Surfactants, Polymers and Drug Delivery Flashcards
the classification of surfactants is based on what empirical system?
HLB (hydrophily lipophile balance )
the HLB of surfactants is a measure of the relative contributions of the __ and __ regions
hydrophilic and lipophilic
what is the use of the HLB system?
helps determine which surfactant to use for specific applications
what are surfactants?
compounds with the tendency to accumulate at the interface between two phases
what are the interchangeable terms used for surfactants?
ampiphiles, amphipathic, surface-active agents, surfactants
surfactants change the nature of the __
interface
a decrease in interfacial tension between oil and water phases results in ___ formation
emulsion
surfactants allow for the adsorption of insoluble particles, which enables their dispersion and the formation of __
suspension
surfactants can form micelles, which result in __ solution
clear
give 2 examples of non-ionic surfactants
sorbitan esters and polysorbates
what are sorbitan esters?
mixtures of the partial esters of sorbitol and its mono and di-anhydrides with oleic acid
sorbitan esters are __ and used as ___ and __
insoluble; wetting agents and emulsifiers
polysorbates are also called __
Tweens
polysorbates are ___ with water and are used as ___
miscible; oil-in water emulsifier
sodium laurel sulphate BP is an example of what type of surfactant?
anionic
sodium lauryl sulphate is a mix of ___, very soluble in __ at rt and is used as a ___ agent in skin cleaner and medicated shampoos
sodium alkyl sulphates; water; foaming
quaternary ammonium and pyridium cationic surfactants are examples of which type of surfactant?
cationic
quaternary ammonium and pyridium cationic surfactants are used as bactericidal agents against gram __ bacteria and some __ bacteria. They are used to clean __ and __
positive, some gram negative; skin of wounds and hospital utensils
surfactants ___ surface and interfacial tension
decrease
an increase in surface activity means a __ in surface tension
decrease
compounds which are most effective at lowering surface tension are those with a high ___
surface activity
there is an equilibrium between surfactant molecules at the surface of the solution and those in the bulk of solution, which is expressed by the __ equation
Gibbs
when surfactant is dissolved in water, how will it orientate?
at the surface with its hydrophilic parts inward and its hydrophobic bits outward
at the interface between two immiscible solvents, how will a surfactant orientate?
with its hydrphillic bits in the aq and its hydrophobic bits in the oil
why does surfactant decrease surface tension when surfactant molecules adsorb at water? what force is reduced?
the surfactant molecules replace some of the water molecules in the surface and the forces of attraction between surfactant and water are less that water on water. Contraction force is reduced
what is adsorption?
process of accumulation at an interface; essential a surface effect that is different than absorption
what is physical adsorption?
the adsorbate is bound to the surface by weak van Der Waals forces that can be reversed
chemical adsorption / chemisorption involves ___ valence forces than that of physical adsorption
stronger
which type of adsorption is more specific?
chemisorption
chemisorption usually involves a ___ process
ion exchange
is it possible to have both physical and chemisorption involved an adsorption process?
yes
give an example of adsorption process that uses both physical and chemical adsorption and explain each contribution
Ex: adsorption of toxin in the stomach by attagpulgite and kaolin
Chemisorption: cation exchange with the basic groups of toxins
Physical: adsorption of the rest of the molecule
micelles are formed at the __
critical micelle concentration
CMC is reached at what point?
inflection point when surface tension is plotted against concentration
most micelles are ___ in shape and consist of __ to ___ surfactant molecules
spherical; 60-100
micelles are used to stabilize __ drugs
water-insoluble
list 4 applications of adsorption as pharmaceutical applications
- adsorption of toxins/poisons
- taste masking
- hemoperfusion
- adsorption in drug formulation
adsorption of toxins employs universal antidotes, provide 3 examples of these
- activated charcoal
- magnesium oxide
- tannic acid
taste masking by adsorption is often employed for what prescription drug?
diazepam
what must be considered when using adsorption to mask taste problems in oral drugs?
need to be careful that you don’t use so much surfactant that it decreases the efficacy of the drug
carbon hemoperfusion is used for treatment of what?
severe drug overdose
adsorption of surfactants onto poorly soluble solids ___ the wetting and dissolution rate
increases
the typical size of a micelle is ___nm, therefore __ visible under microscope
2-3; not
a __ exists between micelles and free surfactant molecules in solution
equilibrium
when surfactant concentration is increased above the CMC, the number of ___ increases, bit ___ stays the same at the CMC value
micelles; free surfactant concentration
when considering solubility in terms of surfactants, you think of the amount needed to _____ in order to promote dissolution
arrange around insoluble molecule
increase in surfactant results in a __ in surface tension
decrease
what happens at the CMC inflection point?
all insoluble molecules will be in micelles and a clear solution will be produced
at high electrolyte concentrations, the micelles of ___ surfactants may become non-spherical, leading to precipitation of the compound
ionic
what is solubilization?
process whereby water-insoluble substance are brought together into solution by incorporation into micelles
solubilization is affected by what 3 factprs?
- temperature
- nature of solubilisate
- nature of surfactants
what is the solubilization site for non-polar compounds?
the aliphatic hydrocarbons dissolve in the hydrocarbon core of ionic and non-ions micelles
what is the solubilization site for polar compounds?
the polar group will be at the core-surface interface with the hydrophobic part buried in the core
the properties of a surfactant are determined by the balance between the __and _ parts of the molecule
hydrophobic and hydrophilic
if the hydrophilic chain length is increased, what happens to the CMC?
it increases bc the molecule is more hydrophilic
if the hydrophobic chai length is increased, what happens to the CMC?
it is decreased (micelles form at lower solution concentration)
electrolyte addition to solution of ionic surfactants ___ CMC and __ micelle size
decreases; increases
give examples of solubilization of phenolic compounds
cresol, chlorrcresol, chloroxylenol and thymol with soap to form clear solutions for disinfecting
provide an example of solubilization of iodine in non-ionic surfactant micelle
iodophors used in sterilization n
provide examples of solubilization of drugs
steroids and water-insoluble vitamins, by non-ionic surfactants (usually polysorbates or polyethylene sorbitan esters of fatty acids
what are polymers?
high compounds of high molecular weight with repeating monomer units
extensive cross-linking of a polymer makes it __ soluble l
less
if the monomer units are identical, the polymer is called
homopolymer
polymers formed of more than one type are called __
copolymers
the MW of polymers is a ___ MW, based on __
average; experimental method
what is polydispersity?
in solution, there are usually a range of sizes of polymer chains
the average molecular weight is biased towards __
large molecules
the viscosity of a polymer depends on what 4 things?
- concentration
- polymer-solvent interactions
- charge interactions
- binding of small molecules
the viscosity of ionized polymers is complicated by ___ which vary with polymer concentration and addictive concentration
charge interactions
the arrangement of the copolymer has effects on ___ properties
physical
polymer gels are __ and may form __ in aqueous soon
surfactants; micelles
at high concentrations of polymer gel, the micelles can pack so tightly that __
the solution becomes immobile (gelation occurs)
gelation of a polymer gel may occur due to what type of temperature change? why is this?
warming; because the solubility of poly(oxyethylene) decreases
as temperature increases, polymer gels become more _
hydrophobic
in polymer gels, a 3-D polymer-solvent systen network can be formed by __ or __
swelling of solid polymer; reduction in solubility of polymer in sole
when gels are formed from soln, each system is characterized by a ___, below which gelation will not occur
critical concentration of gelation
gelation is characterized by a large increase in __ beyond the ___ point
viscosity; gel
gels have what physical characteristics?
elasticity, and rubber-like
gels can be reversible or irreversible based on __
the bonds between chains of the network
what is Gum arabic and its characteristics and application?
1) very soluble polyelectrolyte
2) highly viscous due to branched structure of the macromolecule chains
3. used as emulsifier
what is gum tragacanth, its characteristics an application?
1) gum
2) partially dissolves in water to give highly viscous sol
3) natural emulsifier and thickener, effective a suspending agent
what are alginates, their characteristics and application?
- block co-polymer polysaccharides derived fro seaweed consisting of B-D-mannuronic acid and a-L-guluronic acid residues joined by 1,4 glycosidic bonds
- very viscous and gel on addition of acid or calcium salts
- stabilizers and thickening agents
what are 3 families of water-soluble polymers?
carboxypolymethylene
cellulose derivatives
natural gums and mucilages
what are the applications of carbomer and carbopol?
- suspending agents
2. binders in prolonged and immediate action tablets
what is an application for low-viscosity methyl cellulose?
emulsifier
what is an application for high-viscosity methyl cellulose
thickening agent
what is an application for hydroxypropylmethylicellulose?
viscous colloidal solo for eye drops and artificial tears
water insoluble polymers are affected by what 3 characteristics?
- degree of crystallinity
- permeability to drugs
- permeability to gases
what effect does the degree of crystallinity have on water-insoluble polymers?
affects rigidity, fluidity, resistance to diffusion of small molecules and degradation
drug diffusion is governed by ___ and affected by __, __and __
Ficks Law,; crystallinity, solubility, and method of preparation
water insoluble polymers are typically used for __
making membranes, containers and tubing
silicones are ___ polymers with a structure containing alternate forma of __ and __
water-insoluble; Si and O
dimeticones are a type of __ that are used as ___ substances to protect skin against __
silicone; barrier substance/water repellent; water-soluble irritants
Dimeticine 200 is used a lubricant for __ and to replace degenerative ___ in cases of retinal detachment
artificial eyes; vitreous fluid
dimeticone can act as a lubricant for simple __
joints
what is activated dimeticone (activated polymethylsiloxane) ?
a mix of liquid dimeticones containing finely divided silica to enhance the defaming properties of the silicone
simethicone is used as a __
anti-flatulent / reduce bloating
steroids have an affinity for __ tubing
polyethylene
Glyceryl trinitrate has a high affinity for __ plastics, and can leave tablets, reducing the active content to __
lipophilic ; zero
explain ion exchange properties of water-insoluble polymers
attached ionizable groups can exchange with ions attracted to their ionized groups
give an example of anion exchange in water-insoluble polymers application
polyamide methylene resin and polyaminostyrene used as antacids
give an example of cation exchange in water-insoluble polymers application
calcium and sodium forms used to treat hyperkalaemia
evaporated polymer films leave a __ on tablets
protective coating
what are the 3 types of matrices?
- non-eroding
- reservoir system
- eroding matrix
what are microcapsules?
drug encapsulated as small particles or as a drug soln in a polymer oil or coat
what are microspheres?
solid polymeric spheres which entrap drug
what are nano capsules and nanoparticles ?
structures equivalent to microspheres and capsules, ranging in size from 50 - 500 nm
