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week 18 > the medicine > Flashcards

the medicine Flashcards

1
Q

What are insoluble surfactants?

A

they are molecules that are absorbed at interfaces

They are not soluble in the bulk phase

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2
Q

what does langmuir balance used to measure

A

surface pressure

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3
Q

What is the equation for surface pressure?

A

surface tension of clean film - surface tension of surfactant covered film

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4
Q

Explain how surface pressure of a film is increased

A

as a barrier is moved closer to the float
Surfactant monolayer is compressed
Surface tension reduces
Surface pressure increases

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5
Q

What does Monolayer state

A

That difference surfactants will form different types of absorbed Monolayers at the interface

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6
Q

What is the monolayer state dependent on?

A

Surfactant structure
The degree the surfactant Layer is compressed

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7
Q

What is the solid or condensed monolayer state

A

surfactant molecules do not cover the full surface
There is a low reduction in surface tension
Therefore, surface pressure is low

If the surfactant molecule cover the full surface
There is a high reduction in surface tension
There is a high surface pressure
(in film compression]

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8
Q

What happens in liquid state or expanded Monolayers

A

Close, packing into a condensed film is prohibited by bulky side chains or cis configurations

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9
Q

what happens in gaseous state Manolayers

A

It’s results from molecules lying along the surface
Upon compression that is a gradual change in area

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10
Q

What do molecules often show as the film is compressed?

A

Transition from one state to another

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11
Q

What is a surface acting drug? [surfactant.]

A

A molecule that lowers the surface tension between liquids, or between a liquid and a solid

These drugs are often used to treat conditions that affect the lungs

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12
Q

how do surfactants work

A

they form a film on the surface of a liquid or a solid. Which helps to reduce the energy required for the liquid or solid to flow.

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13
Q

What information can be gained from measuring surface pressure

A

molecules cross section area
Structural characteristics

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14
Q

what type of monolayer would you expect an alcohol with a cis double bond configuration in its hydrocarbon chain form

A

an expanded monolayer

Close, packing of the molecule is prohibited by the hydrocarbon chain configuration

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15
Q

What does solid/liquid interfacial tension influence

A

The wetting of solids
Determines the contact of the solvent with a particle mass
For example, the penetration of water into a tablet

Influences the loss of drug two containers and solid particulate s

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16
Q

what are the possible outcomes of a high interfacial tension and poor wetting

A

A homogenous distribution spread out evenly
High interfacial tension between solid and liquid leads to
an uneven distribution
Solid sticks together or two container to reduce contact with the aqueous phase

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17
Q

what does poor wetting lead to

A

tablet/granules/powder in an aqueous phase, trying to reduce contact with this aqueous phase

This can cause: air to be trapped at the solid surface

Poor tablet break down in the stomach

Powders/particles in the suspension clumping together or sticking to the container

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18
Q

How is wet ability of a solid measured

A

contact angle

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19
Q

What does a higher contact angle mean?

A

The higher, the interfacial tension

no wetting

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20
Q

when is there complete wetting

A

0 degree contact angle

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21
Q

factors affecting contact angles and wetting

A

crystallization techniques
Using surfactant. [wetting agents]

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22
Q

describe surfactant as wetting agents

A

surfactant can be used to lower the solid and liquid interfacial tension

this reduces the contact angle

This aids, the displacing of air at the surface of the solid and improves solid and liquid contact

This helps with wetting if the solid

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23
Q

what does the adsorption of surfactant at the solid/liquid interphase look like

A

surfactant can be adsorbed at the solid/liquid interface
the surfactants hydrophobic, tail binds by Vandewal, is forces to the hydrophobic surface of the solid

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24
Q

I need drugs suspension is to be formulated. The suspension particle has a contact angle of 120°. What problems regarding the suspension stability can you predict

A

The particles will have a high surface/liquid interfacial tension

poor wettability

The suspension will be unstable

To avoid these problems :
The particles can adsorb at the solid liquid interface

This reduces surface tension

This promotes solid and liquid contact and reduces the contact angle

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25
Q

What does high interfacial tension between a solid and liquid result in

A

adsorption of the surfactant molecules [due to the surfactant, hydrophobic tail binding to the hydrophobic surface of a solid.]

adsorption of solid particles [solid solid, hydrophobic interactions]

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26
Q

is adsorption at the solid/liquid interface, an exothermic or an endothermic process

A

an exothermic process, as heat is released as the adsorption occurs

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27
Q

solid/solid interactions can lead to the adsorption of a drug in solution onto

A

A solid particulate system
A container wall

Both reduces contact with the aqueous face

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28
Q

what are some problems associated with? adsorption

A

adsorption of drugs to the container walls and infusion bags

Taking drugs simultaneously with antacids

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29
Q

what does an increase in Surface area have on the rate of adsorption

A

increases

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30
Q

what does increasing solubility have on the rate of adsorption

A

Decreases

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31
Q

what does an increase in temperature have on the rate of adsorption.

A

decreases as adsorption is an exothermic process

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32
Q

when does maximum adsorption of a drug usually occur

A

when the drug is completely uniodized
Because it is less soluble [hydrophobic] and has the affinity for packing with similar properties

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33
Q

what does increasing the drug concentration have on the rate of adsorption

A

increases

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34
Q

what is the langmuir theory

A

if no more than a single monolayer, of solute is adsorbed onto an absorbent then plotting C/N against C where

C= equilibrium concentration of the solute
N= number of moles per gram of solid absorbed by the adsorbent

This will give a straight line

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35
Q

what does the value of Nm give

A

it is a measure of the adsorbtive capacity of the adsorbent for a particular solute

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36
Q

What is the solid/gas interface

A

influence by similar factors to those of the solid/liquid interface

Isotherms used for the solid/liquid interface adsorption were first developed for the solid/gas adsorption

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37
Q

how is adsorption at the solid/liquid interface be exploited pharmaceutically

A

The adsorption of toxins onto activated charcoal

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38
Q

give an example where the adsorption at the solid/liquid into face would be of pharmaceutical concern

A

if a drug is adsorbed to a container and packaging. Therefore, reducing the patient dose

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39
Q

What is an electrical double layer

A

when a solid surface is in contact with a liquid, an electrical charge will be produced at this surface

This electrical charge will result in the surface being covered in a layer of surrounding attracted ions [an electrical Leah]

This electrical layer has two regions

40
Q

Why do solid surfaces become charged?

A

due to the ionization of groups at the surface of the particle, in particular atom for example COOH NH3

adsorption of a particular ionic species present in the solution [for example, in water, for hydration to a car hydroxide ions are adsorbed]

41
Q

how is an electrical? Double layer formed

A

The charge at the solid surface will influence the distribution of surrounding ions in liquid

Ions of the opposite charge. [con to ions] are attracted to the solid.

Ions of the same charge [:co ions] are repelled

42
Q

what is the fixed layer

A

solid positivity atom is surrounded by a LAYER of oppositely charged ions

Ions of the opposite charge will become fixed to the surface of the particle

43
Q

what is the diffuse Layer

A

A second layer forms

This extending out into the liquid until the charge of the particle no longer influences the distribution of ions

44
Q

What are the four regions to the double layer?

A

The surface potential
The stern layer
the surface of shear
the zeta potential

45
Q

what is the stern plane

A

middle of the fixed layer

46
Q

what is the particle surface

A

The surface of the particle

47
Q

what is the surface of the shear

A

the outermost layer of the fixed layer

48
Q

regardless of the passcode being positively or negatively, charged, what is the order of potential’s from most positive to least positive

A

Surface potential
stern potential
zeta potential

49
Q

what is the pharmaceutical relevance of the Zeta potential?

A

Both the surface potential, and stern potential are difficult to measure

The nearest experimental approximation to the surface is potential is the zeta potential

This is a potential at the surface of the shear

This is measured by electrophoresis

50
Q

What are two factors that influence the Zeta potential

A

electrolytes concentration in the aqueous phase:
Increasing the electrolytes concentration decreases the Zeta potential

Electrolyte valancey:
l

51
Q

Why does increasing the electrolytes concentration in the bulk phase increase the number of electrolytes in the double layer

A

The concentration of electrolytes, of the double layer is direct a proportional to the number of electrolytes in the bulk phase

there are more electrolytes present in the fixed Layer

The surface charge will be countered

eg goes from +100mV to +30mV the (positive) Zeta potential is reduced

52
Q

What does a positive surface potential mean?

A

If the electrolytes concentration increases, the zeta potential decreases

53
Q

What is negative surface potential

A

As electrolytes concentration increases Casita potential also increases

54
Q

what does increasing the electrolyte valency do

A

reduces zeta potential

55
Q

why does increasing the electrolyte valency reduce the Zeta potential

A

The more charge the counter ion has
The more it masks, the surface potential
Therefore, there is more reduction in the zeta potential

56
Q

What are three factors that influence the thickness of the double layer

A

Surface potential
Electrolyte concentration
Electrolyte valency

57
Q

describe how surface potential influences the thickness of the double layer

A

The higher the charge at the surface
The larger the electrical, double layer

58
Q

Explain how electrolytes concentration influences the thickness of the double layer

A

increasing electrolytes concentration increases the double layer thickness

Increasing electrolytes valance, he increases the double layer thickness

59
Q

Why does the electrical double layer lead to the repulsion between like particles?

A

Because the double layers do not like to overlap

Close, packing and aggregation of particles surrounded by a double layer is blocked

Because the double layers do not like to overlap

Therefore the electrical double layer result in electrostatic repulsive forces between a like particles

It decays as an exponential function of the distance

60
Q

What is the correlation between the size of the double layer on the distance over which the repulsive force acts?

A

The bigger the double layer, the greater the distance over which the repulsive force acts

61
Q

The presence of double layered around a particles which are alike with prohibits what

A

Aggregation of the particles

Due to the presence of repulsive electrostatic forces between like particles

62
Q

what is the definition of a colloidal system

A

consists of at least two discrete phases

dispersed phase (particles)
continuous phase (water)

63
Q

what is the difference between a colloidal dispersion and a coarse dispersion

A

The distinguishing feature is based loosely on particle size

coarse dispersion is when particles are greater than 0.5um size (pharmaceutical emotions, and suspensions)

colloidal (natural or synthetic polymers)

64
Q

what are the 3 classes of colloidal systems

A

lyophilic colloids
lyophobic colloids
association colloids

65
Q

what are lyophilic colloids

A

they are solvent loving

They despise spontaneously in the continuous phase

They are thermodynamically stable

The dispersed phase consist generally of large organic molecules lying within colloidal size range

66
Q

what is the preparation of lyophilic colloids

A

deform spontaneously when liquid vehicle comes in contact with a solid phase

This is due to the high attraction between the dispersed and continuous face

67
Q

what are lyophobic colloids

A

they are solvent hating

Therefore, there is a higher surface tension

Material does not disperse spontaneously

Dispersed phase generally consists of inorganic particles

68
Q

what is the preparation of lyophilic colloids

A

dispersion method: coarse particles are reduced in size

Condensation method: materials of below colloidal size are caused to aggregate into particles within the size range.

69
Q

what are association colloids

A

they are formed by surfactant molecules

At high concentrations, surfactants can aggregate into association colloids or micelles

70
Q

what three factors may a colloidal particles, be influenced by

A

Thermal energy [osmotic pressure, diffusion]
Gravity [sedimentation]
Resistance to motion [viscosity.]

71
Q

what is brownian motion

A

Random movement of colloidal particles resulting from random, collisions with the molecules of the continuous phase

This is influenced by thermal energy

72
Q

how does osmotic pressure equilibrate

A

colloidal particles are too large to pass through the membrane pores

In an attempt to equalize the chemical potential on both sides of the membrane, a net movement of solvent occurs across the membrane

73
Q

how does sedimentation affect colloidal particles

A

they settle under the influence of gravity as their sizes larger than 0.5um

For smaller particles, a centrifugal force can be used to sediment the colloidal particles

74
Q

what dictates the method of preparation of colloidal particles, and preparations

A

The colloidal particles affinity for the continuous phase

75
Q

what candy kinetic properties of colloids be used to calculate

A

The radius of the colloidal particles

76
Q

What is defined by a suspension?

A

these are dispersions of an insoluble drug or other substance in an aqueous, or non-aqueous continuous phase

77
Q

What are the pharmaceutical applications of a suspension?

A

formulation of:
An insoluble drug
A drug susceptible to degradation
Distasteful drugs
An increase of drug surface area
Topical application

78
Q

What are the typical constituents of pharmaceutical suspensions?

A

The solvent, plus the drug and generally:
wetting agents
Compounds to control stability
Additives to regulate the flow properties
PH regulators
Other additives

79
Q

why must the drug be wetted by the liquid

A

otherwise, separation of the two phases will occur

80
Q

what is an example of a wetting agent

A

hydrophilic colloids

This form a multi molecular coat around the particles

81
Q

What are the four desirable properties of a suspension?

A

suspended material should not settle rapidly

Particles that do settle, should not stick together, or to the bottom of the container. [cake]

Particles should resuspend easily when shaken

Suspension should not be too viscous for the intended administration route

82
Q

what are Solvents

A

these are water soluble

They reduce interfacial tension

They help to displace air from the particle surface

83
Q

What is the definition of a physically stable suspension?

A

A condition in which the particles do not aggregate, and in which they remain uniformly distributed throughout the dispersion

84
Q

What are the physical stability issues associated with suspensions?

A

adhesion to the container walls
Sedimentation
Particle size growth
caking
Flocculation

85
Q

What is sedimentation?

A

Where particles collect at the bottom of the container

86
Q

what does decreasing the particle radius do to the rate of sedimentation?

A

It decreases the rate of sedimentation

87
Q

What does increasing the density due to the rate of sedimentation?

A

It increases the rate of sedimentation

88
Q

what does increasing the viscosity of the continuous phase due to the rate of sedimentation?

A

It decreases the rate of sedimentation

89
Q

Does temperature have an effect on the rate of sedimentation?

A

no

90
Q

Describe particle size growth

A

Crystal growth can occur on storage

This can result from temperature fluctuations [OSTWALD ripening]

91
Q

How do you control Crystal growth?

A

you use a stable polymorph

use a narrow particle size range

use wetting agents

increase the viscosity of the vehicle

If all else fails formulate as a dry powder for reconstitution

92
Q

What is particle size heterogenicity

A

generally, that will be a particle size range

If this is the case, larger particles will settle more rapidly

No clear separation boundary is formed

This results in zone sedimentation

93
Q

What are examples of density modifiers?

A

Sucrose, glycerol, or propylene glycol

However, this is only effective over a small temperature range

94
Q

what happens when p1=p2

A

sedimentation does not occur

stokes law

95
Q

What are some examples of viscosity modifiers?

A

Polysaccharides, water soluble celluloses, hydrated silicates

96
Q

what is caking

A

it is an outcome of sedimentation

Sediment particles become cemented together by strong short range forces

Particles cannot be re-dispersed

It’s arises on the close packing of the sediment particles

It cannot be eliminated [only reduced] by particle size reduction, or increasing the viscosity of the continuous phase

week 18 (3 decks)

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