Lipophilicity is a relative measure of the affinity of a molecule for a lipid medium. Typically, this parameter can be expressed in two ways:

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• Log P, which refers to the logarithm of the partition coefficient of the compound between an organic phase and an aqueous phase at a pH at which all the molecules of the compound are found to be neutral;

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• Log D which corresponds to the distribution coefficient of a compound between an organic phase and an aqueous phase at a specific pH and wherein the molecules of the compound can be in the ionized or neutral form.

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pKa is the pH value at which 50% of the molecules of a given compound are in the ionized state and 50% are in the neutral state.
The pKa of a compound is related to its ADMET properties. The study of pKa of a drug bioactive compound allows:

(i) predicting the ionization state of the compound at different physiological pH values and thus predicting absorption of the compound;

(ii) predict the availability of the compound to enter into biological reactions;

(iii) understanding the binding of the compound to both plasma proteins and their own therapeutic targets.