Physicochemical properties Flashcards

(75 cards)

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
How does solubility changes happen
Solute - solute
26
Highest relative permittivity of solvent
Water
27
What influences solubility of weak acid + weak base
pH
28
Calculate activity coefficient (y)
activity / concentration
29
when y (activity coefficient) = 1....
activity = concentration
30
When should activity be used
when dealing with strong electrolytes / weak electrolytes in solution with other salts
31
When can non-electrolytes + weak electrolytes have their activity = concentration
When present as the only species
32
Activity
reduction in the effective concentration
33
Real solution
Interactions between dissolved solutes which reduce the effective concentration
34
What solutions have their activity = concentration?
Ideal + dilute real solutions
35
Example of polar solvents
Water, methanol, acetic acid
36
What is the relative permittivity of polar solvents
High relative permittivity
37
What do polar solvents dissolve + how
Ionic solutes by reducing force of attraction between oppositely charged ions in crystalline solids
38
What bonds can polar solvents break
Covalent bonds
39
What solvent can solvate molecules + ions + how?
Polar solvents through dipole-dipole forces
40
What is wrong with ranitidine free base
Low aqueous solubility Unstable to light Sulfurous odour
41
How can we make ranitidine free base be absorbed
Reacting with HCl = Ranitidine HCl (salt) | Becomes odourless, stable + greater solubility
42
Examples of semi-polar solvents
Acetone, methanol, ethanol + other alcohols?
43
What can semi-polar solvents dissolve
Polar + non-polar substances
44
How do polar solutes dissolve
Dipole moment or H-bonding groups
45
How can semi-polar solvents be soluble in non-polar solvents
Inducing a degree of polarity
46
Examples of non-polar solvents
Hexane, Pentane, oils + fats, benzene
47
What is the relative permittivity of non-polar solvents
Low
48
What prevents non-polar solvents dissolving ionic/polar solutes
Lack of H-bonding
49
Non-polar solvents are unable to...
break covalent bonds
50
What can non-polar solutes dissolve
Non-polar compounds only
51
How are non-polar solutes held in non-polar solvents
Through van der waals interactions
52
Solubility equation of weakly acidic drugs
``` pKa = pH + log HA / A- pH = pKa + log S - So / So ```
53
Solubility equation of weakly basic drugs
pH = pKa + log So / S - So
54
S in solubility equation
Solubility of weakly acidic/basic drug at given pH
55
So in solubility equation
Solubility of undissociated drug
56
Example of amphoteric drugs
Oxytetracycline | Nitrazepam
57
Amphoteric drugs
Both acidic + basic groups so will have 2+ pKa values
58
What pH values can amphoteric drugs be ionised
All pH values
59
Isoelectric point
pH at which drug carries no net electric charge (equal dissociation of acidic / basic drug group
60
Calculate isoelectric point
(pKa1 + pKa2) / 2
61
When are amphoteric drugs are at its least solubility
At the isoelectric point (no net charge)
62
When do you use the basic drugs equation with amphoteric drugs
pH is below isoelectric point
63
When do you use the acidic drugs equation with amphoteric drugs
pH is above isoelectric point
64
Drugs with high log P can...
partition into rubber / plastic containers | - affecting many formulations
65
Which drugs are affected with high log P partitioning
Storage of lipophilic drugs
66
Ion-pairing
Ionised drugs combining with an oppositely charged ion | Ion pair behave as a neutral species and permeate through gastric mucosa
67
Substances that use active transport
Ions Glucose Vitamins Amino acids
68
Melphalan
Similar to phenylalanine | Absorbed in GI tract
69
__________ drugs can also be absorbed in small intestines
Ionised
70
Structure of Water
104.5 degree bond angle Tetrahedral Form H-bonds
71
Flickering cluster model of water
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
hydration
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
What is Magnesium carbonate hydration number
5
74
Weak bases are likely to be ionised in the stomach so...
Cannot pass lipophilic gastric mucosa
75
How come ionised drugs can be absorbed in the small intestines
Large surface area Good blood flow Long residence time