Physical chemistry: definitions
cLog P
Calculated log P (i.e. a theoretical value).
Log D
Log P when the test is performed at pH 7.4.
Log P
A measure of the lipophilicity of a compound; its partition coefficient between an organic
solvent (usually octanol) and an aqueous buffer.
Conc. of non-ionised drug in octanol
Log P = Log _____________________________________
Conc. of non-ionised drug in buffer
Values usually range from -6 to +6, high positive values indicating high lipid solubility and low or negative values indicating hydrophilic compounds. The test is performed at a pH at which the compound is non-ionised (compare Log D).
Molarity (M)
A measure of the concentration of a solution. A 1M solution contains one mole
of the substance per litre of solution.
No. of grams
Molarity = _________________________
Mol. wt. x volume (litres)
Mole (mol)
The amount of a substance in grams which contains Avogadro's number (6.022 x 10(23))
of atoms or molecules of it.
Molecular Weight
The sum of the atomic weights of the atoms comprising a molecule; alternatively, the
number of grams of a compound which contains a mole of it.
Normal solution
An outdated term referring to the concentration of an acid or base. It equals molarity
times the number of hydrogen ions or hydroxyl ions generated by each molecule of acid or
base respectively. Molarity is the preferred term.
pKa
pH at which 50% of an acid is dissociated into H+ and base. High pKa
values indicate a weak acid.
SAR
Structure-activity relationship. The way in which altering the molecular structure of
drugs alters their interaction with a receptor, enzyme, etc.
Greek
prefixes to SI units
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