L19 - drug sol & DR 5 Flashcards
classification of surfactants
(charge carried by polar part)
- cationic
- anionic
- non ionic
- zwitterionic
non-ionic surfactants
- OH and ether groups
- less polar than ionised group
- need more units to produce effective polar moiety
polyoxyethylene chains as non ionic surfactants
- chains of these with 20 or more ether groups linked to non polar moiety
- several chains linked to cyclic sugar linked to alkyl groups
- POE (number) = number of monomeric polyoxyethylene groups in molecules
application os anionic surfactants
- cheap
- toxicity (external)
- O/W emulsifiers
applications for cationic surfactants
- disinfectants due to preservative properties
- O/W emulsifiers
- toxicity
application of non ionic surfactants
- O/W and W/O emulsifiers
- low toxicity and low irritancy
- oral and parenteral use
ionic parenteral surfactant appication
hemolysis of RBC and destruction of T lymphocyte cell
applications of non ionic parenteral surfactants
- phospholipids
- polysorbates
- cremophor
- toxicity of non ionic residue contamination of ethylene oxide
micellisation
- alt method to adsorption
- causes strong water water interactions that would be prevented if surfactant molecules were in sol as single molecules between water molecules
- hydrophobic effect
hydrophobic portion of surface active drugs
- aromatic or heterocyclic ring system
- tranqulizers
- antidepressants
- antihistamines
- antibiotics
solubilisation
process where water insoluble/ early soluble substances brought into aq sol by incorporation into micelles
core of micelle
hydrocarbons
palisade layer of micelle
- hydrocarbon
- polar parts
- some water
surface or mantle of micelle
polar head groups + water
site of solubilisation
- depends on chemical nature of solubilisate
- the more polar the solute, the more likely to be solubilised close to the surface
- the polar region of a non-ionic micelle is significantly larger than that of ionic micelle
how to quantify micellar solubilisation?
solubilisation capacity (k)
what is solubilisation capacity, k?
- aka solubilisation ratio and efficiency
- measures the ability of a surfactant to solubilise a solute
what is the molar solubilisation capacity?
moles of solute that can be solubilised by 1 mole of micellar surfactant
how to calculate solubilisation capacity?
- K = Stotal - Swater / Csurfactant - c.m.c
OR - K = Sm/Cmic
Sm = molar solubility of the solute in the micelle
Cmic = molar conc of micellar surfactants
what happens if you increase HC chain of non-polar region?
- larger non polar region will solubilise more solute
- decrease c.m.c
what happens if you introduce a polar group or double bond to chain of low polarity solutes?
it is equivalent to decreasing length of HC chain
what happens if your surfactant is branched?
smaller micelles
semi polar solutes
surface and palisade region largely unaffected by non polar region
are long chains good surfactant?
no, bad solubility
- due to decrease in cmc
- which decreases surfactant sol
- so reduces amount of surfactant that can be used
- increasing chain length in 2 C decreases solubility 10 fold
how to stabilise a solute?
short chain: very high c.m.c
what is the best balance of HC chain for good surfactant?
- 12-16 C or 18 with a double bond
- gives low cmc and sufficient water sol
what must the hydrophily provide to bring the insoluble lipophile into sol?
enough interaction with water
what can bring a 16C chin into water at rt?
a - or + ion
as chain length increases
- solubility decreases
- surface activity becomes more pronounced
- tendency of surfactant mols to adsorb at the surface and lower the surface tension
lundelius’s rule?
any factor that tends to decrease solubility of the surfactant promotes surface activity
high HLB numbers
indicate surfactant exhibiting mainly polar or hydrophilic properties
low HLB numbers
represent lipophilic or non-polar properties
how to calculate HLB?
HLB = 7 + sum of (hydrophilic group numbers) - sum of (lipophilic groups numbers)
HBL value of 3-6
- W/O emulsions
- no dispersibility in water
HBL value 7-9
- wetting agents
- poor dispersibility in water
HLB value of 8-15
- O/W emulsions
- unstable milky dispersion in water
HLB value of 13-15
- detergents
- stable milky dispersion in water
HLB value of 15-18
- translucent dispersion
- solubiliser
dispersibility of water 13+
clear sol
HLB of mixture of surfactants
mixture of high and low HLB surfactants can give greater stability than single
emulsification
addition of a surfactant reduces the interfacial tension between oil and water
emulgent
surfactant used to stabilise emulsions
phase inversion temp (PIT)
- HLB of emulisifer varies with tem because the relative solubilities of the lipophile and hydrophily vary with temp
- effect occurs most in non ionic surfactants due to their solubility in water depending on h bonding
- higher temp = h bonds weaken so emulsifier less soluble in water
common non ionic emulsifiers
- water soluble at low T, stabilise O/W emulsions
- oil soluble at high T stabilise W/O emulsions
