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Pharmacy > Science of Medicines Week 7 > Flashcards

Science of Medicines Week 7 Flashcards

1
Q

define interfacial area

A

the total area of contact between two liquids in a liquid-liquid operation –> large one will prevent dissolving

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2
Q

How do inclusion compounds work?

A

by incorporating the non-polar portion of one molecule into the non-polar part of another molecule that is water soluble –> you reduce the non-polar water interfacial area by inserting the solute into the complexing agent

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3
Q

What is the most commonly used inclusion compouns?

A

cyclodextrins

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4
Q

What is a cyclodextrin?

A

an enzymatically modified starch, and their units form a cylindrical ring

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5
Q

What is the structure of a cyclodextrin?

A

the outer surface of the ring is hydrophobic and the internal surface of the cavity is non-polar

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6
Q

define surface tension

A

adhesive forces between the liquid phase of one substance and either a solid, liquid or gas phase of another surface at the interface

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7
Q

How do surfactants work?

A

they reduce the surface tension at an interface without needing large concentrations of them

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8
Q

To be a surfactant, what properties are needed?

A
  1. one element must have a high affinity for the solvent (hydrophilic or polar head, non-ionic or ionic)
  2. one element must have a minimal affinity for the solvent (lipophilic or nonpolar chain)
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9
Q

What must the polar region on a surfactant be able to do?

A
  1. have an affinity for water
  2. must be capable of pulling long-chain hydrocarbons into water
  3. must be polar enough to hold the nonpolar region of the surfactant in solution
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10
Q

How are surfactants classified?

A

by the charge carried by polar part: anionic, cationic, zwitterionic, non-ionic

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11
Q

define critical micelle concentration

A

the concentration of monomer (surfactant) at which micelles form

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12
Q

define aggregation number

A

the number of monomers that aggregate to form a micelle

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13
Q

At the critical micelle concentration, which physical properties of surfactants change?

A
  1. osmotic pressure
  2. turbidity
  3. electrical conductance
  4. surface tension
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14
Q

What factors of surfactants may increase the critical micelle concentration?

A

decrease the carbon chain length, increase the polarity of the head

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15
Q

What factors of surfactants may decrease the critical micelle concentration?

A

temperature, pH, a second surfactant, addition of electrolytes, longer carbon chain length

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16
Q

What are the 4 critical values for micelles?

A
  1. critical micelle concentration
  2. Kraft point (critical micelle temperature)
  3. cloud point
  4. critical micelle pH
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17
Q

define the Kraft point

A

the temperature at which the solubility becomes equal to the critical micelle concentration

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18
Q

What happens when temperature is less than the Kraft point?

A

the critical micelle concentration is greater than the solubility, so micelles can’t form

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19
Q

What happens when temperature is greater than the critical micelle concentration?

A

the surfactant forms micelles

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20
Q

What happens to micelles at the cloud point?

A

an increase in temperature leads to dehydration of POE chains, decreased water solubility and the formation of very large micelles making the solution cloudy

21
Q

What happens at the critical micelle pH?

A

if the ionised form of a compound is surface active and the unionised form is surface inactive (or has a lower CMC than the ionised form) then a change in pH can induce micellisation

22
Q

Can the polar part of a surfactant be non-ionic?

A

yes, for example hydroxyl and ether groups

23
Q

What do surfactants do?

A

decrease the surface tension at the interface

24
Q

What is the downside to non-ionic polar heads?

A

they are less polar than ionised groups, so we need more ‘units’ to produce an effective polar head

25
Q

What is polyoxyethylene (POE)?

A

a chain with 20 or more ether groups linked to the nonpolar part

26
Q

What does POE-23 lauryl ether mean?

A

there are 23 monomeric POE groups in this molecule

27
Q

What are the applications of anionic surfactants?

A

oil/water emulsifiers

28
Q

What are the applications of cationic surfactants?

A

disinfectants, oil/water emulsifers

29
Q

What are the applications of non-ionic surfactants?

A

oil/water and water/oil emulsifiers, also have low toxicity unlike cationic and anionic

30
Q

Can surfactants be used as drugs?

A

yes

31
Q

When does micellisation occur?

A

when micelle concentration exceeds the CMC

32
Q

define solubilisation

A

the process by which water-insoluble or partly soluble substances are brought into aqueous solution by incorporation into micelles

33
Q

What is the solubilisation capacity (k)?

A

a measure of the ability of a surfactant to solubilise a solute

34
Q

What is the molar solubilisation capacity (k)?

A

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

35
Q

What are the equations for solubilisation capacity?

A

k = molar solubility of the solute in the micelle / molar concentration of micellar surfactants

36
Q

Why is a low CMC for surfactant drugs preferred?

A

low CMC means that the surfactant can form micelles at a lower concentration, so when micelles are formed they can solubilise hydrophobic drugs

37
Q

How can we increase the solubilisation capacity of a low polarity solute?

A
  1. increase hydrocarbon chain -> larger nonpolar regions will solubilise more solute and decreases CMC
  2. introduce polar group
  3. used branched surfactants as they form smaller micelles
38
Q

What 4 factors need to be considered when selecting a surfactant?

A
  1. amount of surfactant that can be placed in water
  2. ability of it to solubilise the solute
  3. the chain length -> influences CMC
  4. finding a balance
39
Q

What is Lundelius’ rule?

A

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

40
Q

What does a high HLB surfactant value indicate?

A

a surfactant with mainly polar or hydrophilic properties

41
Q

What does a low HLB surfactant value indicate?

A

surfactant with mainly lipophilic or non-polar properties

42
Q

How do you calculate the HLB of a mixture of surfactants?

A

HLB = x HLB(A) + (1-x) HLB(B) where x are fractions of each surfactant

43
Q

define required HLB

A

the particular HLB of a surfactant needed to form a stable w/o or o/w emulsion

44
Q

Why does HLB of an emulsifier vary with temperature?

A

temperature affects the relative solubilities of the lipophilic and hydrophilic parts

45
Q

What happens to non-ionic surfactants at higher temperature?

A

hydrogen bonds are weakened by thermal forces and the emulsifier is less soluble in water

46
Q

define the Phase Inversion Temperature (PIT)

A

the T at which an emulsifier changes from being an O/W emulsifier to a W/O emulsifier

47
Q

If a non-ionic emulsifier is water soluble at low temperature, what kind is it?

A

it stabilises O/W emulsions

48
Q

If a non-ionic emulsifier is oil soluble at high temperature, what kind is it?

A

it stabilises W/O emulsions

Pharmacy (16 decks)

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