life at low d lecture iii: monolayers and membranes
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Life at Low D
Lecture III: Monolayers and Membranes
Phospholipids
Amphi (“both”)
philia(“love”)
Amphiphilic Molecules
“There seems to be no natural repulsion between water and air such as to keep them from coming into contact with each other.” (Franklin, 1773)
“...the oil, though not more than a teaspoonful, produced an instant calmover a space several yards square which spread amazingly and extended itself…, making all that quarter of the pond, perhaps half an acre as smooth as a looking glass.”
If a drop of oil is put on a highly polished marble table, or on a looking-glass that lies horizontally, the drop remains in its place, spreading very little.
Interfacial Energy and Surface Tension
TSUF GOAL: Minimize Free Energy
UEnergy
aa
a
TkB200~
Entropy
S
Fluids VDW
H-Bonding
96.0
Solids Covalent
TkB3~
TkB10~
2/0 07.02
TkB
OilH
OH 2
OH 2
Oil
2
0 10
a
0
]2ln[
a
TkF B
Hydrophobic Effect
15
2
40
2/0 07.0
2
TkBOilH
Hydrophobic Area/Molecule 2
300
aS
TkTk
SF BB
OilHA 2530007.0 22/02
Surface Tension
OH 2
2/0 2.02
TkB
AirH
Surface Tension
OH 2
2/0 07.02
TkB
OilH
Monolayer reduces Surface Tension
2/0 2.02
TkB
AirH
)(McCMC
OilH /02
AirH /02
Surface Tension
2/0 07.02
TkB
OilH
Monolayer reduces Surface Tension
2/0 2.02
TkB
AirH
)(McCMC
OilH /02
AirH /02
Self-Assembly
Bilayer Properties
2/0 07.02
TkB
OilH
52
50
Flip-Flop (exposing hydrophilic head to hydrocarbon chain) TkE B12
Water Permeable (cost of water passing through)
96.0
2
12
AS
2/0 07.02
TkB
OilH
TkE B
30
2
50
AS
Bilayer Properties
Edge Energy/Length
30
52
50
TkTkLE BB 23007.0/
2
Driving “Force” for the Formation of closed Structures
Bending Energy
R
BBB
Bend RR
dAR
E 84
4
2
2
22
2
2
TkBB 10 TkE BBend 240