Effect of Salt Monoprotic Examples

We have measured the partition behaviour of ibuprofen and chlorpromazine at 0.15 M salt and under conditions of no added background salt. Fig. 11 a shows that the neutral log Pxh of ibuprofen remains unchanged but the ion-pair log Px depends dramatically on the level of background salt. Similarly, chlorpromazine shows salt dependence, as illustrated in Fig. lib. Scherrer demonstrated an effect of a similar magnitude with

IBUPROFEN 25°C; 0.014M KCl, 0.152M KCl 4

IBUPROFEN 25°C; 0.014M KCl, 0.152M KCl 4

logD

logD

CHLORPROMAZINE 6

3 4 5 6 7 8 91011

Figure 11. (a) Ibuprofen lipophiiicity plot at 0.152 M ionic strength (upper curve) and 0.014 M ionic strength (lower curve), (b) Chlor-promazine lipophiiicity plot at 0.15 M KC1 (upper-most curve), 0.15 M NaCI (intermediate curve), and 0.001 M NaCI (lowest curve).

propranolol and a few other compounds [23]. Murthy and Zografi [34] studied the effects of many salts on the ion-pair partitioning of chlorpromazine. They established the relative lipophiiicity order of the anions:

Br" > ch,ch2ch2sov > n03 >> ci > ch3ch2s03-» s042", ch3s03

Akamatsu et al. [35] have also observed salt effects on the partitioning of hydrophilic dipeptides, with the order of effect:

This appears to be a general phenomenon. We will consider this further when we discuss the partition behavior of phenyalanine and tryptophanylphenylalanine.

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