative Structures of Flavonoid Classes
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FlavonoidsBiological Significance

• Not all flavonoids have same function in plants
• Anti-fungal
• Antioxidant
• Color bright colors in plants

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FlavonoidsLocation in Tree

• Found in the heartwood of most tress
• Often responsible for coloration
• Found in lesser amounts in the sapwood
• Are found in large amounts in bark and roots
• Leaves green tea can contain up to 30
  flavonoids
• Flowers color is often due to flavonoids

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FlavonoidsMedicinal Uses

• Higher flavonoid content in diet reduces chance
  of
• Heart Disease
• Strengthen capillaries
• Dilates blood vessels
• Stroke
• Cancer all types reduced
• Finnish study ½ rate of cancer

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Condensed Tannins

• Condensed tannins are formed through the
  polymerization of flavan-3-ol (catechin) and
  flavan3,4-diols (leucoanthocyanidins)
• 2-50 units
• Typically 2-8
• Linkages can be through a variety of sites

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Condensed Tannins
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Condensed TanninsLocation in the Tree

• Western hemlock
• Bark 18 tannins
• Wood 2 tannins

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Condensed TanninsBiological Significance

• Protection of plants against insects/animals
• Bad Taste (bitter taste)
• Toxic to bacteria
• Pine calluses created by fungal invasion
• Tree forms calluses as protective tissue
• Calluses contain high levels of tannins
• Uses of condensed tannins
• Leather tanning 10,000 year old industry
• Adhesives

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Hydrolyzable TanninsStructure

• Polymers (esters) of a sugar (usually glucose)
  with one or more polyphenolic carboxylic acids.
• Gallotannins Gallic acid polymer
• Ellagitannins Ellagic Acid polymer

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Hydrolyzable TanninsPolymer Structure Example
Sugar
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Hydrolyzable TanninsGeneral Information

• Rare to nonexistent in softwoods.
• Hardwoods which contain large amounts
• Oak (gallic and ellagic tannins)
• Eucalyptus (Ellagitannins)
• Chestnut (gallic tannins)
• Hydrolyzable tannins located in heartwood.
• Pulp and paper problems
• Increased consumption of bleaching chemicals.
• Coloration problems.

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Tetraterpenes

• Polymers of isoprene containing 40 carbons (8
  isoprene units)
• Most common are the carotenoids
• Generally derivatives of lycopene
• This is a carontenoid which is in high
  concentration in red fruits (gives color)
  tomatoes, watermelon, guava, etc.

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b Carotene

• Tetraterpene carotenoid found in dark green and
  orange yellow vegetables.
• In the human body, it is converted to vitamin A
• Has been shown to be have many health related
  benefits.

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Alkaloids (1)

• These nitrogen containing compounds are found in
  a variety of different plants.
• Located in the leaves, fruits, and bark.
• Quinine
• Used to treat malaria
• Isolated from bark of cinchonas (South American
  Hardwood)
• some eucalyptus species
• Causes pulping problems
• Strychnine
• Found in seeds of tree Strychnos nux-vomica
  (Tropical hardwood)

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Alkaloids (2)

• You are all aware of the alkaloids shown on this
  page you probably have never seen their
  structures. These are typically found in small
  amounts in plants but are worth large sums of
  cash.

Caffeine
Nicotine
Cocaine
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Inorganic Materials

• Inorganic materials
• Plants contains small amounts of most metals.
• Some are used by living cells
• Some present as contaminants
• Ash content gives a rough idea of the amounts of
  metals present.
• Sugar cane 1.7-3.8 ash
• Corn Cobs 2 ash
• Temperate woods contain 0.1-1 ash while tropical
  and subtropical species contain up to 5 ash.
• Main components Ca (50), potassium and magnesium.

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Inorganics in Grasses

• Grasses contain high levels of inorganics
  particularly silica.
• Wheat straw Reported values 4-12 ash
• Leaves 14-19 ash, 10-14 silica
• Nodes 8-14 ash, 5-7 silica
• Internodes 3 ash, 2 silica