Amphiphilic Compound Physical State Apparent pKa Acetic acid 3% in H2O 4.7 Propionic acid 4% in H2O 4.9 Butyric acid 4% in H2O 4.8 Octanoic acid Monomers in H2O 4.8 Decanoic acid Lamellar liq. crystals (>CMC) 6.8 Oleic acid 5 mole % in PC vesicles (100 mM) 7.5 Oleic acid 1.5 weight% in PC-trioleinmicroemulsion 7.3 Oleic acid Bound to albumin 4.2 Cholic acid 2 mM in H2O (<CMC) 4.98 Cholic acid 100 mM in H2O (>CMC) 5.5 Cholic acid 3 weight% in PC vesicles 6.8 (major) 7.3 (minor)

Table 2: The apparent pKa values of amphiphilic compounds when bound to phospholipid membranes.