Catalysis & Sustainable Processes

• The Polymers Story

• 8 lectureshttp://www.kcpc.usyd.edu.au/CHEM3113.html

username: chem3

password: carbon12

• Lecturer:Associate Professor Sébastien Perrier

s.perrier@chem.usyd.edu.au; tel: 9351 3366, room 351 – KCPC

• 1 assignmentGiven out in Lecture 5 (Friday 20/03/09)

Worth 20%

Course structure

• Understanding the problem:

- Making Polymers

Step Growth Polymerisation – (bio)degradable polymers

Addition polymerisation – recyclable polymers (?)

- The raw material

• Solving the problem:

- Sustainable Process

- Sustainable Synthesis

- Sustainable Materials

Polymers and Sustainability

• Using sustainable raw material...

Peptides and Proteins

Poly(peptides)

• The petide bond is formed by condensation of α-carboxylate and α-amine.

• A protein is a polymer of amino acids strung together by peptide bonds.

• There are 20 naturally occurring amino acids.

• The convention is to number amino acids from left to right, from N to C.

NH3

RH

O

O

NH3

RH

O

O

NH3

RH

O

NH

RH

O

NH

RH

O

O

n + ++

+

α α

AA1AA2AA3AA4

NH3

R1H

O

NH

R2H

O

NH

R3H

O

NH

R4H

O

O

+

Amino terminusN-terminus

Carboxy terminusC-terminus

• Because of the high concentration of water (55.5M) in the cell, the back reaction (bond hydrolysis) is favoured => Eventually all proteins will be hydrolysed.

• BUT spontaneous hydrolysis of proteins is extremely slow.

=> So the peptide bond is kinetically stable, but thermodynamically unstable.

NH3

RH

O

O

NH3

RH

O

O

NH3

R1H

O

NH

R2H

O

O

+ ++ +α α

Ribosomes(Complex of RNA and Proteins)

Thermodynamics

• Each amino acid contains an "amine" group (NH3) and a "carboxy" group (COOH) (shown in black in the diagram) and vary in their side chains (indicated in blue in the diagram).

• The eight amino acids in the orange area are nonpolar and hydrophobic.• The other amino acids are polar and hydrophilic ("water loving").• The two amino acids in the magenta box are acidic ("carboxy" group in the side chain).• The three amino acids in the light blue box are basic ("amine" group in the side chain).

Protein function

• A protein’s function is conferred by its structure.

Structure is specified by the amino acid sequence.

The amino acid sequence is coded in DNA.

Note: Mutations in DNA can cause changes in amino acid sequence, disrupting function and causing disease.

DNATranscription

RNATranslation

Poly(peptide)Folding

Protein

Linear

nucleic

acid

Linear

nucleic

acid

Linear

amino acid

sequence

3D

structure

Levels of Protein structure

• 1. Primary structure (1° structure):

Sequence of amino acids in a polypeptide

Possibilities endless (205000), but only find several thousand

• 2. Secondary structure (2° structure):

local, regular/recognizable conformations

observed for parts of the peptide backbone of a protein

e.g, α-helix, β-strands, collagen helix

• 3. Tertiary structure (3° structure):

3-dimensional conformation of whole polypeptide chain in its folded state

• 4. Quaternary structure (4° structure):

3-dimensional relationship of different polypeptide chains (subunits)

the way the subunits fit together and their symmetry relationships

only in proteins with more than one polypeptide chain

Proteins’ jobs…

• Transport- hemoglobin in blood

• Storage- ferritin in liver

• Immune response- antibodies

• Receptors- sense stimuli, e.g. in neurons

• Channels- control cell contents

• Structure- collagen in skin

• Enzymes- catalyze biochemical reactions

• Cell functions- multi-protein machines

Denaturation of Proteins

• Denaturation involves the loss of quaternary, tertiary, and secondary structure within

a protein.

• Primarily involves breakage of H-bonds.

• Occurs in response to heat, acids, or reactions with other disruptive chemicals.

• Results in loss of function of protein.

Protein-Polymer conjugate

Polysaccharides

Carbohydrates

• ‘Hydrated carbons’: C’s bonded to O and H

• Size ranges from <100 to hundred of thousand of daltons

• Primary roles:

Energy source (C-C and C=O are high energy bonds)

Carbon skeleton used in formation of other organic molecules

Structure (Chitin, cellulose)

Carbohydrates

• 4 types:

• Monosaccharides:

Exist in chain or ring form

Most commonly 5 (pentose; e.g. ribose) or 6 (hexose; e.g. glucose) carbon sugars

E.g. glucose: Energy source for ~all organisms

CH

H OH

OH H

H OH

O

H

CH2OH

OH

O

CH2OH

HH

OH

H

OH

OH

HH

OH

O

CH2OH

HH

OH

H

OH

OH

HOH

H

β-D-glucose

α-D-glucoseD-glucose

OH

OHOH

O

OH

OH

OH

OH

OH

O

OH

OH

• Disaccharides (e.g. sucrose, main transport carbohydrate in plants)

• Oligosaccharides (~3-20 units; often bonded to proteins or lipids in cell membranes)

• Polysaccharides- DP > 100

- Energy storage and Structure

- 3 most important:

Cellulose – plant cell walls, most abundant organic compoundStarch – amylose (plants), glycogen (animals)

Chitin – exoskeleton of insects, crabs, etc.

• Cellulose: β, 1, 4 glycosidic linkage

• ~10,000-20,000 units

• Linear chains well packed

• Reinforced by hydrogen bondings

E.g. cotton:2,000,000 da (g/mol)

OH

OHOH

O

OH

OH

β-D-glucose Cellobiose

OH

OHOH

OH

O

OH

OH

O

OH

OH

OH

O

OOH

O

OH

OH

*

*

n

• Starch: α, 1, 4 glycosidic linkage

• Addition from C1 to C4: amylose

• Addition from C1 to C6: amylopectin

OH

OH

O

OH

OH

OHO

OH

O

OH

OH

OH

OH

OH

O

OH

OH

O

O

OH

O

OH

OH

*

*n

α-D-glucose Maltose

Cellulose vs Starch

• Cellulose is stronger than starch due to its chain packing.

Human body contains enzymes that will break starch down into glucose to fuel the body. But humans don't have enzymes that can break down cellulose (Note: Animals such as termites (wood) or cows (grass)can break down cellulose).

Cellulose makes fibers (e.g. rope, clothing)

Cellulose doesn't dissolve in water the way starch does, and doesn't break down as easily.

• Chitin:Occurs naturally – Shell of insect, crabs, etc.

• Chitosan:Applications cover health care to agriculture to dyes for fabrics

O

OOH

O

NH

OH

*

*

n

O

O

OOH

O

NH2

OH

n

Cellulose Nitrate (Celluloid®)

• Properties:

Thermoplastic

Explosive: Becomes more explosive when increasing nitration

• Applications:

Plastics, lacquers, film media - 10.5-12% N2

Gun Powder (Gun cotton) – 12.5-13.5% N2

O2NO

OO

O

O

NO2*

*n

NO2

CelluloseH2SO4

Cellulose Acetate

• Properties:Thermoplastic

Good toughness

Deep gloss

High transparency

‘Natural’ feel

• Applications:Textile and Fibbers

Film media (Cellulose triacetate)

Wound dressings

Personal hygiene products, Absorbent cloths and wipes, Specialty papers, Filter media

(including cigarette filters)

OO

O

O

O*

*n

CH3

O

O

CH3

O

O

CH3

OCH3

O

CH3

OCelluloseH2SO4

Acetic anhydride

Cellulose xanthate (Rayon, Viscose)

• Replacement for silk (smooth filament)

• Applications:Rayon fibbers:

•Highly absorbent

•Soft and comfortable

•Easy to dye

•Drapes well

OO

O

O

O*

*n

S

S

O

S

S

S

S

CelluloseCS2

NaOH

×1200 Magnification

10 µm

10 µm

λ10 µm

10 µm10 µm

4 h (11%)

24 h (20%)

96 h (26%)

×1200 Magnification

Virgin cellulose fibre

λCellulose-RAFT

Cellulose-g-PS

Water droplet on cellulose-g-polystyrene copolymer

(26% graft ratio) surface

Contact angle ≈ 130o

Hydrophobic Cellulose

Polymers and the environment

• Lower energy to make than many alternatives (glass, steel,

…) – provided structural properties are sufficient

• Less environmental issues than some alternatives, e.g.,

nylon vs. cotton

• Can have significant environmental issues: ‘plastic’ bags

• Need to consider overall environmental issues, e.g.,

disposable nappies

• Used polymers as fuel?

• Challenges for the future:

Raw materials from renewable resources?

Enhanced materials of biological origin (augmented natural rubber, modifications of wood, …)