surfactants/surface active agents/amphiphiles are chemical compounds which tend to
accumulate at the bound between two phases
surfactants may be classified as
anionic, cationic, amphoteric and non-ionic
carbolyate, sulfonate, or sulfate group. Examples include: sodium stearate, sodium dodecyl sulfate, sodium lauryl sulfate
amine salts or quaternary ammonium salts. examples include: cetrimonium bromide
carboxylate or phosphate groups as the anion, and amino or quaternary ammonium groups as the cation.
polypeptides or protein
conisisting of carboxylate anions and amine cations
phosphate anions and quarternary ammonium cations. such as lecithins and cephalines
do not have any charge. examples: heptaoxyethylene
amphiphathic drugs and surface activity
influence therpaeutic activity. differ from a surfactant in that their hydrophobic groups are more complex. Surface activity will increase due to the nature of the functional group present on the hydrophobic moiety
order of increasing surface activity
the more hydrophobic something is then the ---surface activity it will have
the more hydrophilic something is then the
less surface activity it wil have because more activity is within the solution
factors affecting adsorption
1) solubility of the adsorbate 2) pH 3) nature of the adsorbent 4) temperature
is adsorption exothermic or endothermic process?
types of liquid crystals
1) smectic (soap- or grease-like) and 2) nematic/mesophase (thread- like)
liquid cyrstalline state
intermediate mobility in which the molecules are in a liquid, but have limited mobility
molecules that form mesophases are
1) organic, 2) elongated, 3) rectilinear in shape, 4) rigid, 5) strongly dipolar, or contain easily polarizable groups, 6)liquid crystals are anisotropic (they have physical properties of different magniture at different locations)
amphiphatic drug vs. surfactant
the hydrophobic group of the amphiphile is more complex than the surfactant
factors that affect solubilization
1) nature of the surfactant 2) nature of the solubilisate 3) effect of temperature
nature of the surfactant
the longer the hydrophobic side chain than the more solubilization that will occur. it will be more solubilizing efficiency. there is a limit in the chain length of 16-22 for polyoxyethylene
nature of the solubilisate
solubility is favored by decrease in alkyl chain length, unsaturation, cyclisation.
solubility increases with the presence of more polar groups at 17th Carbon. Progesterone<testosterone<deoxycorticosterone
temperature and solubilization
increase temp, increase micellar size, increase solubilzation
bring an insoluble substance into a water solution
is charcoal tablet or powder equally effective?
adsorption is proportional to surface area. more SA then more adsorption. Powder had more efficiency
does charcoal adbord all drugs at the same rate
no. drugs have different efficiencies to get adsorbed.
a homogenous, molecular-level dispersion of a substance in a phase (water)
the distribution of a substance between two phases at equilibrium
less than 1
very slightly soluble
more than 10,000 (nothing is perfectly insoluble)
dielectric constant (e)
a measurement of polarity
polarity, dielectic constant, and solubility
decrease polarity with decrease dielectric constant and decrease water solubility
like dissolves like
solubility of polar sovents such as water
high (e) favors dissolution of polar solutes. H-bonding
solubility of non-polar solvents
induced dipole interactions. kept in solution through weak van der Waal's- London type forces.
step 1 in the process of solubility
solute: solid substance must get loosened. one molecule must come out. cohesive forces: bond strength determines mp, mole hear of fusion/vaporization. cohesive forces.
step 2 in the process of solubility
solvent:reorganizes for incoming materials/solute. cohesive forces.
step 3 in the process of solubility
solute molecule goes into the space. adhesive forces.
three factors which determine if solubility happens?
1) adhesive 2) cohesive 3) cohesive
solubility and structure
1) branched chains are more soluble and straight chains. 2) solubility decreases with increased boiling and melting point. 3) kind of functional group and its location. meta (m) is the most soluble than orthro (o) or para (p). Para is the least soluble because it is the most stable. Orthro has intramolecular H-bonding which decreases its interaction with water
methyltestosterone vs. testosterone
methyl substitution decreases the cohesives binding forces of testerone moelcules as indicated by lower heat of fusion for methyltestosterone in comparison to that of testosterone.
solubility and hydroxyl group placement
equatorial hydroxyl groups are reported to be more compatible with the organizated structure of water. Axil hydroxyl groups cannot bond onto the water "lattice" without causing significant distortion.
sucrose vs mannitol vs sorbitol
surcrose all 6 OH are in the equatorial position. sorbital is 3.5x more soluble than mannitol because it has one more OH group in the equatorial position. Sorbitol and mannital differ in carbon-2
common ion effect
solubility decreases by the addition of another compound having an ion in common. ex: AgCl decreases solubility with the addition of NaCl
precipitating, decrease in solubility
increases in solubility by adding salts with large anions or cations which are very soluble in water themselves
benzoic acid and salting in
benzoic acid increases in the presence of sodium benzoate but decreased in the presence of NaCl.
solubility increases if you add -- of its own anion
solubility and pH acidic drugs
would ionize more in a basic medium; hense would also dissolve in water more. opposite is true in acidic medium.
pH - pKa=log((s-s0)/s0)
s=total solubility of the drug
s0=solubility of the undissociated form of the drug (original drug)
solubility and pH basic drugs
more soluble in acidic medium and are quantified by:
pH - pKa = log(s0/(s-s0))
solubility and pH amphoteric drugs
acidic and basic, the equation you uses depends on the pH of the medium. zwitterions at isoelectric point pH are neutral. at a pH lower than pKa the basic drug would be reacting with acid. pH greater then pKa the acidic drug would be reacting with basic solution.
methods of increasing solubility: controlling pH
acids (phenobarital sodium) is soluble is alkaline solutions, but precipitates out of solution when the pH is lowered to 8.3. bases (atropine sulphate) is soluble in increased pH but decreases