Polymorphic structures of amphiphilic molecules in aqueous solution

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 (T k ) 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 M r 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…… .