PARTITIONING AND THERMODYNAMICS OF DIPYRIDAMOLE IN THE N-OCTANOL BUFFER AND LIPOSOME SYSTEMS

The thermodynamics of partitioning (K) of dipyridamole has been determined in n-octanol/buffer and liposome-buffer systems at pH 7.4. Dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) were used to prepare multilamellar liposomes. Partitioning of dipyridamole did not depend on the amount of n-octanol employed, however, partitioning was dependent upon the quantity, of DMPC employed to prepare liposomes. Plots of log K vs 1/T were linear in the n-octanol and liposome systems. Partitioning was generally greater in liposomes than In the n-octanol/buffer system. Among liposomes, the partitioning was greater in DMPC liposomes at all temperatures. The values of enthalpy (AH) and entropy (AS) were positive in both the n-octanol and liposome systems. These values were lower in DMPC liposomes and were comparable in the n-octanol and DPPC liposomes. Thus, the interaction of dipyridamole depends on the rigidity of lipid bilayers and liposomes constitute a more selective partitioning system than the n-octanol/buffer system.