Surfactants and micelles Flashcards
The double affinity of amphipathic molecules makes them migrate towards the _________ to minimise energy. As a result they _________ surface tension
surface - to reduce hydrophobic region contact with water
reduce
Proteins, peptides, polymers, phospholipids and surfactants are examples of _________
amphipathic molecules
What are surfactants?
Amphipathic molecules exhibiting a surface tension property (reduce)
What are the 4 categories that surfactants can be divided into?
Anionic
Non-ionic
Zwitterionic
Cationic
What are two examples of anionic surfactants?
Sodium dodecanoate Sodium dodecyl (lauryl) sulfate
What are anionic surfactants usually combined with?
alkaline metal or a quaternary ammonium
Why are charged surfactants not usually used in oral formulations?
Because they are toxic
Why don’t non ionic surfactants ionise in solution?
Hydrophilic group is non dissociable at physiological pHs
Tween 20 and tween 80 are examples of what type of surfactant?
Non ionic
Which type of surfactant is found in injections and oral formulations?
Non ionic
Which type of surfactant is mostly combined with halogen type anions?
Cationic
Which type of surfactant is used as bactericides?
Cationic - positive charge binds to the negative surface of cells
Cetrimide (CTAB) is an example of which type of surfactant?
Cationic
Betaines, sulfobetaines and natural substances such as amino acids are examples of which type of surfactant?
Cationic
What happens above cmc (critical micelle concentration)?
Any further addition of surfactant above cmc results in the formation of micelles
The ability of reducing ________ depends on surfactant structure (length/size of hydrophobic/hydrophilic parts)
surface tension
The ability of a surfactant to reduce surface tension is independent of the balance between hydrophobic and hydrophilic properties (HLB). True or false?
False - it does depend
An increase in the length of hydrocarbon chain results in a decrease in surface tension reduction. True or false?
False - results in an increased surface tension reduction (Traube’s rule)
When are micelles formed?
Above cmc
Can dilution result in the disappearance of micelles?
Yes
What is the difference between micelles and inverted micelles?
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
What is solubilisation?
When a water insoluble substance is brought into solution by incorporation in micelles. The incorporated substance is called the solubilisate
Where in a micelle will molecules with a high logP be positioned?
inside the micelle
Non-polar solubilisates are dissolved in the core of a micelle. True or false?
True
What are the pharmaceutical applications of surfactants?
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)
What are liposomes and what are they used for?
Made of phospholipids/surfactants. They are used as controlled release drug delivery systems, in particular in cancer chemotherapy due to EPR
