Lignin Flashcards
the term “lignin” (Latin lignum = ______)
wood
Who introduced the term “lignin” and when?
Schulze in 1865
What does the term “lignin” refer to?
A dissolved part of wood treated with nitric acid
What type of molecule is lignin?
A natural aromatic phenolic biomacromolecule
it is one of the most abundant biopolymer in nature and a large contributor to the residues of the terrestrial biomass, after polysaccharides
lignin
What role does lignin play in terrestrial biomass?
It contributes to the residues of biomass
Why is the definition of lignin complex?
Due to its extreme complexity affecting isolation
What are the key characteristics of lignins according to Brauns?
- Made from phenylpropanoid building units
- Contains wood methoxyl content
- Resistant to acid hydrolysis
- Soluble in hot alkaline and bisulfite
- Yields vanillin and related compounds when reacted with nitrobenzene
- Produces “Hibbert’s ketone” when boiled in hydrochloric acid
What is the primary function of lignin in the cell wall?
Provides structural rigidity to cell walls
Where is lignin found in plant structures?
In primary and secondary walls, middle lamella
What is the role of the epidermal tissue in plants?
It covers the entire surface of the plant
- The outermost cell layer of the cortex of plants.
- It forms a prominent layer immediately under the epidermis in many but not all plants.
Hypodermal
What are the primary building units of lignin?
Cinnamyl alcohols
coniferyl alcohol
sinapyl alcohol
p-coumaryl alcohol
How does lignin composition differ among gymnosperms, angiosperms, and grasses?
Gymnosperms: Mostly guaiacyl propane monomers
Angiosperms: Equal proportions of guaiacyl and syringyl propane units
Grasses: Equal proportions of guaiacyl, syringyl, and p-hydroxyphenyl propane units
What are the methods of lignin isolation mentioned?
- Milled Wood Lignin (Björkman)
- Enzyme Lignin (Pew and Weyna)
- Alkali Lignins
- Organosolv Lignin
first major advance toward separating lignin in a relatively unaltered state
Milled Wood Lignin (Björkman)
lignin separation procedure based on extensive grinding of plant material in a non-swelling liquid (toluene)
Milled Wood Lignin (Björkman)
Lignin in situ (______) is almost insoluble in any solvents unless it is degraded by physical or chemical treatments.
proto lignin
ball milling is essential to isolate lignin from plant cell walls by ______
solvent extractions
lignin is ready to be extracted out by ___________ (usually with dioxane/water)
aqueous dioxane
What is the significance of milled wood lignin (MWL)?
Best preparation for structural studies of lignins
What effect does dry ball milling have on lignin structures?
Causes substantial structural changes
produced as a part of natural energy transfer and carbon cycle especially by wood-degrading fungi and bacteria.
Cellulolytic enzymes
What are cellulolytic enzymes used for in lignin isolation?
To remove polysaccharides from wood meal
What is Milled Wood Enzyme Lignin (MWEL)?
Insoluble residue containing lignin and polysaccharides
milled wood enzyme lignin (MWEL) contains almost all of the lignin and as much as ____ of the polysaccharides.
12%
How is cellulolytic enzyme lignin (CEL) obtained?
By extracting MWEL with 96% aqueous dioxane
What is the advantage of CEL over MWL?
Higher yield with less degradation
CEL procedure is tedious, and the enzyme treatment requires ___ days or more because the cellulose is highly crystalline and inaccessible, which impairs the physical contact between cellulose and enzyme
10
What does the SEL method involve?
Swelling wood in organic solvent before cellulase treatment
Ball-milled wood was swelled in an _________, then regenerated in water and treated with cellulase.
organic solvent
What is the purpose of enzymatic mild acidolysis lignin (EMAL)?
To isolate lignin representative of total lignin
EMAL - The insoluble material remained after the enzymatic hydrolysis was collected by centrifugation, washed twice with acidified deionized water (pH 2), and freeze-dried.
true
How does the yield of EMAL compare to MWL and CEL?
About four times greater than MWL
What conditions are required for alkali lignins to become soluble?
5% sodium hydroxide at 130–170 °C
addition of hydrogen peroxide into alkali aqueous solution promotes the removal of lignin from pulp or even raw materials
true
What is the practical use of lignin dissolved in alkali hydrogen peroxide solution?
Fuel burnt in pulping mills
Organosolv Lignin Come from the root word “__________”
organic solvents
What are organosolv lignins derived from?
Spent organosolv pulping liquor
What solvents are commonly used for organosolv pulping?
Ethanol and methanol
