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Soft Matter
Soft matter is held together by the two weakest types of bonding,
the hydrogen bond and the van der Waals bond. It does not exhibit
the crystalline order that is characteristic of most hard matter.
Nevertheless, some order remains in soft matter. It is driven by the
organization of hydrophobic and hydrophilic molecular groups. That
can lead to self-assembly over a wide range of sizes, all the way from
nano-structures to human beings.
Pierre-Gilles de Gennes
received the 1991 Physics
Nobel Prize for bringing order
into soft matter, such as
polymers and liquid crystals.
Micelles
Surfactant:
Hydrophilic Head
+ Hydrophobic Tail
Phospholipid
= Amphiphilic Molecule
Micelle:
Inverse Micelle:
Heads outside, Water outside
Heads inside, Water inside
Used for drug delivery
Nano-beaker for synthesis of nanocrystals
Bilayer Structures
, Vesicle
Part of a Cell Wall
Drug Delivery via Liposomes
Supramolecular Assemblies
Polymers
Monomer:
A
Oligomer:
A-A-A-A
Homopolymer:
A-A-A-A-A-A-A-A-A-A-A-A-A- …
Heteropolymer = Copolymer:
A-B-B-A-B-A-B-A-B-A-A-B-A-B- …
Block Copolymer:
A-A-A-A-A-A-A-A-A—B-B-B-B
The volume ratio of the A- and B- blocks, together with the
strength of the interaction between A and B determines how
they assemble themselves (see Slides 10,11).
A Hydrophilic-Hydrophobic Block Copolymer
PMMA
(polymethylmethacrylate)
PS
(polystyrene)
Negative charge on the
Neutral hydrocarbons
oxygen makes it hydrophilic.
make it hydrophobic.
Identify Polymers by their Molecular Orbitals
using X-ray Absorption Spectroscopy
* Orbital
EFermi
Photon
C 1s Core Level
Phases of a Diblock Copolymer
Hydrophilic + Hydrophobic
Data
Interaction Strength
Theory
Volume Fraction
Volume Fraction
Volume Fraction
Triblock Copolymers:
Even more Options
Biopolymers:
DNA
Biopolymers: Proteins
The Peptide Bond between Amino Acids in a Protein
N
Two amino acids react.
N forms the bridge.
See the * orbital
of this double bond
in X-ray absorption
O
N
covalent
+
ionic
Detect the peptide bond orbital
with
X-ray absorption spectroscopy
at the N 1s edge
Need a glycine dimer to
establish the peptide bond.
A. Hitchcock et al.
Photon Energy [eV]
The Peptide Bond and Protein Structures
The peptide bond orbital spreads across O=C=N, which produces a planar arrangement.
Hydrophobic
interaction
α-Helix
β-Sheet
Secondary structure
Tertiary structure
Protein
Folding
Hierarchy
Schematic of Hemoglobin
Protein Infrared Spectroscopy
Vibrations reveal the secondary and tertiary structure.
oxygen
0.008
+400 mV
Amide vibrational modes:
b -sheet
0.006
random
turn
S
• Amide I, C=O stretch
secondary structure
a-helix: 1649-1658 cm-1
b-sheet: 1620-1635 cm-1
a-helix
• Amide II, N-H bend
tertiary structure
HD exchange:
15501450 cm-1
0.004
0.002
0.000
1600
1620
1640
1660
1680
-1
Wavenumber / cm
J. Lipkowski
1700