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DYS: Pharmaceutics > Physicochemical properties > Flashcards

Physicochemical properties Flashcards

1
Q

Solution

A

Mixture of 2 or more components that form a homogenous molecular dispersion

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2
Q

Single phase system

A

Not another phase dispersed in another

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3
Q

Solvent

A

Component present in greater amounts

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4
Q

Solute

A

Component present in smaller amounts

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5
Q

Saturated solution

A

Where the solute is at the limit of its solubility at a given temp. + pressure

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6
Q

Solution = _______ phase

A

Single

solid solute dissolved into solvent to make it a single phase

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7
Q

Suspension/emulsion = _________ phase

A

Two

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8
Q

2 types of solution

A

liquid in liquid

solid in liquid

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9
Q

2 categories in liquid in liquid

A

Partially miscible

Completely miscible

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10
Q

Example of completely miscible

A

Ethanol + water

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11
Q

Example of partially miscible

A

Ether + water

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12
Q

What affects partially miscible

A

Temperature

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13
Q

2 solutions in solid in liquid

A

Solution of non-electrolytes (non-ionic)

Solution of electrolytes (form ions in solution)

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14
Q

Examples of solution of non-electrolytes

A

Organic molecules (sucrose, phenol)

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15
Q

Example of solution of electrolytes

A

strong electrolytes = NaCl

weak electrolytes = depends on ph

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16
Q

When is the structure of water disrupted

A

Ions in solution (when solid dissolves)

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17
Q

Partitioning

A

Distribution of a substance between two immiscible phases

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18
Q

Partition coefficient

A

Co / Cw
Co = conc. in organic phase
Cw = conc. in aqueous phase
Measure of relative affinity of the solute for an aqueous + lipid phase @ equilibrium

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19
Q

What does partition coefficient apply to

A

Dilute solutions e.g. ideal solutions

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20
Q

2 commonly used liquids to calculate P

A

Octanol + water

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21
Q

Why is octanol used?

A

Produces p values which correlate better with in vivo biological data

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22
Q

How is P calculated

A

Drug is added to separating funnel which contains the 2 immiscible liquids
Flask is shaken for up to 1 hour then left for phases to separate out
Concentration of aqueous phase is determined by either spectroscopy or titration
Concentration of organic phase is determined by subtraction
P can then be calculated

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23
Q

A suspension can become a…

A

Solution (+vice versa)

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24
Q

What can affect solubility

A

Solute substituents

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25
Q

How does solubility changes happen

A

Solute - solute

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26
Q

Highest relative permittivity of solvent

A

Water

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27
Q

What influences solubility of weak acid + weak base

A

pH

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28
Q

Calculate activity coefficient (y)

A

activity / concentration

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29
Q

when y (activity coefficient) = 1….

A

activity = concentration

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30
Q

When should activity be used

A

when dealing with strong electrolytes / weak electrolytes in solution with other salts

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31
Q

When can non-electrolytes + weak electrolytes have their activity = concentration

A

When present as the only species

32
Q

Activity

A

reduction in the effective concentration

33
Q

Real solution

A

Interactions between dissolved solutes which reduce the effective concentration

34
Q

What solutions have their activity = concentration?

A

Ideal + dilute real solutions

35
Q

Example of polar solvents

A

Water, methanol, acetic acid

36
Q

What is the relative permittivity of polar solvents

A

High relative permittivity

37
Q

What do polar solvents dissolve + how

A

Ionic solutes by reducing force of attraction between oppositely charged ions in crystalline solids

38
Q

What bonds can polar solvents break

A

Covalent bonds

39
Q

What solvent can solvate molecules + ions + how?

A

Polar solvents through dipole-dipole forces

40
Q

What is wrong with ranitidine free base

A

Low aqueous solubility
Unstable to light
Sulfurous odour

41
Q

How can we make ranitidine free base be absorbed

A

Reacting with HCl = Ranitidine HCl (salt)

Becomes odourless, stable + greater solubility

42
Q

Examples of semi-polar solvents

A

Acetone, methanol, ethanol + other alcohols?

43
Q

What can semi-polar solvents dissolve

A

Polar + non-polar substances

44
Q

How do polar solutes dissolve

A

Dipole moment or H-bonding groups

45
Q

How can semi-polar solvents be soluble in non-polar solvents

A

Inducing a degree of polarity

46
Q

Examples of non-polar solvents

A

Hexane, Pentane, oils + fats, benzene

47
Q

What is the relative permittivity of non-polar solvents

A

Low

48
Q

What prevents non-polar solvents dissolving ionic/polar solutes

A

Lack of H-bonding

49
Q

Non-polar solvents are unable to…

A

break covalent bonds

50
Q

What can non-polar solutes dissolve

A

Non-polar compounds only

51
Q

How are non-polar solutes held in non-polar solvents

A

Through van der waals interactions

52
Q

Solubility equation of weakly acidic drugs

A 
pKa = pH + log HA / A-
pH = pKa + log S - So / So
53
Q

Solubility equation of weakly basic drugs

A

pH = pKa + log So / S - So

54
Q

S in solubility equation

A

Solubility of weakly acidic/basic drug at given pH

55
Q

So in solubility equation

A

Solubility of undissociated drug

56
Q

Example of amphoteric drugs

A

Oxytetracycline

Nitrazepam

57
Q

Amphoteric drugs

A

Both acidic + basic groups so will have 2+ pKa values

58
Q

What pH values can amphoteric drugs be ionised

A

All pH values

59
Q

Isoelectric point

A

pH at which drug carries no net electric charge (equal dissociation of acidic / basic drug group

60
Q

Calculate isoelectric point

A

(pKa1 + pKa2) / 2

61
Q

When are amphoteric drugs are at its least solubility

A

At the isoelectric point (no net charge)

62
Q

When do you use the basic drugs equation with amphoteric drugs

A

pH is below isoelectric point

63
Q

When do you use the acidic drugs equation with amphoteric drugs

A

pH is above isoelectric point

64
Q

Drugs with high log P can…

A

partition into rubber / plastic containers

- affecting many formulations

65
Q

Which drugs are affected with high log P partitioning

A

Storage of lipophilic drugs

66
Q

Ion-pairing

A

Ionised drugs combining with an oppositely charged ion

Ion pair behave as a neutral species and permeate through gastric mucosa

67
Q

Substances that use active transport

A

Ions
Glucose
Vitamins
Amino acids

68
Q

Melphalan

A

Similar to phenylalanine

Absorbed in GI tract

69
Q

__________ drugs can also be absorbed in small intestines

A

Ionised

70
Q

Structure of Water

A

104.5 degree bond angle
Tetrahedral
Form H-bonds

71
Q

Flickering cluster model of water

A

Clusters of H-bonded ice-like water within pools of unbound (no hydrogen bonding) water

  • clusters surrounded by fluid non-hydrogen bonded water
  • ice-like clusters of H-bonded water
72
Q

hydration

A

Ions have a layer of tightly bound water

Most small monoatomic ions have 4 water molecules bound in first shell, therefore hydration number is 4

73
Q

What is Magnesium carbonate hydration number

A

5

74
Q

Weak bases are likely to be ionised in the stomach so…

A

Cannot pass lipophilic gastric mucosa

75
Q

How come ionised drugs can be absorbed in the small intestines

A

Large surface area
Good blood flow
Long residence time

DYS: Pharmaceutics (4 decks)

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