Surfactants and micelles

Question 1

The double affinity of amphipathic molecules makes them migrate towards the _________ to minimise energy. As a result they _________ surface tension

Answer 1

surface - to reduce hydrophobic region contact with water

reduce

Question 2

Proteins, peptides, polymers, phospholipids and surfactants are examples of _________

Answer 2

amphipathic molecules

Question 3

What are surfactants?

Answer 3

Amphipathic molecules exhibiting a surface tension property (reduce)

Question 4

What are the 4 categories that surfactants can be divided into?

Answer 4

Anionic
Non-ionic
Zwitterionic
Cationic

Question 5

What are two examples of anionic surfactants?

Answer 5

Sodium dodecanoate
Sodium dodecyl (lauryl) sulfate

Question 6

What are anionic surfactants usually combined with?

Answer 6

alkaline metal or a quaternary ammonium

Question 7

Why are charged surfactants not usually used in oral formulations?

Answer 7

Because they are toxic

Question 8

Why don’t non ionic surfactants ionise in solution?

Answer 8

Hydrophilic group is non dissociable at physiological pHs

Question 9

Tween 20 and tween 80 are examples of what type of surfactant?

Answer 9

Non ionic

Question 10

Which type of surfactant is found in injections and oral formulations?

Answer 10

Non ionic

Question 11

Which type of surfactant is mostly combined with halogen type anions?

Answer 11

Cationic

Question 12

Which type of surfactant is used as bactericides?

Answer 12

Cationic - positive charge binds to the negative surface of cells

Question 13

Cetrimide (CTAB) is an example of which type of surfactant?

Answer 13

Cationic

Question 14

Betaines, sulfobetaines and natural substances such as amino acids are examples of which type of surfactant?

Answer 14

Cationic

Question 15

What happens above cmc (critical micelle concentration)?

Answer 15

Any further addition of surfactant above cmc results in the formation of micelles

Question 16

The ability of reducing ________ depends on surfactant structure (length/size of hydrophobic/hydrophilic parts)

Answer 16

surface tension

Question 17

The ability of a surfactant to reduce surface tension is independent of the balance between hydrophobic and hydrophilic properties (HLB). True or false?

Answer 17

False - it does depend

Question 18

An increase in the length of hydrocarbon chain results in a decrease in surface tension reduction. True or false?

Answer 18

False - results in an increased surface tension reduction (Traube’s rule)

Question 19

When are micelles formed?

Answer 19

Above cmc

Question 20

Can dilution result in the disappearance of micelles?

Answer 20

Yes

Question 21

What is the difference between micelles and inverted micelles?

Answer 21

In micelles the hydrophilic head is in contact with the polar solvent and the hydrophobic tail inside.
In inverted micelles, the hydrophobic tail is in contact with the organic solvent (oil) and hydrophilic head inside

Question 22

What is solubilisation?

Answer 22

When a water insoluble substance is brought into solution by incorporation in micelles. The incorporated substance is called the solubilisate

Question 23

Where in a micelle will molecules with a high logP be positioned?

Answer 23

inside the micelle

Question 24

Non-polar solubilisates are dissolved in the core of a micelle. True or false?

Answer 24

True

Question 25

What are the pharmaceutical applications of surfactants?

Answer 25

Enhancers for percutaneous absorption
Flocculating agents for suspensions
Mouthwashes 
Respiratory distress therapy 
Suppositories
Suspension aerosols 
Water based aerosols 
Contact lens cleansing agents
Hard gelatin capsules
Emulsifiers 
Cerumen removing solutions (ear drops)

Question 26

What are liposomes and what are they used for?

Answer 26

Made of phospholipids/surfactants. They are used as controlled release drug delivery systems, in particular in cancer chemotherapy due to EPR