Figure 4.1 Octanol-water tetrad equilibria. [Avdeef, A., Curr. Topics Med. Chem., 1, 277351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]

To distinguish partition coefficients of neutral species from ionized species, the notation log PN and log P1 may be used, respectively, or the symbol C or A may be used as a substitute for superscript I, denoting a cation or anion, respectively. [362].

It is convenient to summarize the various reactions in a box diagram, such as Fig. 4.1 [17,275,280], illustrated with the equilibria of the weak base, propranolol. In Fig. 4.1 is an equation labeled pK°ct. This constant refers to the octanol pKa, a term first used by Scherrer [280]. When the concentrations of the uncharged and the charged species in octanol are equal, the aqueous pH at that point defines pK[ which is indicated for a weak acid as oct a '

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