Learn more about micelles and bilayers formed by lipids.

1. POLYMORPHIC STRUCTURES OF
AMPHIPHILIC MOLECULES IN AQUEOUS
SOLUTION:
MICELLE AND BILAYERS
ABHISHEK.M

2. AMPHIPHILE:
Derived from Greek words
AMPHI = Both and
PHILIOS = Friend
Thus the word itself means something that
likes or rather is friendly to both.
In chemistry it means a molecule that
likes both water and oil.

3. The use of amphiphilic molecules creates a
means to dissolve water into oil and vice versa.
This is something necessary for many
applications.
Some practical examples are milk, margarine
and digestion of fats.
(and of course washing of your dirty clothes!!)

4. What does an amphiphilic molecule look like?
It may be visualized like a tadpole having a
water loving HEAD and an oil loving TAIL.
Basically a molecule which has a dual polarity.
That is having both a hydrophilic
group(HEAD) and a lypophilic
group(TAIL)

5. Some other terms we generally use to describe
these molecules are soap ,detergent, surfactant,
tenside etc
Schematic picture of a surfactant molecule

6. CRITERIA:
1)The headgroup must be hydrophilic
enough.
2) The hydrophobic part must be of right size.
(carbon chain of 8 or carbons but not
too long either)

7. Amphiphilic molecules like lipids spontaneously
form a variety of structures when added to
aqueous solution.
These structures are formed in ways that
minimize contact between the hydrophobic
lipid chains and the aqueous milieu.
For e.g.: When small amounts of fatty acids are
added to an aq. solution a monolayer is formed
at the water-air interface

8. A MONOLAYER

9. If we keep on adding fatty acids to this aqueous
solution, the monolayer ceases to exist and a
totally new shape is attained by the fatty acids.
This is called as a micelle

10. MICELLE
These are formed when an amphipathic lipid
in water positions its hydrophobic tail to the
centre of lipid aggregation and their polar
head groups facing outwards.

11. The formation of micelles takes place only above a
particular temperature called as
Kraft temperature (Tk )
and also above a particular concentration called as
Critical Micelle Concentration (CMC)
Below the cmc individual lipid molecules
predominate
.

12. CMC of some detergents
Sr
no.
Name of
detergent
Mr CMC
1 TRITON X-100 625 0.24mM
2 Octyl glucoside 292 25mM
3 Dodecyl
octaoxyethylene
ether
538 0.071mM

13. MICELLES

14. BILAYER
Bilayers consists of back to back arrangements
of monolayers
The nonpolar portions of the lipids face the
middle of the bilayer, with the polar head
groups arrayed on the bilayer’s surface.

15. Phospholipid bilayers form spontaneously and
rapidly when they are added to water and they
are stable structures.
As opposed to micelles which are small ,
self-limiting structures of a few hundred
molecules, bilayers may form over large areas.

16. A BILAYER

17. .
As the exposure of the edges of the bilayer to the
solvent is highly unfavorable, extensive bilayers
normally wrap around themselves and form closed
vesicles.
The nature and integrity of these
vesicle structures are dependent on
their lipid composition.

18. Physiochemical studies with these substances
in the laboratory reveals that they may exist
as either
UNILAMELLAR VESICLES
OR
MULTILAMELLAR VESICLES

19. THANKS……
.