Partition Behavior and Ion Pair Formation of Some Prostaglandins

The pKa and intrinsic partition coefficient (PC0) of seven prostaglandins (PGE1, PGE2, PGA1, PGA2, PGB1, PGB2, and PGF2a) were determined from their pH-partition profiles. Structural changes of the prostaglandins were largely reflected in PC0 values rather than the pKa values. Partition of the prostaglandins from aqueous buffer (pH7.0) to cyclohexane containing various alcohols was markedly enhanced by the addition of aliphatic amines in aqueous phase. The influences of temperature and chain length of both alcohol and amine on partition coefficients of the prostaglandins were investigated. Furthermore, extraction constants (Ke) for prostaglandin-amine ion pairs and number of alcohol molecules associated with ion pair (n) were determined to gain insight into the mechanism of enhanced extraction process.