Polysaccharides Flashcards
List the types of chemical bonds from strongest to weakest.
Covalent, metallic, ionic, hydrogen
What is threshold strength for covalent bonds?
All covalent bonds have a bond strength of >100 kJ/mol
What is the range of bond strength for secondary bonds?
1-10 kJ/mol
Why does water act as a plasticizer?
It competes for H bonds
What’s the energy of cellular adhesion?
10 kJ/mol
What’s the binding energy of integrin-RGD (part of fibronectin)?
25 kJ/mol
What is the basic structure of polysaccharides?
Linear chains of cyclic carbohydrates
What side group makes polysaccharide structures very stable and why?
The side OH group because it makes it possible to form a lot of intermolecular and intramolecular H bonds
What are the most abundant polysaccharides on earth and where are they found?
Cellulose (plants)
Chitin (insects)
What are the characteristics of cellulose?
-Most abundant natural polymer on earth
-Basic building block for plants
-20-50% of the plant cell wall
-E=100 GPa, Strength = 1 GPa
-Most studied polysaccharide
Which plant has the highest cellulose content?
Cotton (95%)
What is the typical composition of wood?
40-55% linear cellulose
15-35% lignin
25-40% hemi cellulose (small, branched)
What are the conditions required for polymer crystallization to occur?
-Polymer must be linear
-Polymer must have a regular chain structure
How does the stiffness of semi-crystalline polymers compare to that of amorphous polymers?
Semi-crystalline polymers are 100 to 1000 time stiffer than amorphous polymers
How does the crystallinity of cellulose fibrils affect their mechanical properties?
Cellulose fibrils are semi-crystalline
The crystals are oriented with the fiber which leads to high stiffness and high strength
Describe the properties of cellulose nanofibrils
5-20 nm in diameter, 100s of nm long
E=145 GPa, Strength=7.5 GPa
Relatively cheap and biodegradable
Can be used in manmade composites
What are two methods for orienting polymer crystals?
Drawing and stretching
What is the effect of water on cellulose?
Water decreases the modulus of cellulose but it increases the strength and strain at failure
Why is cellulose stronger than chitin?
Cellulose has the OH side chains but chitin doesn’t. This means that cellulose can be more closely packed and form hydrogen bonds
What are the properties of chitin?
-Second most abundant natural polymer on earth
-E is on the order of GPas, strength is 60 to 200 MPa
-Very similar to cellulose but less studied
-Also capable of crystallizing
What are the characteristics of hyaluronic acid?
A major component of synovial tissues and fluid, ECM, and other soft tissues
-High molecular weight
-Highly charged polymers
-Viscoelastic and rheological properties (lubricant/shock absorber)
What characteristics has hyaluronic acid been linked with in naked mole rats?
-Tough and flexible skin
-Resistance to cancer
-Exceptional longevity
Why are all proteins and polysaccharides sensitive to temperature and hydration?
The H bonds
Do the stiffer and stronger proteins and polysaccharides tend to be amorphous or crystalline?
They tend to be more semi-crystalline
Which proteins obey entropic elasticity?
The elastomeric proteins (elastin, resilin)
