Thermodynamics of partitioning of benzocaine in some organic solvent/buffer and liposome systems.

The thermodynamics of partitioning of benzocaine (BZC) were studied in octanol/buffer (ROH/W), isopropyl myristate/buffer (IPM/W), cyclohexane/buffer (CH/W), and dimyristoyl phosphatidylcholine (DMPC) and dipalmitoyl phosphatidylcholine (DPPC) liposome systems. In all cases the partition coefficients were greater than unity; therefore the free energies of transfer were negative, that is, the processes of transfer of BZC from aqueous media to organic systems were spontaneous. The partition coefficients were approximately three-fold higher in DMPC liposomes compared with the ROH/W system in the 30 degrees -40 degrees C temperature range. The enthalpies of transfer from aqueous media to ROH and IPM were negative, but positive for CH, while this property was negative for DMPC liposomes and positive for DPPC liposomes. The entropies of transfer were positive in almost all cases, except for DMPC. The results presented here confirm the lipophilic nature of BZC.