Unless otherwise stated, all images in this file have been reproduced from:
Blackman, Bottle, Schmid, Mocerino and Wille,
Chemistry, 2007 (John Wiley)
ISBN: 9 78047081 0866
Slide 37-1
Chem 1101
A/Prof Sébastien Perrier
Room: 351
Phone: 9351-3366
Email: [email protected]
Prof Scott Kable
Room: 311
Phone: 9351-2756
Email: [email protected]
A/Prof Adam Bridgeman
Room: 222
Phone: 9351-2731
Slide 37-2
Email: [email protected]
Highlights of last lecture
Intermolecular Forces…
CONCEPTS
H-bonding
intermolecular, intramolecular
the special case of water
Effect of IM forces on
boiling pt, vapour pressure, ∆Hvap
viscosity, surface tension
Slide 37-3
The age of polymers:
-
-
Volume of materials made by
synthetic polymerization exceeds that
of metals.
21st century will see vast expansion of
new polymers based on biosynthetic
processes (often with purely
synthetic polymers)
Slide 37-4
Definitions
Polymer: (poly: many, meros: part)
high-molecular-weight molecules consisting of
repeating subunits which are bond to each
other
IUPAC: "a substance which is built of such
molecules, in which one kind or more kinds of
atoms or groups of atoms are repeatedly linked
together";
mwt > 10,000 u
Monomer
repeating subunits; small molecules
Slide 37-5
What are polymers?
Subunits (monomers) joined together
like beads on a necklace:
e.g.
ethylene
polyethylene
(“Gladwrap®”)
Typically 104 monomer units per polymer
chain
H
H H H H H H H
C C
H
C C C C C C
H
H H H H H H
Slide 37-6
Brief History
Leo Baekeland (1863 - 1944)
1907-1909 first plastic (resin): bakelite (Phenolic resin)
Thermoset,
nonconductive, heat
resistant
use: electric fittings
(insulator), TV
cabinets, knobs,
buckles, dishes,
bowling balls
Slide 37-7
Brief History
Hermann Staudinger (1881 - 1965)
- Introduction of the term "macromolecules" in
1922
- Polymers are not aggregates of small
molecules held together by undefined forces.
Instead, they are macromolecules held
together by ordinary covalent bonds.
1953: Nobel Prize for Chemistry for
demonstrating that polymers are long-chain
molecules
1930s: Staudinger voiced his beliefs on the
important role that macromolecules played
in living systems, especially proteins…
Slide 37-8
Letter to Hermann Staudinger
(dated end 1920s)
"Drop the idea of large molecules, organic
molecules with a molecular weight higher than
5,000 do not exist. Purify your rubber; then it
will crystallise.“
H.Wieland, to H.Staudinger, reported in “Polymers: The Origins
and Growth of a Science", by Herbert Morawetz
Slide 37-9
Brief History
Wallace Hume Carothers (18961937)
1930s synthesis of neoprene (Arnold
Collins, 1931) and nylon (1934) at
DuPont
1939 nylon stockings
1987 approx. 120 000 different
synthetic polymers
Slide 37-10
Synthetic polymers
Slide 37-11
Natural polymers
Some are simple homopolymers:
starch, cellulose
Condensation polymer
natural rubber
Addition polymer
polymers of glucose—can also be branched (many OH groups)
When polymer (starch,
cellulose) is formed from
glucose, water is eliminated
H2O
Slide 37-12
Polypeptides (proteins)
polypeptides are another biopolymer, and we shall examine their
structure further…
Consider an amino acid:
H2O
H
H
O
N
H
C
Cα
“Condensation
polymer”
H
OH H
R
O
N
R = one of 20
different groups
H
Cα
R
C
OH
H
H
O
N
H
Cα
H
C
O
N
R
H
Cα
R
C
OH
“Peptide linkage”
Slide 37-13
20 Natural amino acids
Slide 37-14
Polypeptides (or proteins)
We can consider four
levels of structure in a
protein:
Primary
Secondary
Tertiary
Quaternary
Slide 37-15
Primary structure
The primary structure of a polymer (protein in this case) is just its
chemical structure.
Slide 37-16
Peptide linkage
Cα
The peptide linkage is extremely important in affecting
the shape of a protein. You can draw two resonance
structures of this linkage…
O
So the C-N bond has
partial C=N character
C
Cα and the peptide
N
N
linkage is planar.
H
O
C ψ
O-
Cα
C
C
N+
H
H
Cα
Rotation is possible
about the other two
backbone bonds.
N
R
C
C
O
Slide 37-17
Secondary structure
The C=O and N-H on the
backbone are ripe for Hbonding and can form near
linear H-bonds if the
backbone can rotate about
ψ and ϕ into a specific
orientation.
This H-bonding may give
rise to the α-helix
structure (right), or a βsheet structure.
The main difference
between the two forms is
the angles ψ and ϕ (previous
page)
5.1Å
26º
Slide 37-18
In the α-helix structure, the hydrogen bond between
carbonyl oxygen of residue i and amide proton of residue
i+4 of same poly(peptide).
R1
H
O
N
N
H
H
O
R2
R3
H
H
COLO1120
O
N
N
H
H
O
R4
R5
H
H
O
N
N
H
H
O
R6
H
Slide 37-19
Secondary structure
The beta sheet structure has the amino acids all
lined up to form a pleated sheet structure:
Slide 37-20
Tertiary structure
The type of R-groups determine how the a-helices and b-sheets arrange
themselves together. There is a wide variety of intermolecular
interactions that you can form from various combinations of R-groups, e.g.
Basic groups
In each case, in solution:
N: + H2O NH+ + OHNH2 + H2O NH3+ + OHNH + H2O NH2+ + OH-
Slide 37-21
Tertiary structure
The type of R-groups determine how the a-helices and b-sheets arrange
themselves together. There is a wide variety of intermolecular
interactions that you can form from various combinations of R-groups, e.g.
Acidic groups
In each case, in solution:
COOH + H2O COO- + H3O+
Slide 37-22
Tertiary structure
Non-Polar groups
Polar groups
Slide 37-23
Tertiary structure
Both α-helices and β-sheets can, and often do, occur in
the same protein. The tertiary structure is determined
by the overlap of the various R-groups, and the type and
strength of IM Force.
One amino acid is somewhat special:
Cysteine: -CH2-SH + HS-CH2- → -CH2-S-S-CH2- + H2
This forms a covalent bond between two regions of the
polypeptide strand
Slide 37-24
Forces that maintain protein structure
Slide 37-25
Tertiary structure (exam Q)
All other amino acids can also interact via the
normal IM Forces.
Identify the IM Forces circled below:
Slide 37-26
Example: Insulin
Primary:
Secondary
&
Tertiary:
Slide 37-27
Quaternary structure
Insulin again
Tertiary
Quaternary
Slide 37-28
Another protein
Enzyme: gyrase
(involved in DNA
unwinding process)
Note the stacked
beta-sheets and
alpha helices
Slide 37-29
Denaturing
If you break the IM bonds, e.g. by heating, the protein
adopts the random coil form.
This is called denaturation.
Frequently, the protein will not re-adopted its
structured form on cooling.
Eg.
Egg white denatures at ~68ºC. It does not
become runny again on cooling.
This is an ENTROPY effect… There are just so many
different conformations of the denatured protein, the
chances of it cooling into the active structure again are
very small.
Slide 37-30
Hydrogen Bonding in biological molecules
DNA
Slide 37-31
Hydrogen Bonding in biological molecules
Hemoglobin
Slide 37-32
Polymers – the next generation
Pegylated alpha-2 interferon
Ref. S Brocchini et al, Nature Protocols, 2006, 1, 2241 Slide 37-33
Polymers – the next generation
Non viral DNA delivery
Source: http://www.nano-lifescience.com/research/gene-delivery.html
Slide 37-34
Summary
CONCEPTS
Synthetic polymers:
Polymer structure and notation
Cohesive strength of polymers
Peptide linkage
Primary, secondary, tertiary, quaternary structures
Role of IM Forces in protein structure
Slide 37-35
Summary of Part II of CHEM1101
L20:
21-23:
24,25:
26, 27:
27-29:
30,31:
32-34:
35:
36-38:
38:
Gases
Thermochemistry
Nitrogen chemistry (explosives, atmosphere)
Entropy
Equilibrium
Industrial chem (Mining, manufacture)
Electrochemistry
Batteries, corrosion and mining again
Intermolecular Forces
Polymers
Slide 37-36
Ze End
Good luck with the exam!
Slide 37-37