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SL12102 - the science of medicines > L19 - drug sol & DR 5 > Flashcards

L19 - drug sol & DR 5 Flashcards

1
Q

classification of surfactants

A

(charge carried by polar part)
- cationic
- anionic
- non ionic
- zwitterionic

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2
Q

non-ionic surfactants

A
  • OH and ether groups
  • less polar than ionised group
  • need more units to produce effective polar moiety
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3
Q

polyoxyethylene chains as non ionic surfactants

A
  • 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
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4
Q

application os anionic surfactants

A
  • cheap
  • toxicity (external)
  • O/W emulsifiers
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5
Q

applications for cationic surfactants

A
  • disinfectants due to preservative properties
  • O/W emulsifiers
  • toxicity
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6
Q

application of non ionic surfactants

A
  • O/W and W/O emulsifiers
  • low toxicity and low irritancy
  • oral and parenteral use
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7
Q

ionic parenteral surfactant appication

A

hemolysis of RBC and destruction of T lymphocyte cell

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8
Q

applications of non ionic parenteral surfactants

A
  • phospholipids
  • polysorbates
  • cremophor
  • toxicity of non ionic residue contamination of ethylene oxide
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9
Q

micellisation

A
  • 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
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9
Q

hydrophobic portion of surface active drugs

A
  • aromatic or heterocyclic ring system
  • tranqulizers
  • antidepressants
  • antihistamines
  • antibiotics
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10
Q

solubilisation

A

process where water insoluble/ early soluble substances brought into aq sol by incorporation into micelles

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11
Q

core of micelle

A

hydrocarbons

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12
Q

palisade layer of micelle

A
  • hydrocarbon
  • polar parts
  • some water
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13
Q

surface or mantle of micelle

A

polar head groups + water

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14
Q

site of solubilisation

A
  • 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
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15
Q

how to quantify micellar solubilisation?

A

solubilisation capacity (k)

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16
Q

what is solubilisation capacity, k?

A
  • aka solubilisation ratio and efficiency
  • measures the ability of a surfactant to solubilise a solute
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17
Q

what is the molar solubilisation capacity?

A

moles of solute that can be solubilised by 1 mole of micellar surfactant

18
Q

how to calculate solubilisation capacity?

A
  1. K = Stotal - Swater / Csurfactant - c.m.c
    OR
  2. K = Sm/Cmic
    Sm = molar solubility of the solute in the micelle
    Cmic = molar conc of micellar surfactants
19
Q

what happens if you increase HC chain of non-polar region?

A
  1. larger non polar region will solubilise more solute
  2. decrease c.m.c
20
Q

what happens if you introduce a polar group or double bond to chain of low polarity solutes?

A

it is equivalent to decreasing length of HC chain

21
Q

what happens if your surfactant is branched?

A

smaller micelles

22
Q

semi polar solutes

A

surface and palisade region largely unaffected by non polar region

23
Q

are long chains good surfactant?

A

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

24
Q

how to stabilise a solute?

A

short chain: very high c.m.c

25
Q

what is the best balance of HC chain for good surfactant?

A
  • 12-16 C or 18 with a double bond
  • gives low cmc and sufficient water sol
26
Q

what must the hydrophily provide to bring the insoluble lipophile into sol?

A

enough interaction with water

27
Q

what can bring a 16C chin into water at rt?

A

a - or + ion

28
Q

as chain length increases

A
  1. solubility decreases
  2. surface activity becomes more pronounced
  3. tendency of surfactant mols to adsorb at the surface and lower the surface tension
29
Q

lundelius’s rule?

A

any factor that tends to decrease solubility of the surfactant promotes surface activity

30
Q

high HLB numbers

A

indicate surfactant exhibiting mainly polar or hydrophilic properties

31
Q

low HLB numbers

A

represent lipophilic or non-polar properties

32
Q

how to calculate HLB?

A

HLB = 7 + sum of (hydrophilic group numbers) - sum of (lipophilic groups numbers)

33
Q

HBL value of 3-6

A
  • W/O emulsions
  • no dispersibility in water
34
Q

HBL value 7-9

A
  • wetting agents
  • poor dispersibility in water
35
Q

HLB value of 8-15

A
  • O/W emulsions
  • unstable milky dispersion in water
36
Q

HLB value of 13-15

A
  • detergents
  • stable milky dispersion in water
37
Q

HLB value of 15-18

A
  • translucent dispersion
  • solubiliser
38
Q

dispersibility of water 13+

A

clear sol

39
Q

HLB of mixture of surfactants

A

mixture of high and low HLB surfactants can give greater stability than single

40
Q

emulsification

A

addition of a surfactant reduces the interfacial tension between oil and water

41
Q

emulgent

A

surfactant used to stabilise emulsions

42
Q

phase inversion temp (PIT)

A
  • 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
43
Q

common non ionic emulsifiers

A
  • water soluble at low T, stabilise O/W emulsions
  • oil soluble at high T stabilise W/O emulsions

SL12102 - the science of medicines (26 decks)

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