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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

anionic surfactants

carbolyate, sulfonate, or sulfate group. Examples include: sodium stearate, sodium dodecyl sulfate, sodium lauryl sulfate

cationic surfactants

amine salts or quaternary ammonium salts. examples include: cetrimonium bromide

amphoteric surfactants

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

natural phospholipids

phosphate anions and quarternary ammonium cations. such as lecithins and cephalines

non-ionic surfactants

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.

17th Carbon

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

biocompatible polymers

acrylic hydrogel

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

very soluble

less than 1

freely soluble




sparingly soluble


slightly soluble


very slightly soluble


practially insoluble

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

salting out

precipitating, decrease in solubility

salting in

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

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